Fix RCU-related hangs: incorrect lttng_ht_destroy use

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

/*
 * Copyright (C) 2011 - Julien Desfossez <julien.desfossez@polymtl.ca>
 *                      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *               2012 - David Goulet <dgoulet@efficios.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#define _GNU_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 <common/common.h>
#include <common/utils.h>
#include <common/compat/poll.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 "consumer.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_QUIT,
};

struct consumer_channel_msg {
        enum consumer_channel_action action;
        struct lttng_consumer_channel *chan;
};

/*
 * 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.
 */
volatile 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;

/*
 * Notify a thread 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_pipe(int wpipe)
{
        int ret;

        do {
                struct lttng_consumer_stream *null_stream = NULL;

                ret = write(wpipe, &null_stream, sizeof(null_stream));
        } while (ret < 0 && errno == EINTR);
}

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

        msg.action = action;
        msg.chan = chan;
        do {
                ret = write(ctx->consumer_channel_pipe[1], &msg, sizeof(msg));
        } while (ret < 0 && errno == EINTR);
}

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

        do {
                ret = read(ctx->consumer_channel_pipe[0], &msg, sizeof(msg));
        } while (ret < 0 && errno == EINTR);
        if (ret > 0) {
                *action = msg.action;
                *chan = msg.chan;
        }
        return ret;
}

/*
 * 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(int key, struct lttng_ht *ht)
{
        struct lttng_consumer_stream *stream;

        rcu_read_lock();
        stream = find_stream(key, ht);
        if (stream) {
                stream->key = -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 = -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;
}

static void free_stream_rcu(struct rcu_head *head)
{
        struct lttng_ht_node_u64 *node =
                caa_container_of(head, struct lttng_ht_node_u64, head);
        struct lttng_consumer_stream *stream =
                caa_container_of(node, struct lttng_consumer_stream, node);

        free(stream);
}

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);

        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);

        free(relayd);
}

/*
 * Destroy and free relayd socket pair object.
 *
 * This function MUST be called with the consumer_data lock acquired.
 */
static void 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)
{
        int ret;
        struct lttng_ht_iter iter;

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

        pthread_mutex_lock(&consumer_data.lock);

        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;
        }

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

        call_rcu(&channel->node.head, free_channel_rcu);
end:
        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) {
                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(int 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 %d", 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.
 */
static void cleanup_relayd(struct consumer_relayd_sock_pair *relayd,
                struct lttng_consumer_local_data *ctx)
{
        int netidx;

        assert(relayd);

        DBG("Cleaning up relayd sockets");

        /* 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.
         */
        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.
         */
        if (ctx) {
                notify_thread_pipe(ctx->consumer_data_pipe[1]);
                notify_thread_pipe(ctx->consumer_metadata_pipe[1]);
        }
}

/*
 * 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) {
                destroy_relayd(relayd);
        }
}

/*
 * Remove a stream from the global list protected by a mutex. This
 * function is also responsible for freeing its data structures.
 */
void consumer_del_stream(struct lttng_consumer_stream *stream,
                struct lttng_ht *ht)
{
        int ret;
        struct lttng_ht_iter iter;
        struct lttng_consumer_channel *free_chan = NULL;
        struct consumer_relayd_sock_pair *relayd;

        assert(stream);

        DBG("Consumer del stream %d", stream->wait_fd);

        if (ht == NULL) {
                /* Means the stream was allocated but not successfully added */
                goto free_stream_rcu;
        }

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

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                if (stream->mmap_base != NULL) {
                        ret = munmap(stream->mmap_base, stream->mmap_len);
                        if (ret != 0) {
                                PERROR("munmap");
                        }
                }
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                lttng_ustconsumer_del_stream(stream);
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }

        rcu_read_lock();
        iter.iter.node = &stream->node.node;
        ret = lttng_ht_del(ht, &iter);
        assert(!ret);

        iter.iter.node = &stream->node_channel_id.node;
        ret = lttng_ht_del(consumer_data.stream_per_chan_id_ht, &iter);
        assert(!ret);

        iter.iter.node = &stream->node_session_id.node;
        ret = lttng_ht_del(consumer_data.stream_list_ht, &iter);
        assert(!ret);
        rcu_read_unlock();

        assert(consumer_data.stream_count > 0);
        consumer_data.stream_count--;

        if (stream->out_fd >= 0) {
                ret = close(stream->out_fd);
                if (ret) {
                        PERROR("close");
                }
        }

        /* Check and cleanup relayd */
        rcu_read_lock();
        relayd = consumer_find_relayd(stream->net_seq_idx);
        if (relayd != NULL) {
                uatomic_dec(&relayd->refcount);
                assert(uatomic_read(&relayd->refcount) >= 0);

                /* Closing streams requires to lock the control socket. */
                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_send_close_stream(&relayd->control_sock,
                                stream->relayd_stream_id,
                                stream->next_net_seq_num - 1);
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        DBG("Unable to close stream on the relayd. Continuing");
                        /*
                         * Continue here. There is nothing we can do for the relayd.
                         * Chances are that the relayd has closed the socket so we just
                         * continue cleaning up.
                         */
                }

