Clean-up: consumer: change space to tabs

[lttng-tools.git] / src / common / consumer / consumer.c

/*
 * Copyright (C) 2011 Julien Desfossez <julien.desfossez@polymtl.ca>
 * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 * Copyright (C) 2012 David Goulet <dgoulet@efficios.com>
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 */

#include "common/index/ctf-index.h"
#define _LGPL_SOURCE
#include <assert.h>
#include <poll.h>
#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#include <inttypes.h>
#include <signal.h>

#include <bin/lttng-consumerd/health-consumerd.h>
#include <common/common.h>
#include <common/utils.h>
#include <common/time.h>
#include <common/compat/poll.h>
#include <common/compat/endian.h>
#include <common/index/index.h>
#include <common/kernel-ctl/kernel-ctl.h>
#include <common/sessiond-comm/relayd.h>
#include <common/sessiond-comm/sessiond-comm.h>
#include <common/kernel-consumer/kernel-consumer.h>
#include <common/relayd/relayd.h>
#include <common/ust-consumer/ust-consumer.h>
#include <common/consumer/consumer-timer.h>
#include <common/consumer/consumer.h>
#include <common/consumer/consumer-stream.h>
#include <common/consumer/consumer-testpoint.h>
#include <common/align.h>
#include <common/consumer/consumer-metadata-cache.h>
#include <common/trace-chunk.h>
#include <common/trace-chunk-registry.h>
#include <common/string-utils/format.h>
#include <common/dynamic-array.h>

struct lttng_consumer_global_data consumer_data = {
        .stream_count = 0,
        .need_update = 1,
        .type = LTTNG_CONSUMER_UNKNOWN,
};

enum consumer_channel_action {
        CONSUMER_CHANNEL_ADD,
        CONSUMER_CHANNEL_DEL,
        CONSUMER_CHANNEL_QUIT,
};

struct consumer_channel_msg {
        enum consumer_channel_action action;
        struct lttng_consumer_channel *chan;    /* add */
        uint64_t key;                           /* del */
};

/* Flag used to temporarily pause data consumption from testpoints. */
int data_consumption_paused;

/*
 * Flag to inform the polling thread to quit when all fd hung up. Updated by
 * the consumer_thread_receive_fds when it notices that all fds has hung up.
 * Also updated by the signal handler (consumer_should_exit()). Read by the
 * polling threads.
 */
int consumer_quit;

/*
 * Global hash table containing respectively metadata and data streams. The
 * stream element in this ht should only be updated by the metadata poll thread
 * for the metadata and the data poll thread for the data.
 */
static struct lttng_ht *metadata_ht;
static struct lttng_ht *data_ht;

static const char *get_consumer_domain(void)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return DEFAULT_KERNEL_TRACE_DIR;
        case LTTNG_CONSUMER64_UST:
                /* Fall-through. */
        case LTTNG_CONSUMER32_UST:
                return DEFAULT_UST_TRACE_DIR;
        default:
                abort();
        }
}

/*
 * Notify a thread lttng pipe to poll back again. This usually means that some
 * global state has changed so we just send back the thread in a poll wait
 * call.
 */
static void notify_thread_lttng_pipe(struct lttng_pipe *pipe)
{
        struct lttng_consumer_stream *null_stream = NULL;

        assert(pipe);

        (void) lttng_pipe_write(pipe, &null_stream, sizeof(null_stream));
}

static void notify_health_quit_pipe(int *pipe)
{
        ssize_t ret;

        ret = lttng_write(pipe[1], "4", 1);
        if (ret < 1) {
                PERROR("write consumer health quit");
        }
}

static void notify_channel_pipe(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_channel *chan,
                uint64_t key,
                enum consumer_channel_action action)
{
        struct consumer_channel_msg msg;
        ssize_t ret;

        memset(&msg, 0, sizeof(msg));

        msg.action = action;
        msg.chan = chan;
        msg.key = key;
        ret = lttng_write(ctx->consumer_channel_pipe[1], &msg, sizeof(msg));
        if (ret < sizeof(msg)) {
                PERROR("notify_channel_pipe write error");
        }
}

void notify_thread_del_channel(struct lttng_consumer_local_data *ctx,
                uint64_t key)
{
        notify_channel_pipe(ctx, NULL, key, CONSUMER_CHANNEL_DEL);
}

static int read_channel_pipe(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_channel **chan,
                uint64_t *key,
                enum consumer_channel_action *action)
{
        struct consumer_channel_msg msg;
        ssize_t ret;

        ret = lttng_read(ctx->consumer_channel_pipe[0], &msg, sizeof(msg));
        if (ret < sizeof(msg)) {
                ret = -1;
                goto error;
        }
        *action = msg.action;
        *chan = msg.chan;
        *key = msg.key;
error:
        return (int) ret;
}

/*
 * Cleanup the stream list of a channel. Those streams are not yet globally
 * visible
 */
static void clean_channel_stream_list(struct lttng_consumer_channel *channel)
{
        struct lttng_consumer_stream *stream, *stmp;

        assert(channel);

        /* Delete streams that might have been left in the stream list. */
        cds_list_for_each_entry_safe(stream, stmp, &channel->streams.head,
                        send_node) {
                cds_list_del(&stream->send_node);
                /*
                 * Once a stream is added to this list, the buffers were created so we
                 * have a guarantee that this call will succeed. Setting the monitor
                 * mode to 0 so we don't lock nor try to delete the stream from the
                 * global hash table.
                 */
                stream->monitor = 0;
                consumer_stream_destroy(stream, NULL);
        }
}

/*
 * Find a stream. The consumer_data.lock must be locked during this
 * call.
 */
static struct lttng_consumer_stream *find_stream(uint64_t key,
                struct lttng_ht *ht)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_u64 *node;
        struct lttng_consumer_stream *stream = NULL;

        assert(ht);

        /* -1ULL keys are lookup failures */
        if (key == (uint64_t) -1ULL) {
                return NULL;
        }

        rcu_read_lock();

        lttng_ht_lookup(ht, &key, &iter);
        node = lttng_ht_iter_get_node_u64(&iter);
        if (node != NULL) {
                stream = caa_container_of(node, struct lttng_consumer_stream, node);
        }

        rcu_read_unlock();

        return stream;
}

static void steal_stream_key(uint64_t key, struct lttng_ht *ht)
{
        struct lttng_consumer_stream *stream;

        rcu_read_lock();
        stream = find_stream(key, ht);
        if (stream) {
                stream->key = (uint64_t) -1ULL;
                /*
                 * We don't want the lookup to match, but we still need
                 * to iterate on this stream when iterating over the hash table. Just
                 * change the node key.
                 */
                stream->node.key = (uint64_t) -1ULL;
        }
        rcu_read_unlock();
}

/*
 * Return a channel object for the given key.
 *
 * RCU read side lock MUST be acquired before calling this function and
 * protects the channel ptr.
 */
struct lttng_consumer_channel *consumer_find_channel(uint64_t key)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_u64 *node;
        struct lttng_consumer_channel *channel = NULL;

        /* -1ULL keys are lookup failures */
        if (key == (uint64_t) -1ULL) {
                return NULL;
        }

        lttng_ht_lookup(consumer_data.channel_ht, &key, &iter);
        node = lttng_ht_iter_get_node_u64(&iter);
        if (node != NULL) {
                channel = caa_container_of(node, struct lttng_consumer_channel, node);
        }

        return channel;
}

/*
 * There is a possibility that the consumer does not have enough time between
 * the close of the channel on the session daemon and the cleanup in here thus
 * once we have a channel add with an existing key, we know for sure that this
 * channel will eventually get cleaned up by all streams being closed.
 *
 * This function just nullifies the already existing channel key.
 */
static void steal_channel_key(uint64_t key)
{
        struct lttng_consumer_channel *channel;

        rcu_read_lock();
        channel = consumer_find_channel(key);
        if (channel) {
                channel->key = (uint64_t) -1ULL;
                /*
                 * We don't want the lookup to match, but we still need to iterate on
                 * this channel when iterating over the hash table. Just change the
                 * node key.
                 */
                channel->node.key = (uint64_t) -1ULL;
        }
        rcu_read_unlock();
}

static void free_channel_rcu(struct rcu_head *head)
{
        struct lttng_ht_node_u64 *node =
                caa_container_of(head, struct lttng_ht_node_u64, head);
        struct lttng_consumer_channel *channel =
                caa_container_of(node, struct lttng_consumer_channel, node);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                lttng_ustconsumer_free_channel(channel);
                break;
        default:
                ERR("Unknown consumer_data type");
                abort();
        }
        free(channel);
}

/*
 * RCU protected relayd socket pair free.
 */
static void free_relayd_rcu(struct rcu_head *head)
{
        struct lttng_ht_node_u64 *node =
                caa_container_of(head, struct lttng_ht_node_u64, head);
        struct consumer_relayd_sock_pair *relayd =
                caa_container_of(node, struct consumer_relayd_sock_pair, node);

        /*
         * Close all sockets. This is done in the call RCU since we don't want the
         * socket fds to be reassigned thus potentially creating bad state of the
         * relayd object.
         *
         * We do not have to lock the control socket mutex here since at this stage
         * there is no one referencing to this relayd object.
         */
        (void) relayd_close(&relayd->control_sock);
        (void) relayd_close(&relayd->data_sock);

        pthread_mutex_destroy(&relayd->ctrl_sock_mutex);
        free(relayd);
}

/*
 * Destroy and free relayd socket pair object.
 */
void consumer_destroy_relayd(struct consumer_relayd_sock_pair *relayd)
{
        int ret;
        struct lttng_ht_iter iter;

        if (relayd == NULL) {
                return;
        }

        DBG("Consumer destroy and close relayd socket pair");

        iter.iter.node = &relayd->node.node;
        ret = lttng_ht_del(consumer_data.relayd_ht, &iter);
        if (ret != 0) {
                /* We assume the relayd is being or is destroyed */
                return;
        }

        /* RCU free() call */
        call_rcu(&relayd->node.head, free_relayd_rcu);
}

/*
 * Remove a channel from the global list protected by a mutex. This function is
 * also responsible for freeing its data structures.
 */
void consumer_del_channel(struct lttng_consumer_channel *channel)
{
        struct lttng_ht_iter iter;

        DBG("Consumer delete channel key %" PRIu64, channel->key);

        pthread_mutex_lock(&consumer_data.lock);
        pthread_mutex_lock(&channel->lock);

        /* Destroy streams that might have been left in the stream list. */
        clean_channel_stream_list(channel);

        if (channel->live_timer_enabled == 1) {
                consumer_timer_live_stop(channel);
        }
        if (channel->monitor_timer_enabled == 1) {
                consumer_timer_monitor_stop(channel);
        }

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                lttng_ustconsumer_del_channel(channel);
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }

        lttng_trace_chunk_put(channel->trace_chunk);
        channel->trace_chunk = NULL;

        if (channel->is_published) {
                int ret;

                rcu_read_lock();
                iter.iter.node = &channel->node.node;
                ret = lttng_ht_del(consumer_data.channel_ht, &iter);
                assert(!ret);

                iter.iter.node = &channel->channels_by_session_id_ht_node.node;
                ret = lttng_ht_del(consumer_data.channels_by_session_id_ht,
                                &iter);
                assert(!ret);
                rcu_read_unlock();
        }

        channel->is_deleted = true;
        call_rcu(&channel->node.head, free_channel_rcu);
end:
        pthread_mutex_unlock(&channel->lock);
        pthread_mutex_unlock(&consumer_data.lock);
}

/*
 * Iterate over the relayd hash table and destroy each element. Finally,
 * destroy the whole hash table.
 */
static void cleanup_relayd_ht(void)
{
        struct lttng_ht_iter iter;
        struct consumer_relayd_sock_pair *relayd;

        rcu_read_lock();

        cds_lfht_for_each_entry(consumer_data.relayd_ht->ht, &iter.iter, relayd,
                        node.node) {
                consumer_destroy_relayd(relayd);
        }

        rcu_read_unlock();

        lttng_ht_destroy(consumer_data.relayd_ht);
}

/*
 * Update the end point status of all streams having the given network sequence
 * index (relayd index).
 *
 * It's atomically set without having the stream mutex locked which is fine
 * because we handle the write/read race with a pipe wakeup for each thread.
 */
static void update_endpoint_status_by_netidx(uint64_t net_seq_idx,
                enum consumer_endpoint_status status)
{
        struct lttng_ht_iter iter;
        struct lttng_consumer_stream *stream;

        DBG("Consumer set delete flag on stream by idx %" PRIu64, net_seq_idx);

        rcu_read_lock();

        /* Let's begin with metadata */
        cds_lfht_for_each_entry(metadata_ht->ht, &iter.iter, stream, node.node) {
                if (stream->net_seq_idx == net_seq_idx) {
                        uatomic_set(&stream->endpoint_status, status);
                        DBG("Delete flag set to metadata stream %d", stream->wait_fd);
                }
        }

        /* Follow up by the data streams */
        cds_lfht_for_each_entry(data_ht->ht, &iter.iter, stream, node.node) {
                if (stream->net_seq_idx == net_seq_idx) {
                        uatomic_set(&stream->endpoint_status, status);
                        DBG("Delete flag set to data stream %d", stream->wait_fd);
                }
        }
        rcu_read_unlock();
}

/*
 * Cleanup a relayd object by flagging every associated streams for deletion,
 * destroying the object meaning removing it from the relayd hash table,
 * closing the sockets and freeing the memory in a RCU call.
 *
 * If a local data context is available, notify the threads that the streams'
 * state have changed.
 */
void lttng_consumer_cleanup_relayd(struct consumer_relayd_sock_pair *relayd)
{
        uint64_t netidx;

        assert(relayd);

        DBG("Cleaning up relayd object ID %"PRIu64, relayd->net_seq_idx);

        /* Save the net sequence index before destroying the object */
        netidx = relayd->net_seq_idx;

        /*
         * Delete the relayd from the relayd hash table, close the sockets and free
         * the object in a RCU call.
         */
        consumer_destroy_relayd(relayd);

        /* Set inactive endpoint to all streams */
        update_endpoint_status_by_netidx(netidx, CONSUMER_ENDPOINT_INACTIVE);

        /*
         * With a local data context, notify the threads that the streams' state
         * have changed. The write() action on the pipe acts as an "implicit"
         * memory barrier ordering the updates of the end point status from the
         * read of this status which happens AFTER receiving this notify.
         */
        notify_thread_lttng_pipe(relayd->ctx->consumer_data_pipe);
        notify_thread_lttng_pipe(relayd->ctx->consumer_metadata_pipe);
}

/*
 * Flag a relayd socket pair for destruction. Destroy it if the refcount
 * reaches zero.
 *
 * RCU read side lock MUST be aquired before calling this function.
 */
void consumer_flag_relayd_for_destroy(struct consumer_relayd_sock_pair *relayd)
{
        assert(relayd);

        /* Set destroy flag for this object */
        uatomic_set(&relayd->destroy_flag, 1);

        /* Destroy the relayd if refcount is 0 */
        if (uatomic_read(&relayd->refcount) == 0) {
                consumer_destroy_relayd(relayd);
        }
}

/*
 * Completly destroy stream from every visiable data structure and the given
 * hash table if one.
 *
 * One this call returns, the stream object is not longer usable nor visible.
 */
void consumer_del_stream(struct lttng_consumer_stream *stream,
                struct lttng_ht *ht)
{
        consumer_stream_destroy(stream, ht);
}

/*
 * XXX naming of del vs destroy is all mixed up.
 */
void consumer_del_stream_for_data(struct lttng_consumer_stream *stream)
{
        consumer_stream_destroy(stream, data_ht);
}

void consumer_del_stream_for_metadata(struct lttng_consumer_stream *stream)
{
        consumer_stream_destroy(stream, metadata_ht);
}

void consumer_stream_update_channel_attributes(
                struct lttng_consumer_stream *stream,
                struct lttng_consumer_channel *channel)
{
        stream->channel_read_only_attributes.tracefile_size =
                        channel->tracefile_size;
}

/*
 * Add a stream to the global list protected by a mutex.
 */
void consumer_add_data_stream(struct lttng_consumer_stream *stream)
{
        struct lttng_ht *ht = data_ht;

        assert(stream);
        assert(ht);

        DBG3("Adding consumer stream %" PRIu64, stream->key);

        pthread_mutex_lock(&consumer_data.lock);
        pthread_mutex_lock(&stream->chan->lock);
        pthread_mutex_lock(&stream->chan->timer_lock);
        pthread_mutex_lock(&stream->lock);
        rcu_read_lock();

        /* Steal stream identifier to avoid having streams with the same key */
        steal_stream_key(stream->key, ht);

        lttng_ht_add_unique_u64(ht, &stream->node);

        lttng_ht_add_u64(consumer_data.stream_per_chan_id_ht,
                        &stream->node_channel_id);

        /*
         * Add stream to the stream_list_ht of the consumer data. No need to steal
         * the key since the HT does not use it and we allow to add redundant keys
         * into this table.
         */
        lttng_ht_add_u64(consumer_data.stream_list_ht, &stream->node_session_id);

        /*
         * When nb_init_stream_left reaches 0, we don't need to trigger any action
         * in terms of destroying the associated channel, because the action that
         * causes the count to become 0 also causes a stream to be added. The
         * channel deletion will thus be triggered by the following removal of this
         * stream.
         */
        if (uatomic_read(&stream->chan->nb_init_stream_left) > 0) {
                /* Increment refcount before decrementing nb_init_stream_left */
                cmm_smp_wmb();
                uatomic_dec(&stream->chan->nb_init_stream_left);
        }

        /* Update consumer data once the node is inserted. */
        consumer_data.stream_count++;
        consumer_data.need_update = 1;

        rcu_read_unlock();
        pthread_mutex_unlock(&stream->lock);
        pthread_mutex_unlock(&stream->chan->timer_lock);
        pthread_mutex_unlock(&stream->chan->lock);
        pthread_mutex_unlock(&consumer_data.lock);
}

/*
 * Add relayd socket to global consumer data hashtable. RCU read side lock MUST
 * be acquired before calling this.
 */
static int add_relayd(struct consumer_relayd_sock_pair *relayd)
{
        int ret = 0;
        struct lttng_ht_node_u64 *node;
        struct lttng_ht_iter iter;

        assert(relayd);

        lttng_ht_lookup(consumer_data.relayd_ht,
                        &relayd->net_seq_idx, &iter);
        node = lttng_ht_iter_get_node_u64(&iter);
        if (node != NULL) {
                goto end;
        }
        lttng_ht_add_unique_u64(consumer_data.relayd_ht, &relayd->node);

end:
        return ret;
}

/*
 * Allocate and return a consumer relayd socket.
 */
static struct consumer_relayd_sock_pair *consumer_allocate_relayd_sock_pair(
                uint64_t net_seq_idx)
{
        struct consumer_relayd_sock_pair *obj = NULL;

        /* net sequence index of -1 is a failure */
        if (net_seq_idx == (uint64_t) -1ULL) {
                goto error;
        }

        obj = zmalloc(sizeof(struct consumer_relayd_sock_pair));
        if (obj == NULL) {
                PERROR("zmalloc relayd sock");
                goto error;
        }

        obj->net_seq_idx = net_seq_idx;
        obj->refcount = 0;
        obj->destroy_flag = 0;
        obj->control_sock.sock.fd = -1;
        obj->data_sock.sock.fd = -1;
        lttng_ht_node_init_u64(&obj->node, obj->net_seq_idx);
        pthread_mutex_init(&obj->ctrl_sock_mutex, NULL);

error:
        return obj;
}

/*
 * Find a relayd socket pair in the global consumer data.
 *
 * Return the object if found else NULL.
 * RCU read-side lock must be held across this call and while using the
 * returned object.
 */
struct consumer_relayd_sock_pair *consumer_find_relayd(uint64_t key)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_u64 *node;
        struct consumer_relayd_sock_pair *relayd = NULL;

