Fix deadlock: don't take channel lock in timer

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

/*
 * Copyright (C) 2011 - Julien Desfossez <julien.desfossez@polymtl.ca>
 *                      Mathieu Desnoyers <mathieu.desnoyers@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 <lttng/ust-ctl.h>
#include <poll.h>
#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <inttypes.h>
#include <unistd.h>
#include <urcu/list.h>
#include <signal.h>

#include <common/common.h>
#include <common/sessiond-comm/sessiond-comm.h>
#include <common/relayd/relayd.h>
#include <common/compat/fcntl.h>
#include <common/consumer-metadata-cache.h>
#include <common/consumer-stream.h>
#include <common/consumer-timer.h>
#include <common/utils.h>

#include "ust-consumer.h"

extern struct lttng_consumer_global_data consumer_data;
extern int consumer_poll_timeout;
extern volatile int consumer_quit;

/*
 * Free channel object and all streams associated with it. This MUST be used
 * only and only if the channel has _NEVER_ been added to the global channel
 * hash table.
 */
static void destroy_channel(struct lttng_consumer_channel *channel)
{
        struct lttng_consumer_stream *stream, *stmp;

        assert(channel);

        DBG("UST consumer cleaning stream list");

        cds_list_for_each_entry_safe(stream, stmp, &channel->streams.head,
                        send_node) {
                cds_list_del(&stream->send_node);
                ustctl_destroy_stream(stream->ustream);
                free(stream);
        }

        /*
         * If a channel is available meaning that was created before the streams
         * were, delete it.
         */
        if (channel->uchan) {
                lttng_ustconsumer_del_channel(channel);
        }
        free(channel);
}

/*
 * Add channel to internal consumer state.
 *
 * Returns 0 on success or else a negative value.
 */
static int add_channel(struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx)
{
        int ret = 0;

        assert(channel);
        assert(ctx);

        if (ctx->on_recv_channel != NULL) {
                ret = ctx->on_recv_channel(channel);
                if (ret == 0) {
                        ret = consumer_add_channel(channel, ctx);
                } else if (ret < 0) {
                        /* Most likely an ENOMEM. */
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_OUTFD_ERROR);
                        goto error;
                }
        } else {
                ret = consumer_add_channel(channel, ctx);
        }

        DBG("UST consumer channel added (key: %" PRIu64 ")", channel->key);

error:
        return ret;
}

/*
 * Allocate and return a consumer channel object.
 */
static struct lttng_consumer_channel *allocate_channel(uint64_t session_id,
                const char *pathname, const char *name, uid_t uid, gid_t gid,
                uint64_t relayd_id, uint64_t key, enum lttng_event_output output,
                uint64_t tracefile_size, uint64_t tracefile_count,
                uint64_t session_id_per_pid, unsigned int monitor)
{
        assert(pathname);
        assert(name);

        return consumer_allocate_channel(key, session_id, pathname, name, uid,
                        gid, relayd_id, output, tracefile_size,
                        tracefile_count, session_id_per_pid, monitor);
}

/*
 * Allocate and return a consumer stream object. If _alloc_ret is not NULL, the
 * error value if applicable is set in it else it is kept untouched.
 *
 * Return NULL on error else the newly allocated stream object.
 */
static struct lttng_consumer_stream *allocate_stream(int cpu, int key,
                struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx, int *_alloc_ret)
{
        int alloc_ret;
        struct lttng_consumer_stream *stream = NULL;

        assert(channel);
        assert(ctx);

        stream = consumer_allocate_stream(channel->key,
                        key,
                        LTTNG_CONSUMER_ACTIVE_STREAM,
                        channel->name,
                        channel->uid,
                        channel->gid,
                        channel->relayd_id,
                        channel->session_id,
                        cpu,
                        &alloc_ret,
                        channel->type,
                        channel->monitor);
        if (stream == NULL) {
                switch (alloc_ret) {
                case -ENOENT:
                        /*
                         * We could not find the channel. Can happen if cpu hotplug
                         * happens while tearing down.
                         */
                        DBG3("Could not find channel");
                        break;
                case -ENOMEM:
                case -EINVAL:
                default:
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_OUTFD_ERROR);
                        break;
                }
                goto error;
        }

        stream->chan = channel;

error:
        if (_alloc_ret) {
                *_alloc_ret = alloc_ret;
        }
        return stream;
}

/*
 * Send the given stream pointer to the corresponding thread.
 *
 * Returns 0 on success else a negative value.
 */
static int send_stream_to_thread(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx)
{
        int ret;
        struct lttng_pipe *stream_pipe;

        /* Get the right pipe where the stream will be sent. */
        if (stream->metadata_flag) {
                stream_pipe = ctx->consumer_metadata_pipe;
        } else {
                stream_pipe = ctx->consumer_data_pipe;
        }

        ret = lttng_pipe_write(stream_pipe, &stream, sizeof(stream));
        if (ret < 0) {
                ERR("Consumer write %s stream to pipe %d",
                                stream->metadata_flag ? "metadata" : "data",
                                lttng_pipe_get_writefd(stream_pipe));
        }

        return ret;
}

/*
 * Create streams for the given channel using liblttng-ust-ctl.
 *
 * Return 0 on success else a negative value.
 */
static int create_ust_streams(struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx)
{
        int ret, cpu = 0;
        struct ustctl_consumer_stream *ustream;
        struct lttng_consumer_stream *stream;

        assert(channel);
        assert(ctx);

        /*
         * While a stream is available from ustctl. When NULL is returned, we've
         * reached the end of the possible stream for the channel.
         */
        while ((ustream = ustctl_create_stream(channel->uchan, cpu))) {
                int wait_fd;
                int ust_metadata_pipe[2];

                if (channel->type == CONSUMER_CHANNEL_TYPE_METADATA && channel->monitor) {
                        ret = utils_create_pipe_cloexec_nonblock(ust_metadata_pipe);
                        if (ret < 0) {
                                ERR("Create ust metadata poll pipe");
                                goto error;
                        }
                        wait_fd = ust_metadata_pipe[0];
                } else {
                        wait_fd = ustctl_stream_get_wait_fd(ustream);
                }

                /* Allocate consumer stream object. */
                stream = allocate_stream(cpu, wait_fd, channel, ctx, &ret);
                if (!stream) {
                        goto error_alloc;
                }
                stream->ustream = ustream;
                /*
                 * Store it so we can save multiple function calls afterwards since
                 * this value is used heavily in the stream threads. This is UST
                 * specific so this is why it's done after allocation.
                 */
                stream->wait_fd = wait_fd;

                /*
                 * Increment channel refcount since the channel reference has now been
                 * assigned in the allocation process above.
                 */
                if (stream->chan->monitor) {
                        uatomic_inc(&stream->chan->refcount);
                }

                /*
                 * Order is important this is why a list is used. On error, the caller
                 * should clean this list.
                 */
                cds_list_add_tail(&stream->send_node, &channel->streams.head);

                ret = ustctl_get_max_subbuf_size(stream->ustream,
                                &stream->max_sb_size);
                if (ret < 0) {
                        ERR("ustctl_get_max_subbuf_size failed for stream %s",
                                        stream->name);
                        goto error;
                }

