SoW-2020-0002: Trace Hit Counters: trigger error reporting integration
[lttng-tools.git] / src / common / ust-consumer / ust-consumer.c
index bf0208f1d67adb0dd92e840b03a0c43910771b5d..cd9b273c28f32f36be201df68263100a11c7b7bb 100644 (file)
@@ -1,22 +1,12 @@
 /*
- * Copyright (C) 2011 - Julien Desfossez <julien.desfossez@polymtl.ca>
- *                      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2011 Julien Desfossez <julien.desfossez@polymtl.ca>
+ * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@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.
+ * SPDX-License-Identifier: GPL-2.0-only
  *
- * 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
 #define _LGPL_SOURCE
 #include <assert.h>
 #include <lttng/ust-ctl.h>
@@ -32,6 +22,8 @@
 #include <unistd.h>
 #include <urcu/list.h>
 #include <signal.h>
+#include <stdbool.h>
+#include <stdint.h>
 
 #include <bin/lttng-consumerd/health-consumerd.h>
 #include <common/common.h>
 #include <common/relayd/relayd.h>
 #include <common/compat/fcntl.h>
 #include <common/compat/endian.h>
-#include <common/consumer-metadata-cache.h>
-#include <common/consumer-stream.h>
-#include <common/consumer-timer.h>
+#include <common/consumer/consumer-metadata-cache.h>
+#include <common/consumer/consumer-stream.h>
+#include <common/consumer/consumer-timer.h>
 #include <common/utils.h>
 #include <common/index/index.h>
+#include <common/consumer/consumer.h>
+#include <common/shm.h>
+#include <common/optional.h>
 
 #include "ust-consumer.h"
 
+#define INT_MAX_STR_LEN 12     /* includes \0 */
+
 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
@@ -71,6 +67,7 @@ static void destroy_channel(struct lttng_consumer_channel *channel)
 
                cds_list_del(&stream->send_node);
                ustctl_destroy_stream(stream->ustream);
+               lttng_trace_chunk_put(stream->trace_chunk);
                free(stream);
        }
 
@@ -80,7 +77,13 @@ static void destroy_channel(struct lttng_consumer_channel *channel)
         */
        if (channel->uchan) {
                lttng_ustconsumer_del_channel(channel);
+               lttng_ustconsumer_free_channel(channel);
+       }
+
+       if (channel->trace_chunk) {
+               lttng_trace_chunk_put(channel->trace_chunk);
        }
+
        free(channel);
 }
 
@@ -116,24 +119,6 @@ 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,
-               unsigned int live_timer_interval)
-{
-       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, live_timer_interval);
-}
-
 /*
  * 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.
@@ -150,14 +135,14 @@ static struct lttng_consumer_stream *allocate_stream(int cpu, int key,
        assert(channel);
        assert(ctx);
 
-       stream = consumer_allocate_stream(channel->key,
+       stream = consumer_stream_create(
+                       channel,
+                       channel->key,
                        key,
-                       LTTNG_CONSUMER_ACTIVE_STREAM,
                        channel->name,
-                       channel->uid,
-                       channel->gid,
                        channel->relayd_id,
                        channel->session_id,
+                       channel->trace_chunk,
                        cpu,
                        &alloc_ret,
                        channel->type,
@@ -180,7 +165,7 @@ static struct lttng_consumer_stream *allocate_stream(int cpu, int key,
                goto error;
        }
 
-       stream->chan = channel;
+       consumer_stream_update_channel_attributes(stream, channel);
 
 error:
        if (_alloc_ret) {
@@ -202,28 +187,21 @@ static int send_stream_to_thread(struct lttng_consumer_stream *stream,
 
        /* Get the right pipe where the stream will be sent. */
        if (stream->metadata_flag) {
-               ret = consumer_add_metadata_stream(stream);
-               if (ret) {
-                       ERR("Consumer add metadata stream %" PRIu64 " failed.",
-                                       stream->key);
-                       goto error;
-               }
+               consumer_add_metadata_stream(stream);
                stream_pipe = ctx->consumer_metadata_pipe;
        } else {
-               ret = consumer_add_data_stream(stream);
-               if (ret) {
-                       ERR("Consumer add stream %" PRIu64 " failed.",
-                                       stream->key);
-                       goto error;
-               }
+               consumer_add_data_stream(stream);
                stream_pipe = ctx->consumer_data_pipe;
        }
 
        /*
         * From this point on, the stream's ownership has been moved away from
-        * the channel and becomes globally visible.
+        * the channel and it becomes globally visible. Hence, remove it from
+        * the local stream list to prevent the stream from being both local and
+        * global.
         */
        stream->globally_visible = 1;
+       cds_list_del(&stream->send_node);
 
        ret = lttng_pipe_write(stream_pipe, &stream, sizeof(stream));
        if (ret < 0) {
@@ -235,13 +213,36 @@ static int send_stream_to_thread(struct lttng_consumer_stream *stream,
                } else {
                        consumer_del_stream_for_data(stream);
                }
+               goto error;
        }
+
 error:
        return ret;
 }
 
+static
+int get_stream_shm_path(char *stream_shm_path, const char *shm_path, int cpu)
+{
+       char cpu_nr[INT_MAX_STR_LEN];  /* int max len */
+       int ret;
+
+       strncpy(stream_shm_path, shm_path, PATH_MAX);
+       stream_shm_path[PATH_MAX - 1] = '\0';
+       ret = snprintf(cpu_nr, INT_MAX_STR_LEN, "%i", cpu);
+       if (ret < 0) {
+               PERROR("snprintf");
+               goto end;
+       }
+       strncat(stream_shm_path, cpu_nr,
+               PATH_MAX - strlen(stream_shm_path) - 1);
+       ret = 0;
+end:
+       return ret;
+}
+
 /*
  * Create streams for the given channel using liblttng-ust-ctl.
+ * The channel lock must be acquired by the caller.
  *
  * Return 0 on success else a negative value.
  */
@@ -251,6 +252,7 @@ static int create_ust_streams(struct lttng_consumer_channel *channel,
        int ret, cpu = 0;
        struct ustctl_consumer_stream *ustream;
        struct lttng_consumer_stream *stream;
+       pthread_mutex_t *current_stream_lock = NULL;
 
        assert(channel);
        assert(ctx);
@@ -297,6 +299,8 @@ static int create_ust_streams(struct lttng_consumer_channel *channel,
                        uatomic_inc(&stream->chan->refcount);
                }
 
