Fix: Possible buffer overflows in strncat() usage

[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 <common/common.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,
};

/* timeout parameter, to control the polling thread grace period. */
int consumer_poll_timeout = -1;

/*
 * 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 = 0;

/*
 * Find a stream. The consumer_data.lock must be locked during this
 * call.
 */
static struct lttng_consumer_stream *consumer_find_stream(int key)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;
        struct lttng_consumer_stream *stream = NULL;

        /* Negative keys are lookup failures */
        if (key < 0)
                return NULL;

        rcu_read_lock();

        lttng_ht_lookup(consumer_data.stream_ht, (void *)((unsigned long) key),
                        &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node != NULL) {
                stream = caa_container_of(node, struct lttng_consumer_stream, node);
        }

        rcu_read_unlock();

        return stream;
}

static void consumer_steal_stream_key(int key)
{
        struct lttng_consumer_stream *stream;

        rcu_read_lock();
        stream = consumer_find_stream(key);
        if (stream) {
                stream->key = -1;
                /*
                 * 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 = -1;
        }
        rcu_read_unlock();
}

static struct lttng_consumer_channel *consumer_find_channel(int key)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;
        struct lttng_consumer_channel *channel = NULL;

        /* Negative keys are lookup failures */
        if (key < 0)
                return NULL;

        rcu_read_lock();

        lttng_ht_lookup(consumer_data.channel_ht, (void *)((unsigned long) key),
                        &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node != NULL) {
                channel = caa_container_of(node, struct lttng_consumer_channel, node);
        }

        rcu_read_unlock();

        return channel;
}

static void consumer_steal_channel_key(int key)
{
        struct lttng_consumer_channel *channel;

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

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

        free(stream);
}

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

        free(relayd);
}

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

        if (relayd == NULL) {
                return;
        }

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

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

        /* Close all sockets */
        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
        (void) relayd_close(&relayd->control_sock);
        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
        (void) relayd_close(&relayd->data_sock);

        /* RCU free() call */
        call_rcu(&relayd->node.head, consumer_rcu_free_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)
{
        int ret;
        struct lttng_ht_iter iter;
        struct lttng_consumer_channel *free_chan = NULL;
        struct consumer_relayd_sock_pair *relayd;

        assert(stream);

        pthread_mutex_lock(&consumer_data.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(consumer_data.stream_ht, &iter);
        assert(!ret);

        rcu_read_unlock();

        if (consumer_data.stream_count <= 0) {
                goto end;
        }
        consumer_data.stream_count--;
        if (!stream) {
                goto end;
        }
        if (stream->out_fd >= 0) {
                ret = close(stream->out_fd);
                if (ret) {
                        PERROR("close");
                }
        }
        if (stream->wait_fd >= 0 && !stream->wait_fd_is_copy) {
                ret = close(stream->wait_fd);
                if (ret) {
                        PERROR("close");
                }
        }
        if (stream->shm_fd >= 0 && stream->wait_fd != stream->shm_fd) {
                ret = close(stream->shm_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)) {
                        consumer_destroy_relayd(relayd);
                }
        }
        rcu_read_unlock();

        if (!--stream->chan->refcount) {
                free_chan = stream->chan;
        }


        call_rcu(&stream->node.head, consumer_free_stream);
end:
        consumer_data.need_update = 1;
        pthread_mutex_unlock(&consumer_data.lock);

        if (free_chan)
                consumer_del_channel(free_chan);
}

struct lttng_consumer_stream *consumer_allocate_stream(
                int channel_key, int stream_key,
                int shm_fd, int wait_fd,
                enum lttng_consumer_stream_state state,
                uint64_t mmap_len,
                enum lttng_event_output output,
                const char *path_name,
                uid_t uid,
                gid_t gid,
                int net_index,
                int metadata_flag)
{
        struct lttng_consumer_stream *stream;
        int ret;