                /* Both conditions are met, we destroy the relayd. */
                if (uatomic_read(&relayd->refcount) == 0 &&
                                uatomic_read(&relayd->destroy_flag)) {
                        destroy_relayd(relayd);
                }
        }
        rcu_read_unlock();

        if (!uatomic_sub_return(&stream->chan->refcount, 1)
                        && !uatomic_read(&stream->chan->nb_init_stream_left)) {
                free_chan = stream->chan;
        }

end:
        consumer_data.need_update = 1;
        pthread_mutex_unlock(&stream->lock);
        pthread_mutex_unlock(&consumer_data.lock);

        if (free_chan) {
                consumer_del_channel(free_chan);
        }

free_stream_rcu:
        call_rcu(&stream->node.head, free_stream_rcu);
}

struct lttng_consumer_stream *consumer_allocate_stream(uint64_t channel_key,
                uint64_t stream_key,
                enum lttng_consumer_stream_state state,
                const char *channel_name,
                uid_t uid,
                gid_t gid,
                int relayd_id,
                uint64_t session_id,
                int cpu,
                int *alloc_ret,
                enum consumer_channel_type type)
{
        int ret;
        struct lttng_consumer_stream *stream;

        stream = zmalloc(sizeof(*stream));
        if (stream == NULL) {
                PERROR("malloc struct lttng_consumer_stream");
                ret = -ENOMEM;
                goto end;
        }

        rcu_read_lock();

        stream->key = stream_key;
        stream->out_fd = -1;
        stream->out_fd_offset = 0;
        stream->state = state;
        stream->uid = uid;
        stream->gid = gid;
        stream->net_seq_idx = relayd_id;
        stream->session_id = session_id;
        pthread_mutex_init(&stream->lock, NULL);

        /* If channel is the metadata, flag this stream as metadata. */
        if (type == CONSUMER_CHANNEL_TYPE_METADATA) {
                stream->metadata_flag = 1;
                /* Metadata is flat out. */
                strncpy(stream->name, DEFAULT_METADATA_NAME, sizeof(stream->name));
        } else {
                /* Format stream name to <channel_name>_<cpu_number> */
                ret = snprintf(stream->name, sizeof(stream->name), "%s_%d",
                                channel_name, cpu);
                if (ret < 0) {
                        PERROR("snprintf stream name");
                        goto error;
                }
        }

        /* Key is always the wait_fd for streams. */
        lttng_ht_node_init_u64(&stream->node, stream->key);

        /* Init node per channel id key */
        lttng_ht_node_init_u64(&stream->node_channel_id, channel_key);

        /* Init session id node with the stream session id */
        lttng_ht_node_init_u64(&stream->node_session_id, stream->session_id);

        DBG3("Allocated stream %s (key %" PRIu64 ", chan_key %" PRIu64 " relayd_id %" PRIu64 ", session_id %" PRIu64,
                        stream->name, stream->key, channel_key, stream->net_seq_idx, stream->session_id);

        rcu_read_unlock();
        return stream;

error:
        rcu_read_unlock();
        free(stream);
end:
        if (alloc_ret) {
                *alloc_ret = ret;
        }
        return NULL;
}

/*
 * Add a stream to the global list protected by a mutex.
 */
static int add_stream(struct lttng_consumer_stream *stream,
                struct lttng_ht *ht)
{
        int ret = 0;
        struct consumer_relayd_sock_pair *relayd;

        assert(stream);
        assert(ht);

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

        pthread_mutex_lock(&consumer_data.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);

        /* Check and cleanup relayd */
        relayd = consumer_find_relayd(stream->net_seq_idx);
        if (relayd != NULL) {
                uatomic_inc(&relayd->refcount);
        }

        /* Update channel refcount once added without error(s). */
        uatomic_inc(&stream->chan->refcount);

        /*
         * 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(&consumer_data.lock);

        return ret;
}

/*
 * 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.
 */
struct consumer_relayd_sock_pair *consumer_allocate_relayd_sock_pair(
                int net_seq_idx)
{
        struct consumer_relayd_sock_pair *obj = NULL;

        /* Negative net sequence index is a failure */
        if (net_seq_idx < 0) {
                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;
        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;
}

/*
 * 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;
}

/*
 * 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 char *pathname,
                const char *name,
                uid_t uid,
                gid_t gid,
                int relayd_id,
                enum lttng_event_output output,
                uint64_t tracefile_size,
                uint64_t tracefile_count)
{
        struct lttng_consumer_channel *channel;

        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->uid = uid;
        channel->gid = gid;
        channel->relayd_id = relayd_id;
        channel->output = output;
        channel->tracefile_size = tracefile_size;
        channel->tracefile_count = tracefile_count;

        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';

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

        channel->wait_fd = -1;