+               pthread_mutex_lock(&stream->lock);
+               current_stream_lock = &stream->lock;
                /*
                 * Order is important this is why a list is used. On error, the caller
                 * should clean this list.
@@ -328,32 +332,67 @@ static int create_ust_streams(struct lttng_consumer_channel *channel,
                /* 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];
+                       if (channel->monitor) {
+                               /* Set metadata poll pipe if we created one */
+                               memcpy(stream->ust_metadata_poll_pipe,
+                                               ust_metadata_pipe,
+                                               sizeof(ust_metadata_pipe));
+                       }
                }
+               pthread_mutex_unlock(&stream->lock);
+               current_stream_lock = NULL;
        }
 
        return 0;
 
 error:
 error_alloc:
+       if (current_stream_lock) {
+               pthread_mutex_unlock(current_stream_lock);
+       }
        return ret;
 }
 
+static int open_ust_stream_fd(struct lttng_consumer_channel *channel, int cpu,
+               const struct lttng_credentials *session_credentials)
+{
+       char shm_path[PATH_MAX];
+       int ret;
+
+       if (!channel->shm_path[0]) {
+               return shm_create_anonymous("ust-consumer");
+       }
+       ret = get_stream_shm_path(shm_path, channel->shm_path, cpu);
+       if (ret) {
+               goto error_shm_path;
+       }
+       return run_as_open(shm_path,
+               O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR,
+               lttng_credentials_get_uid(session_credentials),
+               lttng_credentials_get_gid(session_credentials));
+
+error_shm_path:
+       return -1;
+}
+
 /*
  * 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)
+static int create_ust_channel(struct lttng_consumer_channel *channel,
+               struct ustctl_consumer_channel_attr *attr,
+               struct ustctl_consumer_channel **ust_chanp)
 {
-       int ret;
-       struct ustctl_consumer_channel *channel;
+       int ret, nr_stream_fds, i, j;
+       int *stream_fds;
+       struct ustctl_consumer_channel *ust_channel;
 
+       assert(channel);
        assert(attr);
-       assert(chanp);
+       assert(ust_chanp);
+       assert(channel->buffer_credentials.is_set);
 
        DBG3("Creating channel to ustctl with attr: [overwrite: %d, "
                        "subbuf_size: %" PRIu64 ", num_subbuf: %" PRIu64 ", "
@@ -362,17 +401,72 @@ static int create_ust_channel(struct ustctl_consumer_channel_attr *attr,
                        attr->num_subbuf, attr->switch_timer_interval,
                        attr->read_timer_interval, attr->output, attr->type);
 
-       channel = ustctl_create_channel(attr);
-       if (!channel) {
+       if (channel->type == CONSUMER_CHANNEL_TYPE_METADATA)
+               nr_stream_fds = 1;
+       else
+               nr_stream_fds = ustctl_get_nr_stream_per_channel();
+       stream_fds = zmalloc(nr_stream_fds * sizeof(*stream_fds));
+       if (!stream_fds) {
+               ret = -1;
+               goto error_alloc;
+       }
+       for (i = 0; i < nr_stream_fds; i++) {
+               stream_fds[i] = open_ust_stream_fd(channel, i,
+                               &channel->buffer_credentials.value);
+               if (stream_fds[i] < 0) {
+                       ret = -1;
+                       goto error_open;
+               }
+       }
+       ust_channel = ustctl_create_channel(attr, stream_fds, nr_stream_fds);
+       if (!ust_channel) {
                ret = -1;
                goto error_create;
        }
-
-       *chanp = channel;
+       channel->nr_stream_fds = nr_stream_fds;
+       channel->stream_fds = stream_fds;
+       *ust_chanp = ust_channel;
 
        return 0;
 
 error_create:
+error_open:
+       for (j = i - 1; j >= 0; j--) {
+               int closeret;
+
+               closeret = close(stream_fds[j]);
+               if (closeret) {
+                       PERROR("close");
+               }
+               if (channel->shm_path[0]) {
+                       char shm_path[PATH_MAX];
+
+                       closeret = get_stream_shm_path(shm_path,
+                                       channel->shm_path, j);
+                       if (closeret) {
+                               ERR("Cannot get stream shm path");
+                       }
+                       closeret = run_as_unlink(shm_path,
+                                       lttng_credentials_get_uid(LTTNG_OPTIONAL_GET_PTR(
+                                                       channel->buffer_credentials)),
+                                       lttng_credentials_get_gid(LTTNG_OPTIONAL_GET_PTR(
+                                                       channel->buffer_credentials)));
+                       if (closeret) {
+                               PERROR("unlink %s", shm_path);
+                       }
+               }
+       }
+       /* Try to rmdir all directories under shm_path root. */
+       if (channel->root_shm_path[0]) {
+               (void) run_as_rmdir_recursive(channel->root_shm_path,
+                               lttng_credentials_get_uid(LTTNG_OPTIONAL_GET_PTR(
+                                               channel->buffer_credentials)),
+                               lttng_credentials_get_gid(LTTNG_OPTIONAL_GET_PTR(
+                                               channel->buffer_credentials)),
+                               LTTNG_DIRECTORY_HANDLE_SKIP_NON_EMPTY_FLAG);
+       }
+       free(stream_fds);
+error_alloc:
        return ret;
 }
 