        stream = zmalloc(sizeof(*stream));
        if (stream == NULL) {
                perror("malloc struct lttng_consumer_stream");
                goto end;
        }
        stream->chan = consumer_find_channel(channel_key);
        if (!stream->chan) {
                perror("Unable to find channel key");
                goto end;
        }
        stream->chan->refcount++;
        stream->key = stream_key;
        stream->shm_fd = shm_fd;
        stream->wait_fd = wait_fd;
        stream->out_fd = -1;
        stream->out_fd_offset = 0;
        stream->state = state;
        stream->mmap_len = mmap_len;
        stream->mmap_base = NULL;
        stream->output = output;
        stream->uid = uid;
        stream->gid = gid;
        stream->net_seq_idx = net_index;
        stream->metadata_flag = metadata_flag;
        strncpy(stream->path_name, path_name, sizeof(stream->path_name));
        stream->path_name[sizeof(stream->path_name) - 1] = '\0';
        lttng_ht_node_init_ulong(&stream->node, stream->key);
        lttng_ht_node_init_ulong(&stream->waitfd_node, stream->wait_fd);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                stream->cpu = stream->chan->cpucount++;
                ret = lttng_ustconsumer_allocate_stream(stream);
                if (ret) {
                        free(stream);
                        return NULL;
                }
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }
        DBG("Allocated stream %s (key %d, shm_fd %d, wait_fd %d, mmap_len %llu, out_fd %d, net_seq_idx %d)",
                        stream->path_name, stream->key,
                        stream->shm_fd,
                        stream->wait_fd,
                        (unsigned long long) stream->mmap_len,
                        stream->out_fd,
                        stream->net_seq_idx);
end:
        return stream;
}

/*
 * Add a stream to the global list protected by a mutex.
 */
int consumer_add_stream(struct lttng_consumer_stream *stream)
{
        int ret = 0;
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;
        struct consumer_relayd_sock_pair *relayd;

        pthread_mutex_lock(&consumer_data.lock);
        /* Steal stream identifier, for UST */
        consumer_steal_stream_key(stream->key);

        rcu_read_lock();
        lttng_ht_lookup(consumer_data.stream_ht,
                        (void *)((unsigned long) stream->key), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node != NULL) {
                rcu_read_unlock();
                /* Stream already exist. Ignore the insertion */
                goto end;
        }

        lttng_ht_add_unique_ulong(consumer_data.stream_ht, &stream->node);

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

        /* Update consumer data */
        consumer_data.stream_count++;
        consumer_data.need_update = 1;

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                /* Streams are in CPU number order (we rely on this) */
                stream->cpu = stream->chan->nr_streams++;
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }

end:
        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.
 */

int consumer_add_relayd(struct consumer_relayd_sock_pair *relayd)
{
        int ret = 0;
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;

        if (relayd == NULL) {
                ret = -1;
                goto end;
        }

        lttng_ht_lookup(consumer_data.relayd_ht,
                        (void *)((unsigned long) relayd->net_seq_idx), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node != NULL) {
                /* Relayd already exist. Ignore the insertion */
                goto end;
        }
        lttng_ht_add_unique_ulong(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_ulong(&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(int key)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;
        struct consumer_relayd_sock_pair *relayd = NULL;

        /* Negative keys are lookup failures */
        if (key < 0) {
                goto error;
        }

        lttng_ht_lookup(consumer_data.relayd_ht, (void *)((unsigned long) key),
                        &iter);
        node = lttng_ht_iter_get_node_ulong(&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, 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.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.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;
                }

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

error:
        return outfd;
}

/*
 * Update a stream according to what we just received.
 */
void consumer_change_stream_state(int stream_key,
                enum lttng_consumer_stream_state state)
{
        struct lttng_consumer_stream *stream;

        pthread_mutex_lock(&consumer_data.lock);
        stream = consumer_find_stream(stream_key);
        if (stream) {
                stream->state = state;
        }
        consumer_data.need_update = 1;
        pthread_mutex_unlock(&consumer_data.lock);
}