                /* Do actions once stream has been received. */
                if (ctx->on_recv_stream) {
                        ret = ctx->on_recv_stream(stream);
                        if (ret < 0) {
                                goto error;
                        }
                }

                DBG("UST consumer add stream %s (key: %" PRIu64 ") with relayd id %" PRIu64,
                                stream->name, stream->key, stream->relayd_stream_id);

                /* Set next CPU stream. */
                channel->streams.count = ++cpu;

                /* Keep stream reference when creating metadata. */
                if (channel->type == CONSUMER_CHANNEL_TYPE_METADATA) {
                        channel->metadata_stream = stream;
                        stream->ust_metadata_poll_pipe[0] = ust_metadata_pipe[0];
                        stream->ust_metadata_poll_pipe[1] = ust_metadata_pipe[1];
                }
        }

        return 0;

error:
error_alloc:
        return ret;
}

/*
 * Create an UST channel with the given attributes and send it to the session
 * daemon using the ust ctl API.
 *
 * Return 0 on success or else a negative value.
 */
static int create_ust_channel(struct ustctl_consumer_channel_attr *attr,
                struct ustctl_consumer_channel **chanp)
{
        int ret;
        struct ustctl_consumer_channel *channel;

        assert(attr);
        assert(chanp);

        DBG3("Creating channel to ustctl with attr: [overwrite: %d, "
                        "subbuf_size: %" PRIu64 ", num_subbuf: %" PRIu64 ", "
                        "switch_timer_interval: %u, read_timer_interval: %u, "
                        "output: %d, type: %d", attr->overwrite, attr->subbuf_size,
                        attr->num_subbuf, attr->switch_timer_interval,
                        attr->read_timer_interval, attr->output, attr->type);

        channel = ustctl_create_channel(attr);
        if (!channel) {
                ret = -1;
                goto error_create;
        }

        *chanp = channel;

        return 0;

error_create:
        return ret;
}

/*
 * Send a single given stream to the session daemon using the sock.
 *
 * Return 0 on success else a negative value.
 */
static int send_sessiond_stream(int sock, struct lttng_consumer_stream *stream)
{
        int ret;

        assert(stream);
        assert(sock >= 0);

        DBG("UST consumer sending stream %" PRIu64 " to sessiond", stream->key);

        /* Send stream to session daemon. */
        ret = ustctl_send_stream_to_sessiond(sock, stream->ustream);
        if (ret < 0) {
                goto error;
        }

error:
        return ret;
}

/*
 * Send channel to sessiond.
 *
 * Return 0 on success or else a negative value.
 */
static int send_sessiond_channel(int sock,
                struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx, int *relayd_error)
{
        int ret, ret_code = LTTNG_OK;
        struct lttng_consumer_stream *stream;

        assert(channel);
        assert(ctx);
        assert(sock >= 0);

        DBG("UST consumer sending channel %s to sessiond", channel->name);

        if (channel->relayd_id != (uint64_t) -1ULL) {
                cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
                        /* Try to send the stream to the relayd if one is available. */
                        ret = consumer_send_relayd_stream(stream, stream->chan->pathname);
                        if (ret < 0) {
                                /*
                                 * Flag that the relayd was the problem here probably due to a
                                 * communicaton error on the socket.
                                 */
                                if (relayd_error) {
                                        *relayd_error = 1;
                                }
                                ret_code = LTTNG_ERR_RELAYD_CONNECT_FAIL;
                        }
                }
        }

        /* Inform sessiond that we are about to send channel and streams. */
        ret = consumer_send_status_msg(sock, ret_code);
        if (ret < 0 || ret_code != LTTNG_OK) {
                /*
                 * Either the session daemon is not responding or the relayd died so we
                 * stop now.
                 */
                goto error;
        }

        /* Send channel to sessiond. */
        ret = ustctl_send_channel_to_sessiond(sock, channel->uchan);
        if (ret < 0) {
                goto error;
        }

        ret = ustctl_channel_close_wakeup_fd(channel->uchan);
        if (ret < 0) {
                goto error;
        }

        /* The channel was sent successfully to the sessiond at this point. */
        cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
                /* Send stream to session daemon. */
                ret = send_sessiond_stream(sock, stream);
                if (ret < 0) {
                        goto error;
                }
        }

        /* Tell sessiond there is no more stream. */
        ret = ustctl_send_stream_to_sessiond(sock, NULL);
        if (ret < 0) {
                goto error;
        }

        DBG("UST consumer NULL stream sent to sessiond");

        return 0;

error:
        if (ret_code != LTTNG_OK) {
                ret = -1;
        }
        return ret;
}

/*
 * Creates a channel and streams and add the channel it to the channel internal
 * state. The created stream must ONLY be sent once the GET_CHANNEL command is
 * received.
 *
 * Return 0 on success or else, a negative value is returned and the channel
 * MUST be destroyed by consumer_del_channel().
 */
static int ask_channel(struct lttng_consumer_local_data *ctx, int sock,
                struct lttng_consumer_channel *channel,
                struct ustctl_consumer_channel_attr *attr)
{
        int ret;

        assert(ctx);
        assert(channel);
        assert(attr);

        /*
         * This value is still used by the kernel consumer since for the kernel,
         * the stream ownership is not IN the consumer so we need to have the
         * number of left stream that needs to be initialized so we can know when
         * to delete the channel (see consumer.c).
         *
         * As for the user space tracer now, the consumer creates and sends the
         * stream to the session daemon which only sends them to the application
         * once every stream of a channel is received making this value useless
         * because we they will be added to the poll thread before the application
         * receives them. This ensures that a stream can not hang up during
         * initilization of a channel.
         */
        channel->nb_init_stream_left = 0;

        /* The reply msg status is handled in the following call. */
        ret = create_ust_channel(attr, &channel->uchan);
        if (ret < 0) {
                goto end;
        }

        channel->wait_fd = ustctl_channel_get_wait_fd(channel->uchan);

        /*
         * For the snapshots (no monitor), we create the metadata streams
         * on demand, not during the channel creation.
         */
        if (channel->type == CONSUMER_CHANNEL_TYPE_METADATA && !channel->monitor) {
                ret = 0;
                goto end;
        }

        /* Open all streams for this channel. */
        ret = create_ust_streams(channel, ctx);
        if (ret < 0) {
                goto end;
        }

end:
        return ret;
}

/*
 * Send all stream of a channel to the right thread handling it.
 *
 * On error, return a negative value else 0 on success.
 */
static int send_streams_to_thread(struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx)
{
        int ret = 0;
        struct lttng_consumer_stream *stream, *stmp;

        assert(channel);
        assert(ctx);

        /* Send streams to the corresponding thread. */
        cds_list_for_each_entry_safe(stream, stmp, &channel->streams.head,
                        send_node) {
                /* Sending the stream to the thread. */
                ret = send_stream_to_thread(stream, ctx);
                if (ret < 0) {
                        /*
                         * If we are unable to send the stream to the thread, there is
                         * a big problem so just stop everything.
                         */
                        goto error;
                }