@@ -401,11 +495,11 @@ error:
 }
 
 /*
- * Send channel to sessiond.
+ * Send channel to sessiond and relayd if applicable.
  *
  * Return 0 on success or else a negative value.
  */
-static int send_sessiond_channel(int sock,
+static int send_channel_to_sessiond_and_relayd(int sock,
                struct lttng_consumer_channel *channel,
                struct lttng_consumer_local_data *ctx, int *relayd_error)
 {
@@ -425,6 +519,8 @@ static int send_sessiond_channel(int sock,
                        health_code_update();
 
                        /* Try to send the stream to the relayd if one is available. */
+                       DBG("Sending stream %" PRIu64 " of channel \"%s\" to relayd",
+                                       stream->key, channel->name);
                        ret = consumer_send_relayd_stream(stream, stream->chan->pathname);
                        if (ret < 0) {
                                /*
@@ -500,7 +596,7 @@ error:
  * 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,
+static int ask_channel(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_channel *channel,
                struct ustctl_consumer_channel_attr *attr)
 {
@@ -526,7 +622,7 @@ static int ask_channel(struct lttng_consumer_local_data *ctx, int sock,
        channel->nb_init_stream_left = 0;
 
        /* The reply msg status is handled in the following call. */
-       ret = create_ust_channel(attr, &channel->uchan);
+       ret = create_ust_channel(channel, attr, &channel->uchan);
        if (ret < 0) {
                goto end;
        }
@@ -543,7 +639,9 @@ static int ask_channel(struct lttng_consumer_local_data *ctx, int sock,
        }
 
        /* Open all streams for this channel. */
+       pthread_mutex_lock(&channel->lock);
        ret = create_ust_streams(channel, ctx);
+       pthread_mutex_unlock(&channel->lock);
        if (ret < 0) {
                goto end;
        }
@@ -579,14 +677,8 @@ static int send_streams_to_thread(struct lttng_consumer_channel *channel,
                         * If we are unable to send the stream to the thread, there is
                         * a big problem so just stop everything.
                         */
-                       /* Remove node from the channel stream list. */
-                       cds_list_del(&stream->send_node);
                        goto error;
                }
-
-               /* Remove node from the channel stream list. */
-               cds_list_del(&stream->send_node);
-
        }
 
 error:
@@ -625,7 +717,63 @@ static int flush_channel(uint64_t chan_key)
 
                health_code_update();
 
-               ustctl_flush_buffer(stream->ustream, 1);
+               pthread_mutex_lock(&stream->lock);
+
+               /*
+                * Protect against concurrent teardown of a stream.
+                */
+               if (cds_lfht_is_node_deleted(&stream->node.node)) {
+                       goto next;
+               }
+
+               if (!stream->quiescent) {
+                       ustctl_flush_buffer(stream->ustream, 0);
+                       stream->quiescent = true;
+               }
+next:
+               pthread_mutex_unlock(&stream->lock);
+       }
+error:
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * Clear quiescent state from channel's streams using the given key to
+ * retrieve the channel.
+ *
+ * Return 0 on success else an LTTng error code.
+ */
+static int clear_quiescent_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 clear quiescent channel key %" PRIu64, chan_key);
+
+       rcu_read_lock();
+       channel = consumer_find_channel(chan_key);
+       if (!channel) {
+               ERR("UST consumer clear quiescent 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, clear quiescent state. */
+       cds_lfht_for_each_entry_duplicate(ht->ht,
+                       ht->hash_fct(&channel->key, lttng_ht_seed), ht->match_fct,
+                       &channel->key, &iter.iter, stream, node_channel_id.node) {
+
+               health_code_update();
+
+               pthread_mutex_lock(&stream->lock);
+               stream->quiescent = false;
+               pthread_mutex_unlock(&stream->lock);
        }
 error:
        rcu_read_unlock();
@@ -634,7 +782,6 @@ error:
 
 /*
  * 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.
  */
@@ -642,6 +789,7 @@ static int close_metadata(uint64_t chan_key)
 {
        int ret = 0;
        struct lttng_consumer_channel *channel;
+       unsigned int channel_monitor;
 
        DBG("UST consumer close metadata key %" PRIu64, chan_key);
 
@@ -660,13 +808,48 @@ static int close_metadata(uint64_t chan_key)
 
        pthread_mutex_lock(&consumer_data.lock);
        pthread_mutex_lock(&channel->lock);
-
+       channel_monitor = channel->monitor;
        if (cds_lfht_is_node_deleted(&channel->node.node)) {
                goto error_unlock;
        }
 
        lttng_ustconsumer_close_metadata(channel);
+       pthread_mutex_unlock(&channel->lock);
+       pthread_mutex_unlock(&consumer_data.lock);
+
+       /*
+        * The ownership of a metadata channel depends on the type of
+        * session to which it belongs. In effect, the monitor flag is checked
+        * to determine if this metadata channel is in "snapshot" mode or not.
+        *
+        * In the non-snapshot case, the metadata channel is created along with
+        * a single stream which will remain present until the metadata channel
+        * is destroyed (on the destruction of its session). In this case, the
+        * metadata stream in "monitored" by the metadata poll thread and holds
+        * the ownership of its channel.
+        *
+        * Closing the metadata will cause the metadata stream's "metadata poll
+        * pipe" to be closed. Closing this pipe will wake-up the metadata poll
+        * thread which will teardown the metadata stream which, in return,
+        * deletes the metadata channel.
+        *
+        * In the snapshot case, the metadata stream is created and destroyed
+        * on every snapshot record. Since the channel doesn't have an owner
+        * other than the session daemon, it is safe to destroy it immediately
+        * on reception of the CLOSE_METADATA command.
+        */
+       if (!channel_monitor) {
+               /*
+                * The channel and consumer_data locks must be
+                * released before this call since consumer_del_channel
+                * re-acquires the channel and consumer_data locks to teardown
+                * the channel and queue its reclamation by the "call_rcu"
+                * worker thread.
+                */
+               consumer_del_channel(channel);
+       }
 