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

        free(channel);
}

/*
 * 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;

        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();

        if (channel->mmap_base != NULL) {
                ret = munmap(channel->mmap_base, channel->mmap_len);
                if (ret != 0) {
                        perror("munmap");
                }
        }
        if (channel->wait_fd >= 0 && !channel->wait_fd_is_copy) {
                ret = close(channel->wait_fd);
                if (ret) {
                        PERROR("close");
                }
        }
        if (channel->shm_fd >= 0 && channel->wait_fd != channel->shm_fd) {
                ret = close(channel->shm_fd);
                if (ret) {
                        PERROR("close");
                }
        }

        call_rcu(&channel->node.head, consumer_free_channel);
end:
        pthread_mutex_unlock(&consumer_data.lock);
}

struct lttng_consumer_channel *consumer_allocate_channel(
                int channel_key,
                int shm_fd, int wait_fd,
                uint64_t mmap_len,
                uint64_t max_sb_size)
{
        struct lttng_consumer_channel *channel;
        int ret;

        channel = zmalloc(sizeof(*channel));
        if (channel == NULL) {
                perror("malloc struct lttng_consumer_channel");
                goto end;
        }
        channel->key = channel_key;
        channel->shm_fd = shm_fd;
        channel->wait_fd = wait_fd;
        channel->mmap_len = mmap_len;
        channel->max_sb_size = max_sb_size;
        channel->refcount = 0;
        channel->nr_streams = 0;
        lttng_ht_node_init_ulong(&channel->node, channel->key);

        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                channel->mmap_base = NULL;
                channel->mmap_len = 0;
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                ret = lttng_ustconsumer_allocate_channel(channel);
                if (ret) {
                        free(channel);
                        return NULL;
                }
                break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                goto end;
        }
        DBG("Allocated channel (key %d, shm_fd %d, wait_fd %d, mmap_len %llu, max_sb_size %llu)",
                        channel->key, channel->shm_fd, channel->wait_fd,
                        (unsigned long long) channel->mmap_len,
                        (unsigned long long) channel->max_sb_size);
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_ht_node_ulong *node;
        struct lttng_ht_iter iter;

        pthread_mutex_lock(&consumer_data.lock);
        /* Steal channel identifier, for UST */
        consumer_steal_channel_key(channel->key);
        rcu_read_lock();

        lttng_ht_lookup(consumer_data.channel_ht,
                        (void *)((unsigned long) channel->key), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node != NULL) {
                /* Channel already exist. Ignore the insertion */
                goto end;
        }

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

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

        return 0;
}

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

        DBG("Updating poll fd array");
        rcu_read_lock();
        cds_lfht_for_each_entry(consumer_data.stream_ht->ht, &iter.iter, stream,
                        node.node) {
                if (stream->state != LTTNG_CONSUMER_ACTIVE_STREAM) {
                        continue;
                }
                DBG("Active FD %d", stream->wait_fd);
                (*pollfd)[i].fd = stream->wait_fd;
                (*pollfd)[i].events = POLLIN | POLLPRI;
                if (stream->metadata_flag && metadata_ht) {
                        lttng_ht_add_unique_ulong(metadata_ht, &stream->waitfd_node);
                        DBG("Active FD added to metadata hash table");
                }
                local_stream[i] = stream;
                i++;
        }
        rcu_read_unlock();

        /*
         * Insert the consumer_poll_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_poll_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, should be called when all instances
 * are destroyed.
 */
void lttng_consumer_cleanup(void)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;

        rcu_read_lock();