                /* Remove node from the channel stream list. */
                cds_list_del(&stream->send_node);

                /*
                 * From this point on, the stream's ownership has been moved away from
                 * the channel and becomes globally visible.
                 */
                stream->globally_visible = 1;
        }

error:
        return ret;
}

/*
 * Flush channel's streams using the given key to retrieve the channel.
 *
 * Return 0 on success else an LTTng error code.
 */
static int flush_channel(uint64_t chan_key)
{
        int ret = 0;
        struct lttng_consumer_channel *channel;
        struct lttng_consumer_stream *stream;
        struct lttng_ht *ht;
        struct lttng_ht_iter iter;

        DBG("UST consumer flush channel key %" PRIu64, chan_key);

        rcu_read_lock();
        channel = consumer_find_channel(chan_key);
        if (!channel) {
                ERR("UST consumer flush channel %" PRIu64 " not found", chan_key);
                ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                goto error;
        }

        ht = consumer_data.stream_per_chan_id_ht;

        /* For each stream of the channel id, flush it. */
        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) {
                        ustctl_flush_buffer(stream->ustream, 1);
        }
error:
        rcu_read_unlock();
        return ret;
}

/*
 * Close metadata stream wakeup_fd using the given key to retrieve the channel.
 * RCU read side lock MUST be acquired before calling this function.
 *
 * Return 0 on success else an LTTng error code.
 */
static int close_metadata(uint64_t chan_key)
{
        int ret = 0;
        struct lttng_consumer_channel *channel;

        DBG("UST consumer close metadata key %" PRIu64, chan_key);

        channel = consumer_find_channel(chan_key);
        if (!channel) {
                /*
                 * This is possible if the metadata thread has issue a delete because
                 * the endpoint point of the stream hung up. There is no way the
                 * session daemon can know about it thus use a DBG instead of an actual
                 * error.
                 */
                DBG("UST consumer close metadata %" PRIu64 " not found", chan_key);
                ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                goto error;
        }

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

        if (cds_lfht_is_node_deleted(&channel->node.node)) {
                goto error_unlock;
        }

        if (channel->switch_timer_enabled == 1) {
                DBG("Deleting timer on metadata channel");
                consumer_timer_switch_stop(channel);
        }

        if (channel->metadata_stream) {
                ret = ustctl_stream_close_wakeup_fd(channel->metadata_stream->ustream);
                if (ret < 0) {
                        ERR("UST consumer unable to close fd of metadata (ret: %d)", ret);
                        ret = LTTCOMM_CONSUMERD_ERROR_METADATA;
                        goto error_unlock;
                }
                if (channel->monitor) {
                        /* close the read-side in consumer_del_metadata_stream */
                        ret = close(channel->metadata_stream->ust_metadata_poll_pipe[1]);
                        if (ret < 0) {
                                PERROR("Close UST metadata write-side poll pipe");
                        }
                }
        }

error_unlock:
        pthread_mutex_unlock(&channel->lock);
        pthread_mutex_unlock(&consumer_data.lock);
error:
        return ret;
}

/*
 * RCU read side lock MUST be acquired before calling this function.
 *
 * Return 0 on success else an LTTng error code.
 */
static int setup_metadata(struct lttng_consumer_local_data *ctx, uint64_t key)
{
        int ret;
        struct lttng_consumer_channel *metadata;

        DBG("UST consumer setup metadata key %" PRIu64, key);

        metadata = consumer_find_channel(key);
        if (!metadata) {
                ERR("UST consumer push metadata %" PRIu64 " not found", key);
                ret = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                goto end;
        }

        /*
         * In no monitor mode, the metadata channel has no stream(s) so skip the
         * ownership transfer to the metadata thread.
         */
        if (!metadata->monitor) {
                DBG("Metadata channel in no monitor");
                ret = 0;
                goto end;
        }

        /*
         * Send metadata stream to relayd if one available. Availability is
         * known if the stream is still in the list of the channel.
         */
        if (cds_list_empty(&metadata->streams.head)) {
                ERR("Metadata channel key %" PRIu64 ", no stream available.", key);
                ret = LTTCOMM_CONSUMERD_ERROR_METADATA;
                goto error_no_stream;
        }

        /* Send metadata stream to relayd if needed. */
        if (metadata->metadata_stream->net_seq_idx != (uint64_t) -1ULL) {
                ret = consumer_send_relayd_stream(metadata->metadata_stream,
                                metadata->pathname);
                if (ret < 0) {
                        ret = LTTCOMM_CONSUMERD_ERROR_METADATA;
                        goto error;
                }
        }

        ret = send_streams_to_thread(metadata, ctx);
        if (ret < 0) {
                /*
                 * If we are unable to send the stream to the thread, there is
                 * a big problem so just stop everything.
                 */
                ret = LTTCOMM_CONSUMERD_FATAL;
                goto error;
        }
        /* List MUST be empty after or else it could be reused. */
        assert(cds_list_empty(&metadata->streams.head));

        ret = 0;
        goto end;

error:
        /*
         * Delete metadata channel on error. At this point, the metadata stream can
         * NOT be monitored by the metadata thread thus having the guarantee that
         * the stream is still in the local stream list of the channel. This call
         * will make sure to clean that list.
         */
        cds_list_del(&metadata->metadata_stream->send_node);
        consumer_stream_destroy(metadata->metadata_stream, NULL);
error_no_stream:
end:
        return ret;
}

/*
 * Snapshot the whole metadata.
 *
 * Returns 0 on success, < 0 on error
 */
static int snapshot_metadata(uint64_t key, char *path, uint64_t relayd_id,
                struct lttng_consumer_local_data *ctx)
{
        int ret = 0;
        struct lttng_consumer_channel *metadata_channel;
        struct lttng_consumer_stream *metadata_stream;

        assert(path);
        assert(ctx);

        DBG("UST consumer snapshot metadata with key %" PRIu64 " at path %s",
                        key, path);

        rcu_read_lock();

        metadata_channel = consumer_find_channel(key);
        if (!metadata_channel) {
                ERR("UST snapshot metadata channel not found for key %lu", key);
                ret = -1;
                goto error;
        }
        assert(!metadata_channel->monitor);

        /*
         * Ask the sessiond if we have new metadata waiting and update the
         * consumer metadata cache.
         */
        ret = lttng_ustconsumer_request_metadata(ctx, metadata_channel, 0);
        if (ret < 0) {
                goto error;
        }