+       return ret;
 error_unlock:
        pthread_mutex_unlock(&channel->lock);
        pthread_mutex_unlock(&consumer_data.lock);
@@ -729,6 +912,10 @@ static int setup_metadata(struct lttng_consumer_local_data *ctx, uint64_t key)
                }
        }
 
+       /*
+        * Ownership of metadata stream is passed along. Freeing is handled by
+        * the callee.
+        */
        ret = send_streams_to_thread(metadata, ctx);
        if (ret < 0) {
                /*
@@ -736,7 +923,7 @@ static int setup_metadata(struct lttng_consumer_local_data *ctx, uint64_t key)
                 * a big problem so just stop everything.
                 */
                ret = LTTCOMM_CONSUMERD_FATAL;
-               goto error;
+               goto send_streams_error;
        }
        /* List MUST be empty after or else it could be reused. */
        assert(cds_list_empty(&metadata->streams.head));
@@ -754,6 +941,7 @@ error:
        consumer_stream_destroy(metadata->metadata_stream, NULL);
        cds_list_del(&metadata->metadata_stream->send_node);
        metadata->metadata_stream = NULL;
+send_streams_error:
 error_no_stream:
 end:
        return ret;
@@ -761,14 +949,15 @@ end:
 
 /*
  * Snapshot the whole metadata.
+ * RCU read-side lock must be held by the caller.
  *
  * Returns 0 on success, < 0 on error
  */
-static int snapshot_metadata(uint64_t key, char *path, uint64_t relayd_id,
+static int snapshot_metadata(struct lttng_consumer_channel *metadata_channel,
+               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);
@@ -779,13 +968,6 @@ static int snapshot_metadata(uint64_t key, char *path, uint64_t relayd_id,
 
        rcu_read_lock();
 
-       metadata_channel = consumer_find_channel(key);
-       if (!metadata_channel) {
-               ERR("UST snapshot metadata channel not found for key %" PRIu64,
-                       key);
-               ret = -1;
-               goto error;
-       }
        assert(!metadata_channel->monitor);
 
        health_code_update();
@@ -813,28 +995,23 @@ static int snapshot_metadata(uint64_t key, char *path, uint64_t relayd_id,
        metadata_stream = metadata_channel->metadata_stream;
        assert(metadata_stream);
 
+       pthread_mutex_lock(&metadata_stream->lock);
        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, NULL);
-               if (ret < 0) {
-                       goto error_stream;
-               }
-               metadata_stream->out_fd = ret;
-               metadata_stream->tracefile_size_current = 0;
+               ret = consumer_stream_create_output_files(metadata_stream,
+                               false);
+       }
+       pthread_mutex_unlock(&metadata_stream->lock);
+       if (ret < 0) {
+               goto error_stream;
        }
 
        do {
                health_code_update();
 
-               ret = lttng_consumer_read_subbuffer(metadata_stream, ctx);
+               ret = lttng_consumer_read_subbuffer(metadata_stream, ctx, true);
                if (ret < 0) {
                        goto error_stream;
                }
@@ -854,18 +1031,49 @@ error:
        return ret;
 }
 
+static
+int get_current_subbuf_addr(struct lttng_consumer_stream *stream,
+               const char **addr)
+{
+       int ret;
+       unsigned long mmap_offset;
+       const char *mmap_base;
+
+       mmap_base = ustctl_get_mmap_base(stream->ustream);
+       if (!mmap_base) {
+               ERR("Failed to get mmap base for stream `%s`",
+                               stream->name);
+               ret = -EPERM;
+               goto error;
+       }
+
+       ret = ustctl_get_mmap_read_offset(stream->ustream, &mmap_offset);
+       if (ret != 0) {
+               ERR("Failed to get mmap offset for stream `%s`", stream->name);
+               ret = -EINVAL;
+               goto error;
+       }
+
+       *addr = mmap_base + mmap_offset;
+error:
+       return ret;
+
+}
+
 /*
  * Take a snapshot of all the stream of a channel.
+ * RCU read-side lock and the channel lock must be held by the caller.
  *
  * Returns 0 on success, < 0 on error
  */
-static int snapshot_channel(uint64_t key, char *path, uint64_t relayd_id,
-               uint64_t nb_packets_per_stream, struct lttng_consumer_local_data *ctx)
+static int snapshot_channel(struct lttng_consumer_channel *channel,
+               uint64_t key, char *path, uint64_t relayd_id,
+               uint64_t nb_packets_per_stream,
+               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);
@@ -877,21 +1085,27 @@ static int snapshot_channel(uint64_t key, char *path, uint64_t relayd_id,
                use_relayd = 1;
        }
 
-       channel = consumer_find_channel(key);
-       if (!channel) {
-               ERR("UST snapshot channel not found for key %" PRIu64, key);
-               ret = -1;
-               goto error;
-       }
        assert(!channel->monitor);
        DBG("UST consumer snapshot channel %" PRIu64, key);
 
        cds_list_for_each_entry(stream, &channel->streams.head, send_node) {
-
                health_code_update();
 