        /* Negative keys are lookup failures */
        if (key == (uint64_t) -1ULL) {
                goto error;
        }

        lttng_ht_lookup(consumer_data.relayd_ht, &key,
                        &iter);
        node = lttng_ht_iter_get_node_u64(&iter);
        if (node != NULL) {
                relayd = caa_container_of(node, struct consumer_relayd_sock_pair, node);
        }

error:
        return relayd;
}

/*
 * Find a relayd and send the stream
 *
 * Returns 0 on success, < 0 on error
 */
int consumer_send_relayd_stream(struct lttng_consumer_stream *stream,
                char *path)
{
        int ret = 0;
        struct consumer_relayd_sock_pair *relayd;

        assert(stream);
        assert(stream->net_seq_idx != -1ULL);
        assert(path);

        /* The stream is not metadata. Get relayd reference if exists. */
        rcu_read_lock();
        relayd = consumer_find_relayd(stream->net_seq_idx);
        if (relayd != NULL) {
                /* Add stream on the relayd */
                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_add_stream(&relayd->control_sock, stream->name,
                                get_consumer_domain(), path, &stream->relayd_stream_id,
                                stream->chan->tracefile_size,
                                stream->chan->tracefile_count,
                                stream->trace_chunk);
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        ERR("Relayd add stream failed. Cleaning up relayd %" PRIu64".", relayd->net_seq_idx);
                        lttng_consumer_cleanup_relayd(relayd);
                        goto end;
                }

                uatomic_inc(&relayd->refcount);
                stream->sent_to_relayd = 1;
        } else {
                ERR("Stream %" PRIu64 " relayd ID %" PRIu64 " unknown. Can't send it.",
                                stream->key, stream->net_seq_idx);
                ret = -1;
                goto end;
        }

        DBG("Stream %s with key %" PRIu64 " sent to relayd id %" PRIu64,
                        stream->name, stream->key, stream->net_seq_idx);

end:
        rcu_read_unlock();
        return ret;
}

/*
 * Find a relayd and send the streams sent message
 *
 * Returns 0 on success, < 0 on error
 */
int consumer_send_relayd_streams_sent(uint64_t net_seq_idx)
{
        int ret = 0;
        struct consumer_relayd_sock_pair *relayd;

        assert(net_seq_idx != -1ULL);

        /* The stream is not metadata. Get relayd reference if exists. */
        rcu_read_lock();
        relayd = consumer_find_relayd(net_seq_idx);
        if (relayd != NULL) {
                /* Add stream on the relayd */
                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_streams_sent(&relayd->control_sock);
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        ERR("Relayd streams sent failed. Cleaning up relayd %" PRIu64".", relayd->net_seq_idx);
                        lttng_consumer_cleanup_relayd(relayd);
                        goto end;
                }
        } else {
                ERR("Relayd ID %" PRIu64 " unknown. Can't send streams_sent.",
                                net_seq_idx);
                ret = -1;
                goto end;
        }

        ret = 0;
        DBG("All streams sent relayd id %" PRIu64, net_seq_idx);

end:
        rcu_read_unlock();
        return ret;
}

/*
 * Find a relayd and close the stream
 */
void close_relayd_stream(struct lttng_consumer_stream *stream)
{
        struct consumer_relayd_sock_pair *relayd;

        /* The stream is not metadata. Get relayd reference if exists. */
        rcu_read_lock();
        relayd = consumer_find_relayd(stream->net_seq_idx);
        if (relayd) {
                consumer_stream_relayd_close(stream, relayd);
        }
        rcu_read_unlock();
}

/*
 * Handle stream for relayd transmission if the stream applies for network
 * streaming where the net sequence index is set.
 *
 * Return destination file descriptor or negative value on error.
 */
static int write_relayd_stream_header(struct lttng_consumer_stream *stream,
                size_t data_size, unsigned long padding,
                struct consumer_relayd_sock_pair *relayd)
{
        int outfd = -1, ret;
        struct lttcomm_relayd_data_hdr data_hdr;

        /* Safety net */
        assert(stream);
        assert(relayd);

        /* Reset data header */
        memset(&data_hdr, 0, sizeof(data_hdr));

        if (stream->metadata_flag) {
                /* Caller MUST acquire the relayd control socket lock */
                ret = relayd_send_metadata(&relayd->control_sock, data_size);
                if (ret < 0) {
                        goto error;
                }

                /* Metadata are always sent on the control socket. */
                outfd = relayd->control_sock.sock.fd;
        } else {
                /* Set header with stream information */
                data_hdr.stream_id = htobe64(stream->relayd_stream_id);
                data_hdr.data_size = htobe32(data_size);
                data_hdr.padding_size = htobe32(padding);

                /*
                 * Note that net_seq_num below is assigned with the *current* value of
                 * next_net_seq_num and only after that the next_net_seq_num will be
                 * increment. This is why when issuing a command on the relayd using
                 * this next value, 1 should always be substracted in order to compare
                 * the last seen sequence number on the relayd side to the last sent.
                 */
                data_hdr.net_seq_num = htobe64(stream->next_net_seq_num);
                /* Other fields are zeroed previously */

                ret = relayd_send_data_hdr(&relayd->data_sock, &data_hdr,
                                sizeof(data_hdr));
                if (ret < 0) {
                        goto error;
                }

                ++stream->next_net_seq_num;

                /* Set to go on data socket */
                outfd = relayd->data_sock.sock.fd;
        }

error:
        return outfd;
}

/*
 * Trigger a dump of the metadata content. Following/during the succesful
 * completion of this call, the metadata poll thread will start receiving
 * metadata packets to consume.
 *
 * The caller must hold the channel and stream locks.
 */
static
int consumer_metadata_stream_dump(struct lttng_consumer_stream *stream)
{
        int ret;

        ASSERT_LOCKED(stream->chan->lock);
        ASSERT_LOCKED(stream->lock);
        assert(stream->metadata_flag);
        assert(stream->chan->trace_chunk);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                /*
                 * Reset the position of what has been read from the
                 * metadata cache to 0 so we can dump it again.
                 */
                ret = kernctl_metadata_cache_dump(stream->wait_fd);
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                /*
                 * Reset the position pushed from the metadata cache so it
                 * will write from the beginning on the next push.
                 */
                stream->ust_metadata_pushed = 0;
                ret = consumer_metadata_wakeup_pipe(stream->chan);
                break;
        default:
                ERR("Unknown consumer_data type");
                abort();
        }
        if (ret < 0) {
                ERR("Failed to dump the metadata cache");
        }
        return ret;
}

static
int lttng_consumer_channel_set_trace_chunk(
                struct lttng_consumer_channel *channel,
                struct lttng_trace_chunk *new_trace_chunk)
{
        pthread_mutex_lock(&channel->lock);
        if (channel->is_deleted) {
                /*
                 * The channel has been logically deleted and should no longer
                 * be used. It has released its reference to its current trace
                 * chunk and should not acquire a new one.
                 *
                 * Return success as there is nothing for the caller to do.
                 */
                goto end;
        }

        /*
         * The acquisition of the reference cannot fail (barring
         * a severe internal error) since a reference to the published
         * chunk is already held by the caller.
         */
        if (new_trace_chunk) {
                const bool acquired_reference = lttng_trace_chunk_get(
                                new_trace_chunk);

                assert(acquired_reference);
        }

        lttng_trace_chunk_put(channel->trace_chunk);
        channel->trace_chunk = new_trace_chunk;
end:
        pthread_mutex_unlock(&channel->lock);
        return 0;
}

/*
 * Allocate and return a new lttng_consumer_channel object using the given key
 * to initialize the hash table node.
 *
 * On error, return NULL.
 */
struct lttng_consumer_channel *consumer_allocate_channel(uint64_t key,
                uint64_t session_id,
                const uint64_t *chunk_id,
                const char *pathname,
                const char *name,
                uint64_t relayd_id,
                enum lttng_event_output output,
                uint64_t tracefile_size,
                uint64_t tracefile_count,
                uint64_t session_id_per_pid,
                unsigned int monitor,
                unsigned int live_timer_interval,
                bool is_in_live_session,
                const char *root_shm_path,
                const char *shm_path)
{
        struct lttng_consumer_channel *channel = NULL;
        struct lttng_trace_chunk *trace_chunk = NULL;

        if (chunk_id) {
                trace_chunk = lttng_trace_chunk_registry_find_chunk(
                                consumer_data.chunk_registry, session_id,
                                *chunk_id);
                if (!trace_chunk) {
                        ERR("Failed to find trace chunk reference during creation of channel");
                        goto end;
                }
        }

        channel = zmalloc(sizeof(*channel));
        if (channel == NULL) {
                PERROR("malloc struct lttng_consumer_channel");
                goto end;
        }

        channel->key = key;
        channel->refcount = 0;
        channel->session_id = session_id;
        channel->session_id_per_pid = session_id_per_pid;
        channel->relayd_id = relayd_id;
        channel->tracefile_size = tracefile_size;
        channel->tracefile_count = tracefile_count;
        channel->monitor = monitor;
        channel->live_timer_interval = live_timer_interval;
        channel->is_live = is_in_live_session;
        pthread_mutex_init(&channel->lock, NULL);
        pthread_mutex_init(&channel->timer_lock, NULL);

        switch (output) {
        case LTTNG_EVENT_SPLICE:
                channel->output = CONSUMER_CHANNEL_SPLICE;
                break;
        case LTTNG_EVENT_MMAP:
                channel->output = CONSUMER_CHANNEL_MMAP;
                break;
        default:
                assert(0);
                free(channel);
                channel = NULL;
                goto end;
        }

        /*
         * In monitor mode, the streams associated with the channel will be put in
         * a special list ONLY owned by this channel. So, the refcount is set to 1
         * here meaning that the channel itself has streams that are referenced.
         *
         * On a channel deletion, once the channel is no longer visible, the
         * refcount is decremented and checked for a zero value to delete it. With
         * streams in no monitor mode, it will now be safe to destroy the channel.
         */
        if (!channel->monitor) {
                channel->refcount = 1;
        }

        strncpy(channel->pathname, pathname, sizeof(channel->pathname));
        channel->pathname[sizeof(channel->pathname) - 1] = '\0';

        strncpy(channel->name, name, sizeof(channel->name));
        channel->name[sizeof(channel->name) - 1] = '\0';

        if (root_shm_path) {
                strncpy(channel->root_shm_path, root_shm_path, sizeof(channel->root_shm_path));
                channel->root_shm_path[sizeof(channel->root_shm_path) - 1] = '\0';
        }
        if (shm_path) {
                strncpy(channel->shm_path, shm_path, sizeof(channel->shm_path));
                channel->shm_path[sizeof(channel->shm_path) - 1] = '\0';
        }

        lttng_ht_node_init_u64(&channel->node, channel->key);
        lttng_ht_node_init_u64(&channel->channels_by_session_id_ht_node,
                        channel->session_id);

        channel->wait_fd = -1;
        CDS_INIT_LIST_HEAD(&channel->streams.head);

        if (trace_chunk) {
                int ret = lttng_consumer_channel_set_trace_chunk(channel,
                                trace_chunk);
                if (ret) {
                        goto error;
                }
        }

        DBG("Allocated channel (key %" PRIu64 ")", channel->key);

end:
        lttng_trace_chunk_put(trace_chunk);
        return channel;
error:
        consumer_del_channel(channel);
        channel = NULL;
        goto end;
}

/*
 * Add a channel to the global list protected by a mutex.
 *
 * Always return 0 indicating success.
 */
int consumer_add_channel(struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx)
{
        pthread_mutex_lock(&consumer_data.lock);
        pthread_mutex_lock(&channel->lock);
        pthread_mutex_lock(&channel->timer_lock);

        /*
         * This gives us a guarantee that the channel we are about to add to the
         * channel hash table will be unique. See this function comment on the why
         * we need to steel the channel key at this stage.
         */
        steal_channel_key(channel->key);

        rcu_read_lock();
        lttng_ht_add_unique_u64(consumer_data.channel_ht, &channel->node);
        lttng_ht_add_u64(consumer_data.channels_by_session_id_ht,
                        &channel->channels_by_session_id_ht_node);
        rcu_read_unlock();
        channel->is_published = true;

        pthread_mutex_unlock(&channel->timer_lock);
        pthread_mutex_unlock(&channel->lock);
        pthread_mutex_unlock(&consumer_data.lock);

        if (channel->wait_fd != -1 && channel->type == CONSUMER_CHANNEL_TYPE_DATA) {
                notify_channel_pipe(ctx, channel, -1, CONSUMER_CHANNEL_ADD);
        }

        return 0;
}

/*
 * Allocate the pollfd structure and the local view of the out fds to avoid
 * doing a lookup in the linked list and concurrency issues when writing is
 * needed. Called with consumer_data.lock held.
 *
 * Returns the number of fds in the structures.
 */
static int update_poll_array(struct lttng_consumer_local_data *ctx,
                struct pollfd **pollfd, struct lttng_consumer_stream **local_stream,
                struct lttng_ht *ht, int *nb_inactive_fd)
{
        int i = 0;
        struct lttng_ht_iter iter;
        struct lttng_consumer_stream *stream;

        assert(ctx);
        assert(ht);
        assert(pollfd);
        assert(local_stream);

        DBG("Updating poll fd array");
        *nb_inactive_fd = 0;
        rcu_read_lock();
        cds_lfht_for_each_entry(ht->ht, &iter.iter, stream, node.node) {
                /*
                 * Only active streams with an active end point can be added to the
                 * poll set and local stream storage of the thread.
                 *
                 * There is a potential race here for endpoint_status to be updated
                 * just after the check. However, this is OK since the stream(s) will
                 * be deleted once the thread is notified that the end point state has
                 * changed where this function will be called back again.
                 *
                 * We track the number of inactive FDs because they still need to be
                 * closed by the polling thread after a wakeup on the data_pipe or
                 * metadata_pipe.
                 */
                if (stream->endpoint_status == CONSUMER_ENDPOINT_INACTIVE) {
                        (*nb_inactive_fd)++;
                        continue;
                }
                /*
                 * This clobbers way too much the debug output. Uncomment that if you
                 * need it for debugging purposes.
                 */
                (*pollfd)[i].fd = stream->wait_fd;
                (*pollfd)[i].events = POLLIN | POLLPRI;
                local_stream[i] = stream;
                i++;
        }
        rcu_read_unlock();

        /*
         * Insert the consumer_data_pipe at the end of the array and don't
         * increment i so nb_fd is the number of real FD.
         */
        (*pollfd)[i].fd = lttng_pipe_get_readfd(ctx->consumer_data_pipe);
        (*pollfd)[i].events = POLLIN | POLLPRI;

        (*pollfd)[i + 1].fd = lttng_pipe_get_readfd(ctx->consumer_wakeup_pipe);
        (*pollfd)[i + 1].events = POLLIN | POLLPRI;
        return i;
}

/*
 * Poll on the should_quit pipe and the command socket return -1 on
 * error, 1 if should exit, 0 if data is available on the command socket
 */
int lttng_consumer_poll_socket(struct pollfd *consumer_sockpoll)
{
        int num_rdy;

restart:
        num_rdy = poll(consumer_sockpoll, 2, -1);
        if (num_rdy == -1) {
                /*
                 * Restart interrupted system call.
                 */
                if (errno == EINTR) {
                        goto restart;
                }
                PERROR("Poll error");
                return -1;
        }
        if (consumer_sockpoll[0].revents & (POLLIN | POLLPRI)) {
                DBG("consumer_should_quit wake up");
                return 1;
        }
        return 0;
}

/*
 * Set the error socket.
 */
void lttng_consumer_set_error_sock(struct lttng_consumer_local_data *ctx,
                int sock)
{
        ctx->consumer_error_socket = sock;
}

/*
 * Set the command socket path.
 */
void lttng_consumer_set_command_sock_path(
                struct lttng_consumer_local_data *ctx, char *sock)
{
        ctx->consumer_command_sock_path = sock;
}

/*
 * Send return code to the session daemon.
 * If the socket is not defined, we return 0, it is not a fatal error
 */
int lttng_consumer_send_error(struct lttng_consumer_local_data *ctx, int cmd)
{
        if (ctx->consumer_error_socket > 0) {
                return lttcomm_send_unix_sock(ctx->consumer_error_socket, &cmd,
                                sizeof(enum lttcomm_sessiond_command));
        }

        return 0;
}

/*
 * Close all the tracefiles and stream fds and MUST be called when all
 * instances are destroyed i.e. when all threads were joined and are ended.
 */
void lttng_consumer_cleanup(void)
{
        struct lttng_ht_iter iter;
        struct lttng_consumer_channel *channel;
        unsigned int trace_chunks_left;

        rcu_read_lock();

        cds_lfht_for_each_entry(consumer_data.channel_ht->ht, &iter.iter, channel,
                        node.node) {
                consumer_del_channel(channel);
        }

        rcu_read_unlock();

        lttng_ht_destroy(consumer_data.channel_ht);
        lttng_ht_destroy(consumer_data.channels_by_session_id_ht);

        cleanup_relayd_ht();

        lttng_ht_destroy(consumer_data.stream_per_chan_id_ht);

        /*
         * This HT contains streams that are freed by either the metadata thread or
         * the data thread so we do *nothing* on the hash table and simply destroy
         * it.
         */
        lttng_ht_destroy(consumer_data.stream_list_ht);

        /*
         * Trace chunks in the registry may still exist if the session
         * daemon has encountered an internal error and could not
         * tear down its sessions and/or trace chunks properly.
         *
         * Release the session daemon's implicit reference to any remaining
         * trace chunk and print an error if any trace chunk was found. Note
         * that there are _no_ legitimate cases for trace chunks to be left,
         * it is a leak. However, it can happen following a crash of the
         * session daemon and not emptying the registry would cause an assertion
         * to hit.
         */
        trace_chunks_left = lttng_trace_chunk_registry_put_each_chunk(
                        consumer_data.chunk_registry);
        if (trace_chunks_left) {
                ERR("%u trace chunks are leaked by lttng-consumerd. "
                                "This can be caused by an internal error of the session daemon.",
                                trace_chunks_left);
        }
        /* Run all callbacks freeing each chunk. */
        rcu_barrier();
        lttng_trace_chunk_registry_destroy(consumer_data.chunk_registry);
}

/*
 * Called from signal handler.
 */
void lttng_consumer_should_exit(struct lttng_consumer_local_data *ctx)
{
        ssize_t ret;

        CMM_STORE_SHARED(consumer_quit, 1);
        ret = lttng_write(ctx->consumer_should_quit[1], "4", 1);
        if (ret < 1) {
                PERROR("write consumer quit");
        }

        DBG("Consumer flag that it should quit");
}


/*
 * Flush pending writes to trace output disk file.
 */
static
void lttng_consumer_sync_trace_file(struct lttng_consumer_stream *stream,
                off_t orig_offset)
{
        int ret;
        int outfd = stream->out_fd;