        /*
         * The metadata stream is NOT created in no monitor mode when the channel
         * is created on a sessiond ask channel command.
         */
        ret = create_ust_streams(metadata_channel, ctx);
        if (ret < 0) {
                goto error;
        }

        metadata_stream = metadata_channel->metadata_stream;
        assert(metadata_stream);

        if (relayd_id != (uint64_t) -1ULL) {
                metadata_stream->net_seq_idx = relayd_id;
                ret = consumer_send_relayd_stream(metadata_stream, path);
                if (ret < 0) {
                        goto error_stream;
                }
        } else {
                ret = utils_create_stream_file(path, metadata_stream->name,
                                metadata_stream->chan->tracefile_size,
                                metadata_stream->tracefile_count_current,
                                metadata_stream->uid, metadata_stream->gid);
                if (ret < 0) {
                        goto error_stream;
                }
                metadata_stream->out_fd = ret;
                metadata_stream->tracefile_size_current = 0;
        }

        pthread_mutex_lock(&metadata_channel->metadata_cache->lock);

        do {
                ret = lttng_consumer_read_subbuffer(metadata_stream, ctx);
                if (ret < 0) {
                        goto error_unlock;
                }
        } while (ret > 0);

error_unlock:
        pthread_mutex_unlock(&metadata_channel->metadata_cache->lock);

error_stream:
        /*
         * Clean up the stream completly because the next snapshot will use a new
         * metadata stream.
         */
        cds_list_del(&metadata_stream->send_node);
        consumer_stream_destroy(metadata_stream, NULL);
        metadata_channel->metadata_stream = NULL;

error:
        rcu_read_unlock();
        return ret;
}

/*
 * Take a snapshot of all the stream of a channel.
 *
 * Returns 0 on success, < 0 on error
 */
static int snapshot_channel(uint64_t key, char *path, uint64_t relayd_id,
                uint64_t max_stream_size, struct lttng_consumer_local_data *ctx)
{
        int ret;
        unsigned use_relayd = 0;
        unsigned long consumed_pos, produced_pos;
        struct lttng_consumer_channel *channel;
        struct lttng_consumer_stream *stream;

        assert(path);
        assert(ctx);

        rcu_read_lock();

        if (relayd_id != (uint64_t) -1ULL) {
                use_relayd = 1;
        }

        channel = consumer_find_channel(key);
        if (!channel) {
                ERR("UST snapshot channel not found for key %lu", key);
                ret = -1;
                goto error;
        }
        assert(!channel->monitor);
        DBG("UST consumer snapshot channel %lu", key);

        cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
                /* Lock stream because we are about to change its state. */
                pthread_mutex_lock(&stream->lock);
                stream->net_seq_idx = relayd_id;

                if (use_relayd) {
                        ret = consumer_send_relayd_stream(stream, path);
                        if (ret < 0) {
                                goto error_unlock;
                        }
                } else {
                        ret = utils_create_stream_file(path, stream->name,
                                        stream->chan->tracefile_size,
                                        stream->tracefile_count_current,
                                        stream->uid, stream->gid);
                        if (ret < 0) {
                                goto error_unlock;
                        }
                        stream->out_fd = ret;
                        stream->tracefile_size_current = 0;

                        DBG("UST consumer snapshot stream %s/%s (%" PRIu64 ")", path,
                                        stream->name, stream->key);
                }

                ustctl_flush_buffer(stream->ustream, 1);

                ret = lttng_ustconsumer_take_snapshot(stream);
                if (ret < 0) {
                        ERR("Taking UST snapshot");
                        goto error_unlock;
                }

                ret = lttng_ustconsumer_get_produced_snapshot(stream, &produced_pos);
                if (ret < 0) {
                        ERR("Produced UST snapshot position");
                        goto error_unlock;
                }

                ret = lttng_ustconsumer_get_consumed_snapshot(stream, &consumed_pos);
                if (ret < 0) {
                        ERR("Consumerd UST snapshot position");
                        goto error_unlock;
                }

                /*
                 * The original value is sent back if max stream size is larger than
                 * the possible size of the snapshot. Also, we asume that the session
                 * daemon should never send a maximum stream size that is lower than
                 * subbuffer size.
                 */
                consumed_pos = consumer_get_consumed_maxsize(consumed_pos,
                                produced_pos, max_stream_size);

                while (consumed_pos < produced_pos) {
                        ssize_t read_len;
                        unsigned long len, padded_len;

                        DBG("UST consumer taking snapshot at pos %lu", consumed_pos);

                        ret = ustctl_get_subbuf(stream->ustream, &consumed_pos);
                        if (ret < 0) {
                                if (ret != -EAGAIN) {
                                        PERROR("ustctl_get_subbuf snapshot");
                                        goto error_close_stream;
                                }
                                DBG("UST consumer get subbuf failed. Skipping it.");
                                consumed_pos += stream->max_sb_size;
                                continue;
                        }

                        ret = ustctl_get_subbuf_size(stream->ustream, &len);
                        if (ret < 0) {
                                ERR("Snapshot ustctl_get_subbuf_size");
                                goto error_put_subbuf;
                        }

                        ret = ustctl_get_padded_subbuf_size(stream->ustream, &padded_len);
                        if (ret < 0) {
                                ERR("Snapshot ustctl_get_padded_subbuf_size");
                                goto error_put_subbuf;
                        }

                        read_len = lttng_consumer_on_read_subbuffer_mmap(ctx, stream, len,
                                        padded_len - len);
                        if (use_relayd) {
                                if (read_len != len) {
                                        ret = -1;
                                        goto error_put_subbuf;
                                }
                        } else {
                                if (read_len != padded_len) {
                                        ret = -1;
                                        goto error_put_subbuf;
                                }
                        }

                        ret = ustctl_put_subbuf(stream->ustream);
                        if (ret < 0) {
                                ERR("Snapshot ustctl_put_subbuf");
                                goto error_close_stream;
                        }
                        consumed_pos += stream->max_sb_size;
                }

                /* Simply close the stream so we can use it on the next snapshot. */
                consumer_stream_close(stream);
                pthread_mutex_unlock(&stream->lock);
        }

        rcu_read_unlock();
        return 0;

error_put_subbuf:
        if (ustctl_put_subbuf(stream->ustream) < 0) {
                ERR("Snapshot ustctl_put_subbuf");
        }
error_close_stream:
        consumer_stream_close(stream);
error_unlock:
        pthread_mutex_unlock(&stream->lock);
error:
        rcu_read_unlock();
        return ret;
}

/*
 * Receive the metadata updates from the sessiond.
 */
int lttng_ustconsumer_recv_metadata(int sock, uint64_t key, uint64_t offset,
                uint64_t len, struct lttng_consumer_channel *channel,
                int timer)
{
        int ret, ret_code = LTTNG_OK;
        char *metadata_str;

        DBG("UST consumer push metadata key %" PRIu64 " of len %" PRIu64, key, len);

        metadata_str = zmalloc(len * sizeof(char));
        if (!metadata_str) {
                PERROR("zmalloc metadata string");
                ret_code = LTTCOMM_CONSUMERD_ENOMEM;
                goto end;
        }