                /* Lock stream because we are about to change its state. */
                pthread_mutex_lock(&stream->lock);
+               assert(channel->trace_chunk);
+               if (!lttng_trace_chunk_get(channel->trace_chunk)) {
+                       /*
+                        * Can't happen barring an internal error as the channel
+                        * holds a reference to the trace chunk.
+                        */
+                       ERR("Failed to acquire reference to channel's trace chunk");
+                       ret = -1;
+                       goto error_unlock;
+               }
+               assert(!stream->trace_chunk);
+               stream->trace_chunk = channel->trace_chunk;
+
                stream->net_seq_idx = relayd_id;
 
                if (use_relayd) {
@@ -900,27 +1114,22 @@ static int snapshot_channel(uint64_t key, char *path, uint64_t relayd_id,
                                goto error_unlock;
                        }
                } else {
-                       ret = utils_create_stream_file(path, stream->name,
-                                       stream->chan->tracefile_size,
-                                       stream->tracefile_count_current,
-                                       stream->uid, stream->gid, NULL);
-                       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);
-               }
-               if (relayd_id != -1ULL) {
-                       ret = consumer_send_relayd_streams_sent(relayd_id);
+                       ret = consumer_stream_create_output_files(stream,
+                                       false);
                        if (ret < 0) {
                                goto error_unlock;
                        }
+                       DBG("UST consumer snapshot stream (%" PRIu64 ")",
+                                       stream->key);
                }
 
-               ustctl_flush_buffer(stream->ustream, 1);
+               /*
+                * If tracing is active, we want to perform a "full" buffer flush.
+                * Else, if quiescent, it has already been done by the prior stop.
+                */
+               if (!stream->quiescent) {
+                       ustctl_flush_buffer(stream->ustream, 0);
+               }
 
                ret = lttng_ustconsumer_take_snapshot(stream);
                if (ret < 0) {
@@ -950,9 +1159,11 @@ static int snapshot_channel(uint64_t key, char *path, uint64_t relayd_id,
                                produced_pos, nb_packets_per_stream,
                                stream->max_sb_size);
 
-               while (consumed_pos < produced_pos) {
+               while ((long) (consumed_pos - produced_pos) < 0) {
                        ssize_t read_len;
                        unsigned long len, padded_len;
+                       const char *subbuf_addr;
+                       struct lttng_buffer_view subbuf_view;
 
                        health_code_update();
 
@@ -966,6 +1177,7 @@ static int snapshot_channel(uint64_t key, char *path, uint64_t relayd_id,
                                }
                                DBG("UST consumer get subbuf failed. Skipping it.");
                                consumed_pos += stream->max_sb_size;
+                               stream->chan->lost_packets++;
                                continue;
                        }
 
@@ -981,8 +1193,15 @@ static int snapshot_channel(uint64_t key, char *path, uint64_t relayd_id,
                                goto error_put_subbuf;
                        }
 
-                       read_len = lttng_consumer_on_read_subbuffer_mmap(ctx, stream, len,
-                                       padded_len - len, NULL);
+                       ret = get_current_subbuf_addr(stream, &subbuf_addr);
+                       if (ret) {
+                               goto error_put_subbuf;
+                       }
+
+                       subbuf_view = lttng_buffer_view_init(
+                                       subbuf_addr, 0, padded_len);
+                       read_len = lttng_consumer_on_read_subbuffer_mmap(
+                                       stream, &subbuf_view, padded_len - len);
                        if (use_relayd) {
                                if (read_len != len) {
                                        ret = -EPERM;
@@ -1019,17 +1238,21 @@ 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.
+ * Receive the metadata updates from the sessiond. Supports receiving
+ * overlapping metadata, but is needs to always belong to a contiguous
+ * range starting from 0.
+ * Be careful about the locks held when calling this function: it needs
+ * the metadata cache flush to concurrently progress in order to
+ * complete.
  */
 int lttng_ustconsumer_recv_metadata(int sock, uint64_t key, uint64_t offset,
-               uint64_t len, struct lttng_consumer_channel *channel,
-               int timer, int wait)
+               uint64_t len, uint64_t version,
+               struct lttng_consumer_channel *channel, int timer, int wait)
 {
        int ret, ret_code = LTTCOMM_CONSUMERD_SUCCESS;
        char *metadata_str;
@@ -1056,7 +1279,8 @@ int lttng_ustconsumer_recv_metadata(int sock, uint64_t key, uint64_t offset,
        health_code_update();
 
        pthread_mutex_lock(&channel->metadata_cache->lock);
-       ret = consumer_metadata_cache_write(channel, offset, len, metadata_str);
+       ret = consumer_metadata_cache_write(channel, offset, len, version,
+                       metadata_str);
        if (ret < 0) {
                /* Unable to handle metadata. Notify session daemon. */
                ret_code = LTTCOMM_CONSUMERD_ERROR_METADATA;
@@ -1131,7 +1355,7 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
        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,
+               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,
                                msg.u.relayd_sock.relayd_session_id);
@@ -1199,22 +1423,37 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
        {
                int ret;
                struct ustctl_consumer_channel_attr attr;
+               const uint64_t chunk_id = msg.u.ask_channel.chunk_id.value;
+               const struct lttng_credentials buffer_credentials = {
+                       .uid = LTTNG_OPTIONAL_INIT_VALUE(msg.u.ask_channel.buffer_credentials.uid),
+                       .gid = LTTNG_OPTIONAL_INIT_VALUE(msg.u.ask_channel.buffer_credentials.gid),
+               };
 
                /* 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,
+               channel = consumer_allocate_channel(
+                               msg.u.ask_channel.key,
+                               msg.u.ask_channel.session_id,
+                               msg.u.ask_channel.chunk_id.is_set ?
+                                               &chunk_id : NULL,
+                               msg.u.ask_channel.pathname,
+                               msg.u.ask_channel.name,
+                               msg.u.ask_channel.relayd_id,
                                (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,
-                               msg.u.ask_channel.live_timer_interval);
+                               msg.u.ask_channel.live_timer_interval,
+                               msg.u.ask_channel.is_live,
+                               msg.u.ask_channel.root_shm_path,
+                               msg.u.ask_channel.shm_path);
                if (!channel) {
                        goto end_channel_error;
                }
 