        /*
         * close all outfd. Called when there are no more threads running (after
         * joining on the threads), no need to protect list iteration with mutex.
         */
        cds_lfht_for_each_entry(consumer_data.stream_ht->ht, &iter.iter, node,
                        node) {
                struct lttng_consumer_stream *stream =
                        caa_container_of(node, struct lttng_consumer_stream, node);
                consumer_del_stream(stream);
        }

        cds_lfht_for_each_entry(consumer_data.channel_ht->ht, &iter.iter, node,
                        node) {
                struct lttng_consumer_channel *channel =
                        caa_container_of(node, struct lttng_consumer_channel, node);
                consumer_del_channel(channel);
        }

        rcu_read_unlock();

        lttng_ht_destroy(consumer_data.stream_ht);
        lttng_ht_destroy(consumer_data.channel_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) {
                perror("write consumer 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->chan->max_sb_size) {
                return;
        }
        lttng_sync_file_range(outfd, orig_offset - stream->chan->max_sb_size,
                        stream->chan->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->chan->max_sb_size,
                        stream->chan->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, i;
        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;
        /* 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_poll_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_poll_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_poll_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;
        }

        return ctx;


error_thread_pipe:
        for (i = 0; i < 2; i++) {
                int err;

                err = close(ctx->consumer_should_quit[i]);
                if (err) {
                        PERROR("close");
                }
        }
error_poll_fcntl:
error_quit_pipe:
        for (i = 0; i < 2; i++) {
                int err;

                err = close(ctx->consumer_poll_pipe[i]);
                if (err) {
                        PERROR("close");
                }
        }
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;

        ret = close(ctx->consumer_error_socket);
        if (ret) {
                PERROR("close");
        }
        ret = close(ctx->consumer_thread_pipe[0]);
        if (ret) {
                PERROR("close");
        }
        ret = close(ctx->consumer_thread_pipe[1]);
        if (ret) {
                PERROR("close");
        }
        ret = close(ctx->consumer_poll_pipe[0]);
        if (ret) {
                PERROR("close");
        }
        ret = close(ctx->consumer_poll_pipe[1]);
        if (ret) {
                PERROR("close");
        }
        ret = close(ctx->consumer_should_quit[0]);
        if (ret) {
                PERROR("close");
        }
        ret = close(ctx->consumer_should_quit[1]);
        if (ret) {
                PERROR("close");
        }
        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)
{
        int ret;
        uint64_t metadata_id;

        metadata_id = htobe64(stream->relayd_stream_id);
        do {
                ret = write(fd, (void *) &metadata_id,
                                sizeof(stream->relayd_stream_id));
        } while (ret < 0 && errno == EINTR);
        if (ret < 0) {
                PERROR("write metadata stream id");
                goto end;
        }
        DBG("Metadata stream id %" PRIu64 " written before data",
                        stream->relayd_stream_id);

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.
 *
 * 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 mmap_offset;
        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;

        /* 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:
                ret = kernctl_get_mmap_read_offset(stream->wait_fd, &mmap_offset);
                break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                ret = lttng_ustctl_get_mmap_read_offset(stream->chan->handle,
                                stream->buf, &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(stream->relayd_stream_id);
                }

                ret = write_relayd_stream_header(stream, netlen, 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);
                                if (ret < 0) {
                                        written = ret;
                                        goto end;
                                }
                        }
                }
                /* Else, use the default set before which is the filesystem. */
        }

        while (len > 0) {
                do {
                        ret = write(outfd, stream->mmap_base + mmap_offset, len);
                } while (ret < 0 && errno == EINTR);
                if (ret < 0) {
                        PERROR("Error in file write");
                        if (written == 0) {
                                written = ret;
                        }
                        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;
                }
                DBG("Consumer mmap write() ret %zd (len %lu)", ret, len);

                /* 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);

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.
 *
 * 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)
{
        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;

        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;
                }
        }

        /* Write metadata stream id before payload */
        if (stream->metadata_flag && relayd) {
                /*
                 * 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(ctx->consumer_thread_pipe[1],
                                stream, relayd);
                if (ret < 0) {
                        written = ret;
                        goto end;
                }
        }

        while (len > 0) {
                DBG("splice chan to pipe offset %lu of len %lu (fd : %d)",
                                (unsigned long)offset, len, fd);
                ret_splice = splice(fd, &offset, ctx->consumer_thread_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) {
                                /* Update counter to fit the spliced data */
                                ret_splice += sizeof(stream->relayd_stream_id);
                                len += sizeof(stream->relayd_stream_id);
                                /*
                                 * We do this so the return value can match the len passed as
                                 * argument to this function.
                                 */
                                written -= sizeof(stream->relayd_stream_id);
                        }