        /*
         * This does a blocking write-and-wait on any page that belongs to the
         * subbuffer prior to the one we just wrote.
         * Don't care about error values, as these are just hints and ways to
         * limit the amount of page cache used.
         */
        if (orig_offset < stream->max_sb_size) {
                return;
        }
        lttng_sync_file_range(outfd, orig_offset - stream->max_sb_size,
                        stream->max_sb_size,
                        SYNC_FILE_RANGE_WAIT_BEFORE
                        | SYNC_FILE_RANGE_WRITE
                        | SYNC_FILE_RANGE_WAIT_AFTER);
        /*
         * Give hints to the kernel about how we access the file:
         * POSIX_FADV_DONTNEED : we won't re-access data in a near future after
         * we write it.
         *
         * We need to call fadvise again after the file grows because the
         * kernel does not seem to apply fadvise to non-existing parts of the
         * file.
         *
         * Call fadvise _after_ having waited for the page writeback to
         * complete because the dirty page writeback semantic is not well
         * defined. So it can be expected to lead to lower throughput in
         * streaming.
         */
        ret = posix_fadvise(outfd, orig_offset - stream->max_sb_size,
                        stream->max_sb_size, POSIX_FADV_DONTNEED);
        if (ret && ret != -ENOSYS) {
                errno = ret;
                PERROR("posix_fadvise on fd %i", outfd);
        }
}

/*
 * Initialise the necessary environnement :
 * - create a new context
 * - create the poll_pipe
 * - create the should_quit pipe (for signal handler)
 * - create the thread pipe (for splice)
 *
 * Takes a function pointer as argument, this function is called when data is
 * available on a buffer. This function is responsible to do the
 * kernctl_get_next_subbuf, read the data with mmap or splice depending on the
 * buffer configuration and then kernctl_put_next_subbuf at the end.
 *
 * Returns a pointer to the new context or NULL on error.
 */
struct lttng_consumer_local_data *lttng_consumer_create(
                enum lttng_consumer_type type,
                ssize_t (*buffer_ready)(struct lttng_consumer_stream *stream,
                        struct lttng_consumer_local_data *ctx, bool locked_by_caller),
                int (*recv_channel)(struct lttng_consumer_channel *channel),
                int (*recv_stream)(struct lttng_consumer_stream *stream),
                int (*update_stream)(uint64_t stream_key, uint32_t state))
{
        int ret;
        struct lttng_consumer_local_data *ctx;

        assert(consumer_data.type == LTTNG_CONSUMER_UNKNOWN ||
                consumer_data.type == type);
        consumer_data.type = type;

        ctx = zmalloc(sizeof(struct lttng_consumer_local_data));
        if (ctx == NULL) {
                PERROR("allocating context");
                goto error;
        }

        ctx->consumer_error_socket = -1;
        ctx->consumer_metadata_socket = -1;
        pthread_mutex_init(&ctx->metadata_socket_lock, NULL);
        /* assign the callbacks */
        ctx->on_buffer_ready = buffer_ready;
        ctx->on_recv_channel = recv_channel;
        ctx->on_recv_stream = recv_stream;
        ctx->on_update_stream = update_stream;

        ctx->consumer_data_pipe = lttng_pipe_open(0);
        if (!ctx->consumer_data_pipe) {
                goto error_poll_pipe;
        }

        ctx->consumer_wakeup_pipe = lttng_pipe_open(0);
        if (!ctx->consumer_wakeup_pipe) {
                goto error_wakeup_pipe;
        }

        ret = pipe(ctx->consumer_should_quit);
        if (ret < 0) {
                PERROR("Error creating recv pipe");
                goto error_quit_pipe;
        }

        ret = pipe(ctx->consumer_channel_pipe);
        if (ret < 0) {
                PERROR("Error creating channel pipe");
                goto error_channel_pipe;
        }

        ctx->consumer_metadata_pipe = lttng_pipe_open(0);
        if (!ctx->consumer_metadata_pipe) {
                goto error_metadata_pipe;
        }

        ctx->channel_monitor_pipe = -1;

        return ctx;

error_metadata_pipe:
        utils_close_pipe(ctx->consumer_channel_pipe);
error_channel_pipe:
        utils_close_pipe(ctx->consumer_should_quit);
error_quit_pipe:
        lttng_pipe_destroy(ctx->consumer_wakeup_pipe);
error_wakeup_pipe:
        lttng_pipe_destroy(ctx->consumer_data_pipe);
error_poll_pipe:
        free(ctx);
error:
        return NULL;
}

/*
 * Iterate over all streams of the hashtable and free them properly.
 */
static void destroy_data_stream_ht(struct lttng_ht *ht)
{
        struct lttng_ht_iter iter;
        struct lttng_consumer_stream *stream;

        if (ht == NULL) {
                return;
        }

        rcu_read_lock();
        cds_lfht_for_each_entry(ht->ht, &iter.iter, stream, node.node) {
                /*
                 * Ignore return value since we are currently cleaning up so any error
                 * can't be handled.
                 */
                (void) consumer_del_stream(stream, ht);
        }
        rcu_read_unlock();

        lttng_ht_destroy(ht);
}

/*
 * Iterate over all streams of the metadata hashtable and free them
 * properly.
 */
static void destroy_metadata_stream_ht(struct lttng_ht *ht)
{
        struct lttng_ht_iter iter;
        struct lttng_consumer_stream *stream;

        if (ht == NULL) {
                return;
        }

        rcu_read_lock();
        cds_lfht_for_each_entry(ht->ht, &iter.iter, stream, node.node) {
                /*
                 * Ignore return value since we are currently cleaning up so any error
                 * can't be handled.
                 */
                (void) consumer_del_metadata_stream(stream, ht);
        }
        rcu_read_unlock();

        lttng_ht_destroy(ht);
}

/*
 * Close all fds associated with the instance and free the context.
 */
void lttng_consumer_destroy(struct lttng_consumer_local_data *ctx)
{
        int ret;

        DBG("Consumer destroying it. Closing everything.");

        if (!ctx) {
                return;
        }

        destroy_data_stream_ht(data_ht);
        destroy_metadata_stream_ht(metadata_ht);

        ret = close(ctx->consumer_error_socket);
        if (ret) {
                PERROR("close");
        }
        ret = close(ctx->consumer_metadata_socket);
        if (ret) {
                PERROR("close");
        }
        utils_close_pipe(ctx->consumer_channel_pipe);
        lttng_pipe_destroy(ctx->consumer_data_pipe);
        lttng_pipe_destroy(ctx->consumer_metadata_pipe);
        lttng_pipe_destroy(ctx->consumer_wakeup_pipe);
        utils_close_pipe(ctx->consumer_should_quit);

        unlink(ctx->consumer_command_sock_path);
        free(ctx);
}

/*
 * Write the metadata stream id on the specified file descriptor.
 */
static int write_relayd_metadata_id(int fd,
                struct lttng_consumer_stream *stream,
                unsigned long padding)
{
        ssize_t ret;
        struct lttcomm_relayd_metadata_payload hdr;

        hdr.stream_id = htobe64(stream->relayd_stream_id);
        hdr.padding_size = htobe32(padding);
        ret = lttng_write(fd, (void *) &hdr, sizeof(hdr));
        if (ret < sizeof(hdr)) {
                /*
                 * This error means that the fd's end is closed so ignore the PERROR
                 * not to clubber the error output since this can happen in a normal
                 * code path.
                 */
                if (errno != EPIPE) {
                        PERROR("write metadata stream id");
                }
                DBG3("Consumer failed to write relayd metadata id (errno: %d)", errno);
                /*
                 * Set ret to a negative value because if ret != sizeof(hdr), we don't
                 * handle writting the missing part so report that as an error and
                 * don't lie to the caller.
                 */
                ret = -1;
                goto end;
        }
        DBG("Metadata stream id %" PRIu64 " with padding %lu written before data",
                        stream->relayd_stream_id, padding);

end:
        return (int) ret;
}

/*
 * Mmap the ring buffer, read it and write the data to the tracefile. This is a
 * core function for writing trace buffers to either the local filesystem or
 * the network.
 *
 * It must be called with the stream and the channel lock held.
 *
 * Careful review MUST be put if any changes occur!
 *
 * Returns the number of bytes written
 */
ssize_t lttng_consumer_on_read_subbuffer_mmap(
                struct lttng_consumer_stream *stream,
                const struct lttng_buffer_view *buffer,
                unsigned long padding)
{
        ssize_t ret = 0;
        off_t orig_offset = stream->out_fd_offset;
        /* Default is on the disk */
        int outfd = stream->out_fd;
        struct consumer_relayd_sock_pair *relayd = NULL;
        unsigned int relayd_hang_up = 0;
        const size_t subbuf_content_size = buffer->size - padding;
        size_t write_len;

        /* RCU lock for the relayd pointer */
        rcu_read_lock();
        assert(stream->net_seq_idx != (uint64_t) -1ULL ||
                        stream->trace_chunk);

        /* Flag that the current stream if set for network streaming. */
        if (stream->net_seq_idx != (uint64_t) -1ULL) {
                relayd = consumer_find_relayd(stream->net_seq_idx);
                if (relayd == NULL) {
                        ret = -EPIPE;
                        goto end;
                }
        }

        /* Handle stream on the relayd if the output is on the network */
        if (relayd) {
                unsigned long netlen = subbuf_content_size;

                /*
                 * Lock the control socket for the complete duration of the function
                 * since from this point on we will use the socket.
                 */
                if (stream->metadata_flag) {
                        /* Metadata requires the control socket. */
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                        if (stream->reset_metadata_flag) {
                                ret = relayd_reset_metadata(&relayd->control_sock,
                                                stream->relayd_stream_id,
                                                stream->metadata_version);
                                if (ret < 0) {
                                        relayd_hang_up = 1;
                                        goto write_error;
                                }
                                stream->reset_metadata_flag = 0;
                        }
                        netlen += sizeof(struct lttcomm_relayd_metadata_payload);
                }

                ret = write_relayd_stream_header(stream, netlen, padding, relayd);
                if (ret < 0) {
                        relayd_hang_up = 1;
                        goto write_error;
                }
                /* Use the returned socket. */
                outfd = ret;

                /* Write metadata stream id before payload */
                if (stream->metadata_flag) {
                        ret = write_relayd_metadata_id(outfd, stream, padding);
                        if (ret < 0) {
                                relayd_hang_up = 1;
                                goto write_error;
                        }
                }

                write_len = subbuf_content_size;
        } else {
                /* No streaming; we have to write the full padding. */
                if (stream->metadata_flag && stream->reset_metadata_flag) {
                        ret = utils_truncate_stream_file(stream->out_fd, 0);
                        if (ret < 0) {
                                ERR("Reset metadata file");
                                goto end;
                        }
                        stream->reset_metadata_flag = 0;
                }

                /*
                 * Check if we need to change the tracefile before writing the packet.
                 */
                if (stream->chan->tracefile_size > 0 &&
                                (stream->tracefile_size_current + buffer->size) >
                                stream->chan->tracefile_size) {
                        ret = consumer_stream_rotate_output_files(stream);
                        if (ret) {
                                goto end;
                        }
                        outfd = stream->out_fd;
                        orig_offset = 0;
                }
                stream->tracefile_size_current += buffer->size;
                write_len = buffer->size;
        }

        /*
         * This call guarantee that len or less is returned. It's impossible to
         * receive a ret value that is bigger than len.
         */
        ret = lttng_write(outfd, buffer->data, write_len);
        DBG("Consumer mmap write() ret %zd (len %zu)", ret, write_len);
        if (ret < 0 || ((size_t) ret != write_len)) {
                /*
                 * Report error to caller if nothing was written else at least send the
                 * amount written.
                 */
                if (ret < 0) {
                        ret = -errno;
                }
                relayd_hang_up = 1;

                /* Socket operation failed. We consider the relayd dead */
                if (errno == EPIPE) {
                        /*
                         * This is possible if the fd is closed on the other side
                         * (outfd) or any write problem. It can be verbose a bit for a
                         * normal execution if for instance the relayd is stopped
                         * abruptly. This can happen so set this to a DBG statement.
                         */
                        DBG("Consumer mmap write detected relayd hang up");
                } else {
                        /* Unhandled error, print it and stop function right now. */
                        PERROR("Error in write mmap (ret %zd != write_len %zu)", ret,
                                        write_len);
                }
                goto write_error;
        }
        stream->output_written += ret;

        /* This call is useless on a socket so better save a syscall. */
        if (!relayd) {
                /* This won't block, but will start writeout asynchronously */
                lttng_sync_file_range(outfd, stream->out_fd_offset, write_len,
                                SYNC_FILE_RANGE_WRITE);
                stream->out_fd_offset += write_len;
                lttng_consumer_sync_trace_file(stream, orig_offset);
        }

write_error:
        /*
         * This is a special case that the relayd has closed its socket. Let's
         * cleanup the relayd object and all associated streams.
         */
        if (relayd && relayd_hang_up) {
                ERR("Relayd hangup. Cleaning up relayd %" PRIu64".", relayd->net_seq_idx);
                lttng_consumer_cleanup_relayd(relayd);
        }

end:
        /* Unlock only if ctrl socket used */
        if (relayd && stream->metadata_flag) {
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
        }

        rcu_read_unlock();
        return ret;
}

/*
 * Splice the data from the ring buffer to the tracefile.
 *
 * It must be called with the stream lock held.
 *
 * Returns the number of bytes spliced.
 */
ssize_t lttng_consumer_on_read_subbuffer_splice(
                struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_stream *stream, unsigned long len,
                unsigned long padding)
{
        ssize_t ret = 0, written = 0, ret_splice = 0;
        loff_t offset = 0;
        off_t orig_offset = stream->out_fd_offset;
        int fd = stream->wait_fd;
        /* Default is on the disk */
        int outfd = stream->out_fd;
        struct consumer_relayd_sock_pair *relayd = NULL;
        int *splice_pipe;
        unsigned int relayd_hang_up = 0;

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                /* Not supported for user space tracing */
                return -ENOSYS;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
        }

        /* RCU lock for the relayd pointer */
        rcu_read_lock();

        /* Flag that the current stream if set for network streaming. */
        if (stream->net_seq_idx != (uint64_t) -1ULL) {
                relayd = consumer_find_relayd(stream->net_seq_idx);
                if (relayd == NULL) {
                        written = -ret;
                        goto end;
                }
        }
        splice_pipe = stream->splice_pipe;

        /* Write metadata stream id before payload */
        if (relayd) {
                unsigned long total_len = len;

                if (stream->metadata_flag) {
                        /*
                         * Lock the control socket for the complete duration of the function
                         * since from this point on we will use the socket.
                         */
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);

                        if (stream->reset_metadata_flag) {
                                ret = relayd_reset_metadata(&relayd->control_sock,
                                                stream->relayd_stream_id,
                                                stream->metadata_version);
                                if (ret < 0) {
                                        relayd_hang_up = 1;
                                        goto write_error;
                                }
                                stream->reset_metadata_flag = 0;
                        }
                        ret = write_relayd_metadata_id(splice_pipe[1], stream,
                                        padding);
                        if (ret < 0) {
                                written = ret;
                                relayd_hang_up = 1;
                                goto write_error;
                        }

                        total_len += sizeof(struct lttcomm_relayd_metadata_payload);
                }

                ret = write_relayd_stream_header(stream, total_len, padding, relayd);
                if (ret < 0) {
                        written = ret;
                        relayd_hang_up = 1;
                        goto write_error;
                }
                /* Use the returned socket. */
                outfd = ret;
        } else {
                /* No streaming, we have to set the len with the full padding */
                len += padding;

                if (stream->metadata_flag && stream->reset_metadata_flag) {
                        ret = utils_truncate_stream_file(stream->out_fd, 0);
                        if (ret < 0) {
                                ERR("Reset metadata file");
                                goto end;
                        }
                        stream->reset_metadata_flag = 0;
                }
                /*
                 * Check if we need to change the tracefile before writing the packet.
                 */
                if (stream->chan->tracefile_size > 0 &&
                                (stream->tracefile_size_current + len) >
                                stream->chan->tracefile_size) {
                        ret = consumer_stream_rotate_output_files(stream);
                        if (ret < 0) {
                                written = ret;
                                goto end;
                        }
                        outfd = stream->out_fd;
                        orig_offset = 0;
                }
                stream->tracefile_size_current += len;
        }

        while (len > 0) {
                DBG("splice chan to pipe offset %lu of len %lu (fd : %d, pipe: %d)",
                                (unsigned long)offset, len, fd, splice_pipe[1]);
                ret_splice = splice(fd, &offset, splice_pipe[1], NULL, len,
                                SPLICE_F_MOVE | SPLICE_F_MORE);
                DBG("splice chan to pipe, ret %zd", ret_splice);
                if (ret_splice < 0) {
                        ret = errno;
                        written = -ret;
                        PERROR("Error in relay splice");
                        goto splice_error;
                }

                /* Handle stream on the relayd if the output is on the network */
                if (relayd && stream->metadata_flag) {
                        size_t metadata_payload_size =
                                sizeof(struct lttcomm_relayd_metadata_payload);

                        /* Update counter to fit the spliced data */
                        ret_splice += metadata_payload_size;
                        len += metadata_payload_size;
                        /*
                         * We do this so the return value can match the len passed as
                         * argument to this function.
                         */
                        written -= metadata_payload_size;
                }

                /* Splice data out */
                ret_splice = splice(splice_pipe[0], NULL, outfd, NULL,
                                ret_splice, SPLICE_F_MOVE | SPLICE_F_MORE);
                DBG("Consumer splice pipe to file (out_fd: %d), ret %zd",
                                outfd, ret_splice);
                if (ret_splice < 0) {
                        ret = errno;
                        written = -ret;
                        relayd_hang_up = 1;
                        goto write_error;
                } else if (ret_splice > len) {
                        /*
                         * We don't expect this code path to be executed but you never know
                         * so this is an extra protection agains a buggy splice().
                         */
                        ret = errno;
                        written += ret_splice;
                        PERROR("Wrote more data than requested %zd (len: %lu)", ret_splice,
                                        len);
                        goto splice_error;
                } else {
                        /* All good, update current len and continue. */
                        len -= ret_splice;
                }

                /* This call is useless on a socket so better save a syscall. */
                if (!relayd) {
                        /* This won't block, but will start writeout asynchronously */
                        lttng_sync_file_range(outfd, stream->out_fd_offset, ret_splice,
                                        SYNC_FILE_RANGE_WRITE);
                        stream->out_fd_offset += ret_splice;
                }
                stream->output_written += ret_splice;
                written += ret_splice;
        }
        if (!relayd) {
                lttng_consumer_sync_trace_file(stream, orig_offset);
        }
        goto end;

write_error:
        /*
         * This is a special case that the relayd has closed its socket. Let's
         * cleanup the relayd object and all associated streams.
         */
        if (relayd && relayd_hang_up) {
                ERR("Relayd hangup. Cleaning up relayd %" PRIu64".", relayd->net_seq_idx);
                lttng_consumer_cleanup_relayd(relayd);
                /* Skip splice error so the consumer does not fail */
                goto end;
        }

splice_error:
        /* send the appropriate error description to sessiond */
        switch (ret) {
        case EINVAL:
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_SPLICE_EINVAL);
                break;
        case ENOMEM:
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_SPLICE_ENOMEM);
                break;
        case ESPIPE:
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_SPLICE_ESPIPE);
                break;
        }

end:
        if (relayd && stream->metadata_flag) {
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
        }

        rcu_read_unlock();
        return written;
}

/*
 * Sample the snapshot positions for a specific fd
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_sample_snapshot_positions(struct lttng_consumer_stream *stream)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_sample_snapshot_positions(stream);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_sample_snapshot_positions(stream);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}
/*
 * Take a snapshot for a specific fd
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_take_snapshot(struct lttng_consumer_stream *stream)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_take_snapshot(stream);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_take_snapshot(stream);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

/*
 * Get the produced position
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_get_produced_snapshot(struct lttng_consumer_stream *stream,
                unsigned long *pos)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_get_produced_snapshot(stream, pos);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_get_produced_snapshot(stream, pos);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