+               LTTNG_OPTIONAL_SET(&channel->buffer_credentials,
+                               buffer_credentials);
+
                /*
                 * Assign UST application UID to the channel. This value is ignored for
                 * per PID buffers. This is specific to UST thus setting this after the
@@ -1230,6 +1469,7 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                attr.read_timer_interval = msg.u.ask_channel.read_timer_interval;
                attr.chan_id = msg.u.ask_channel.chan_id;
                memcpy(attr.uuid, msg.u.ask_channel.uuid, sizeof(attr.uuid));
+               attr.blocking_timeout= msg.u.ask_channel.blocking_timeout;
 
                /* Match channel buffer type to the UST abi. */
                switch (msg.u.ask_channel.output) {
@@ -1262,7 +1502,7 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
 
                health_code_update();
 
-               ret = ask_channel(ctx, sock, channel, &attr);
+               ret = ask_channel(ctx, channel, &attr);
                if (ret < 0) {
                        goto end_channel_error;
                }
@@ -1276,8 +1516,17 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                        consumer_timer_switch_start(channel, attr.switch_timer_interval);
                        attr.switch_timer_interval = 0;
                } else {
+                       int monitor_start_ret;
+
                        consumer_timer_live_start(channel,
                                        msg.u.ask_channel.live_timer_interval);
+                       monitor_start_ret = consumer_timer_monitor_start(
+                                       channel,
+                                       msg.u.ask_channel.monitor_timer_interval);
+                       if (monitor_start_ret < 0) {
+                               ERR("Starting channel monitoring timer failed");
+                               goto end_channel_error;
+                       }
                }
 
                health_code_update();
@@ -1300,6 +1549,9 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                        if (channel->live_timer_enabled == 1) {
                                consumer_timer_live_stop(channel);
                        }
+                       if (channel->monitor_timer_enabled == 1) {
+                               consumer_timer_monitor_stop(channel);
+                       }
                        goto end_channel_error;
                }
 
@@ -1330,13 +1582,14 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                if (!channel) {
                        ERR("UST consumer get channel key %" PRIu64 " not found", key);
                        ret_code = LTTCOMM_CONSUMERD_CHAN_NOT_FOUND;
-                       goto end_msg_sessiond;
+                       goto end_get_channel;
                }
 
                health_code_update();
 
-               /* Send everything to sessiond. */
-               ret = send_sessiond_channel(sock, channel, ctx, &relayd_err);
+               /* Send the channel to sessiond (and relayd, if applicable). */
+               ret = send_channel_to_sessiond_and_relayd(sock, channel, ctx,
+                               &relayd_err);
                if (ret < 0) {
                        if (relayd_err) {
                                /*
@@ -1345,13 +1598,13 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                                 * and the consumer can continue its work. The above call
                                 * has sent the error status message to the sessiond.
                                 */
-                               goto end_nosignal;
+                               goto end_get_channel_nosignal;
                        }
                        /*
                         * The communicaton was broken hence there is a bad state between
                         * the consumer and sessiond so stop everything.
                         */
-                       goto error_fatal;
+                       goto error_get_channel_fatal;
                }
 
                health_code_update();
@@ -1361,7 +1614,7 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                 * so don't send them to the data thread.
                 */
                if (!channel->monitor) {
-                       goto end_msg_sessiond;
+                       goto end_get_channel;
                }
 
                ret = send_streams_to_thread(channel, ctx);
@@ -1370,11 +1623,16 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                         * If we are unable to send the stream to the thread, there is
                         * a big problem so just stop everything.
                         */
-                       goto error_fatal;
+                       goto error_get_channel_fatal;
                }
                /* List MUST be empty after or else it could be reused. */
                assert(cds_list_empty(&channel->streams.head));
+end_get_channel:
                goto end_msg_sessiond;
+error_get_channel_fatal:
+               goto error_fatal;
+end_get_channel_nosignal:
+               goto end_nosignal;
        }
        case LTTNG_CONSUMER_DESTROY_CHANNEL:
        {
@@ -1410,12 +1668,25 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
 
                goto end_msg_sessiond;
        }
+       case LTTNG_CONSUMER_CLEAR_QUIESCENT_CHANNEL:
+       {
+               int ret;
+
+               ret = clear_quiescent_channel(
+                               msg.u.clear_quiescent_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;
+               uint64_t version = msg.u.push_metadata.version;
                struct lttng_consumer_channel *channel;
 
                DBG("UST consumer push metadata key %" PRIu64 " of len %" PRIu64, key,
@@ -1432,16 +1703,25 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                         */
                        DBG("UST consumer push metadata %" PRIu64 " not found", key);
                        ret_code = LTTCOMM_CONSUMERD_CHANNEL_FAIL;
-                       goto end_msg_sessiond;
+                       goto end_push_metadata_msg_sessiond;
                }
 
                health_code_update();
 