        CDS_INIT_LIST_HEAD(&channel->streams.head);

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

end:
        return channel;
}

/*
 * Add a channel to the global list protected by a mutex.
 */
int consumer_add_channel(struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx)
{
        int ret = 0;
        struct lttng_ht_node_u64 *node;
        struct lttng_ht_iter iter;

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

        lttng_ht_lookup(consumer_data.channel_ht, &channel->key, &iter);
        node = lttng_ht_iter_get_node_u64(&iter);
        if (node != NULL) {
                /* Channel already exist. Ignore the insertion */
                ERR("Consumer add channel key %" PRIu64 " already exists!",
                        channel->key);
                ret = -1;
                goto end;
        }

        lttng_ht_add_unique_u64(consumer_data.channel_ht, &channel->node);

end:
        rcu_read_unlock();
        pthread_mutex_unlock(&consumer_data.lock);

        if (!ret && channel->wait_fd != -1 &&
                        channel->metadata_stream == NULL) {
                notify_channel_pipe(ctx, channel, CONSUMER_CHANNEL_ADD);
        }
        return ret;
}

/*
 * 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 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");
        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.
                 */
                if (stream->state != LTTNG_CONSUMER_ACTIVE_STREAM ||
                                stream->endpoint_status == CONSUMER_ENDPOINT_INACTIVE) {
                        continue;
                }
                /*
                 * This clobbers way too much the debug output. Uncomment that if you
                 * need it for debugging purposes.
                 *
                 * DBG("Active FD %d", stream->wait_fd);
                 */
                (*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 = ctx->consumer_data_pipe[0];
        (*pollfd)[i].events = POLLIN | POLLPRI;
        return i;
}

/*
 * Poll on the should_quit pipe and the command socket return -1 on error and
 * 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");
                goto exit;
        }
        if (consumer_sockpoll[0].revents & (POLLIN | POLLPRI)) {
                DBG("consumer_should_quit wake up");
                goto exit;
        }
        return 0;

exit:
        return -1;
}

/*
 * 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;

        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);

        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);
}

/*
 * Called from signal handler.
 */
void lttng_consumer_should_exit(struct lttng_consumer_local_data *ctx)
{
        int ret;
        consumer_quit = 1;
        do {
                ret = write(ctx->consumer_should_quit[1], "4", 1);
        } while (ret < 0 && errno == EINTR);
        if (ret < 0 || ret != 1) {
                PERROR("write consumer quit");
        }

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

void lttng_consumer_sync_trace_file(struct lttng_consumer_stream *stream,
                off_t orig_offset)
{
        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.
         */
        posix_fadvise(outfd, orig_offset - stream->max_sb_size,
                        stream->max_sb_size, POSIX_FADV_DONTNEED);
}

/*
 * 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),
                int (*recv_channel)(struct lttng_consumer_channel *channel),
                int (*recv_stream)(struct lttng_consumer_stream *stream),
                int (*update_stream)(int 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;
        /* 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;

        ret = pipe(ctx->consumer_data_pipe);
        if (ret < 0) {
                PERROR("Error creating poll pipe");
                goto error_poll_pipe;
        }

        /* set read end of the pipe to non-blocking */
        ret = fcntl(ctx->consumer_data_pipe[0], F_SETFL, O_NONBLOCK);
        if (ret < 0) {
                PERROR("fcntl O_NONBLOCK");
                goto error_poll_fcntl;
        }

        /* set write end of the pipe to non-blocking */
        ret = fcntl(ctx->consumer_data_pipe[1], F_SETFL, O_NONBLOCK);
        if (ret < 0) {
                PERROR("fcntl O_NONBLOCK");
                goto error_poll_fcntl;
        }

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

        ret = pipe(ctx->consumer_thread_pipe);
        if (ret < 0) {
                PERROR("Error creating thread pipe");
                goto error_thread_pipe;
        }

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

        ret = utils_create_pipe(ctx->consumer_metadata_pipe);
        if (ret < 0) {
                goto error_metadata_pipe;
        }

        ret = utils_create_pipe(ctx->consumer_splice_metadata_pipe);
        if (ret < 0) {
                goto error_splice_pipe;
        }

        return ctx;

error_splice_pipe:
        utils_close_pipe(ctx->consumer_metadata_pipe);
error_metadata_pipe:
        utils_close_pipe(ctx->consumer_channel_pipe);
error_channel_pipe:
        utils_close_pipe(ctx->consumer_thread_pipe);
error_thread_pipe:
        utils_close_pipe(ctx->consumer_should_quit);
error_poll_fcntl:
error_quit_pipe:
        utils_close_pipe(ctx->consumer_data_pipe);
error_poll_pipe:
        free(ctx);
error:
        return NULL;
}

/*
 * 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.");

        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_thread_pipe);
        utils_close_pipe(ctx->consumer_channel_pipe);
        utils_close_pipe(ctx->consumer_data_pipe);
        utils_close_pipe(ctx->consumer_should_quit);
        utils_close_pipe(ctx->consumer_splice_metadata_pipe);