/*
 * Get the consumed position (free-running counter position in bytes).
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_get_consumed_snapshot(struct lttng_consumer_stream *stream,
                unsigned long *pos)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_get_consumed_snapshot(stream, pos);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_get_consumed_snapshot(stream, pos);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

int lttng_consumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                int sock, struct pollfd *consumer_sockpoll)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_recv_cmd(ctx, sock, consumer_sockpoll);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_recv_cmd(ctx, sock, consumer_sockpoll);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

static
void lttng_consumer_close_all_metadata(void)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                /*
                 * The Kernel consumer has a different metadata scheme so we don't
                 * close anything because the stream will be closed by the session
                 * daemon.
                 */
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                /*
                 * Close all metadata streams. The metadata hash table is passed and
                 * this call iterates over it by closing all wakeup fd. This is safe
                 * because at this point we are sure that the metadata producer is
                 * either dead or blocked.
                 */
                lttng_ustconsumer_close_all_metadata(metadata_ht);
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
        }
}

/*
 * Clean up a metadata stream and free its memory.
 */
void consumer_del_metadata_stream(struct lttng_consumer_stream *stream,
                struct lttng_ht *ht)
{
        struct lttng_consumer_channel *channel = NULL;
        bool free_channel = false;

        assert(stream);
        /*
         * This call should NEVER receive regular stream. It must always be
         * metadata stream and this is crucial for data structure synchronization.
         */
        assert(stream->metadata_flag);

        DBG3("Consumer delete metadata stream %d", stream->wait_fd);

        pthread_mutex_lock(&consumer_data.lock);
        /*
         * Note that this assumes that a stream's channel is never changed and
         * that the stream's lock doesn't need to be taken to sample its
         * channel.
         */
        channel = stream->chan;
        pthread_mutex_lock(&channel->lock);
        pthread_mutex_lock(&stream->lock);
        if (channel->metadata_cache) {
                /* Only applicable to userspace consumers. */
                pthread_mutex_lock(&channel->metadata_cache->lock);
        }

        /* Remove any reference to that stream. */
        consumer_stream_delete(stream, ht);

        /* Close down everything including the relayd if one. */
        consumer_stream_close(stream);
        /* Destroy tracer buffers of the stream. */
        consumer_stream_destroy_buffers(stream);

        /* Atomically decrement channel refcount since other threads can use it. */
        if (!uatomic_sub_return(&channel->refcount, 1)
                        && !uatomic_read(&channel->nb_init_stream_left)) {
                /* Go for channel deletion! */
                free_channel = true;
        }
        stream->chan = NULL;

        /*
         * Nullify the stream reference so it is not used after deletion. The
         * channel lock MUST be acquired before being able to check for a NULL
         * pointer value.
         */
        channel->metadata_stream = NULL;

        if (channel->metadata_cache) {
                pthread_mutex_unlock(&channel->metadata_cache->lock);
        }
        pthread_mutex_unlock(&stream->lock);
        pthread_mutex_unlock(&channel->lock);
        pthread_mutex_unlock(&consumer_data.lock);

        if (free_channel) {
                consumer_del_channel(channel);
        }

        lttng_trace_chunk_put(stream->trace_chunk);
        stream->trace_chunk = NULL;
        consumer_stream_free(stream);
}

/*
 * Action done with the metadata stream when adding it to the consumer internal
 * data structures to handle it.
 */
void consumer_add_metadata_stream(struct lttng_consumer_stream *stream)
{
        struct lttng_ht *ht = metadata_ht;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_u64 *node;

        assert(stream);
        assert(ht);

        DBG3("Adding metadata stream %" PRIu64 " to hash table", stream->key);

        pthread_mutex_lock(&consumer_data.lock);
        pthread_mutex_lock(&stream->chan->lock);
        pthread_mutex_lock(&stream->chan->timer_lock);
        pthread_mutex_lock(&stream->lock);

        /*
         * From here, refcounts are updated so be _careful_ when returning an error
         * after this point.
         */

        rcu_read_lock();

        /*
         * Lookup the stream just to make sure it does not exist in our internal
         * state. This should NEVER happen.
         */
        lttng_ht_lookup(ht, &stream->key, &iter);
        node = lttng_ht_iter_get_node_u64(&iter);
        assert(!node);

        /*
         * When nb_init_stream_left reaches 0, we don't need to trigger any action
         * in terms of destroying the associated channel, because the action that
         * causes the count to become 0 also causes a stream to be added. The
         * channel deletion will thus be triggered by the following removal of this
         * stream.
         */
        if (uatomic_read(&stream->chan->nb_init_stream_left) > 0) {
                /* Increment refcount before decrementing nb_init_stream_left */
                cmm_smp_wmb();
                uatomic_dec(&stream->chan->nb_init_stream_left);
        }

        lttng_ht_add_unique_u64(ht, &stream->node);

        lttng_ht_add_u64(consumer_data.stream_per_chan_id_ht,
                &stream->node_channel_id);

        /*
         * Add stream to the stream_list_ht of the consumer data. No need to steal
         * the key since the HT does not use it and we allow to add redundant keys
         * into this table.
         */
        lttng_ht_add_u64(consumer_data.stream_list_ht, &stream->node_session_id);

        rcu_read_unlock();

        pthread_mutex_unlock(&stream->lock);
        pthread_mutex_unlock(&stream->chan->lock);
        pthread_mutex_unlock(&stream->chan->timer_lock);
        pthread_mutex_unlock(&consumer_data.lock);
}

/*
 * Delete data stream that are flagged for deletion (endpoint_status).
 */
static void validate_endpoint_status_data_stream(void)
{
        struct lttng_ht_iter iter;
        struct lttng_consumer_stream *stream;

        DBG("Consumer delete flagged data stream");

        rcu_read_lock();
        cds_lfht_for_each_entry(data_ht->ht, &iter.iter, stream, node.node) {
                /* Validate delete flag of the stream */
                if (stream->endpoint_status == CONSUMER_ENDPOINT_ACTIVE) {
                        continue;
                }
                /* Delete it right now */
                consumer_del_stream(stream, data_ht);
        }
        rcu_read_unlock();
}

/*
 * Delete metadata stream that are flagged for deletion (endpoint_status).
 */
static void validate_endpoint_status_metadata_stream(
                struct lttng_poll_event *pollset)
{
        struct lttng_ht_iter iter;
        struct lttng_consumer_stream *stream;

        DBG("Consumer delete flagged metadata stream");

        assert(pollset);

        rcu_read_lock();
        cds_lfht_for_each_entry(metadata_ht->ht, &iter.iter, stream, node.node) {
                /* Validate delete flag of the stream */
                if (stream->endpoint_status == CONSUMER_ENDPOINT_ACTIVE) {
                        continue;
                }
                /*
                 * Remove from pollset so the metadata thread can continue without
                 * blocking on a deleted stream.
                 */
                lttng_poll_del(pollset, stream->wait_fd);

                /* Delete it right now */
                consumer_del_metadata_stream(stream, metadata_ht);
        }
        rcu_read_unlock();
}

/*
 * Thread polls on metadata file descriptor and write them on disk or on the
 * network.
 */
void *consumer_thread_metadata_poll(void *data)
{
        int ret, i, pollfd, err = -1;
        uint32_t revents, nb_fd;
        struct lttng_consumer_stream *stream = NULL;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_u64 *node;
        struct lttng_poll_event events;
        struct lttng_consumer_local_data *ctx = data;
        ssize_t len;

        rcu_register_thread();

        health_register(health_consumerd, HEALTH_CONSUMERD_TYPE_METADATA);

        if (testpoint(consumerd_thread_metadata)) {
                goto error_testpoint;
        }

        health_code_update();

        DBG("Thread metadata poll started");

        /* Size is set to 1 for the consumer_metadata pipe */
        ret = lttng_poll_create(&events, 2, LTTNG_CLOEXEC);
        if (ret < 0) {
                ERR("Poll set creation failed");
                goto end_poll;
        }

        ret = lttng_poll_add(&events,
                        lttng_pipe_get_readfd(ctx->consumer_metadata_pipe), LPOLLIN);
        if (ret < 0) {
                goto end;
        }

        /* Main loop */
        DBG("Metadata main loop started");

        while (1) {
restart:
                health_code_update();
                health_poll_entry();
                DBG("Metadata poll wait");
                ret = lttng_poll_wait(&events, -1);
                DBG("Metadata poll return from wait with %d fd(s)",
                                LTTNG_POLL_GETNB(&events));
                health_poll_exit();
                DBG("Metadata event caught in thread");
                if (ret < 0) {
                        if (errno == EINTR) {
                                ERR("Poll EINTR caught");
                                goto restart;
                        }
                        if (LTTNG_POLL_GETNB(&events) == 0) {
                                err = 0;        /* All is OK */
                        }
                        goto end;
                }

                nb_fd = ret;

                /* From here, the event is a metadata wait fd */
                for (i = 0; i < nb_fd; i++) {
                        health_code_update();

                        revents = LTTNG_POLL_GETEV(&events, i);
                        pollfd = LTTNG_POLL_GETFD(&events, i);

                        if (pollfd == lttng_pipe_get_readfd(ctx->consumer_metadata_pipe)) {
                                if (revents & LPOLLIN) {
                                        ssize_t pipe_len;

                                        pipe_len = lttng_pipe_read(ctx->consumer_metadata_pipe,
                                                        &stream, sizeof(stream));
                                        if (pipe_len < sizeof(stream)) {
                                                if (pipe_len < 0) {
                                                        PERROR("read metadata stream");
                                                }
                                                /*
                                                 * Remove the pipe from the poll set and continue the loop
                                                 * since their might be data to consume.
                                                 */
                                                lttng_poll_del(&events,
                                                                lttng_pipe_get_readfd(ctx->consumer_metadata_pipe));
                                                lttng_pipe_read_close(ctx->consumer_metadata_pipe);
                                                continue;
                                        }

                                        /* A NULL stream means that the state has changed. */
                                        if (stream == NULL) {
                                                /* Check for deleted streams. */
                                                validate_endpoint_status_metadata_stream(&events);
                                                goto restart;
                                        }

                                        DBG("Adding metadata stream %d to poll set",
                                                        stream->wait_fd);

                                        /* Add metadata stream to the global poll events list */
                                        lttng_poll_add(&events, stream->wait_fd,
                                                        LPOLLIN | LPOLLPRI | LPOLLHUP);
                                } else if (revents & (LPOLLERR | LPOLLHUP)) {
                                        DBG("Metadata thread pipe hung up");
                                        /*
                                         * Remove the pipe from the poll set and continue the loop
                                         * since their might be data to consume.
                                         */
                                        lttng_poll_del(&events,
                                                        lttng_pipe_get_readfd(ctx->consumer_metadata_pipe));
                                        lttng_pipe_read_close(ctx->consumer_metadata_pipe);
                                        continue;
                                } else {
                                        ERR("Unexpected poll events %u for sock %d", revents, pollfd);
                                        goto end;
                                }

                                /* Handle other stream */
                                continue;
                        }

                        rcu_read_lock();
                        {
                                uint64_t tmp_id = (uint64_t) pollfd;

                                lttng_ht_lookup(metadata_ht, &tmp_id, &iter);
                        }
                        node = lttng_ht_iter_get_node_u64(&iter);
                        assert(node);

                        stream = caa_container_of(node, struct lttng_consumer_stream,
                                        node);

                        if (revents & (LPOLLIN | LPOLLPRI)) {
                                /* Get the data out of the metadata file descriptor */
                                DBG("Metadata available on fd %d", pollfd);
                                assert(stream->wait_fd == pollfd);

                                do {
                                        health_code_update();

                                        len = ctx->on_buffer_ready(stream, ctx, false);
                                        /*
                                         * We don't check the return value here since if we get
                                         * a negative len, it means an error occurred thus we
                                         * simply remove it from the poll set and free the
                                         * stream.
                                         */
                                } while (len > 0);

                                /* It's ok to have an unavailable sub-buffer */
                                if (len < 0 && len != -EAGAIN && len != -ENODATA) {
                                        /* Clean up stream from consumer and free it. */
                                        lttng_poll_del(&events, stream->wait_fd);
                                        consumer_del_metadata_stream(stream, metadata_ht);
                                }
                        } else if (revents & (LPOLLERR | LPOLLHUP)) {
                                DBG("Metadata fd %d is hup|err.", pollfd);
                                if (!stream->hangup_flush_done
                                                && (consumer_data.type == LTTNG_CONSUMER32_UST
                                                        || consumer_data.type == LTTNG_CONSUMER64_UST)) {
                                        DBG("Attempting to flush and consume the UST buffers");
                                        lttng_ustconsumer_on_stream_hangup(stream);

                                        /* We just flushed the stream now read it. */
                                        do {
                                                health_code_update();

                                                len = ctx->on_buffer_ready(stream, ctx, false);
                                                /*
                                                 * We don't check the return value here since if we get
                                                 * a negative len, it means an error occurred thus we
                                                 * simply remove it from the poll set and free the
                                                 * stream.
                                                 */
                                        } while (len > 0);
                                }

                                lttng_poll_del(&events, stream->wait_fd);
                                /*
                                 * This call update the channel states, closes file descriptors
                                 * and securely free the stream.
                                 */
                                consumer_del_metadata_stream(stream, metadata_ht);
                        } else {
                                ERR("Unexpected poll events %u for sock %d", revents, pollfd);
                                rcu_read_unlock();
                                goto end;
                        }
                        /* Release RCU lock for the stream looked up */
                        rcu_read_unlock();
                }
        }

        /* All is OK */
        err = 0;
end:
        DBG("Metadata poll thread exiting");

        lttng_poll_clean(&events);
end_poll:
error_testpoint:
        if (err) {
                health_error();
                ERR("Health error occurred in %s", __func__);
        }
        health_unregister(health_consumerd);
        rcu_unregister_thread();
        return NULL;
}

/*
 * This thread polls the fds in the set to consume the data and write
 * it to tracefile if necessary.
 */
void *consumer_thread_data_poll(void *data)
{
        int num_rdy, num_hup, high_prio, ret, i, err = -1;
        struct pollfd *pollfd = NULL;
        /* local view of the streams */
        struct lttng_consumer_stream **local_stream = NULL, *new_stream = NULL;
        /* local view of consumer_data.fds_count */
        int nb_fd = 0;
        /* 2 for the consumer_data_pipe and wake up pipe */
        const int nb_pipes_fd = 2;
        /* Number of FDs with CONSUMER_ENDPOINT_INACTIVE but still open. */
        int nb_inactive_fd = 0;
        struct lttng_consumer_local_data *ctx = data;
        ssize_t len;

        rcu_register_thread();

        health_register(health_consumerd, HEALTH_CONSUMERD_TYPE_DATA);

        if (testpoint(consumerd_thread_data)) {
                goto error_testpoint;
        }

        health_code_update();

        local_stream = zmalloc(sizeof(struct lttng_consumer_stream *));
        if (local_stream == NULL) {
                PERROR("local_stream malloc");
                goto end;
        }

        while (1) {
                health_code_update();

                high_prio = 0;
                num_hup = 0;

                /*
                 * the fds set has been updated, we need to update our
                 * local array as well
                 */
                pthread_mutex_lock(&consumer_data.lock);
                if (consumer_data.need_update) {
                        free(pollfd);
                        pollfd = NULL;

                        free(local_stream);
                        local_stream = NULL;

                        /* Allocate for all fds */
                        pollfd = zmalloc((consumer_data.stream_count + nb_pipes_fd) * sizeof(struct pollfd));
                        if (pollfd == NULL) {
                                PERROR("pollfd malloc");
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }

                        local_stream = zmalloc((consumer_data.stream_count + nb_pipes_fd) *
                                        sizeof(struct lttng_consumer_stream *));
                        if (local_stream == NULL) {
                                PERROR("local_stream malloc");
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }
                        ret = update_poll_array(ctx, &pollfd, local_stream,
                                        data_ht, &nb_inactive_fd);
                        if (ret < 0) {
                                ERR("Error in allocating pollfd or local_outfds");
                                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_POLL_ERROR);
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }
                        nb_fd = ret;
                        consumer_data.need_update = 0;
                }
                pthread_mutex_unlock(&consumer_data.lock);

                /* No FDs and consumer_quit, consumer_cleanup the thread */
                if (nb_fd == 0 && nb_inactive_fd == 0 &&
                                CMM_LOAD_SHARED(consumer_quit) == 1) {
                        err = 0;        /* All is OK */
                        goto end;
                }
                /* poll on the array of fds */
        restart:
                DBG("polling on %d fd", nb_fd + nb_pipes_fd);
                if (testpoint(consumerd_thread_data_poll)) {
                        goto end;
                }
                health_poll_entry();
                num_rdy = poll(pollfd, nb_fd + nb_pipes_fd, -1);
                health_poll_exit();
                DBG("poll num_rdy : %d", num_rdy);
                if (num_rdy == -1) {
                        /*
                         * Restart interrupted system call.
                         */
                        if (errno == EINTR) {
                                goto restart;
                        }
                        PERROR("Poll error");
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_POLL_ERROR);
                        goto end;
                } else if (num_rdy == 0) {
                        DBG("Polling thread timed out");
                        goto end;
                }

                if (caa_unlikely(data_consumption_paused)) {
                        DBG("Data consumption paused, sleeping...");
                        sleep(1);
                        goto restart;
                }

                /*
                 * If the consumer_data_pipe triggered poll go directly to the
                 * beginning of the loop to update the array. We want to prioritize
                 * array update over low-priority reads.
                 */
                if (pollfd[nb_fd].revents & (POLLIN | POLLPRI)) {
                        ssize_t pipe_readlen;

                        DBG("consumer_data_pipe wake up");
                        pipe_readlen = lttng_pipe_read(ctx->consumer_data_pipe,
                                        &new_stream, sizeof(new_stream));
                        if (pipe_readlen < sizeof(new_stream)) {
                                PERROR("Consumer data pipe");
                                /* Continue so we can at least handle the current stream(s). */
                                continue;
                        }

                        /*
                         * If the stream is NULL, just ignore it. It's also possible that
                         * the sessiond poll thread changed the consumer_quit state and is
                         * waking us up to test it.
                         */
                        if (new_stream == NULL) {
                                validate_endpoint_status_data_stream();
                                continue;
                        }

                        /* Continue to update the local streams and handle prio ones */
                        continue;
                }

                /* Handle wakeup pipe. */
                if (pollfd[nb_fd + 1].revents & (POLLIN | POLLPRI)) {
                        char dummy;
                        ssize_t pipe_readlen;

                        pipe_readlen = lttng_pipe_read(ctx->consumer_wakeup_pipe, &dummy,
                                        sizeof(dummy));
                        if (pipe_readlen < 0) {
                                PERROR("Consumer data wakeup pipe");
                        }
                        /* We've been awakened to handle stream(s). */
                        ctx->has_wakeup = 0;
                }

                /* Take care of high priority channels first. */
                for (i = 0; i < nb_fd; i++) {
                        health_code_update();

                        if (local_stream[i] == NULL) {
                                continue;
                        }
                        if (pollfd[i].revents & POLLPRI) {
                                DBG("Urgent read on fd %d", pollfd[i].fd);
                                high_prio = 1;
                                len = ctx->on_buffer_ready(local_stream[i], ctx, false);
                                /* it's ok to have an unavailable sub-buffer */
                                if (len < 0 && len != -EAGAIN && len != -ENODATA) {
                                        /* Clean the stream and free it. */
                                        consumer_del_stream(local_stream[i], data_ht);
                                        local_stream[i] = NULL;
                                } else if (len > 0) {
                                        local_stream[i]->data_read = 1;
                                }
                        }
                }

                /*
                 * If we read high prio channel in this loop, try again
                 * for more high prio data.
                 */
                if (high_prio) {
                        continue;
                }