        /* Receive metadata string. */
        ret = lttcomm_recv_unix_sock(sock, metadata_str, len);
        if (ret < 0) {
                /* Session daemon is dead so return gracefully. */
                ret_code = ret;
                goto end_free;
        }

        pthread_mutex_lock(&channel->metadata_cache->lock);
        ret = consumer_metadata_cache_write(channel, offset, len, metadata_str);
        if (ret < 0) {
                /* Unable to handle metadata. Notify session daemon. */
                ret_code = LTTCOMM_CONSUMERD_ERROR_METADATA;
                /*
                 * Skip metadata flush on write error since the offset and len might
                 * not have been updated which could create an infinite loop below when
                 * waiting for the metadata cache to be flushed.
                 */
                pthread_mutex_unlock(&channel->metadata_cache->lock);
                goto end_free;
        }
        pthread_mutex_unlock(&channel->metadata_cache->lock);

        while (consumer_metadata_cache_flushed(channel, offset + len, timer)) {
                DBG("Waiting for metadata to be flushed");
                usleep(DEFAULT_METADATA_AVAILABILITY_WAIT_TIME);
        }

end_free:
        free(metadata_str);
end:
        return ret_code;
}

/*
 * Receive command from session daemon and process it.
 *
 * Return 1 on success else a negative value or 0.
 */
int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                int sock, struct pollfd *consumer_sockpoll)
{
        ssize_t ret;
        enum lttng_error_code ret_code = LTTNG_OK;
        struct lttcomm_consumer_msg msg;
        struct lttng_consumer_channel *channel = NULL;

        ret = lttcomm_recv_unix_sock(sock, &msg, sizeof(msg));
        if (ret != sizeof(msg)) {
                DBG("Consumer received unexpected message size %zd (expects %zu)",
                        ret, sizeof(msg));
                /*
                 * The ret value might 0 meaning an orderly shutdown but this is ok
                 * since the caller handles this.
                 */
                if (ret > 0) {
                        lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_ERROR_RECV_CMD);
                        ret = -1;
                }
                return ret;
        }
        if (msg.cmd_type == LTTNG_CONSUMER_STOP) {
                /*
                 * Notify the session daemon that the command is completed.
                 *
                 * On transport layer error, the function call will print an error
                 * message so handling the returned code is a bit useless since we
                 * return an error code anyway.
                 */
                (void) consumer_send_status_msg(sock, ret_code);
                return -ENOENT;
        }

        /* relayd needs RCU read-side lock */
        rcu_read_lock();

        switch (msg.cmd_type) {
        case LTTNG_CONSUMER_ADD_RELAYD_SOCKET:
        {
                /* Session daemon status message are handled in the following call. */
                ret = consumer_add_relayd_socket(msg.u.relayd_sock.net_index,
                                msg.u.relayd_sock.type, ctx, sock, consumer_sockpoll,
                                &msg.u.relayd_sock.sock, msg.u.relayd_sock.session_id);
                goto end_nosignal;
        }
        case LTTNG_CONSUMER_DESTROY_RELAYD:
        {
                uint64_t index = msg.u.destroy_relayd.net_seq_idx;
                struct consumer_relayd_sock_pair *relayd;

                DBG("UST consumer destroying relayd %" PRIu64, index);

                /* Get relayd reference if exists. */
                relayd = consumer_find_relayd(index);
                if (relayd == NULL) {
                        DBG("Unable to find relayd %" PRIu64, index);
                        ret_code = LTTNG_ERR_NO_CONSUMER;
                }

                /*
                 * Each relayd socket pair has a refcount of stream attached to it
                 * which tells if the relayd is still active or not depending on the
                 * refcount value.
                 *
                 * This will set the destroy flag of the relayd object and destroy it
                 * if the refcount reaches zero when called.
                 *
                 * The destroy can happen either here or when a stream fd hangs up.
                 */
                if (relayd) {
                        consumer_flag_relayd_for_destroy(relayd);
                }

                goto end_msg_sessiond;
        }
        case LTTNG_CONSUMER_UPDATE_STREAM:
        {
                rcu_read_unlock();
                return -ENOSYS;
        }
        case LTTNG_CONSUMER_DATA_PENDING:
        {
                int ret, is_data_pending;
                uint64_t id = msg.u.data_pending.session_id;

                DBG("UST consumer data pending command for id %" PRIu64, id);

                is_data_pending = consumer_data_pending(id);

                /* Send back returned value to session daemon */
                ret = lttcomm_send_unix_sock(sock, &is_data_pending,
                                sizeof(is_data_pending));
                if (ret < 0) {
                        DBG("Error when sending the data pending ret code: %d", ret);
                        goto error_fatal;
                }

                /*
                 * No need to send back a status message since the data pending
                 * returned value is the response.
                 */
                break;
        }
        case LTTNG_CONSUMER_ASK_CHANNEL_CREATION:
        {
                int ret;
                struct ustctl_consumer_channel_attr attr;

                /* Create a plain object and reserve a channel key. */
                channel = allocate_channel(msg.u.ask_channel.session_id,
                                msg.u.ask_channel.pathname, msg.u.ask_channel.name,
                                msg.u.ask_channel.uid, msg.u.ask_channel.gid,
                                msg.u.ask_channel.relayd_id, msg.u.ask_channel.key,
                                (enum lttng_event_output) msg.u.ask_channel.output,
                                msg.u.ask_channel.tracefile_size,
                                msg.u.ask_channel.tracefile_count,
                                msg.u.ask_channel.session_id_per_pid,
                                msg.u.ask_channel.monitor);
                if (!channel) {
                        goto end_channel_error;
                }

                /* Build channel attributes from received message. */
                attr.subbuf_size = msg.u.ask_channel.subbuf_size;
                attr.num_subbuf = msg.u.ask_channel.num_subbuf;
                attr.overwrite = msg.u.ask_channel.overwrite;
                attr.switch_timer_interval = msg.u.ask_channel.switch_timer_interval;
                attr.read_timer_interval = msg.u.ask_channel.read_timer_interval;
                attr.chan_id = msg.u.ask_channel.chan_id;
                attr.output = msg.u.ask_channel.output;
                memcpy(attr.uuid, msg.u.ask_channel.uuid, sizeof(attr.uuid));

                /* Translate and save channel type. */
                switch (msg.u.ask_channel.type) {
                case LTTNG_UST_CHAN_PER_CPU:
                        channel->type = CONSUMER_CHANNEL_TYPE_DATA;
                        attr.type = LTTNG_UST_CHAN_PER_CPU;
                        /*
                         * Set refcount to 1 for owner. Below, we will
                         * pass ownership to the
                         * consumer_thread_channel_poll() thread.
                         */
                        channel->refcount = 1;
                        break;
                case LTTNG_UST_CHAN_METADATA:
                        channel->type = CONSUMER_CHANNEL_TYPE_METADATA;
                        attr.type = LTTNG_UST_CHAN_METADATA;
                        break;
                default:
                        assert(0);
                        goto error_fatal;
                };

                ret = ask_channel(ctx, sock, channel, &attr);
                if (ret < 0) {
                        goto end_channel_error;
                }

                if (msg.u.ask_channel.type == LTTNG_UST_CHAN_METADATA) {
                        ret = consumer_metadata_cache_allocate(channel);
                        if (ret < 0) {
                                ERR("Allocating metadata cache");
                                goto end_channel_error;
                        }
                        consumer_timer_switch_start(channel, attr.switch_timer_interval);
                        attr.switch_timer_interval = 0;
                }