        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,
                struct consumer_relayd_sock_pair *relayd, unsigned long padding)
{
        int ret;
        struct lttcomm_relayd_metadata_payload hdr;

        hdr.stream_id = htobe64(stream->relayd_stream_id);
        hdr.padding_size = htobe32(padding);
        do {
                ret = write(fd, (void *) &hdr, sizeof(hdr));
        } while (ret < 0 && errno == EINTR);
        if (ret < 0 || 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 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 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_local_data *ctx,
                struct lttng_consumer_stream *stream, unsigned long len,
                unsigned long padding)
{
        unsigned long mmap_offset;
        void *mmap_base;
        ssize_t ret = 0, written = 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;

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

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

        /* get the offset inside the fd to mmap */
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                mmap_base = stream->mmap_base;
                ret = kernctl_get_mmap_read_offset(stream->wait_fd, &mmap_offset);
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                mmap_base = lttng_ustctl_get_mmap_base(stream);
                if (!mmap_base) {
                        ERR("read mmap get mmap base for stream %s", stream->name);
                        written = -1;
                        goto end;
                }
                ret = lttng_ustctl_get_mmap_read_offset(stream, &mmap_offset);

                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
        }
        if (ret != 0) {
                errno = -ret;
                PERROR("tracer ctl get_mmap_read_offset");
                written = ret;
                goto end;
        }

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

                /*
                 * 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);
                        netlen += sizeof(struct lttcomm_relayd_metadata_payload);
                }

                ret = write_relayd_stream_header(stream, netlen, padding, relayd);
                if (ret >= 0) {
                        /* Use the returned socket. */
                        outfd = ret;

                        /* Write metadata stream id before payload */
                        if (stream->metadata_flag) {
                                ret = write_relayd_metadata_id(outfd, stream, relayd, padding);
                                if (ret < 0) {
                                        written = ret;
                                        /* Socket operation failed. We consider the relayd dead */
                                        if (ret == -EPIPE || ret == -EINVAL) {
                                                relayd_hang_up = 1;
                                                goto write_error;
                                        }
                                        goto end;
                                }
                        }
                } else {
                        /* Socket operation failed. We consider the relayd dead */
                        if (ret == -EPIPE || ret == -EINVAL) {
                                relayd_hang_up = 1;
                                goto write_error;
                        }
                        /* Else, use the default set before which is the filesystem. */
                }
        } else {
                /* No streaming, we have to set the len with the full padding */
                len += padding;

                /*
                 * 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 = utils_rotate_stream_file(stream->chan->pathname,
                                        stream->name, stream->chan->tracefile_size,
                                        stream->chan->tracefile_count, stream->uid, stream->gid,
                                        stream->out_fd, &(stream->tracefile_count_current));
                        if (ret < 0) {
                                ERR("Rotating output file");
                                goto end;
                        }
                        outfd = stream->out_fd = ret;
                }
                stream->tracefile_size_current += len;
        }

        while (len > 0) {
                do {
                        ret = write(outfd, mmap_base + mmap_offset, len);
                } while (ret < 0 && errno == EINTR);
                DBG("Consumer mmap write() ret %zd (len %lu)", ret, len);
                if (ret < 0) {
                        /*
                         * 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("Error in file write mmap");
                        if (written == 0) {
                                written = ret;
                        }
                        /* Socket operation failed. We consider the relayd dead */
                        if (errno == EPIPE || errno == EINVAL) {
                                relayd_hang_up = 1;
                                goto write_error;
                        }
                        goto end;
                } else if (ret > len) {
                        PERROR("Error in file write (ret %zd > len %lu)", ret, len);
                        written += ret;
                        goto end;
                } else {
                        len -= ret;
                        mmap_offset += 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, ret,
                                        SYNC_FILE_RANGE_WRITE);
                        stream->out_fd_offset += ret;
                }
                written += ret;
        }
        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) {
                cleanup_relayd(relayd, ctx);
        }

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

        rcu_read_unlock();
        return written;
}

/*
 * 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 != -1) {
                relayd = consumer_find_relayd(stream->net_seq_idx);
                if (relayd == NULL) {
                        goto end;
                }
        }

        /*
         * Choose right pipe for splice. Metadata and trace data are handled by
         * different threads hence the use of two pipes in order not to race or
         * corrupt the written data.
         */
        if (stream->metadata_flag) {
                splice_pipe = ctx->consumer_splice_metadata_pipe;
        } else {
                splice_pipe = ctx->consumer_thread_pipe;
        }

        /* Write metadata stream id before payload */
        if (relayd) {
                int 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);

                        ret = write_relayd_metadata_id(splice_pipe[1], stream, relayd,
                                        padding);
                        if (ret < 0) {
                                written = ret;
                                /* Socket operation failed. We consider the relayd dead */
                                if (ret == -EBADF) {
                                        WARN("Remote relayd disconnected. Stopping");
                                        relayd_hang_up = 1;
                                        goto write_error;
                                }
                                goto end;
                        }