                /* Take care of low priority channels. */
                for (i = 0; i < nb_fd; i++) {
                        health_code_update();

                        if (local_stream[i] == NULL) {
                                continue;
                        }
                        if ((pollfd[i].revents & POLLIN) ||
                                        local_stream[i]->hangup_flush_done ||
                                        local_stream[i]->has_data) {
                                DBG("Normal read on fd %d", pollfd[i].fd);
                                len = ctx->on_buffer_ready(local_stream[i], ctx, false);
                                /* it's ok to have an unavailable sub-buffer */
                                if (len < 0 && len != -EAGAIN && len != -ENODATA) {
                                        /* Clean the stream and free it. */
                                        consumer_del_stream(local_stream[i], data_ht);
                                        local_stream[i] = NULL;
                                } else if (len > 0) {
                                        local_stream[i]->data_read = 1;
                                }
                        }
                }

                /* Handle hangup and errors */
                for (i = 0; i < nb_fd; i++) {
                        health_code_update();

                        if (local_stream[i] == NULL) {
                                continue;
                        }
                        if (!local_stream[i]->hangup_flush_done
                                        && (pollfd[i].revents & (POLLHUP | POLLERR | POLLNVAL))
                                        && (consumer_data.type == LTTNG_CONSUMER32_UST
                                                || consumer_data.type == LTTNG_CONSUMER64_UST)) {
                                DBG("fd %d is hup|err|nval. Attempting flush and read.",
                                                pollfd[i].fd);
                                lttng_ustconsumer_on_stream_hangup(local_stream[i]);
                                /* Attempt read again, for the data we just flushed. */
                                local_stream[i]->data_read = 1;
                        }
                        /*
                         * If the poll flag is HUP/ERR/NVAL and we have
                         * read no data in this pass, we can remove the
                         * stream from its hash table.
                         */
                        if ((pollfd[i].revents & POLLHUP)) {
                                DBG("Polling fd %d tells it has hung up.", pollfd[i].fd);
                                if (!local_stream[i]->data_read) {
                                        consumer_del_stream(local_stream[i], data_ht);
                                        local_stream[i] = NULL;
                                        num_hup++;
                                }
                        } else if (pollfd[i].revents & POLLERR) {
                                ERR("Error returned in polling fd %d.", pollfd[i].fd);
                                if (!local_stream[i]->data_read) {
                                        consumer_del_stream(local_stream[i], data_ht);
                                        local_stream[i] = NULL;
                                        num_hup++;
                                }
                        } else if (pollfd[i].revents & POLLNVAL) {
                                ERR("Polling fd %d tells fd is not open.", pollfd[i].fd);
                                if (!local_stream[i]->data_read) {
                                        consumer_del_stream(local_stream[i], data_ht);
                                        local_stream[i] = NULL;
                                        num_hup++;
                                }
                        }
                        if (local_stream[i] != NULL) {
                                local_stream[i]->data_read = 0;
                        }
                }
        }
        /* All is OK */
        err = 0;
end:
        DBG("polling thread exiting");
        free(pollfd);
        free(local_stream);

        /*
         * Close the write side of the pipe so epoll_wait() in
         * consumer_thread_metadata_poll can catch it. The thread is monitoring the
         * read side of the pipe. If we close them both, epoll_wait strangely does
         * not return and could create a endless wait period if the pipe is the
         * only tracked fd in the poll set. The thread will take care of closing
         * the read side.
         */
        (void) lttng_pipe_write_close(ctx->consumer_metadata_pipe);

error_testpoint:
        if (err) {
                health_error();
                ERR("Health error occurred in %s", __func__);
        }
        health_unregister(health_consumerd);

        rcu_unregister_thread();
        return NULL;
}

/*
 * Close wake-up end of each stream belonging to the channel. This will
 * allow the poll() on the stream read-side to detect when the
 * write-side (application) finally closes them.
 */
static
void consumer_close_channel_streams(struct lttng_consumer_channel *channel)
{
        struct lttng_ht *ht;
        struct lttng_consumer_stream *stream;
        struct lttng_ht_iter iter;

        ht = consumer_data.stream_per_chan_id_ht;

        rcu_read_lock();
        cds_lfht_for_each_entry_duplicate(ht->ht,
                        ht->hash_fct(&channel->key, lttng_ht_seed),
                        ht->match_fct, &channel->key,
                        &iter.iter, stream, node_channel_id.node) {
                /*
                 * Protect against teardown with mutex.
                 */
                pthread_mutex_lock(&stream->lock);
                if (cds_lfht_is_node_deleted(&stream->node.node)) {
                        goto next;
                }
                switch (consumer_data.type) {
                case LTTNG_CONSUMER_KERNEL:
                        break;
                case LTTNG_CONSUMER32_UST:
                case LTTNG_CONSUMER64_UST:
                        if (stream->metadata_flag) {
                                /* Safe and protected by the stream lock. */
                                lttng_ustconsumer_close_metadata(stream->chan);
                        } else {
                                /*
                                 * Note: a mutex is taken internally within
                                 * liblttng-ust-ctl to protect timer wakeup_fd
                                 * use from concurrent close.
                                 */
                                lttng_ustconsumer_close_stream_wakeup(stream);
                        }
                        break;
                default:
                        ERR("Unknown consumer_data type");
                        assert(0);
                }
        next:
                pthread_mutex_unlock(&stream->lock);
        }
        rcu_read_unlock();
}

static void destroy_channel_ht(struct lttng_ht *ht)
{
        struct lttng_ht_iter iter;
        struct lttng_consumer_channel *channel;
        int ret;

        if (ht == NULL) {
                return;
        }

        rcu_read_lock();
        cds_lfht_for_each_entry(ht->ht, &iter.iter, channel, wait_fd_node.node) {
                ret = lttng_ht_del(ht, &iter);
                assert(ret != 0);
        }
        rcu_read_unlock();

        lttng_ht_destroy(ht);
}

/*
 * This thread polls the channel fds to detect when they are being
 * closed. It closes all related streams if the channel is detected as
 * closed. It is currently only used as a shim layer for UST because the
 * consumerd needs to keep the per-stream wakeup end of pipes open for
 * periodical flush.
 */
void *consumer_thread_channel_poll(void *data)
{
        int ret, i, pollfd, err = -1;
        uint32_t revents, nb_fd;
        struct lttng_consumer_channel *chan = NULL;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_u64 *node;
        struct lttng_poll_event events;
        struct lttng_consumer_local_data *ctx = data;
        struct lttng_ht *channel_ht;

        rcu_register_thread();

        health_register(health_consumerd, HEALTH_CONSUMERD_TYPE_CHANNEL);

        if (testpoint(consumerd_thread_channel)) {
                goto error_testpoint;
        }

        health_code_update();

        channel_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!channel_ht) {
                /* ENOMEM at this point. Better to bail out. */
                goto end_ht;
        }

        DBG("Thread channel poll started");

        /* Size is set to 1 for the consumer_channel pipe */
        ret = lttng_poll_create(&events, 2, LTTNG_CLOEXEC);
        if (ret < 0) {
                ERR("Poll set creation failed");
                goto end_poll;
        }

        ret = lttng_poll_add(&events, ctx->consumer_channel_pipe[0], LPOLLIN);
        if (ret < 0) {
                goto end;
        }

        /* Main loop */
        DBG("Channel main loop started");

        while (1) {
restart:
                health_code_update();
                DBG("Channel poll wait");
                health_poll_entry();
                ret = lttng_poll_wait(&events, -1);
                DBG("Channel poll return from wait with %d fd(s)",
                                LTTNG_POLL_GETNB(&events));
                health_poll_exit();
                DBG("Channel event caught in thread");
                if (ret < 0) {
                        if (errno == EINTR) {
                                ERR("Poll EINTR caught");
                                goto restart;
                        }
                        if (LTTNG_POLL_GETNB(&events) == 0) {
                                err = 0;        /* All is OK */
                        }
                        goto end;
                }

                nb_fd = ret;

                /* From here, the event is a channel wait fd */
                for (i = 0; i < nb_fd; i++) {
                        health_code_update();

                        revents = LTTNG_POLL_GETEV(&events, i);
                        pollfd = LTTNG_POLL_GETFD(&events, i);

                        if (pollfd == ctx->consumer_channel_pipe[0]) {
                                if (revents & LPOLLIN) {
                                        enum consumer_channel_action action;
                                        uint64_t key;

                                        ret = read_channel_pipe(ctx, &chan, &key, &action);
                                        if (ret <= 0) {
                                                if (ret < 0) {
                                                        ERR("Error reading channel pipe");
                                                }
                                                lttng_poll_del(&events, ctx->consumer_channel_pipe[0]);
                                                continue;
                                        }

                                        switch (action) {
                                        case CONSUMER_CHANNEL_ADD:
                                                DBG("Adding channel %d to poll set",
                                                        chan->wait_fd);

                                                lttng_ht_node_init_u64(&chan->wait_fd_node,
                                                        chan->wait_fd);
                                                rcu_read_lock();
                                                lttng_ht_add_unique_u64(channel_ht,
                                                                &chan->wait_fd_node);
                                                rcu_read_unlock();
                                                /* Add channel to the global poll events list */
                                                lttng_poll_add(&events, chan->wait_fd,
                                                                LPOLLERR | LPOLLHUP);
                                                break;
                                        case CONSUMER_CHANNEL_DEL:
                                        {
                                                /*
                                                 * This command should never be called if the channel
                                                 * has streams monitored by either the data or metadata
                                                 * thread. The consumer only notify this thread with a
                                                 * channel del. command if it receives a destroy
                                                 * channel command from the session daemon that send it
                                                 * if a command prior to the GET_CHANNEL failed.
                                                 */

                                                rcu_read_lock();
                                                chan = consumer_find_channel(key);
                                                if (!chan) {
                                                        rcu_read_unlock();
                                                        ERR("UST consumer get channel key %" PRIu64 " not found for del channel", key);
                                                        break;
                                                }
                                                lttng_poll_del(&events, chan->wait_fd);
                                                iter.iter.node = &chan->wait_fd_node.node;
                                                ret = lttng_ht_del(channel_ht, &iter);
                                                assert(ret == 0);

                                                switch (consumer_data.type) {
                                                case LTTNG_CONSUMER_KERNEL:
                                                        break;
                                                case LTTNG_CONSUMER32_UST:
                                                case LTTNG_CONSUMER64_UST:
                                                        health_code_update();
                                                        /* Destroy streams that might have been left in the stream list. */
                                                        clean_channel_stream_list(chan);
                                                        break;
                                                default:
                                                        ERR("Unknown consumer_data type");
                                                        assert(0);
                                                }

                                                /*
                                                 * Release our own refcount. Force channel deletion even if
                                                 * streams were not initialized.
                                                 */
                                                if (!uatomic_sub_return(&chan->refcount, 1)) {
                                                        consumer_del_channel(chan);
                                                }
                                                rcu_read_unlock();
                                                goto restart;
                                        }
                                        case CONSUMER_CHANNEL_QUIT:
                                                /*
                                                 * Remove the pipe from the poll set and continue the loop
                                                 * since their might be data to consume.
                                                 */
                                                lttng_poll_del(&events, ctx->consumer_channel_pipe[0]);
                                                continue;
                                        default:
                                                ERR("Unknown action");
                                                break;
                                        }
                                } else if (revents & (LPOLLERR | LPOLLHUP)) {
                                        DBG("Channel thread pipe hung up");
                                        /*
                                         * Remove the pipe from the poll set and continue the loop
                                         * since their might be data to consume.
                                         */
                                        lttng_poll_del(&events, ctx->consumer_channel_pipe[0]);
                                        continue;
                                } else {
                                        ERR("Unexpected poll events %u for sock %d", revents, pollfd);
                                        goto end;
                                }

                                /* Handle other stream */
                                continue;
                        }

                        rcu_read_lock();
                        {
                                uint64_t tmp_id = (uint64_t) pollfd;

                                lttng_ht_lookup(channel_ht, &tmp_id, &iter);
                        }
                        node = lttng_ht_iter_get_node_u64(&iter);
                        assert(node);

                        chan = caa_container_of(node, struct lttng_consumer_channel,
                                        wait_fd_node);

                        /* Check for error event */
                        if (revents & (LPOLLERR | LPOLLHUP)) {
                                DBG("Channel fd %d is hup|err.", pollfd);

                                lttng_poll_del(&events, chan->wait_fd);
                                ret = lttng_ht_del(channel_ht, &iter);
                                assert(ret == 0);

                                /*
                                 * This will close the wait fd for each stream associated to
                                 * this channel AND monitored by the data/metadata thread thus
                                 * will be clean by the right thread.
                                 */
                                consumer_close_channel_streams(chan);

                                /* Release our own refcount */
                                if (!uatomic_sub_return(&chan->refcount, 1)
                                                && !uatomic_read(&chan->nb_init_stream_left)) {
                                        consumer_del_channel(chan);
                                }
                        } else {
                                ERR("Unexpected poll events %u for sock %d", revents, pollfd);
                                rcu_read_unlock();
                                goto end;
                        }

                        /* Release RCU lock for the channel looked up */
                        rcu_read_unlock();
                }
        }

        /* All is OK */
        err = 0;
end:
        lttng_poll_clean(&events);
end_poll:
        destroy_channel_ht(channel_ht);
end_ht:
error_testpoint:
        DBG("Channel poll thread exiting");
        if (err) {
                health_error();
                ERR("Health error occurred in %s", __func__);
        }
        health_unregister(health_consumerd);
        rcu_unregister_thread();
        return NULL;
}

static int set_metadata_socket(struct lttng_consumer_local_data *ctx,
                struct pollfd *sockpoll, int client_socket)
{
        int ret;

        assert(ctx);
        assert(sockpoll);

        ret = lttng_consumer_poll_socket(sockpoll);
        if (ret) {
                goto error;
        }
        DBG("Metadata connection on client_socket");

        /* Blocking call, waiting for transmission */
        ctx->consumer_metadata_socket = lttcomm_accept_unix_sock(client_socket);
        if (ctx->consumer_metadata_socket < 0) {
                WARN("On accept metadata");
                ret = -1;
                goto error;
        }
        ret = 0;

error:
        return ret;
}

/*
 * This thread listens on the consumerd socket and receives the file
 * descriptors from the session daemon.
 */
void *consumer_thread_sessiond_poll(void *data)
{
        int sock = -1, client_socket, ret, err = -1;
        /*
         * structure to poll for incoming data on communication socket avoids
         * making blocking sockets.
         */
        struct pollfd consumer_sockpoll[2];
        struct lttng_consumer_local_data *ctx = data;

        rcu_register_thread();

        health_register(health_consumerd, HEALTH_CONSUMERD_TYPE_SESSIOND);

        if (testpoint(consumerd_thread_sessiond)) {
                goto error_testpoint;
        }

        health_code_update();

        DBG("Creating command socket %s", ctx->consumer_command_sock_path);
        unlink(ctx->consumer_command_sock_path);
        client_socket = lttcomm_create_unix_sock(ctx->consumer_command_sock_path);
        if (client_socket < 0) {
                ERR("Cannot create command socket");
                goto end;
        }

        ret = lttcomm_listen_unix_sock(client_socket);
        if (ret < 0) {
                goto end;
        }

        DBG("Sending ready command to lttng-sessiond");
        ret = lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_COMMAND_SOCK_READY);
        /* return < 0 on error, but == 0 is not fatal */
        if (ret < 0) {
                ERR("Error sending ready command to lttng-sessiond");
                goto end;
        }

        /* prepare the FDs to poll : to client socket and the should_quit pipe */
        consumer_sockpoll[0].fd = ctx->consumer_should_quit[0];
        consumer_sockpoll[0].events = POLLIN | POLLPRI;
        consumer_sockpoll[1].fd = client_socket;
        consumer_sockpoll[1].events = POLLIN | POLLPRI;

        ret = lttng_consumer_poll_socket(consumer_sockpoll);
        if (ret) {
                if (ret > 0) {
                        /* should exit */
                        err = 0;
                }
                goto end;
        }
        DBG("Connection on client_socket");

        /* Blocking call, waiting for transmission */
        sock = lttcomm_accept_unix_sock(client_socket);
        if (sock < 0) {
                WARN("On accept");
                goto end;
        }

        /*
         * Setup metadata socket which is the second socket connection on the
         * command unix socket.
         */
        ret = set_metadata_socket(ctx, consumer_sockpoll, client_socket);
        if (ret) {
                if (ret > 0) {
                        /* should exit */
                        err = 0;
                }
                goto end;
        }

        /* This socket is not useful anymore. */
        ret = close(client_socket);
        if (ret < 0) {
                PERROR("close client_socket");
        }
        client_socket = -1;

        /* update the polling structure to poll on the established socket */
        consumer_sockpoll[1].fd = sock;
        consumer_sockpoll[1].events = POLLIN | POLLPRI;

        while (1) {
                health_code_update();

                health_poll_entry();
                ret = lttng_consumer_poll_socket(consumer_sockpoll);
                health_poll_exit();
                if (ret) {
                        if (ret > 0) {
                                /* should exit */
                                err = 0;
                        }
                        goto end;
                }
                DBG("Incoming command on sock");
                ret = lttng_consumer_recv_cmd(ctx, sock, consumer_sockpoll);
                if (ret <= 0) {
                        /*
                         * This could simply be a session daemon quitting. Don't output
                         * ERR() here.
                         */
                        DBG("Communication interrupted on command socket");
                        err = 0;
                        goto end;
                }
                if (CMM_LOAD_SHARED(consumer_quit)) {
                        DBG("consumer_thread_receive_fds received quit from signal");
                        err = 0;        /* All is OK */
                        goto end;
                }
                DBG("Received command on sock");
        }
        /* All is OK */
        err = 0;

end:
        DBG("Consumer thread sessiond poll exiting");

        /*
         * Close metadata streams since the producer is the session daemon which
         * just died.
         *
         * NOTE: for now, this only applies to the UST tracer.
         */
        lttng_consumer_close_all_metadata();

        /*
         * when all fds have hung up, the polling thread
         * can exit cleanly
         */
        CMM_STORE_SHARED(consumer_quit, 1);

        /*
         * Notify the data poll thread to poll back again and test the
         * consumer_quit state that we just set so to quit gracefully.
         */
        notify_thread_lttng_pipe(ctx->consumer_data_pipe);

        notify_channel_pipe(ctx, NULL, -1, CONSUMER_CHANNEL_QUIT);

        notify_health_quit_pipe(health_quit_pipe);

        /* Cleaning up possibly open sockets. */
        if (sock >= 0) {
                ret = close(sock);
                if (ret < 0) {
                        PERROR("close sock sessiond poll");
                }
        }
        if (client_socket >= 0) {
                ret = close(client_socket);
                if (ret < 0) {
                        PERROR("close client_socket sessiond poll");
                }
        }

error_testpoint:
        if (err) {
                health_error();
                ERR("Health error occurred in %s", __func__);
        }
        health_unregister(health_consumerd);

        rcu_unregister_thread();
        return NULL;
}

static int post_consume(struct lttng_consumer_stream *stream,
                const struct stream_subbuffer *subbuffer,
                struct lttng_consumer_local_data *ctx)
{
        size_t i;
        int ret = 0;
        const size_t count = lttng_dynamic_array_get_count(
                        &stream->read_subbuffer_ops.post_consume_cbs);

        for (i = 0; i < count; i++) {
                const post_consume_cb op = *(post_consume_cb *) lttng_dynamic_array_get_element(
                                &stream->read_subbuffer_ops.post_consume_cbs,
                                i);

                ret = op(stream, subbuffer, ctx);
                if (ret) {
                        goto end;
                }
        }
end:
        return ret;
}

ssize_t lttng_consumer_read_subbuffer(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx,
                bool locked_by_caller)
{
        ssize_t ret, written_bytes = 0;
        int rotation_ret;
        struct stream_subbuffer subbuffer = {};

        if (!locked_by_caller) {
                stream->read_subbuffer_ops.lock(stream);
        }

        if (stream->read_subbuffer_ops.on_wake_up) {
                ret = stream->read_subbuffer_ops.on_wake_up(stream);
                if (ret) {
                        goto end;
                }
        }