                        ret = write_relayd_stream_header(stream, ret_splice, relayd);
                        if (ret >= 0) {
                                /* Use the returned socket. */
                                outfd = ret;
                        } else {
                                ERR("Remote relayd disconnected. Stopping");
                                goto end;
                        }
                }

                /* Splice data out */
                ret_splice = splice(ctx->consumer_thread_pipe[0], NULL, outfd, NULL,
                                ret_splice, SPLICE_F_MOVE | SPLICE_F_MORE);
                DBG("Kernel consumer splice pipe to file, ret %zd", ret_splice);
                if (ret_splice < 0) {
                        PERROR("Error in file splice");
                        if (written == 0) {
                                written = ret_splice;
                        }
                        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;

splice_error:
        /* send the appropriate error description to sessiond */
        switch (ret) {
        case EBADF:
                lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_EBADF);
                break;
        case EINVAL:
                lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_EINVAL);
                break;
        case ENOMEM:
                lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_ENOMEM);
                break;
        case ESPIPE:
                lttng_consumer_send_error(ctx, 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_local_data *ctx,
                struct lttng_consumer_stream *stream)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_take_snapshot(ctx, stream);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_take_snapshot(ctx, 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_local_data *ctx,
                struct lttng_consumer_stream *stream,
                unsigned long *pos)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_get_produced_snapshot(ctx, stream, pos);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_get_produced_snapshot(ctx, 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;
        }
}

/*
 * This thread polls the fds in the set to consume the data and write
 * it to tracefile if necessary.
 */
void *lttng_consumer_thread_poll_fds(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;
        /* local view of consumer_data.fds_count */
        int nb_fd = 0;
        struct lttng_consumer_local_data *ctx = data;
        struct lttng_ht *metadata_ht;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;
        struct lttng_consumer_stream *metadata_stream;
        ssize_t len;

        metadata_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);

        rcu_register_thread();

        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) {
                        if (pollfd != NULL) {
                                free(pollfd);
                                pollfd = NULL;
                        }
                        if (local_stream != NULL) {
                                free(local_stream);
                                local_stream = NULL;
                        }

                        /* allocate for all fds + 1 for the consumer_poll_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_poll_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 = consumer_update_poll_array(ctx, &pollfd, local_stream,
                                        metadata_ht);
                        if (ret < 0) {
                                ERR("Error in allocating pollfd or local_outfds");
                                lttng_consumer_send_error(ctx, 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, consumer_poll_timeout);
                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, CONSUMERD_POLL_ERROR);
                        goto end;
                } else if (num_rdy == 0) {
                        DBG("Polling thread timed out");
                        goto end;
                }

                /*
                 * If the consumer_poll_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)) {
                        size_t pipe_readlen;
                        char tmp;

                        DBG("consumer_poll_pipe wake up");
                        /* Consume 1 byte of pipe data */
                        do {
                                pipe_readlen = read(ctx->consumer_poll_pipe[0], &tmp, 1);
                        } while (pipe_readlen == -1 && errno == EINTR);
                        continue;
                }