                        total_len += sizeof(struct lttcomm_relayd_metadata_payload);
                }

                ret = write_relayd_stream_header(stream, total_len, padding, relayd);
                if (ret >= 0) {
                        /* Use the returned socket. */
                        outfd = ret;
                } else {
                        /* Socket operation failed. We consider the relayd dead */
                        if (ret == -EBADF) {
                                WARN("Remote relayd disconnected. Stopping");
                                relayd_hang_up = 1;
                                goto write_error;
                        }
                        goto end;
                }
        } else {
                /* No streaming, we have to set the len with the full padding */
                len += padding;

                /*
                 * 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 = utils_rotate_stream_file(stream->chan->pathname,
                                        stream->name, stream->chan->tracefile_size,
                                        stream->chan->tracefile_count, stream->uid, stream->gid,
                                        stream->out_fd, &(stream->tracefile_count_current));
                        if (ret < 0) {
                                ERR("Rotating output file");
                                goto end;
                        }
                        outfd = stream->out_fd = ret;
                }
                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) {
                        PERROR("Error in relay splice");
                        if (written == 0) {
                                written = ret_splice;
                        }
                        ret = errno;
                        goto splice_error;
                }

                /* Handle stream on the relayd if the output is on the network */
                if (relayd) {
                        if (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, ret %zd", ret_splice);
                if (ret_splice < 0) {
                        PERROR("Error in file splice");
                        if (written == 0) {
                                written = ret_splice;
                        }
                        /* Socket operation failed. We consider the relayd dead */
                        if (errno == EBADF || errno == EPIPE) {
                                WARN("Remote relayd disconnected. Stopping");
                                relayd_hang_up = 1;
                                goto write_error;
                        }
                        ret = errno;
                        goto splice_error;
                } else if (ret_splice > len) {
                        errno = EINVAL;
                        PERROR("Wrote more data than requested %zd (len: %lu)",
                                        ret_splice, len);
                        written += ret_splice;
                        ret = errno;
                        goto splice_error;
                }
                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;
                }
                written += ret_splice;
        }
        lttng_consumer_sync_trace_file(stream, orig_offset);

        ret = ret_splice;

        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) {
                cleanup_relayd(relayd, ctx);
                /* 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;
}

/*
 * 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;
        }
}

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;
        }
}

/*
 * Iterate over all streams of the hashtable and free them properly.
 *
 * WARNING: *MUST* be used with data stream only.
 */
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 hashtable and free them properly.
 *
 * XXX: Should not be only for metadata stream or else use an other name.
 */
static void destroy_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);
}

void lttng_consumer_close_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_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)
{
        int ret;
        struct lttng_ht_iter iter;
        struct lttng_consumer_channel *free_chan = NULL;
        struct consumer_relayd_sock_pair *relayd;

        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);

        if (ht == NULL) {
                /* Means the stream was allocated but not successfully added */
                goto free_stream_rcu;
        }

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

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                if (stream->mmap_base != NULL) {
                        ret = munmap(stream->mmap_base, stream->mmap_len);
                        if (ret != 0) {
                                PERROR("munmap metadata stream");
                        }
                }
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                lttng_ustconsumer_del_stream(stream);
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }

        rcu_read_lock();
        iter.iter.node = &stream->node.node;
        ret = lttng_ht_del(ht, &iter);
        assert(!ret);

        iter.iter.node = &stream->node_channel_id.node;
        ret = lttng_ht_del(consumer_data.stream_per_chan_id_ht, &iter);
        assert(!ret);

        iter.iter.node = &stream->node_session_id.node;
        ret = lttng_ht_del(consumer_data.stream_list_ht, &iter);
        assert(!ret);
        rcu_read_unlock();

        if (stream->out_fd >= 0) {
                ret = close(stream->out_fd);
                if (ret) {
                        PERROR("close");
                }
        }

        /* Check and cleanup relayd */
        rcu_read_lock();
        relayd = consumer_find_relayd(stream->net_seq_idx);
        if (relayd != NULL) {
                uatomic_dec(&relayd->refcount);
                assert(uatomic_read(&relayd->refcount) >= 0);

                /* Closing streams requires to lock the control socket. */
                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_send_close_stream(&relayd->control_sock,
                                stream->relayd_stream_id, stream->next_net_seq_num - 1);
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        DBG("Unable to close stream on the relayd. Continuing");
                        /*
                         * Continue here. There is nothing we can do for the relayd.
                         * Chances are that the relayd has closed the socket so we just
                         * continue cleaning up.
                         */
                }

                /* Both conditions are met, we destroy the relayd. */
                if (uatomic_read(&relayd->refcount) == 0 &&
                                uatomic_read(&relayd->destroy_flag)) {
                        destroy_relayd(relayd);
                }
        }
        rcu_read_unlock();