        /*
         * If the stream was flagged to be ready for rotation before we extract
         * the next packet, rotate it now.
         */
        if (stream->rotate_ready) {
                DBG("Rotate stream before consuming data");
                ret = lttng_consumer_rotate_stream(ctx, stream);
                if (ret < 0) {
                        ERR("Stream rotation error before consuming data");
                        goto end;
                }
        }

        ret = stream->read_subbuffer_ops.get_next_subbuffer(stream, &subbuffer);
        if (ret) {
                if (ret == -ENODATA) {
                        /* Not an error. */
                        ret = 0;
                        goto sleep_stream;
                }
                goto end;
        }

        ret = stream->read_subbuffer_ops.pre_consume_subbuffer(
                        stream, &subbuffer);
        if (ret) {
                goto error_put_subbuf;
        }

        written_bytes = stream->read_subbuffer_ops.consume_subbuffer(
                        ctx, stream, &subbuffer);
        if (written_bytes <= 0) {
                ERR("Error consuming subbuffer: (%zd)", written_bytes);
                ret = (int) written_bytes;
                goto error_put_subbuf;
        }

        ret = stream->read_subbuffer_ops.put_next_subbuffer(stream, &subbuffer);
        if (ret) {
                goto end;
        }

        ret = post_consume(stream, &subbuffer, ctx);
        if (ret) {
                goto end;
        }

        /*
         * After extracting the packet, we check if the stream is now ready to
         * be rotated and perform the action immediately.
         *
         * Don't overwrite `ret` as callers expect the number of bytes
         * consumed to be returned on success.
         */
        rotation_ret = lttng_consumer_stream_is_rotate_ready(stream);
        if (rotation_ret == 1) {
                rotation_ret = lttng_consumer_rotate_stream(ctx, stream);
                if (rotation_ret < 0) {
                        ret = rotation_ret;
                        ERR("Stream rotation error after consuming data");
                        goto end;
                }

        } else if (rotation_ret < 0) {
                ret = rotation_ret;
                ERR("Failed to check if stream was ready to rotate after consuming data");
                goto end;
        }

sleep_stream:
        if (stream->read_subbuffer_ops.on_sleep) {
                stream->read_subbuffer_ops.on_sleep(stream, ctx);
        }

        ret = written_bytes;
end:
        if (!locked_by_caller) {
                stream->read_subbuffer_ops.unlock(stream);
        }

        return ret;
error_put_subbuf:
        (void) stream->read_subbuffer_ops.put_next_subbuffer(stream, &subbuffer);
        goto end;
}

int lttng_consumer_on_recv_stream(struct lttng_consumer_stream *stream)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_on_recv_stream(stream);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_on_recv_stream(stream);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

/*
 * Allocate and set consumer data hash tables.
 */
int lttng_consumer_init(void)
{
        consumer_data.channel_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!consumer_data.channel_ht) {
                goto error;
        }

        consumer_data.channels_by_session_id_ht =
                        lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!consumer_data.channels_by_session_id_ht) {
                goto error;
        }

        consumer_data.relayd_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!consumer_data.relayd_ht) {
                goto error;
        }

        consumer_data.stream_list_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!consumer_data.stream_list_ht) {
                goto error;
        }

        consumer_data.stream_per_chan_id_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!consumer_data.stream_per_chan_id_ht) {
                goto error;
        }

        data_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!data_ht) {
                goto error;
        }

        metadata_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!metadata_ht) {
                goto error;
        }

        consumer_data.chunk_registry = lttng_trace_chunk_registry_create();
        if (!consumer_data.chunk_registry) {
                goto error;
        }

        return 0;

error:
        return -1;
}

/*
 * Process the ADD_RELAYD command receive by a consumer.
 *
 * This will create a relayd socket pair and add it to the relayd hash table.
 * The caller MUST acquire a RCU read side lock before calling it.
 */
 void consumer_add_relayd_socket(uint64_t net_seq_idx, int sock_type,
                struct lttng_consumer_local_data *ctx, int sock,
                struct pollfd *consumer_sockpoll,
                struct lttcomm_relayd_sock *relayd_sock, uint64_t sessiond_id,
                uint64_t relayd_session_id)
{
        int fd = -1, ret = -1, relayd_created = 0;
        enum lttcomm_return_code ret_code = LTTCOMM_CONSUMERD_SUCCESS;
        struct consumer_relayd_sock_pair *relayd = NULL;

        assert(ctx);
        assert(relayd_sock);

        DBG("Consumer adding relayd socket (idx: %" PRIu64 ")", net_seq_idx);

        /* Get relayd reference if exists. */
        relayd = consumer_find_relayd(net_seq_idx);
        if (relayd == NULL) {
                assert(sock_type == LTTNG_STREAM_CONTROL);
                /* Not found. Allocate one. */
                relayd = consumer_allocate_relayd_sock_pair(net_seq_idx);
                if (relayd == NULL) {
                        ret_code = LTTCOMM_CONSUMERD_ENOMEM;
                        goto error;
                } else {
                        relayd->sessiond_session_id = sessiond_id;
                        relayd_created = 1;
                }

                /*
                 * This code path MUST continue to the consumer send status message to
                 * we can notify the session daemon and continue our work without
                 * killing everything.
                 */
        } else {
                /*
                 * relayd key should never be found for control socket.
                 */
                assert(sock_type != LTTNG_STREAM_CONTROL);
        }

        /* First send a status message before receiving the fds. */
        ret = consumer_send_status_msg(sock, LTTCOMM_CONSUMERD_SUCCESS);
        if (ret < 0) {
                /* Somehow, the session daemon is not responding anymore. */
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_FATAL);
                goto error_nosignal;
        }

        /* Poll on consumer socket. */
        ret = lttng_consumer_poll_socket(consumer_sockpoll);
        if (ret) {
                /* Needing to exit in the middle of a command: error. */
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_POLL_ERROR);
                goto error_nosignal;
        }

        /* Get relayd socket from session daemon */
        ret = lttcomm_recv_fds_unix_sock(sock, &fd, 1);
        if (ret != sizeof(fd)) {
                fd = -1;        /* Just in case it gets set with an invalid value. */

                /*
                 * Failing to receive FDs might indicate a major problem such as
                 * reaching a fd limit during the receive where the kernel returns a
                 * MSG_CTRUNC and fails to cleanup the fd in the queue. Any case, we
                 * don't take any chances and stop everything.
                 *
                 * XXX: Feature request #558 will fix that and avoid this possible
                 * issue when reaching the fd limit.
                 */
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_ERROR_RECV_FD);
                ret_code = LTTCOMM_CONSUMERD_ERROR_RECV_FD;
                goto error;
        }

        /* Copy socket information and received FD */
        switch (sock_type) {
        case LTTNG_STREAM_CONTROL:
                /* Copy received lttcomm socket */
                lttcomm_copy_sock(&relayd->control_sock.sock, &relayd_sock->sock);
                ret = lttcomm_create_sock(&relayd->control_sock.sock);
                /* Handle create_sock error. */
                if (ret < 0) {
                        ret_code = LTTCOMM_CONSUMERD_ENOMEM;
                        goto error;
                }
                /*
                 * Close the socket created internally by
                 * lttcomm_create_sock, so we can replace it by the one
                 * received from sessiond.
                 */
                if (close(relayd->control_sock.sock.fd)) {
                        PERROR("close");
                }

                /* Assign new file descriptor */
                relayd->control_sock.sock.fd = fd;
                /* Assign version values. */
                relayd->control_sock.major = relayd_sock->major;
                relayd->control_sock.minor = relayd_sock->minor;

                relayd->relayd_session_id = relayd_session_id;

                break;
        case LTTNG_STREAM_DATA:
                /* Copy received lttcomm socket */
                lttcomm_copy_sock(&relayd->data_sock.sock, &relayd_sock->sock);
                ret = lttcomm_create_sock(&relayd->data_sock.sock);
                /* Handle create_sock error. */
                if (ret < 0) {
                        ret_code = LTTCOMM_CONSUMERD_ENOMEM;
                        goto error;
                }
                /*
                 * Close the socket created internally by
                 * lttcomm_create_sock, so we can replace it by the one
                 * received from sessiond.
                 */
                if (close(relayd->data_sock.sock.fd)) {
                        PERROR("close");
                }

                /* Assign new file descriptor */
                relayd->data_sock.sock.fd = fd;
                /* Assign version values. */
                relayd->data_sock.major = relayd_sock->major;
                relayd->data_sock.minor = relayd_sock->minor;
                break;
        default:
                ERR("Unknown relayd socket type (%d)", sock_type);
                ret_code = LTTCOMM_CONSUMERD_FATAL;
                goto error;
        }

        DBG("Consumer %s socket created successfully with net idx %" PRIu64 " (fd: %d)",
                        sock_type == LTTNG_STREAM_CONTROL ? "control" : "data",
                        relayd->net_seq_idx, fd);
        /*
         * We gave the ownership of the fd to the relayd structure. Set the
         * fd to -1 so we don't call close() on it in the error path below.
         */
        fd = -1;

        /* We successfully added the socket. Send status back. */
        ret = consumer_send_status_msg(sock, ret_code);
        if (ret < 0) {
                /* Somehow, the session daemon is not responding anymore. */
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_FATAL);
                goto error_nosignal;
        }

        /*
         * Add relayd socket pair to consumer data hashtable. If object already
         * exists or on error, the function gracefully returns.
         */
        relayd->ctx = ctx;
        add_relayd(relayd);

        /* All good! */
        return;

error:
        if (consumer_send_status_msg(sock, ret_code) < 0) {
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_FATAL);
        }

error_nosignal:
        /* Close received socket if valid. */
        if (fd >= 0) {
                if (close(fd)) {
                        PERROR("close received socket");
                }
        }

        if (relayd_created) {
                free(relayd);
        }
}

/*
 * Search for a relayd associated to the session id and return the reference.
 *
 * A rcu read side lock MUST be acquire before calling this function and locked
 * until the relayd object is no longer necessary.
 */
static struct consumer_relayd_sock_pair *find_relayd_by_session_id(uint64_t id)
{
        struct lttng_ht_iter iter;
        struct consumer_relayd_sock_pair *relayd = NULL;

        /* Iterate over all relayd since they are indexed by net_seq_idx. */
        cds_lfht_for_each_entry(consumer_data.relayd_ht->ht, &iter.iter, relayd,
                        node.node) {
                /*
                 * Check by sessiond id which is unique here where the relayd session
                 * id might not be when having multiple relayd.
                 */
                if (relayd->sessiond_session_id == id) {
                        /* Found the relayd. There can be only one per id. */
                        goto found;
                }
        }

        return NULL;

found:
        return relayd;
}

/*
 * Check if for a given session id there is still data needed to be extract
 * from the buffers.
 *
 * Return 1 if data is pending or else 0 meaning ready to be read.
 */
int consumer_data_pending(uint64_t id)
{
        int ret;
        struct lttng_ht_iter iter;
        struct lttng_ht *ht;
        struct lttng_consumer_stream *stream;
        struct consumer_relayd_sock_pair *relayd = NULL;
        int (*data_pending)(struct lttng_consumer_stream *);

        DBG("Consumer data pending command on session id %" PRIu64, id);

        rcu_read_lock();
        pthread_mutex_lock(&consumer_data.lock);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                data_pending = lttng_kconsumer_data_pending;
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                data_pending = lttng_ustconsumer_data_pending;
                break;
        default:
                ERR("Unknown consumer data type");
                assert(0);
        }

        /* Ease our life a bit */
        ht = consumer_data.stream_list_ht;

        cds_lfht_for_each_entry_duplicate(ht->ht,
                        ht->hash_fct(&id, lttng_ht_seed),
                        ht->match_fct, &id,
                        &iter.iter, stream, node_session_id.node) {
                pthread_mutex_lock(&stream->lock);

                /*
                 * A removed node from the hash table indicates that the stream has
                 * been deleted thus having a guarantee that the buffers are closed
                 * on the consumer side. However, data can still be transmitted
                 * over the network so don't skip the relayd check.
                 */
                ret = cds_lfht_is_node_deleted(&stream->node.node);
                if (!ret) {
                        /* Check the stream if there is data in the buffers. */
                        ret = data_pending(stream);
                        if (ret == 1) {
                                pthread_mutex_unlock(&stream->lock);
                                goto data_pending;
                        }
                }

                pthread_mutex_unlock(&stream->lock);
        }

        relayd = find_relayd_by_session_id(id);
        if (relayd) {
                unsigned int is_data_inflight = 0;

                /* Send init command for data pending. */
                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_begin_data_pending(&relayd->control_sock,
                                relayd->relayd_session_id);
                if (ret < 0) {
                        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                        /* Communication error thus the relayd so no data pending. */
                        goto data_not_pending;
                }

                cds_lfht_for_each_entry_duplicate(ht->ht,
                                ht->hash_fct(&id, lttng_ht_seed),
                                ht->match_fct, &id,
                                &iter.iter, stream, node_session_id.node) {
                        if (stream->metadata_flag) {
                                ret = relayd_quiescent_control(&relayd->control_sock,
                                                stream->relayd_stream_id);
                        } else {
                                ret = relayd_data_pending(&relayd->control_sock,
                                                stream->relayd_stream_id,
                                                stream->next_net_seq_num - 1);
                        }

                        if (ret == 1) {
                                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                                goto data_pending;
                        } else if (ret < 0) {
                                ERR("Relayd data pending failed. Cleaning up relayd %" PRIu64".", relayd->net_seq_idx);
                                lttng_consumer_cleanup_relayd(relayd);
                                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                                goto data_not_pending;
                        }
                }

                /* Send end command for data pending. */
                ret = relayd_end_data_pending(&relayd->control_sock,
                                relayd->relayd_session_id, &is_data_inflight);
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        ERR("Relayd end data pending failed. Cleaning up relayd %" PRIu64".", relayd->net_seq_idx);
                        lttng_consumer_cleanup_relayd(relayd);
                        goto data_not_pending;
                }
                if (is_data_inflight) {
                        goto data_pending;
                }
        }

        /*
         * Finding _no_ node in the hash table and no inflight data means that the
         * stream(s) have been removed thus data is guaranteed to be available for
         * analysis from the trace files.
         */

data_not_pending:
        /* Data is available to be read by a viewer. */
        pthread_mutex_unlock(&consumer_data.lock);
        rcu_read_unlock();
        return 0;

data_pending:
        /* Data is still being extracted from buffers. */
        pthread_mutex_unlock(&consumer_data.lock);
        rcu_read_unlock();
        return 1;
}

/*
 * Send a ret code status message to the sessiond daemon.
 *
 * Return the sendmsg() return value.
 */
int consumer_send_status_msg(int sock, int ret_code)
{
        struct lttcomm_consumer_status_msg msg;

        memset(&msg, 0, sizeof(msg));
        msg.ret_code = ret_code;

        return lttcomm_send_unix_sock(sock, &msg, sizeof(msg));
}

/*
 * Send a channel status message to the sessiond daemon.
 *
 * Return the sendmsg() return value.
 */
int consumer_send_status_channel(int sock,
                struct lttng_consumer_channel *channel)
{
        struct lttcomm_consumer_status_channel msg;

        assert(sock >= 0);

        memset(&msg, 0, sizeof(msg));
        if (!channel) {
                msg.ret_code = LTTCOMM_CONSUMERD_CHANNEL_FAIL;
        } else {
                msg.ret_code = LTTCOMM_CONSUMERD_SUCCESS;
                msg.key = channel->key;
                msg.stream_count = channel->streams.count;
        }

        return lttcomm_send_unix_sock(sock, &msg, sizeof(msg));
}

unsigned long consumer_get_consume_start_pos(unsigned long consumed_pos,
                unsigned long produced_pos, uint64_t nb_packets_per_stream,
                uint64_t max_sb_size)
{
        unsigned long start_pos;

        if (!nb_packets_per_stream) {
                return consumed_pos;    /* Grab everything */
        }
        start_pos = produced_pos - offset_align_floor(produced_pos, max_sb_size);
        start_pos -= max_sb_size * nb_packets_per_stream;
        if ((long) (start_pos - consumed_pos) < 0) {
                return consumed_pos;    /* Grab everything */
        }
        return start_pos;
}

/* Stream lock must be held by the caller. */
static int sample_stream_positions(struct lttng_consumer_stream *stream,
                            unsigned long *produced, unsigned long *consumed)
{
        int ret;

        ASSERT_LOCKED(stream->lock);

        ret = lttng_consumer_sample_snapshot_positions(stream);
        if (ret < 0) {
                ERR("Failed to sample snapshot positions");
                goto end;
        }

        ret = lttng_consumer_get_produced_snapshot(stream, produced);
        if (ret < 0) {
                ERR("Failed to sample produced position");
                goto end;
        }

        ret = lttng_consumer_get_consumed_snapshot(stream, consumed);
        if (ret < 0) {
                ERR("Failed to sample consumed position");
                goto end;
        }

end:
        return ret;
}

/*
 * Sample the rotate position for all the streams of a channel. If a stream
 * is already at the rotate position (produced == consumed), we flag it as
 * ready for rotation. The rotation of ready streams occurs after we have
 * replied to the session daemon that we have finished sampling the positions.
 * Must be called with RCU read-side lock held to ensure existence of channel.
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_rotate_channel(struct lttng_consumer_channel *channel,
                uint64_t key, uint64_t relayd_id, uint32_t metadata,
                struct lttng_consumer_local_data *ctx)
{
        int ret;
        struct lttng_consumer_stream *stream;
        struct lttng_ht_iter iter;
        struct lttng_ht *ht = consumer_data.stream_per_chan_id_ht;
        struct lttng_dynamic_array stream_rotation_positions;
        uint64_t next_chunk_id, stream_count = 0;
        enum lttng_trace_chunk_status chunk_status;
        const bool is_local_trace = relayd_id == -1ULL;
        struct consumer_relayd_sock_pair *relayd = NULL;
        bool rotating_to_new_chunk = true;
        /* Array of `struct lttng_consumer_stream *` */
        struct lttng_dynamic_pointer_array streams_packet_to_open;
        size_t stream_idx;

        DBG("Consumer sample rotate position for channel %" PRIu64, key);

        lttng_dynamic_array_init(&stream_rotation_positions,
                        sizeof(struct relayd_stream_rotation_position), NULL);
        lttng_dynamic_pointer_array_init(&streams_packet_to_open, NULL);

        rcu_read_lock();

        pthread_mutex_lock(&channel->lock);
        assert(channel->trace_chunk);
        chunk_status = lttng_trace_chunk_get_id(channel->trace_chunk,
                        &next_chunk_id);
        if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                ret = -1;
                goto end_unlock_channel;
        }

        cds_lfht_for_each_entry_duplicate(ht->ht,
                        ht->hash_fct(&channel->key, lttng_ht_seed),
                        ht->match_fct, &channel->key, &iter.iter,
                        stream, node_channel_id.node) {
                unsigned long produced_pos = 0, consumed_pos = 0;

                health_code_update();

                /*
                 * Lock stream because we are about to change its state.
                 */
                pthread_mutex_lock(&stream->lock);

                if (stream->trace_chunk == stream->chan->trace_chunk) {
                        rotating_to_new_chunk = false;
                }