+               if (!len) {
+                       /*
+                        * There is nothing to receive. We have simply
+                        * checked whether the channel can be found.
+                        */
+                       ret_code = LTTCOMM_CONSUMERD_SUCCESS;
+                       goto end_push_metadata_msg_sessiond;
+               }
+
                /* Tell session daemon we are ready to receive the metadata. */
                ret = consumer_send_status_msg(sock, LTTCOMM_CONSUMERD_SUCCESS);
                if (ret < 0) {
                        /* Somehow, the session daemon is not responding anymore. */
-                       goto error_fatal;
+                       goto error_push_metadata_fatal;
                }
 
                health_code_update();
@@ -1451,20 +1731,24 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                ret = lttng_consumer_poll_socket(consumer_sockpoll);
                health_poll_exit();
                if (ret) {
-                       goto error_fatal;
+                       goto error_push_metadata_fatal;
                }
 
                health_code_update();
 
                ret = lttng_ustconsumer_recv_metadata(sock, key, offset,
-                               len, channel, 0, 1);
+                               len, version, channel, 0, 1);
                if (ret < 0) {
                        /* error receiving from sessiond */
-                       goto error_fatal;
+                       goto error_push_metadata_fatal;
                } else {
                        ret_code = ret;
-                       goto end_msg_sessiond;
+                       goto end_push_metadata_msg_sessiond;
                }
+end_push_metadata_msg_sessiond:
+               goto end_msg_sessiond;
+error_push_metadata_fatal:
+               goto error_fatal;
        }
        case LTTNG_CONSUMER_SETUP_METADATA:
        {
@@ -1478,27 +1762,35 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
        }
        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 = LTTCOMM_CONSUMERD_ERROR_METADATA;
-                       }
+               struct lttng_consumer_channel *channel;
+               uint64_t key = msg.u.snapshot_channel.key;
+
+               channel = consumer_find_channel(key);
+               if (!channel) {
+                       DBG("UST snapshot channel not found for key %" PRIu64, key);
+                       ret_code = LTTCOMM_CONSUMERD_CHAN_NOT_FOUND;
                } else {
-                       ret = snapshot_channel(msg.u.snapshot_channel.key,
-                                       msg.u.snapshot_channel.pathname,
-                                       msg.u.snapshot_channel.relayd_id,
-                                       msg.u.snapshot_channel.nb_packets_per_stream,
-                                       ctx);
-                       if (ret < 0) {
-                               ERR("Snapshot channel failed");
-                               ret_code = LTTCOMM_CONSUMERD_CHANNEL_FAIL;
+                       if (msg.u.snapshot_channel.metadata) {
+                               ret = snapshot_metadata(channel, key,
+                                               msg.u.snapshot_channel.pathname,
+                                               msg.u.snapshot_channel.relayd_id,
+                                               ctx);
+                               if (ret < 0) {
+                                       ERR("Snapshot metadata failed");
+                                       ret_code = LTTCOMM_CONSUMERD_SNAPSHOT_FAILED;
+                               }
+                       } else {
+                               ret = snapshot_channel(channel, key,
+                                               msg.u.snapshot_channel.pathname,
+                                               msg.u.snapshot_channel.relayd_id,
+                                               msg.u.snapshot_channel.nb_packets_per_stream,
+                                               ctx);
+                               if (ret < 0) {
+                                       ERR("Snapshot channel failed");
+                                       ret_code = LTTCOMM_CONSUMERD_SNAPSHOT_FAILED;
+                               }
                        }
                }
-
                health_code_update();
                ret = consumer_send_status_msg(sock, ret_code);
                if (ret < 0) {
@@ -1508,37 +1800,399 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
                health_code_update();
                break;
        }
-       default:
-               break;
-       }
+       case LTTNG_CONSUMER_DISCARDED_EVENTS:
+       {
+               int ret = 0;
+               uint64_t discarded_events;
+               struct lttng_ht_iter iter;
+               struct lttng_ht *ht;
+               struct lttng_consumer_stream *stream;
+               uint64_t id = msg.u.discarded_events.session_id;
+               uint64_t key = msg.u.discarded_events.channel_key;
 
-end_nosignal:
-       rcu_read_unlock();
+               DBG("UST consumer discarded events command for session id %"
+                               PRIu64, id);
+               rcu_read_lock();
+               pthread_mutex_lock(&consumer_data.lock);
 
-       health_code_update();
+               ht = consumer_data.stream_list_ht;
 
-       /*
-        * Return 1 to indicate success since the 0 value can be a socket
-        * shutdown during the recv() or send() call.
-        */
-       return 1;
+               /*
+                * We only need a reference to the channel, but they are not
+                * directly indexed, so we just use the first matching stream
+                * to extract the information we need, we default to 0 if not
+                * found (no events are dropped if the channel is not yet in
+                * use).
+                */
+               discarded_events = 0;
+               cds_lfht_for_each_entry_duplicate(ht->ht,
+                               ht->hash_fct(&id, lttng_ht_seed),
+                               ht->match_fct, &id,
+                               &iter.iter, stream, node_session_id.node) {
+                       if (stream->chan->key == key) {
+                               discarded_events = stream->chan->discarded_events;
+                               break;
+                       }
+               }
+               pthread_mutex_unlock(&consumer_data.lock);
+               rcu_read_unlock();
 
-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();
+               DBG("UST consumer discarded events command for session id %"
+                               PRIu64 ", channel key %" PRIu64, id, key);
 
-       health_code_update();
+               health_code_update();
 