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

end:
        pthread_mutex_unlock(&stream->lock);
        pthread_mutex_unlock(&consumer_data.lock);

        if (free_chan) {
                consumer_del_channel(free_chan);
        }

free_stream_rcu:
        call_rcu(&stream->node.head, free_stream_rcu);
}

/*
 * Action done with the metadata stream when adding it to the consumer internal
 * data structures to handle it.
 */
static int add_metadata_stream(struct lttng_consumer_stream *stream,
                struct lttng_ht *ht)
{
        int ret = 0;
        struct consumer_relayd_sock_pair *relayd;
        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->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);

        /* Find relayd and, if one is found, increment refcount. */
        relayd = consumer_find_relayd(stream->net_seq_idx);
        if (relayd != NULL) {
                uatomic_inc(&relayd->refcount);
        }

        /* Update channel refcount once added without error(s). */
        uatomic_inc(&stream->chan->refcount);

        /*
         * 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_unique_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(&consumer_data.lock);
        return ret;
}

/*
 * 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;
        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();

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

        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, ctx->consumer_metadata_pipe[0], LPOLLIN);
        if (ret < 0) {
                goto end;
        }

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

        while (1) {
                /* Only the metadata pipe is set */
                if (LTTNG_POLL_GETNB(&events) == 0 && consumer_quit == 1) {
                        goto end;
                }

restart:
                DBG("Metadata poll wait with %d fd(s)", LTTNG_POLL_GETNB(&events));
                ret = lttng_poll_wait(&events, -1);
                DBG("Metadata event catched in thread");
                if (ret < 0) {
                        if (errno == EINTR) {
                                ERR("Poll EINTR catched");
                                goto restart;
                        }
                        goto error;
                }

                nb_fd = ret;

                /* From here, the event is a metadata wait fd */
                for (i = 0; i < nb_fd; i++) {
                        revents = LTTNG_POLL_GETEV(&events, i);
                        pollfd = LTTNG_POLL_GETFD(&events, i);

                        /* Just don't waste time if no returned events for the fd */
                        if (!revents) {
                                continue;
                        }

                        if (pollfd == ctx->consumer_metadata_pipe[0]) {
                                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, ctx->consumer_metadata_pipe[0]);
                                        ret = close(ctx->consumer_metadata_pipe[0]);
                                        if (ret < 0) {
                                                PERROR("close metadata pipe");
                                        }
                                        continue;
                                } else if (revents & LPOLLIN) {
                                        do {
                                                /* Get the stream pointer received */
                                                ret = read(pollfd, &stream, sizeof(stream));
                                        } while (ret < 0 && errno == EINTR);
                                        if (ret < 0 ||
                                                        ret < sizeof(struct lttng_consumer_stream *)) {
                                                PERROR("read metadata stream");
                                                /*
                                                 * Let's continue here and hope we can still work
                                                 * without stopping the consumer. XXX: Should we?
                                                 */
                                                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);

                                        ret = add_metadata_stream(stream, metadata_ht);
                                        if (ret) {
                                                ERR("Unable to add metadata stream");
                                                /* Stream was not setup properly. Continuing. */
                                                consumer_del_metadata_stream(stream, NULL);
                                                continue;
                                        }

                                        /* Add metadata stream to the global poll events list */
                                        lttng_poll_add(&events, stream->wait_fd,
                                                        LPOLLIN | LPOLLPRI);
                                }

                                /* 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);

                        /* Check for error event */
                        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 {
                                                len = ctx->on_buffer_ready(stream, ctx);
                                                /*
                                                 * We don't check the return value here since if we get
                                                 * a negative len, it means an error occured 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 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);

                                len = ctx->on_buffer_ready(stream, ctx);
                                /* 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 (len > 0) {
                                        stream->data_read = 1;
                                }
                        }

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

error:
end:
        DBG("Metadata poll thread exiting");

        lttng_poll_clean(&events);
end_poll:
        destroy_stream_ht(metadata_ht);
end_ht:
        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;
        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;
        struct lttng_consumer_local_data *ctx = data;
        ssize_t len;

        rcu_register_thread();

        data_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (data_ht == NULL) {
                /* ENOMEM at this point. Better to bail out. */
                goto end;
        }

        local_stream = zmalloc(sizeof(struct lttng_consumer_stream));

        while (1) {
                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 + 1 for the consumer_data_pipe */
                        pollfd = zmalloc((consumer_data.stream_count + 1) * sizeof(struct pollfd));
                        if (pollfd == NULL) {
                                PERROR("pollfd malloc");
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }

                        /* allocate for all fds + 1 for the consumer_data_pipe */
                        local_stream = zmalloc((consumer_data.stream_count + 1) *
                                        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);
                        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 && consumer_quit == 1) {
                        goto end;
                }
                /* poll on the array of fds */
        restart:
                DBG("polling on %d fd", nb_fd + 1);
                num_rdy = poll(pollfd, nb_fd + 1, -1);
                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 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");
                        /* Consume 1 byte of pipe data */
                        do {
                                pipe_readlen = read(ctx->consumer_data_pipe[0], &new_stream,
                                                sizeof(new_stream));
                        } while (pipe_readlen == -1 && errno == EINTR);
                        if (pipe_readlen < 0) {
                                PERROR("read 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;
                        }