                /*
                 * Add the channel to the internal state AFTER all streams were created
                 * and successfully sent to session daemon. This way, all streams must
                 * be ready before this channel is visible to the threads.
                 * If add_channel succeeds, ownership of the channel is
                 * passed to consumer_thread_channel_poll().
                 */
                ret = add_channel(channel, ctx);
                if (ret < 0) {
                        if (msg.u.ask_channel.type == LTTNG_UST_CHAN_METADATA) {
                                if (channel->switch_timer_enabled == 1) {
                                        consumer_timer_switch_stop(channel);
                                }
                                consumer_metadata_cache_destroy(channel);
                        }
                        goto end_channel_error;
                }

                /*
                 * Channel and streams are now created. Inform the session daemon that
                 * everything went well and should wait to receive the channel and
                 * streams with ustctl API.
                 */
                ret = consumer_send_status_channel(sock, channel);
                if (ret < 0) {
                        /*
                         * There is probably a problem on the socket.
                         */
                        goto error_fatal;
                }

                break;
        }
        case LTTNG_CONSUMER_GET_CHANNEL:
        {
                int ret, relayd_err = 0;
                uint64_t key = msg.u.get_channel.key;
                struct lttng_consumer_channel *channel;

                channel = consumer_find_channel(key);
                if (!channel) {
                        ERR("UST consumer get channel key %" PRIu64 " not found", key);
                        ret_code = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                        goto end_msg_sessiond;
                }

                /* Send everything to sessiond. */
                ret = send_sessiond_channel(sock, channel, ctx, &relayd_err);
                if (ret < 0) {
                        if (relayd_err) {
                                /*
                                 * We were unable to send to the relayd the stream so avoid
                                 * sending back a fatal error to the thread since this is OK
                                 * and the consumer can continue its work. The above call
                                 * has sent the error status message to the sessiond.
                                 */
                                goto end_nosignal;
                        }
                        /*
                         * The communicaton was broken hence there is a bad state between
                         * the consumer and sessiond so stop everything.
                         */
                        goto error_fatal;
                }

                /*
                 * In no monitor mode, the streams ownership is kept inside the channel
                 * so don't send them to the data thread.
                 */
                if (!channel->monitor) {
                        goto end_msg_sessiond;
                }

                ret = send_streams_to_thread(channel, ctx);
                if (ret < 0) {
                        /*
                         * If we are unable to send the stream to the thread, there is
                         * a big problem so just stop everything.
                         */
                        goto error_fatal;
                }
                /* List MUST be empty after or else it could be reused. */
                assert(cds_list_empty(&channel->streams.head));
                goto end_msg_sessiond;
        }
        case LTTNG_CONSUMER_DESTROY_CHANNEL:
        {
                uint64_t key = msg.u.destroy_channel.key;

                /*
                 * Only called if streams have not been sent to stream
                 * manager thread. However, channel has been sent to
                 * channel manager thread.
                 */
                notify_thread_del_channel(ctx, key);
                goto end_msg_sessiond;
        }
        case LTTNG_CONSUMER_CLOSE_METADATA:
        {
                int ret;

                ret = close_metadata(msg.u.close_metadata.key);
                if (ret != 0) {
                        ret_code = ret;
                }

                goto end_msg_sessiond;
        }
        case LTTNG_CONSUMER_FLUSH_CHANNEL:
        {
                int ret;

                ret = flush_channel(msg.u.flush_channel.key);
                if (ret != 0) {
                        ret_code = ret;
                }

                goto end_msg_sessiond;
        }
        case LTTNG_CONSUMER_PUSH_METADATA:
        {
                int ret;
                uint64_t len = msg.u.push_metadata.len;
                uint64_t key = msg.u.push_metadata.key;
                uint64_t offset = msg.u.push_metadata.target_offset;
                struct lttng_consumer_channel *channel;

                DBG("UST consumer push metadata key %" PRIu64 " of len %" PRIu64, key,
                                len);

                channel = consumer_find_channel(key);
                if (!channel) {
                        ERR("UST consumer push metadata %" PRIu64 " not found", key);
                        ret_code = LTTNG_ERR_UST_CHAN_NOT_FOUND;
                        goto end_msg_sessiond;
                }

                /* Tell session daemon we are ready to receive the metadata. */
                ret = consumer_send_status_msg(sock, LTTNG_OK);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto error_fatal;
                }

                /* Wait for more data. */
                if (lttng_consumer_poll_socket(consumer_sockpoll) < 0) {
                        goto error_fatal;
                }

                ret = lttng_ustconsumer_recv_metadata(sock, key, offset,
                                len, channel, 0);
                if (ret < 0) {
                        /* error receiving from sessiond */
                        goto error_fatal;
                } else {
                        ret_code = ret;
                        goto end_msg_sessiond;
                }
        }
        case LTTNG_CONSUMER_SETUP_METADATA:
        {
                int ret;

                ret = setup_metadata(ctx, msg.u.setup_metadata.key);
                if (ret) {
                        ret_code = ret;
                }
                goto end_msg_sessiond;
        }
        case LTTNG_CONSUMER_SNAPSHOT_CHANNEL:
        {
                if (msg.u.snapshot_channel.metadata) {
                        ret = snapshot_metadata(msg.u.snapshot_channel.key,
                                        msg.u.snapshot_channel.pathname,
                                        msg.u.snapshot_channel.relayd_id,
                                        ctx);
                        if (ret < 0) {
                                ERR("Snapshot metadata failed");
                                ret_code = LTTNG_ERR_UST_META_FAIL;
                        }
                } else {
                        ret = snapshot_channel(msg.u.snapshot_channel.key,
                                        msg.u.snapshot_channel.pathname,
                                        msg.u.snapshot_channel.relayd_id,
                                        msg.u.snapshot_channel.max_stream_size,
                                        ctx);
                        if (ret < 0) {
                                ERR("Snapshot channel failed");
                                ret_code = LTTNG_ERR_UST_CHAN_FAIL;
                        }
                }

                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
                        goto end_nosignal;
                }
                break;
        }
        default:
                break;
        }

end_nosignal:
        rcu_read_unlock();

        /*
         * Return 1 to indicate success since the 0 value can be a socket
         * shutdown during the recv() or send() call.
         */
        return 1;

end_msg_sessiond:
        /*
         * The returned value here is not useful since either way we'll return 1 to
         * the caller because the session daemon socket management is done
         * elsewhere. Returning a negative code or 0 will shutdown the consumer.
         */
        ret = consumer_send_status_msg(sock, ret_code);
        if (ret < 0) {
                goto error_fatal;
        }
        rcu_read_unlock();
        return 1;
end_channel_error:
        if (channel) {
                /*
                 * Free channel here since no one has a reference to it. We don't
                 * free after that because a stream can store this pointer.
                 */
                destroy_channel(channel);
        }
        /* We have to send a status channel message indicating an error. */
        ret = consumer_send_status_channel(sock, NULL);
        if (ret < 0) {
                /* Stop everything if session daemon can not be notified. */
                goto error_fatal;
        }
        rcu_read_unlock();
        return 1;
error_fatal:
        rcu_read_unlock();
        /* This will issue a consumer stop. */
        return -1;
}