                /*
                 * Do not flush a packet when rotating from a NULL trace
                 * chunk. The stream has no means to output data, and the prior
                 * rotation which rotated to NULL performed that side-effect
                 * already. No new data can be produced when a stream has no
                 * associated trace chunk (e.g. a stop followed by a rotate).
                 */
                if (stream->trace_chunk) {
                        bool flush_active;

                        if (stream->metadata_flag) {
                                /*
                                 * Don't produce an empty metadata packet,
                                 * simply close the current one.
                                 *
                                 * Metadata is regenerated on every trace chunk
                                 * switch; there is no concern that no data was
                                 * produced.
                                 */
                                flush_active = true;
                        } else {
                                /*
                                 * Only flush an empty packet if the "packet
                                 * open" could not be performed on transition
                                 * to a new trace chunk and no packets were
                                 * consumed within the chunk's lifetime.
                                 */
                                if (stream->opened_packet_in_current_trace_chunk) {
                                        flush_active = true;
                                } else {
                                        /*
                                         * Stream could have been full at the
                                         * time of rotation, but then have had
                                         * no activity at all.
                                         *
                                         * It is important to flush a packet
                                         * to prevent 0-length files from being
                                         * produced as most viewers choke on
                                         * them.
                                         *
                                         * Unfortunately viewers will not be
                                         * able to know that tracing was active
                                         * for this stream during this trace
                                         * chunk's lifetime.
                                         */
                                        ret = sample_stream_positions(stream, &produced_pos, &consumed_pos);
                                        if (ret) {
                                                goto end_unlock_stream;
                                        }

                                        /*
                                         * Don't flush an empty packet if data
                                         * was produced; it will be consumed
                                         * before the rotation completes.
                                         */
                                        flush_active = produced_pos != consumed_pos;
                                        if (!flush_active) {
                                                enum lttng_trace_chunk_status chunk_status;
                                                const char *trace_chunk_name;
                                                uint64_t trace_chunk_id;

                                                chunk_status = lttng_trace_chunk_get_name(
                                                                stream->trace_chunk,
                                                                &trace_chunk_name,
                                                                NULL);
                                                if (chunk_status == LTTNG_TRACE_CHUNK_STATUS_NONE) {
                                                        trace_chunk_name = "none";
                                                }

                                                /*
                                                 * Consumer trace chunks are
                                                 * never anonymous.
                                                 */
                                                chunk_status = lttng_trace_chunk_get_id(
                                                                stream->trace_chunk,
                                                                &trace_chunk_id);
                                                assert(chunk_status ==
                                                                LTTNG_TRACE_CHUNK_STATUS_OK);

                                                DBG("Unable to open packet for stream during trace chunk's lifetime. "
                                                                "Flushing an empty packet to prevent an empty file from being created: "
                                                                "stream id = %" PRIu64 ", trace chunk name = `%s`, trace chunk id = %" PRIu64,
                                                                stream->key, trace_chunk_name, trace_chunk_id);
                                        }
                                }
                        }

                        /*
                         * Close the current packet before sampling the
                         * ring buffer positions.
                         */
                        ret = consumer_stream_flush_buffer(stream, flush_active);
                        if (ret < 0) {
                                ERR("Failed to flush stream %" PRIu64 " during channel rotation",
                                                stream->key);
                                goto end_unlock_stream;
                        }
                }

                ret = lttng_consumer_take_snapshot(stream);
                if (ret < 0 && ret != -ENODATA && ret != -EAGAIN) {
                        ERR("Failed to sample snapshot position during channel rotation");
                        goto end_unlock_stream;
                }
                if (!ret) {
                        ret = lttng_consumer_get_produced_snapshot(stream,
                                        &produced_pos);
                        if (ret < 0) {
                                ERR("Failed to sample produced position during channel rotation");
                                goto end_unlock_stream;
                        }

                        ret = lttng_consumer_get_consumed_snapshot(stream,
                                        &consumed_pos);
                        if (ret < 0) {
                                ERR("Failed to sample consumed position during channel rotation");
                                goto end_unlock_stream;
                        }
                }
                /*
                 * Align produced position on the start-of-packet boundary of the first
                 * packet going into the next trace chunk.
                 */
                produced_pos = ALIGN_FLOOR(produced_pos, stream->max_sb_size);
                if (consumed_pos == produced_pos) {
                        DBG("Set rotate ready for stream %" PRIu64 " produced = %lu consumed = %lu",
                                        stream->key, produced_pos, consumed_pos);
                        stream->rotate_ready = true;
                } else {
                        DBG("Different consumed and produced positions "
                                        "for stream %" PRIu64 " produced = %lu consumed = %lu",
                                        stream->key, produced_pos, consumed_pos);
                }
                /*
                 * The rotation position is based on the packet_seq_num of the
                 * packet following the last packet that was consumed for this
                 * stream, incremented by the offset between produced and
                 * consumed positions. This rotation position is a lower bound
                 * (inclusive) at which the next trace chunk starts. Since it
                 * is a lower bound, it is OK if the packet_seq_num does not
                 * correspond exactly to the same packet identified by the
                 * consumed_pos, which can happen in overwrite mode.
                 */
                if (stream->sequence_number_unavailable) {
                        /*
                         * Rotation should never be performed on a session which
                         * interacts with a pre-2.8 lttng-modules, which does
                         * not implement packet sequence number.
                         */
                        ERR("Failure to rotate stream %" PRIu64 ": sequence number unavailable",
                                        stream->key);
                        ret = -1;
                        goto end_unlock_stream;
                }
                stream->rotate_position = stream->last_sequence_number + 1 +
                                ((produced_pos - consumed_pos) / stream->max_sb_size);
                DBG("Set rotation position for stream %" PRIu64 " at position %" PRIu64,
                                stream->key, stream->rotate_position);

                if (!is_local_trace) {
                        /*
                         * The relay daemon control protocol expects a rotation
                         * position as "the sequence number of the first packet
                         * _after_ the current trace chunk".
                         */
                        const struct relayd_stream_rotation_position position = {
                                .stream_id = stream->relayd_stream_id,
                                .rotate_at_seq_num = stream->rotate_position,
                        };

                        ret = lttng_dynamic_array_add_element(
                                        &stream_rotation_positions,
                                        &position);
                        if (ret) {
                                ERR("Failed to allocate stream rotation position");
                                goto end_unlock_stream;
                        }
                        stream_count++;
                }

                stream->opened_packet_in_current_trace_chunk = false;

                if (rotating_to_new_chunk && !stream->metadata_flag) {
                        /*
                         * Attempt to flush an empty packet as close to the
                         * rotation point as possible. In the event where a
                         * stream remains inactive after the rotation point,
                         * this ensures that the new trace chunk has a
                         * beginning timestamp set at the begining of the
                         * trace chunk instead of only creating an empty
                         * packet when the trace chunk is stopped.
                         *
                         * This indicates to the viewers that the stream
                         * was being recorded, but more importantly it
                         * allows viewers to determine a useable trace
                         * intersection.
                         *
                         * This presents a problem in the case where the
                         * ring-buffer is completely full.
                         *
                         * Consider the following scenario:
                         *   - The consumption of data is slow (slow network,
                         *     for instance),
                         *   - The ring buffer is full,
                         *   - A rotation is initiated,
                         *     - The flush below does nothing (no space left to
                         *       open a new packet),
                         *   - The other streams rotate very soon, and new
                         *     data is produced in the new chunk,
                         *   - This stream completes its rotation long after the
                         *     rotation was initiated
                         *   - The session is stopped before any event can be
                         *     produced in this stream's buffers.
                         *
                         * The resulting trace chunk will have a single packet
                         * temporaly at the end of the trace chunk for this
                         * stream making the stream intersection more narrow
                         * than it should be.
                         *
                         * To work-around this, an empty flush is performed
                         * after the first consumption of a packet during a
                         * rotation if open_packet fails. The idea is that
                         * consuming a packet frees enough space to switch
                         * packets in this scenario and allows the tracer to
                         * "stamp" the beginning of the new trace chunk at the
                         * earliest possible point.
                         *
                         * The packet open is performed after the channel
                         * rotation to ensure that no attempt to open a packet
                         * is performed in a stream that has no active trace
                         * chunk.
                         */
                        ret = lttng_dynamic_pointer_array_add_pointer(
                                        &streams_packet_to_open, stream);
                        if (ret) {
                                PERROR("Failed to add a stream pointer to array of streams in which to open a packet");
                                ret = -1;
                                goto end_unlock_stream;
                        }
                }

                pthread_mutex_unlock(&stream->lock);
        }
        stream = NULL;

        if (!is_local_trace) {
                relayd = consumer_find_relayd(relayd_id);
                if (!relayd) {
                        ERR("Failed to find relayd %" PRIu64, relayd_id);
                        ret = -1;
                        goto end_unlock_channel;
                }

                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_rotate_streams(&relayd->control_sock, stream_count,
                                rotating_to_new_chunk ? &next_chunk_id : NULL,
                                (const struct relayd_stream_rotation_position *)
                                                stream_rotation_positions.buffer
                                                                .data);
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        ERR("Relayd rotate stream failed. Cleaning up relayd %" PRIu64,
                                        relayd->net_seq_idx);
                        lttng_consumer_cleanup_relayd(relayd);
                        goto end_unlock_channel;
                }
        }

        for (stream_idx = 0;
                        stream_idx < lttng_dynamic_pointer_array_get_count(
                                &streams_packet_to_open);
                        stream_idx++) {
                enum consumer_stream_open_packet_status status;

                stream = lttng_dynamic_pointer_array_get_pointer(
                                &streams_packet_to_open, stream_idx);

                pthread_mutex_lock(&stream->lock);
                status = consumer_stream_open_packet(stream);
                pthread_mutex_unlock(&stream->lock);
                switch (status) {
                case CONSUMER_STREAM_OPEN_PACKET_STATUS_OPENED:
                        DBG("Opened a packet after a rotation: stream id = %" PRIu64
                            ", channel name = %s, session id = %" PRIu64,
                                        stream->key, stream->chan->name,
                                        stream->chan->session_id);
                        break;
                case CONSUMER_STREAM_OPEN_PACKET_STATUS_NO_SPACE:
                        /*
                         * Can't open a packet as there is no space left
                         * in the buffer. A new packet will be opened
                         * once one has been consumed.
                         */
                        DBG("No space left to open a packet after a rotation: stream id = %" PRIu64
                            ", channel name = %s, session id = %" PRIu64,
                                        stream->key, stream->chan->name,
                                        stream->chan->session_id);
                        break;
                case CONSUMER_STREAM_OPEN_PACKET_STATUS_ERROR:
                        /* Logged by callee. */
                        ret = -1;
                        goto end_unlock_channel;
                default:
                        abort();
                }
        }

        pthread_mutex_unlock(&channel->lock);
        ret = 0;
        goto end;

end_unlock_stream:
        pthread_mutex_unlock(&stream->lock);
end_unlock_channel:
        pthread_mutex_unlock(&channel->lock);
end:
        rcu_read_unlock();
        lttng_dynamic_array_reset(&stream_rotation_positions);
        lttng_dynamic_pointer_array_reset(&streams_packet_to_open);
        return ret;
}

static
int consumer_clear_buffer(struct lttng_consumer_stream *stream)
{
        int ret = 0;
        unsigned long consumed_pos_before, consumed_pos_after;

        ret = lttng_consumer_sample_snapshot_positions(stream);
        if (ret < 0) {
                ERR("Taking snapshot positions");
                goto end;
        }

        ret = lttng_consumer_get_consumed_snapshot(stream, &consumed_pos_before);
        if (ret < 0) {
                ERR("Consumed snapshot position");
                goto end;
        }

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                ret = kernctl_buffer_clear(stream->wait_fd);
                if (ret < 0) {
                        ERR("Failed to clear kernel stream (ret = %d)", ret);
                        goto end;
                }
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                lttng_ustconsumer_clear_buffer(stream);
                break;
        default:
                ERR("Unknown consumer_data type");
                abort();
        }

        ret = lttng_consumer_sample_snapshot_positions(stream);
        if (ret < 0) {
                ERR("Taking snapshot positions");
                goto end;
        }
        ret = lttng_consumer_get_consumed_snapshot(stream, &consumed_pos_after);
        if (ret < 0) {
                ERR("Consumed snapshot position");
                goto end;
        }
        DBG("clear: before: %lu after: %lu", consumed_pos_before, consumed_pos_after);
end:
        return ret;
}

static
int consumer_clear_stream(struct lttng_consumer_stream *stream)
{
        int ret;

        ret = consumer_stream_flush_buffer(stream, 1);
        if (ret < 0) {
                ERR("Failed to flush stream %" PRIu64 " during channel clear",
                                stream->key);
                ret = LTTCOMM_CONSUMERD_FATAL;
                goto error;
        }

        ret = consumer_clear_buffer(stream);
        if (ret < 0) {
                ERR("Failed to clear stream %" PRIu64 " during channel clear",
                                stream->key);
                ret = LTTCOMM_CONSUMERD_FATAL;
                goto error;
        }

        ret = LTTCOMM_CONSUMERD_SUCCESS;
error:
        return ret;
}

static
int consumer_clear_unmonitored_channel(struct lttng_consumer_channel *channel)
{
        int ret;
        struct lttng_consumer_stream *stream;

        rcu_read_lock();
        pthread_mutex_lock(&channel->lock);
        cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
                health_code_update();
                pthread_mutex_lock(&stream->lock);
                ret = consumer_clear_stream(stream);
                if (ret) {
                        goto error_unlock;
                }
                pthread_mutex_unlock(&stream->lock);
        }
        pthread_mutex_unlock(&channel->lock);
        rcu_read_unlock();
        return 0;

error_unlock:
        pthread_mutex_unlock(&stream->lock);
        pthread_mutex_unlock(&channel->lock);
        rcu_read_unlock();
        return ret;
}

/*
 * Check if a stream is ready to be rotated after extracting it.
 *
 * Return 1 if it is ready for rotation, 0 if it is not, a negative value on
 * error. Stream lock must be held.
 */
int lttng_consumer_stream_is_rotate_ready(struct lttng_consumer_stream *stream)
{
        DBG("Check is rotate ready for stream %" PRIu64
                        " ready %u rotate_position %" PRIu64
                        " last_sequence_number %" PRIu64,
                        stream->key, stream->rotate_ready,
                        stream->rotate_position, stream->last_sequence_number);
        if (stream->rotate_ready) {
                return 1;
        }

        /*
         * If packet seq num is unavailable, it means we are interacting
         * with a pre-2.8 lttng-modules which does not implement the
         * sequence number. Rotation should never be used by sessiond in this
         * scenario.
         */
        if (stream->sequence_number_unavailable) {
                ERR("Internal error: rotation used on stream %" PRIu64
                                " with unavailable sequence number",
                                stream->key);
                return -1;
        }

        if (stream->rotate_position == -1ULL ||
                        stream->last_sequence_number == -1ULL) {
                return 0;
        }

        /*
         * Rotate position not reached yet. The stream rotate position is
         * the position of the next packet belonging to the next trace chunk,
         * but consumerd considers rotation ready when reaching the last
         * packet of the current chunk, hence the "rotate_position - 1".
         */

        DBG("Check is rotate ready for stream %" PRIu64
                        " last_sequence_number %" PRIu64
                        " rotate_position %" PRIu64,
                        stream->key, stream->last_sequence_number,
                        stream->rotate_position);
        if (stream->last_sequence_number >= stream->rotate_position - 1) {
                return 1;
        }

        return 0;
}

/*
 * Reset the state for a stream after a rotation occurred.
 */
void lttng_consumer_reset_stream_rotate_state(struct lttng_consumer_stream *stream)
{
        DBG("lttng_consumer_reset_stream_rotate_state for stream %" PRIu64,
                        stream->key);
        stream->rotate_position = -1ULL;
        stream->rotate_ready = false;
}

/*
 * Perform the rotation a local stream file.
 */
static
int rotate_local_stream(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_stream *stream)
{
        int ret = 0;

        DBG("Rotate local stream: stream key %" PRIu64 ", channel key %" PRIu64,
                        stream->key,
                        stream->chan->key);
        stream->tracefile_size_current = 0;
        stream->tracefile_count_current = 0;

        if (stream->out_fd >= 0) {
                ret = close(stream->out_fd);
                if (ret) {
                        PERROR("Failed to close stream out_fd of channel \"%s\"",
                                stream->chan->name);
                }
                stream->out_fd = -1;
        }

        if (stream->index_file) {
                lttng_index_file_put(stream->index_file);
                stream->index_file = NULL;
        }

        if (!stream->trace_chunk) {
                goto end;
        }

        ret = consumer_stream_create_output_files(stream, true);
end:
        return ret;
}

/*
 * Performs the stream rotation for the rotate session feature if needed.
 * It must be called with the channel and stream locks held.
 *
 * Return 0 on success, a negative number of error.
 */
int lttng_consumer_rotate_stream(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_stream *stream)
{
        int ret;

        DBG("Consumer rotate stream %" PRIu64, stream->key);

        /*
         * Update the stream's 'current' chunk to the session's (channel)
         * now-current chunk.
         */
        lttng_trace_chunk_put(stream->trace_chunk);
        if (stream->chan->trace_chunk == stream->trace_chunk) {
                /*
                 * A channel can be rotated and not have a "next" chunk
                 * to transition to. In that case, the channel's "current chunk"
                 * has not been closed yet, but it has not been updated to
                 * a "next" trace chunk either. Hence, the stream, like its
                 * parent channel, becomes part of no chunk and can't output
                 * anything until a new trace chunk is created.
                 */
                stream->trace_chunk = NULL;
        } else if (stream->chan->trace_chunk &&
                        !lttng_trace_chunk_get(stream->chan->trace_chunk)) {
                ERR("Failed to acquire a reference to channel's trace chunk during stream rotation");
                ret = -1;
                goto error;
        } else {
                /*
                 * Update the stream's trace chunk to its parent channel's
                 * current trace chunk.
                 */
                stream->trace_chunk = stream->chan->trace_chunk;
        }

        if (stream->net_seq_idx == (uint64_t) -1ULL) {
                ret = rotate_local_stream(ctx, stream);
                if (ret < 0) {
                        ERR("Failed to rotate stream, ret = %i", ret);
                        goto error;
                }
        }

        if (stream->metadata_flag && stream->trace_chunk) {
                /*
                 * If the stream has transitioned to a new trace
                 * chunk, the metadata should be re-dumped to the
                 * newest chunk.
                 *
                 * However, it is possible for a stream to transition to
                 * a "no-chunk" state. This can happen if a rotation
                 * occurs on an inactive session. In such cases, the metadata
                 * regeneration will happen when the next trace chunk is
                 * created.
                 */
                ret = consumer_metadata_stream_dump(stream);
                if (ret) {
                        goto error;
                }
        }
        lttng_consumer_reset_stream_rotate_state(stream);

        ret = 0;

error:
        return ret;
}

/*
 * Rotate all the ready streams now.
 *
 * This is especially important for low throughput streams that have already
 * been consumed, we cannot wait for their next packet to perform the
 * rotation.
 * Need to be called with RCU read-side lock held to ensure existence of
 * channel.
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_consumer_rotate_ready_streams(struct lttng_consumer_channel *channel,
                uint64_t key, struct lttng_consumer_local_data *ctx)
{
        int ret;
        struct lttng_consumer_stream *stream;
        struct lttng_ht_iter iter;
        struct lttng_ht *ht = consumer_data.stream_per_chan_id_ht;

        rcu_read_lock();