                        ret = add_stream(new_stream, data_ht);
                        if (ret) {
                                ERR("Consumer add stream %" PRIu64 " failed. Continuing",
                                                new_stream->key);
                                /*
                                 * At this point, if the add_stream fails, it is not in the
                                 * hash table thus passing the NULL value here.
                                 */
                                consumer_del_stream(new_stream, NULL);
                        }

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

                /* Take care of high priority channels first. */
                for (i = 0; i < nb_fd; i++) {
                        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);
                                /* 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++) {
                        if (local_stream[i] == NULL) {
                                continue;
                        }
                        if ((pollfd[i].revents & POLLIN) ||
                                        local_stream[i]->hangup_flush_done) {
                                DBG("Normal read on fd %d", pollfd[i].fd);
                                len = ctx->on_buffer_ready(local_stream[i], ctx);
                                /* 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++) {
                        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;
                        }
                }
        }
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.
         */
        ret = close(ctx->consumer_metadata_pipe[1]);
        if (ret < 0) {
                PERROR("close data pipe");
        }

        destroy_data_stream_ht(data_ht);

        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:
                        /*
                         * 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;
        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();

        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) {
                /* Only the channel pipe is set */
                if (LTTNG_POLL_GETNB(&events) == 0 && consumer_quit == 1) {
                        goto end;
                }

restart:
                DBG("Channel poll wait with %d fd(s)", LTTNG_POLL_GETNB(&events));
                ret = lttng_poll_wait(&events, -1);
                DBG("Channel event catched in thread");
                if (ret < 0) {
                        if (errno == EINTR) {
                                ERR("Poll EINTR catched");
                                goto restart;
                        }
                        goto end;
                }

                nb_fd = ret;

                /* From here, the event is a channel wait fd */
                for (i = 0; i < nb_fd; i++) {
                        revents = LTTNG_POLL_GETEV(&events, i);
                        pollfd = LTTNG_POLL_GETFD(&events, i);

                        /* Just don't waste time if no returned events for the fd */
                        if (!revents) {
                                continue;
                        }
                        if (pollfd == ctx->consumer_channel_pipe[0]) {
                                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 if (revents & LPOLLIN) {
                                        enum consumer_channel_action action;

                                        ret = read_channel_pipe(ctx, &chan, &action);
                                        if (ret <= 0) {
                                                ERR("Error reading channel pipe");
                                                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);
                                                lttng_ht_add_unique_u64(channel_ht,
                                                                &chan->wait_fd_node);
                                                /* Add channel to the global poll events list */
                                                lttng_poll_add(&events, chan->wait_fd,
                                                                LPOLLIN | LPOLLPRI);
                                                break;
                                        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;
                                        }
                                }

                                /* 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);
                                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);
                                }
                        }

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

end:
        lttng_poll_clean(&events);
end_poll:
        destroy_channel_ht(channel_ht);
end_ht:
        DBG("Channel poll thread exiting");
        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);

        if (lttng_consumer_poll_socket(sockpoll) < 0) {
                ret = -1;
                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;
        /*
         * 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();

        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;
        }

        ret = fcntl(client_socket, F_SETFL, O_NONBLOCK);
        if (ret < 0) {
                PERROR("fcntl O_NONBLOCK");
                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;

        if (lttng_consumer_poll_socket(consumer_sockpoll) < 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;
        }
        ret = fcntl(sock, F_SETFL, O_NONBLOCK);
        if (ret < 0) {
                PERROR("fcntl O_NONBLOCK");
                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 < 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) {
                if (lttng_consumer_poll_socket(consumer_sockpoll) < 0) {
                        goto end;
                }
                DBG("Incoming command on sock");
                ret = lttng_consumer_recv_cmd(ctx, sock, consumer_sockpoll);
                if (ret == -ENOENT) {
                        DBG("Received STOP command");
                        goto end;
                }
                if (ret <= 0) {
                        /*
                         * This could simply be a session daemon quitting. Don't output
                         * ERR() here.
                         */
                        DBG("Communication interrupted on command socket");
                        goto end;
                }
                if (consumer_quit) {
                        DBG("consumer_thread_receive_fds received quit from signal");
                        goto end;
                }
                DBG("received command on sock");
        }
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_metadata();

        /*
         * when all fds have hung up, the polling thread
         * can exit cleanly
         */
        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_pipe(ctx->consumer_data_pipe[1]);

        notify_channel_pipe(ctx, NULL, CONSUMER_CHANNEL_QUIT);