/*
 * Wrapper over the mmap() read offset from ust-ctl library. Since this can be
 * compiled out, we isolate it in this library.
 */
int lttng_ustctl_get_mmap_read_offset(struct lttng_consumer_stream *stream,
                unsigned long *off)
{
        assert(stream);
        assert(stream->ustream);

        return ustctl_get_mmap_read_offset(stream->ustream, off);
}

/*
 * Wrapper over the mmap() read offset from ust-ctl library. Since this can be
 * compiled out, we isolate it in this library.
 */
void *lttng_ustctl_get_mmap_base(struct lttng_consumer_stream *stream)
{
        assert(stream);
        assert(stream->ustream);

        return ustctl_get_mmap_base(stream->ustream);
}

/*
 * Take a snapshot for a specific fd
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_ustconsumer_take_snapshot(struct lttng_consumer_stream *stream)
{
        assert(stream);
        assert(stream->ustream);

        return ustctl_snapshot(stream->ustream);
}

/*
 * Get the produced position
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_ustconsumer_get_produced_snapshot(
                struct lttng_consumer_stream *stream, unsigned long *pos)
{
        assert(stream);
        assert(stream->ustream);
        assert(pos);

        return ustctl_snapshot_get_produced(stream->ustream, pos);
}

/*
 * Get the consumed position
 *
 * Returns 0 on success, < 0 on error
 */
int lttng_ustconsumer_get_consumed_snapshot(
                struct lttng_consumer_stream *stream, unsigned long *pos)
{
        assert(stream);
        assert(stream->ustream);
        assert(pos);

        return ustctl_snapshot_get_consumed(stream->ustream, pos);
}

/*
 * Called when the stream signal the consumer that it has hang up.
 */
void lttng_ustconsumer_on_stream_hangup(struct lttng_consumer_stream *stream)
{
        assert(stream);
        assert(stream->ustream);

        ustctl_flush_buffer(stream->ustream, 0);
        stream->hangup_flush_done = 1;
}

void lttng_ustconsumer_del_channel(struct lttng_consumer_channel *chan)
{
        assert(chan);
        assert(chan->uchan);

        if (chan->switch_timer_enabled == 1) {
                consumer_timer_switch_stop(chan);
        }
        consumer_metadata_cache_destroy(chan);
        ustctl_destroy_channel(chan->uchan);
}

void lttng_ustconsumer_del_stream(struct lttng_consumer_stream *stream)
{
        assert(stream);
        assert(stream->ustream);

        if (stream->chan->switch_timer_enabled == 1) {
                consumer_timer_switch_stop(stream->chan);
        }
        ustctl_destroy_stream(stream->ustream);
}

int lttng_ustconsumer_read_subbuffer(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx)
{
        unsigned long len, subbuf_size, padding;
        int err;
        long ret = 0;
        char dummy;
        struct ustctl_consumer_stream *ustream;

        assert(stream);
        assert(stream->ustream);
        assert(ctx);

        DBG("In UST read_subbuffer (wait_fd: %d, name: %s)", stream->wait_fd,
                        stream->name);

        /* Ease our life for what's next. */
        ustream = stream->ustream;

        /* We can consume the 1 byte written into the wait_fd by UST */
        if (stream->monitor && !stream->hangup_flush_done) {
                ssize_t readlen;

                do {
                        readlen = read(stream->wait_fd, &dummy, 1);
                } while (readlen == -1 && errno == EINTR);
                if (readlen == -1 && errno != EAGAIN && errno != EWOULDBLOCK) {
                        ret = readlen;
                        goto end;
                }
        }

retry:
        /* Get the next subbuffer */
        err = ustctl_get_next_subbuf(ustream);
        if (err != 0) {
                /*
                 * Populate metadata info if the existing info has
                 * already been read.
                 */
                if (stream->metadata_flag) {
                        ssize_t write_len;

                        if (stream->chan->metadata_cache->contiguous
                                        == stream->ust_metadata_pushed) {
                                ret = 0;
                                goto end;
                        }

                        write_len = ustctl_write_one_packet_to_channel(stream->chan->uchan,
                                        &stream->chan->metadata_cache->data[stream->ust_metadata_pushed],
                                        stream->chan->metadata_cache->contiguous
                                                - stream->ust_metadata_pushed);
                        assert(write_len != 0);
                        if (write_len < 0) {
                                ERR("Writing one metadata packet");
                                ret = -1;
                                goto end;
                        }
                        stream->ust_metadata_pushed += write_len;
                        ustctl_flush_buffer(stream->ustream, 1);
                        goto retry;
                }

                ret = err;      /* ustctl_get_next_subbuf returns negative, caller expect positive. */
                /*
                 * This is a debug message even for single-threaded consumer,
                 * because poll() have more relaxed criterions than get subbuf,
                 * so get_subbuf may fail for short race windows where poll()
                 * would issue wakeups.
                 */
                DBG("Reserving sub buffer failed (everything is normal, "
                                "it is due to concurrency) [ret: %d]", err);
                goto end;
        }
        assert(stream->chan->output == CONSUMER_CHANNEL_MMAP);
        /* Get the full padded subbuffer size */
        err = ustctl_get_padded_subbuf_size(ustream, &len);
        assert(err == 0);

        /* Get subbuffer data size (without padding) */
        err = ustctl_get_subbuf_size(ustream, &subbuf_size);
        assert(err == 0);

        /* Make sure we don't get a subbuffer size bigger than the padded */
        assert(len >= subbuf_size);

        padding = len - subbuf_size;
        /* write the subbuffer to the tracefile */
        ret = lttng_consumer_on_read_subbuffer_mmap(ctx, stream, subbuf_size, padding);
        /*
         * The mmap operation should write subbuf_size amount of data when network
         * streaming or the full padding (len) size when we are _not_ streaming.
         */
        if ((ret != subbuf_size && stream->net_seq_idx != (uint64_t) -1ULL) ||
                        (ret != len && stream->net_seq_idx == (uint64_t) -1ULL)) {
                /*
                 * Display the error but continue processing to try to release the
                 * subbuffer. This is a DBG statement since any unexpected kill or
                 * signal, the application gets unregistered, relayd gets closed or
                 * anything that affects the buffer lifetime will trigger this error.
                 * So, for the sake of the user, don't print this error since it can
                 * happen and it is OK with the code flow.
                 */
                DBG("Error writing to tracefile "
                                "(ret: %ld != len: %lu != subbuf_size: %lu)",
                                ret, len, subbuf_size);
        }
        err = ustctl_put_next_subbuf(ustream);
        assert(err == 0);

end:
        return ret;
}

/*
 * Called when a stream is created.
 *
 * Return 0 on success or else a negative value.
 */
int lttng_ustconsumer_on_recv_stream(struct lttng_consumer_stream *stream)
{
        int ret;

        assert(stream);