                /* Take care of high priority channels first. */
                for (i = 0; i < nb_fd; i++) {
                        /* Lookup for metadata which is the highest priority */
                        lttng_ht_lookup(metadata_ht,
                                        (void *)((unsigned long) pollfd[i].fd), &iter);
                        node = lttng_ht_iter_get_node_ulong(&iter);
                        if (node != NULL &&
                                        (pollfd[i].revents & (POLLIN | POLLPRI))) {
                                DBG("Urgent metadata read on fd %d", pollfd[i].fd);
                                metadata_stream = caa_container_of(node,
                                                struct lttng_consumer_stream, waitfd_node);
                                high_prio = 1;
                                len = ctx->on_buffer_ready(metadata_stream, ctx);
                                /* it's ok to have an unavailable sub-buffer */
                                if (len < 0 && len != -EAGAIN) {
                                        goto end;
                                } else if (len > 0) {
                                        metadata_stream->data_read = 1;
                                }
                        } else 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) {
                                        goto end;
                                } 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 ((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) {
                                        goto end;
                                } 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]->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) {
                                        if (local_stream[i]->metadata_flag) {
                                                iter.iter.node = &local_stream[i]->waitfd_node.node;
                                                ret = lttng_ht_del(metadata_ht, &iter);
                                                assert(!ret);
                                        }
                                        consumer_del_stream(local_stream[i]);
                                        num_hup++;
                                }
                        } else if (pollfd[i].revents & POLLERR) {
                                ERR("Error returned in polling fd %d.", pollfd[i].fd);
                                if (!local_stream[i]->data_read) {
                                        if (local_stream[i]->metadata_flag) {
                                                iter.iter.node = &local_stream[i]->waitfd_node.node;
                                                ret = lttng_ht_del(metadata_ht, &iter);
                                                assert(!ret);
                                        }
                                        consumer_del_stream(local_stream[i]);
                                        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) {
                                        if (local_stream[i]->metadata_flag) {
                                                iter.iter.node = &local_stream[i]->waitfd_node.node;
                                                ret = lttng_ht_del(metadata_ht, &iter);
                                                assert(!ret);
                                        }
                                        consumer_del_stream(local_stream[i]);
                                        num_hup++;
                                }
                        }
                        local_stream[i]->data_read = 0;
                }
        }
end:
        DBG("polling thread exiting");
        if (pollfd != NULL) {
                free(pollfd);
                pollfd = NULL;
        }
        if (local_stream != NULL) {
                free(local_stream);
                local_stream = NULL;
        }
        rcu_unregister_thread();
        return NULL;
}

/*
 * This thread listens on the consumerd socket and receives the file
 * descriptors from the session daemon.
 */
void *lttng_consumer_thread_receive_fds(void *data)
{
        int sock, 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, 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;
        }

        /* 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) {
                        ERR("Communication interrupted on command socket");
                        goto end;
                }
                if (consumer_quit) {
                        DBG("consumer_thread_receive_fds received quit from signal");
                        goto end;
                }
                DBG("received fds on sock");
        }
end:
        DBG("consumer_thread_receive_fds exiting");

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

        /*
         * 2s of grace period, if no polling events occur during
         * this period, the polling thread will exit even if there
         * are still open FDs (should not happen, but safety mechanism).
         */
        consumer_poll_timeout = LTTNG_CONSUMER_POLL_TIMEOUT;

        /*
         * Wake-up the other end by writing a null byte in the pipe
         * (non-blocking). Important note: Because writing into the
         * pipe is non-blocking (and therefore we allow dropping wakeup
         * data, as long as there is wakeup data present in the pipe
         * buffer to wake up the other end), the other end should
         * perform the following sequence for waiting:
         * 1) empty the pipe (reads).
         * 2) perform update operation.
         * 3) wait on the pipe (poll).
         */
        do {
                ret = write(ctx->consumer_poll_pipe[1], "", 1);
        } while (ret < 0 && errno == EINTR);
        rcu_unregister_thread();
        return NULL;
}

ssize_t lttng_consumer_read_subbuffer(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx)
{
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                return lttng_kconsumer_read_subbuffer(stream, ctx);
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
                return lttng_ustconsumer_read_subbuffer(stream, ctx);
        default:
                ERR("Unknown consumer_data type");
                assert(0);
                return -ENOSYS;
        }
}

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.stream_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        consumer_data.channel_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        consumer_data.relayd_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
}