        DBG("Consumer rotate ready streams in channel %" PRIu64, key);

        cds_lfht_for_each_entry_duplicate(ht->ht,
                        ht->hash_fct(&channel->key, lttng_ht_seed),
                        ht->match_fct, &channel->key, &iter.iter,
                        stream, node_channel_id.node) {
                health_code_update();

                pthread_mutex_lock(&stream->chan->lock);
                pthread_mutex_lock(&stream->lock);

                if (!stream->rotate_ready) {
                        pthread_mutex_unlock(&stream->lock);
                        pthread_mutex_unlock(&stream->chan->lock);
                        continue;
                }
                DBG("Consumer rotate ready stream %" PRIu64, stream->key);

                ret = lttng_consumer_rotate_stream(ctx, stream);
                pthread_mutex_unlock(&stream->lock);
                pthread_mutex_unlock(&stream->chan->lock);
                if (ret) {
                        goto end;
                }
        }

        ret = 0;

end:
        rcu_read_unlock();
        return ret;
}

enum lttcomm_return_code lttng_consumer_init_command(
                struct lttng_consumer_local_data *ctx,
                const lttng_uuid sessiond_uuid)
{
        enum lttcomm_return_code ret;
        char uuid_str[LTTNG_UUID_STR_LEN];

        if (ctx->sessiond_uuid.is_set) {
                ret = LTTCOMM_CONSUMERD_ALREADY_SET;
                goto end;
        }

        ctx->sessiond_uuid.is_set = true;
        memcpy(ctx->sessiond_uuid.value, sessiond_uuid, sizeof(lttng_uuid));
        ret = LTTCOMM_CONSUMERD_SUCCESS;
        lttng_uuid_to_str(sessiond_uuid, uuid_str);
        DBG("Received session daemon UUID: %s", uuid_str);
end:
        return ret;
}

enum lttcomm_return_code lttng_consumer_create_trace_chunk(
                const uint64_t *relayd_id, uint64_t session_id,
                uint64_t chunk_id,
                time_t chunk_creation_timestamp,
                const char *chunk_override_name,
                const struct lttng_credentials *credentials,
                struct lttng_directory_handle *chunk_directory_handle)
{
        int ret;
        enum lttcomm_return_code ret_code = LTTCOMM_CONSUMERD_SUCCESS;
        struct lttng_trace_chunk *created_chunk = NULL, *published_chunk = NULL;
        enum lttng_trace_chunk_status chunk_status;
        char relayd_id_buffer[MAX_INT_DEC_LEN(*relayd_id)];
        char creation_timestamp_buffer[ISO8601_STR_LEN];
        const char *relayd_id_str = "(none)";
        const char *creation_timestamp_str;
        struct lttng_ht_iter iter;
        struct lttng_consumer_channel *channel;

        if (relayd_id) {
                /* Only used for logging purposes. */
                ret = snprintf(relayd_id_buffer, sizeof(relayd_id_buffer),
                                "%" PRIu64, *relayd_id);
                if (ret > 0 && ret < sizeof(relayd_id_buffer)) {
                        relayd_id_str = relayd_id_buffer;
                } else {
                        relayd_id_str = "(formatting error)";
                }
        }

        /* Local protocol error. */
        assert(chunk_creation_timestamp);
        ret = time_to_iso8601_str(chunk_creation_timestamp,
                        creation_timestamp_buffer,
                        sizeof(creation_timestamp_buffer));
        creation_timestamp_str = !ret ? creation_timestamp_buffer :
                        "(formatting error)";

        DBG("Consumer create trace chunk command: relay_id = %s"
                        ", session_id = %" PRIu64 ", chunk_id = %" PRIu64
                        ", chunk_override_name = %s"
                        ", chunk_creation_timestamp = %s",
                        relayd_id_str, session_id, chunk_id,
                        chunk_override_name ? : "(none)",
                        creation_timestamp_str);

        /*
         * The trace chunk registry, as used by the consumer daemon, implicitly
         * owns the trace chunks. This is only needed in the consumer since
         * the consumer has no notion of a session beyond session IDs being
         * used to identify other objects.
         *
         * The lttng_trace_chunk_registry_publish() call below provides a
         * reference which is not released; it implicitly becomes the session
         * daemon's reference to the chunk in the consumer daemon.
         *
         * The lifetime of trace chunks in the consumer daemon is managed by
         * the session daemon through the LTTNG_CONSUMER_CREATE_TRACE_CHUNK
         * and LTTNG_CONSUMER_DESTROY_TRACE_CHUNK commands.
         */
        created_chunk = lttng_trace_chunk_create(chunk_id,
                        chunk_creation_timestamp, NULL);
        if (!created_chunk) {
                ERR("Failed to create trace chunk");
                ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
                goto error;
        }

        if (chunk_override_name) {
                chunk_status = lttng_trace_chunk_override_name(created_chunk,
                                chunk_override_name);
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
                        goto error;
                }
        }

        if (chunk_directory_handle) {
                chunk_status = lttng_trace_chunk_set_credentials(created_chunk,
                                credentials);
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        ERR("Failed to set trace chunk credentials");
                        ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
                        goto error;
                }
                /*
                 * The consumer daemon has no ownership of the chunk output
                 * directory.
                 */
                chunk_status = lttng_trace_chunk_set_as_user(created_chunk,
                                chunk_directory_handle);
                chunk_directory_handle = NULL;
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        ERR("Failed to set trace chunk's directory handle");
                        ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
                        goto error;
                }
        }

        published_chunk = lttng_trace_chunk_registry_publish_chunk(
                        consumer_data.chunk_registry, session_id,
                        created_chunk);
        lttng_trace_chunk_put(created_chunk);
        created_chunk = NULL;
        if (!published_chunk) {
                ERR("Failed to publish trace chunk");
                ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
                goto error;
        }

        rcu_read_lock();
        cds_lfht_for_each_entry_duplicate(consumer_data.channels_by_session_id_ht->ht,
                        consumer_data.channels_by_session_id_ht->hash_fct(
                                        &session_id, lttng_ht_seed),
                        consumer_data.channels_by_session_id_ht->match_fct,
                        &session_id, &iter.iter, channel,
                        channels_by_session_id_ht_node.node) {
                ret = lttng_consumer_channel_set_trace_chunk(channel,
                                published_chunk);
                if (ret) {
                        /*
                         * Roll-back the creation of this chunk.
                         *
                         * This is important since the session daemon will
                         * assume that the creation of this chunk failed and
                         * will never ask for it to be closed, resulting
                         * in a leak and an inconsistent state for some
                         * channels.
                         */
                        enum lttcomm_return_code close_ret;
                        char path[LTTNG_PATH_MAX];

                        DBG("Failed to set new trace chunk on existing channels, rolling back");
                        close_ret = lttng_consumer_close_trace_chunk(relayd_id,
                                        session_id, chunk_id,
                                        chunk_creation_timestamp, NULL,
                                        path);
                        if (close_ret != LTTCOMM_CONSUMERD_SUCCESS) {
                                ERR("Failed to roll-back the creation of new chunk: session_id = %" PRIu64 ", chunk_id = %" PRIu64,
                                                session_id, chunk_id);
                        }

                        ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
                        break;
                }
        }

        if (relayd_id) {
                struct consumer_relayd_sock_pair *relayd;

                relayd = consumer_find_relayd(*relayd_id);
                if (relayd) {
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                        ret = relayd_create_trace_chunk(
                                        &relayd->control_sock, published_chunk);
                        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                } else {
                        ERR("Failed to find relay daemon socket: relayd_id = %" PRIu64, *relayd_id);
                }

                if (!relayd || ret) {
                        enum lttcomm_return_code close_ret;
                        char path[LTTNG_PATH_MAX];

                        close_ret = lttng_consumer_close_trace_chunk(relayd_id,
                                        session_id,
                                        chunk_id,
                                        chunk_creation_timestamp,
                                        NULL, path);
                        if (close_ret != LTTCOMM_CONSUMERD_SUCCESS) {
                                ERR("Failed to roll-back the creation of new chunk: session_id = %" PRIu64 ", chunk_id = %" PRIu64,
                                                session_id,
                                                chunk_id);
                        }

                        ret_code = LTTCOMM_CONSUMERD_CREATE_TRACE_CHUNK_FAILED;
                        goto error_unlock;
                }
        }
error_unlock:
        rcu_read_unlock();
error:
        /* Release the reference returned by the "publish" operation. */
        lttng_trace_chunk_put(published_chunk);
        lttng_trace_chunk_put(created_chunk);
        return ret_code;
}

enum lttcomm_return_code lttng_consumer_close_trace_chunk(
                const uint64_t *relayd_id, uint64_t session_id,
                uint64_t chunk_id, time_t chunk_close_timestamp,
                const enum lttng_trace_chunk_command_type *close_command,
                char *path)
{
        enum lttcomm_return_code ret_code = LTTCOMM_CONSUMERD_SUCCESS;
        struct lttng_trace_chunk *chunk;
        char relayd_id_buffer[MAX_INT_DEC_LEN(*relayd_id)];
        const char *relayd_id_str = "(none)";
        const char *close_command_name = "none";
        struct lttng_ht_iter iter;
        struct lttng_consumer_channel *channel;
        enum lttng_trace_chunk_status chunk_status;

        if (relayd_id) {
                int ret;

                /* Only used for logging purposes. */
                ret = snprintf(relayd_id_buffer, sizeof(relayd_id_buffer),
                                "%" PRIu64, *relayd_id);
                if (ret > 0 && ret < sizeof(relayd_id_buffer)) {
                        relayd_id_str = relayd_id_buffer;
                } else {
                        relayd_id_str = "(formatting error)";
                }
        }
        if (close_command) {
                close_command_name = lttng_trace_chunk_command_type_get_name(
                                *close_command);
        }

        DBG("Consumer close trace chunk command: relayd_id = %s"
                        ", session_id = %" PRIu64 ", chunk_id = %" PRIu64
                        ", close command = %s",
                        relayd_id_str, session_id, chunk_id,
                        close_command_name);

        chunk = lttng_trace_chunk_registry_find_chunk(
                        consumer_data.chunk_registry, session_id, chunk_id);
        if (!chunk) {
                ERR("Failed to find chunk: session_id = %" PRIu64
                                ", chunk_id = %" PRIu64,
                                session_id, chunk_id);
                ret_code = LTTCOMM_CONSUMERD_UNKNOWN_TRACE_CHUNK;
                goto end;
        }

        chunk_status = lttng_trace_chunk_set_close_timestamp(chunk,
                        chunk_close_timestamp);
        if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                ret_code = LTTCOMM_CONSUMERD_CLOSE_TRACE_CHUNK_FAILED;
                goto end;
        }

        if (close_command) {
                chunk_status = lttng_trace_chunk_set_close_command(
                                chunk, *close_command);
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        ret_code = LTTCOMM_CONSUMERD_CLOSE_TRACE_CHUNK_FAILED;
                        goto end;
                }
        }

        /*
         * chunk is now invalid to access as we no longer hold a reference to
         * it; it is only kept around to compare it (by address) to the
         * current chunk found in the session's channels.
         */
        rcu_read_lock();
        cds_lfht_for_each_entry(consumer_data.channel_ht->ht, &iter.iter,
                        channel, node.node) {
                int ret;

                /*
                 * Only change the channel's chunk to NULL if it still
                 * references the chunk being closed. The channel may
                 * reference a newer channel in the case of a session
                 * rotation. When a session rotation occurs, the "next"
                 * chunk is created before the "current" chunk is closed.
                 */
                if (channel->trace_chunk != chunk) {
                        continue;
                }
                ret = lttng_consumer_channel_set_trace_chunk(channel, NULL);
                if (ret) {
                        /*
                         * Attempt to close the chunk on as many channels as
                         * possible.
                         */
                        ret_code = LTTCOMM_CONSUMERD_CLOSE_TRACE_CHUNK_FAILED;
                }
        }

        if (relayd_id) {
                int ret;
                struct consumer_relayd_sock_pair *relayd;

                relayd = consumer_find_relayd(*relayd_id);
                if (relayd) {
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                        ret = relayd_close_trace_chunk(
                                        &relayd->control_sock, chunk,
                                        path);
                        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                } else {
                        ERR("Failed to find relay daemon socket: relayd_id = %" PRIu64,
                                        *relayd_id);
                }

                if (!relayd || ret) {
                        ret_code = LTTCOMM_CONSUMERD_CLOSE_TRACE_CHUNK_FAILED;
                        goto error_unlock;
                }
        }
error_unlock:
        rcu_read_unlock();
end:
        /*
         * Release the reference returned by the "find" operation and
         * the session daemon's implicit reference to the chunk.
         */
        lttng_trace_chunk_put(chunk);
        lttng_trace_chunk_put(chunk);

        return ret_code;
}

enum lttcomm_return_code lttng_consumer_trace_chunk_exists(
                const uint64_t *relayd_id, uint64_t session_id,
                uint64_t chunk_id)
{
        int ret;
        enum lttcomm_return_code ret_code;
        char relayd_id_buffer[MAX_INT_DEC_LEN(*relayd_id)];
        const char *relayd_id_str = "(none)";
        const bool is_local_trace = !relayd_id;
        struct consumer_relayd_sock_pair *relayd = NULL;
        bool chunk_exists_local, chunk_exists_remote;

        if (relayd_id) {
                int ret;

                /* Only used for logging purposes. */
                ret = snprintf(relayd_id_buffer, sizeof(relayd_id_buffer),
                                "%" PRIu64, *relayd_id);
                if (ret > 0 && ret < sizeof(relayd_id_buffer)) {
                        relayd_id_str = relayd_id_buffer;
                } else {
                        relayd_id_str = "(formatting error)";
                }
        }

        DBG("Consumer trace chunk exists command: relayd_id = %s"
                        ", chunk_id = %" PRIu64, relayd_id_str,
                        chunk_id);
        ret = lttng_trace_chunk_registry_chunk_exists(
                        consumer_data.chunk_registry, session_id,
                        chunk_id, &chunk_exists_local);
        if (ret) {
                /* Internal error. */
                ERR("Failed to query the existence of a trace chunk");
                ret_code = LTTCOMM_CONSUMERD_FATAL;
                goto end;
        }
        DBG("Trace chunk %s locally",
                        chunk_exists_local ? "exists" : "does not exist");
        if (chunk_exists_local) {
                ret_code = LTTCOMM_CONSUMERD_TRACE_CHUNK_EXISTS_LOCAL;
                goto end;
        } else if (is_local_trace) {
                ret_code = LTTCOMM_CONSUMERD_UNKNOWN_TRACE_CHUNK;
                goto end;
        }

        rcu_read_lock();
        relayd = consumer_find_relayd(*relayd_id);
        if (!relayd) {
                ERR("Failed to find relayd %" PRIu64, *relayd_id);
                ret_code = LTTCOMM_CONSUMERD_INVALID_PARAMETERS;
                goto end_rcu_unlock;
        }
        DBG("Looking up existence of trace chunk on relay daemon");
        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
        ret = relayd_trace_chunk_exists(&relayd->control_sock, chunk_id,
                        &chunk_exists_remote);
        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
        if (ret < 0) {
                ERR("Failed to look-up the existence of trace chunk on relay daemon");
                ret_code = LTTCOMM_CONSUMERD_RELAYD_FAIL;
                goto end_rcu_unlock;
        }

        ret_code = chunk_exists_remote ?
                        LTTCOMM_CONSUMERD_TRACE_CHUNK_EXISTS_REMOTE :
                        LTTCOMM_CONSUMERD_UNKNOWN_TRACE_CHUNK;
        DBG("Trace chunk %s on relay daemon",
                        chunk_exists_remote ? "exists" : "does not exist");

end_rcu_unlock:
        rcu_read_unlock();
end:
        return ret_code;
}

static
int consumer_clear_monitored_channel(struct lttng_consumer_channel *channel)
{
        struct lttng_ht *ht;
        struct lttng_consumer_stream *stream;
        struct lttng_ht_iter iter;
        int ret;

        ht = consumer_data.stream_per_chan_id_ht;

        rcu_read_lock();
        cds_lfht_for_each_entry_duplicate(ht->ht,
                        ht->hash_fct(&channel->key, lttng_ht_seed),
                        ht->match_fct, &channel->key,
                        &iter.iter, stream, node_channel_id.node) {
                /*
                 * Protect against teardown with mutex.
                 */
                pthread_mutex_lock(&stream->lock);
                if (cds_lfht_is_node_deleted(&stream->node.node)) {
                        goto next;
                }
                ret = consumer_clear_stream(stream);
                if (ret) {
                        goto error_unlock;
                }
        next:
                pthread_mutex_unlock(&stream->lock);
        }
        rcu_read_unlock();
        return LTTCOMM_CONSUMERD_SUCCESS;

error_unlock:
        pthread_mutex_unlock(&stream->lock);
        rcu_read_unlock();
        return ret;
}

int lttng_consumer_clear_channel(struct lttng_consumer_channel *channel)
{
        int ret;

        DBG("Consumer clear channel %" PRIu64, channel->key);

        if (channel->type == CONSUMER_CHANNEL_TYPE_METADATA) {
                /*
                 * Nothing to do for the metadata channel/stream.
                 * Snapshot mechanism already take care of the metadata
                 * handling/generation, and monitored channels only need to
                 * have their data stream cleared..
                 */
                ret = LTTCOMM_CONSUMERD_SUCCESS;
                goto end;
        }

        if (!channel->monitor) {
                ret = consumer_clear_unmonitored_channel(channel);
        } else {
                ret = consumer_clear_monitored_channel(channel);
        }
end:
        return ret;
}

enum lttcomm_return_code lttng_consumer_open_channel_packets(
                struct lttng_consumer_channel *channel)
{
        struct lttng_consumer_stream *stream;
        enum lttcomm_return_code ret = LTTCOMM_CONSUMERD_SUCCESS;

        if (channel->metadata_stream) {
                ERR("Open channel packets command attempted on a metadata channel");
                ret = LTTCOMM_CONSUMERD_INVALID_PARAMETERS;
                goto end;
        }

        rcu_read_lock();
        cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
                enum consumer_stream_open_packet_status status;

                pthread_mutex_lock(&stream->lock);
                if (cds_lfht_is_node_deleted(&stream->node.node)) {
                        goto next;
                }

                status = consumer_stream_open_packet(stream);
                switch (status) {
                case CONSUMER_STREAM_OPEN_PACKET_STATUS_OPENED:
                        DBG("Opened a packet in \"open channel packets\" command: stream id = %" PRIu64
                                        ", channel name = %s, session id = %" PRIu64,
                                        stream->key, stream->chan->name,
                                        stream->chan->session_id);
                        stream->opened_packet_in_current_trace_chunk = true;
                        break;
                case CONSUMER_STREAM_OPEN_PACKET_STATUS_NO_SPACE:
                        DBG("No space left to open a packet in \"open channel packets\" command: stream id = %" PRIu64
                                        ", channel name = %s, session id = %" PRIu64,
                                        stream->key, stream->chan->name,
                                        stream->chan->session_id);
                        break;
                case CONSUMER_STREAM_OPEN_PACKET_STATUS_ERROR:
                        /*
                         * Only unexpected internal errors can lead to this
                         * failing. Report an unknown error.
                         */
                        ERR("Failed to flush empty buffer in \"open channel packets\" command: stream id = %" PRIu64
                                        ", channel id = %" PRIu64
                                        ", channel name = %s"
                                        ", session id = %" PRIu64,
                                        stream->key, channel->key,
                                        channel->name, channel->session_id);
                        ret = LTTCOMM_CONSUMERD_UNKNOWN_ERROR;
                        goto error_unlock;
                default:
                        abort();
                }

        next:
                pthread_mutex_unlock(&stream->lock);
        }

end_rcu_unlock:
        rcu_read_unlock();
end:
        return ret;

error_unlock:
        pthread_mutex_unlock(&stream->lock);
        goto end_rcu_unlock;
}