        /* Don't create anything if this is set for streaming. */
        if (stream->net_seq_idx == (uint64_t) -1ULL && stream->chan->monitor) {
                ret = utils_create_stream_file(stream->chan->pathname, stream->name,
                                stream->chan->tracefile_size, stream->tracefile_count_current,
                                stream->uid, stream->gid);
                if (ret < 0) {
                        goto error;
                }
                stream->out_fd = ret;
                stream->tracefile_size_current = 0;
        }
        ret = 0;

error:
        return ret;
}

/*
 * Check if data is still being extracted from the buffers for a specific
 * stream. Consumer data lock MUST be acquired before calling this function
 * and the stream lock.
 *
 * Return 1 if the traced data are still getting read else 0 meaning that the
 * data is available for trace viewer reading.
 */
int lttng_ustconsumer_data_pending(struct lttng_consumer_stream *stream)
{
        int ret;

        assert(stream);
        assert(stream->ustream);

        DBG("UST consumer checking data pending");

        if (stream->endpoint_status != CONSUMER_ENDPOINT_ACTIVE) {
                ret = 0;
                goto end;
        }

        if (stream->chan->type == CONSUMER_CHANNEL_TYPE_METADATA) {
                /*
                 * We can simply check whether all contiguously available data
                 * has been pushed to the ring buffer, since the push operation
                 * is performed within get_next_subbuf(), and because both
                 * get_next_subbuf() and put_next_subbuf() are issued atomically
                 * thanks to the stream lock within
                 * lttng_ustconsumer_read_subbuffer(). This basically means that
                 * whetnever ust_metadata_pushed is incremented, the associated
                 * metadata has been consumed from the metadata stream.
                 */
                DBG("UST consumer metadata pending check: contiguous %" PRIu64 " vs pushed %" PRIu64,
                        stream->chan->metadata_cache->contiguous,
                        stream->ust_metadata_pushed);
                if (stream->chan->metadata_cache->contiguous
                                != stream->ust_metadata_pushed) {
                        ret = 1;        /* Data is pending */
                        goto end;
                }
        } else {
                ret = ustctl_get_next_subbuf(stream->ustream);
                if (ret == 0) {
                        /*
                         * There is still data so let's put back this
                         * subbuffer.
                         */
                        ret = ustctl_put_subbuf(stream->ustream);
                        assert(ret == 0);
                        ret = 1;        /* Data is pending */
                        goto end;
                }
        }

        /* Data is NOT pending so ready to be read. */
        ret = 0;

end:
        return ret;
}

/*
 * Close every metadata stream wait fd of the metadata hash table. This
 * function MUST be used very carefully so not to run into a race between the
 * metadata thread handling streams and this function closing their wait fd.
 *
 * For UST, this is used when the session daemon hangs up. Its the metadata
 * producer so calling this is safe because we are assured that no state change
 * can occur in the metadata thread for the streams in the hash table.
 */
void lttng_ustconsumer_close_metadata(struct lttng_ht *metadata_ht)
{
        int ret;
        struct lttng_ht_iter iter;
        struct lttng_consumer_stream *stream;

        assert(metadata_ht);
        assert(metadata_ht->ht);

        DBG("UST consumer closing all metadata streams");

        rcu_read_lock();
        cds_lfht_for_each_entry(metadata_ht->ht, &iter.iter, stream,
                        node.node) {
                int fd = stream->wait_fd;

                /*
                 * Whatever happens here we have to continue to try to close every
                 * streams. Let's report at least the error on failure.
                 */
                ret = ustctl_stream_close_wakeup_fd(stream->ustream);
                if (ret) {
                        ERR("Unable to close metadata stream fd %d ret %d", fd, ret);
                }
                DBG("Metadata wait fd %d closed", fd);
        }
        rcu_read_unlock();
}

void lttng_ustconsumer_close_stream_wakeup(struct lttng_consumer_stream *stream)
{
        int ret;

        ret = ustctl_stream_close_wakeup_fd(stream->ustream);
        if (ret < 0) {
                ERR("Unable to close wakeup fd");
        }
}

/*
 * Please refer to consumer-timer.c before adding any lock within this
 * function or any of its callees. Timers have a very strict locking
 * semantic with respect to teardown. Failure to respect this semantic
 * introduces deadlocks.
 */
int lttng_ustconsumer_request_metadata(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_channel *channel, int timer)
{
        struct lttcomm_metadata_request_msg request;
        struct lttcomm_consumer_msg msg;
        enum lttng_error_code ret_code = LTTNG_OK;
        uint64_t len, key, offset;
        int ret;

        assert(channel);
        assert(channel->metadata_cache);

        /* send the metadata request to sessiond */
        switch (consumer_data.type) {
        case LTTNG_CONSUMER64_UST:
                request.bits_per_long = 64;
                break;
        case LTTNG_CONSUMER32_UST:
                request.bits_per_long = 32;
                break;
        default:
                request.bits_per_long = 0;
                break;
        }

        request.session_id = channel->session_id;
        request.session_id_per_pid = channel->session_id_per_pid;
        request.uid = channel->uid;
        request.key = channel->key;
        DBG("Sending metadata request to sessiond, session id %" PRIu64
                        ", per-pid %" PRIu64,
                        channel->session_id,
                        channel->session_id_per_pid);

        pthread_mutex_lock(&ctx->metadata_socket_lock);
        ret = lttcomm_send_unix_sock(ctx->consumer_metadata_socket, &request,
                        sizeof(request));
        if (ret < 0) {
                ERR("Asking metadata to sessiond");
                goto end;
        }

        /* Receive the metadata from sessiond */
        ret = lttcomm_recv_unix_sock(ctx->consumer_metadata_socket, &msg,
                        sizeof(msg));
        if (ret != sizeof(msg)) {
                DBG("Consumer received unexpected message size %d (expects %zu)",
                        ret, sizeof(msg));
                lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_ERROR_RECV_CMD);
                /*
                 * The ret value might 0 meaning an orderly shutdown but this is ok
                 * since the caller handles this.
                 */
                goto end;
        }

        if (msg.cmd_type == LTTNG_ERR_UND) {
                /* No registry found */
                (void) consumer_send_status_msg(ctx->consumer_metadata_socket,
                                ret_code);
                ret = 0;
                goto end;
        } else if (msg.cmd_type != LTTNG_CONSUMER_PUSH_METADATA) {
                ERR("Unexpected cmd_type received %d", msg.cmd_type);
                ret = -1;
                goto end;
        }

        len = msg.u.push_metadata.len;
        key = msg.u.push_metadata.key;
        offset = msg.u.push_metadata.target_offset;

        assert(key == channel->key);
        if (len == 0) {
                DBG("No new metadata to receive for key %" PRIu64, key);
        }

        /* Tell session daemon we are ready to receive the metadata. */
        ret = consumer_send_status_msg(ctx->consumer_metadata_socket,
                        LTTNG_OK);
        if (ret < 0 || len == 0) {
                /*
                 * Somehow, the session daemon is not responding anymore or there is
                 * nothing to receive.
                 */
                goto end;
        }

        ret_code = lttng_ustconsumer_recv_metadata(ctx->consumer_metadata_socket,
                        key, offset, len, channel, timer);
        if (ret_code >= 0) {
                /*
                 * Only send the status msg if the sessiond is alive meaning a positive
                 * ret code.
                 */
                (void) consumer_send_status_msg(ctx->consumer_metadata_socket, ret_code);
        }
        ret = 0;

end:
        pthread_mutex_unlock(&ctx->metadata_socket_lock);
        return ret;
}