        /* 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(sock);
                if (ret < 0) {
                        PERROR("close client_socket sessiond poll");
                }
        }

        rcu_unregister_thread();
        return NULL;
}

ssize_t lttng_consumer_read_subbuffer(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx)
{
        ssize_t ret;

        pthread_mutex_lock(&stream->lock);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                ret = lttng_kconsumer_read_subbuffer(stream, ctx);
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                ret = lttng_ustconsumer_read_subbuffer(stream, ctx);
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                ret = -ENOSYS;
                break;
        }

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

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.
 */
void lttng_consumer_init(void)
{
        consumer_data.channel_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        consumer_data.relayd_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        consumer_data.stream_list_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        consumer_data.stream_per_chan_id_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
}

/*
 * 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.
 */
int consumer_add_relayd_socket(int net_seq_idx, int sock_type,
                struct lttng_consumer_local_data *ctx, int sock,
                struct pollfd *consumer_sockpoll,
                struct lttcomm_relayd_sock *relayd_sock, unsigned int sessiond_id)
{
        int fd = -1, ret = -1, relayd_created = 0;
        enum lttng_error_code ret_code = LTTNG_OK;
        struct consumer_relayd_sock_pair *relayd = NULL;

        assert(ctx);
        assert(relayd_sock);

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

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

        /* Get relayd reference if exists. */
        relayd = consumer_find_relayd(net_seq_idx);
        if (relayd == NULL) {
                /* Not found. Allocate one. */
                relayd = consumer_allocate_relayd_sock_pair(net_seq_idx);
                if (relayd == NULL) {
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_OUTFD_ERROR);
                        ret = -1;
                        goto error;
                }
                relayd->sessiond_session_id = (uint64_t) sessiond_id;
                relayd_created = 1;
        }

        /* Poll on consumer socket. */
        if (lttng_consumer_poll_socket(consumer_sockpoll) < 0) {
                ret = -EINTR;
                goto error;
        }

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

        /* We have the fds without error. Send status back. */
        ret = consumer_send_status_msg(sock, ret_code);
        if (ret < 0) {
                /* Somehow, the session daemon is not responding anymore. */
                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);
                /* Immediately try to close the created socket if valid. */
                if (relayd->control_sock.sock.fd >= 0) {
                        if (close(relayd->control_sock.sock.fd)) {
                                PERROR("close relayd control socket");
                        }
                }
                /* Handle create_sock error. */
                if (ret < 0) {
                        goto error;
                }

                /* 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;

                /*
                 * Create a session on the relayd and store the returned id. Lock the
                 * control socket mutex if the relayd was NOT created before.
                 */
                if (!relayd_created) {
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                }
                ret = relayd_create_session(&relayd->control_sock,
                                &relayd->relayd_session_id);
                if (!relayd_created) {
                        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                }
                if (ret < 0) {
                        /*
                         * Close all sockets of a relayd object. It will be freed if it was
                         * created at the error code path or else it will be garbage
                         * collect.
                         */
                        (void) relayd_close(&relayd->control_sock);
                        (void) relayd_close(&relayd->data_sock);
                        goto error;
                }

                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);
                /* Immediately try to close the created socket if valid. */
                if (relayd->data_sock.sock.fd >= 0) {
                        if (close(relayd->data_sock.sock.fd)) {
                                PERROR("close relayd data socket");
                        }
                }
                /* Handle create_sock error. */
                if (ret < 0) {
                        goto error;
                }

                /* 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 = -1;
                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);

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

        /* All good! */
        return 0;

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

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

        return ret;
}

/*
 * Try to lock the stream mutex.
 *
 * On success, 1 is returned else 0 indicating that the mutex is NOT lock.
 */
static int stream_try_lock(struct lttng_consumer_stream *stream)
{
        int ret;

        assert(stream);

        /*
         * Try to lock the stream mutex. On failure, we know that the stream is
         * being used else where hence there is data still being extracted.
         */
        ret = pthread_mutex_trylock(&stream->lock);
        if (ret) {
                /* For both EBUSY and EINVAL error, the mutex is NOT locked. */
                ret = 0;
                goto end;
        }

        ret = 1;

end:
        return ret;
}

/*
 * 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;

        relayd = find_relayd_by_session_id(id);
        if (relayd) {
                /* 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);
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        /* 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 this call fails, the stream is being used hence data pending. */
                ret = stream_try_lock(stream);
                if (!ret) {
                        goto data_pending;
                }

                /*
                 * 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;
                        }
                }

                /* Relayd check */
                if (relayd) {
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                        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);
                        }
                        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                        if (ret == 1) {
                                pthread_mutex_unlock(&stream->lock);
                                goto data_pending;
                        }
                }
                pthread_mutex_unlock(&stream->lock);
        }

        if (relayd) {
                unsigned int is_data_inflight = 0;

                /* Send init command for data pending. */
                pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                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) {
                        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;

        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);

        if (!channel) {
                msg.ret_code = -LTTNG_ERR_UST_CHAN_FAIL;
        } else {
                msg.ret_code = LTTNG_OK;
                msg.key = channel->key;
                msg.stream_count = channel->streams.count;
        }

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