-       return 1;
-end_channel_error:
+               /* Send back returned value to session daemon */
+               ret = lttcomm_send_unix_sock(sock, &discarded_events, sizeof(discarded_events));
+               if (ret < 0) {
+                       PERROR("send discarded events");
+                       goto error_fatal;
+               }
+
+               break;
+       }
+       case LTTNG_CONSUMER_LOST_PACKETS:
+       {
+               int ret;
+               uint64_t lost_packets;
+               struct lttng_ht_iter iter;
+               struct lttng_ht *ht;
+               struct lttng_consumer_stream *stream;
+               uint64_t id = msg.u.lost_packets.session_id;
+               uint64_t key = msg.u.lost_packets.channel_key;
+
+               DBG("UST consumer lost packets command for session id %"
+                               PRIu64, id);
+               rcu_read_lock();
+               pthread_mutex_lock(&consumer_data.lock);
+
+               ht = consumer_data.stream_list_ht;
+
+               /*
+                * We only need a reference to the channel, but they are not
+                * directly indexed, so we just use the first matching stream
+                * to extract the information we need, we default to 0 if not
+                * found (no packets lost if the channel is not yet in use).
+                */
+               lost_packets = 0;
+               cds_lfht_for_each_entry_duplicate(ht->ht,
+                               ht->hash_fct(&id, lttng_ht_seed),
+                               ht->match_fct, &id,
+                               &iter.iter, stream, node_session_id.node) {
+                       if (stream->chan->key == key) {
+                               lost_packets = stream->chan->lost_packets;
+                               break;
+                       }
+               }
+               pthread_mutex_unlock(&consumer_data.lock);
+               rcu_read_unlock();
+
+               DBG("UST consumer lost packets command for session id %"
+                               PRIu64 ", channel key %" PRIu64, id, key);
+
+               health_code_update();
+
+               /* Send back returned value to session daemon */
+               ret = lttcomm_send_unix_sock(sock, &lost_packets,
+                               sizeof(lost_packets));
+               if (ret < 0) {
+                       PERROR("send lost packets");
+                       goto error_fatal;
+               }
+
+               break;
+       }
+       case LTTNG_CONSUMER_SET_CHANNEL_MONITOR_PIPE:
+       {
+               int channel_monitor_pipe;
+
+               ret_code = LTTCOMM_CONSUMERD_SUCCESS;
+               /* Successfully received the command's type. */
+               ret = consumer_send_status_msg(sock, ret_code);
+               if (ret < 0) {
+                       goto error_fatal;
+               }
+
+               ret = lttcomm_recv_fds_unix_sock(sock, &channel_monitor_pipe,
+                               1);
+               if (ret != sizeof(channel_monitor_pipe)) {
+                       ERR("Failed to receive channel monitor pipe");
+                       goto error_fatal;
+               }
+
+               DBG("Received channel monitor pipe (%d)", channel_monitor_pipe);
+               ret = consumer_timer_thread_set_channel_monitor_pipe(
+                               channel_monitor_pipe);
+               if (!ret) {
+                       int flags;
+
+                       ret_code = LTTCOMM_CONSUMERD_SUCCESS;
+                       /* Set the pipe as non-blocking. */
+                       ret = fcntl(channel_monitor_pipe, F_GETFL, 0);
+                       if (ret == -1) {
+                               PERROR("fcntl get flags of the channel monitoring pipe");
+                               goto error_fatal;
+                       }
+                       flags = ret;
+
+                       ret = fcntl(channel_monitor_pipe, F_SETFL,
+                                       flags | O_NONBLOCK);
+                       if (ret == -1) {
+                               PERROR("fcntl set O_NONBLOCK flag of the channel monitoring pipe");
+                               goto error_fatal;
+                       }
+                       DBG("Channel monitor pipe set as non-blocking");
+               } else {
+                       ret_code = LTTCOMM_CONSUMERD_ALREADY_SET;
+               }
+               goto end_msg_sessiond;
+       }
+       case LTTNG_CONSUMER_ROTATE_CHANNEL:
+       {
+               struct lttng_consumer_channel *channel;
+               uint64_t key = msg.u.rotate_channel.key;
+
+               channel = consumer_find_channel(key);
+               if (!channel) {
+                       DBG("Channel %" PRIu64 " not found", key);
+                       ret_code = LTTCOMM_CONSUMERD_CHAN_NOT_FOUND;
+               } else {
+                       /*
+                        * Sample the rotate position of all the streams in
+                        * this channel.
+                        */
+                       ret = lttng_consumer_rotate_channel(channel, key,
+                                       msg.u.rotate_channel.relayd_id,
+                                       msg.u.rotate_channel.metadata,
+                                       ctx);
+                       if (ret < 0) {
+                               ERR("Rotate channel failed");
+                               ret_code = LTTCOMM_CONSUMERD_ROTATION_FAIL;
+                       }
+
+                       health_code_update();
+               }
+               ret = consumer_send_status_msg(sock, ret_code);
+               if (ret < 0) {
+                       /* Somehow, the session daemon is not responding anymore. */
+                       goto end_rotate_channel_nosignal;
+               }
+
+               /*
+                * Rotate the streams that are ready right now.
+                * FIXME: this is a second consecutive iteration over the
+                * streams in a channel, there is probably a better way to
+                * handle this, but it needs to be after the
+                * consumer_send_status_msg() call.
+                */
+               if (channel) {
+                       ret = lttng_consumer_rotate_ready_streams(
+                                       channel, key, ctx);
+                       if (ret < 0) {
+                               ERR("Rotate channel failed");
+                       }
+               }
+               break;
+end_rotate_channel_nosignal:
+               goto end_nosignal;
+       }
+       case LTTNG_CONSUMER_CLEAR_CHANNEL:
+       {
+               struct lttng_consumer_channel *channel;
+               uint64_t key = msg.u.clear_channel.key;
+
+               channel = consumer_find_channel(key);
+               if (!channel) {
+                       DBG("Channel %" PRIu64 " not found", key);
+                       ret_code = LTTCOMM_CONSUMERD_CHAN_NOT_FOUND;
+               } else {
+                       ret = lttng_consumer_clear_channel(channel);
+                       if (ret) {
+                               ERR("Clear channel failed key %" PRIu64, key);
+                               ret_code = ret;
+                       }
+
+                       health_code_update();
+               }
+               ret = consumer_send_status_msg(sock, ret_code);
+               if (ret < 0) {
+                       /* Somehow, the session daemon is not responding anymore. */
+                       goto end_nosignal;
+               }
+               break;
+       }
+       case LTTNG_CONSUMER_INIT:
+       {
+               ret_code = lttng_consumer_init_command(ctx,
+                               msg.u.init.sessiond_uuid);
+               health_code_update();
+               ret = consumer_send_status_msg(sock, ret_code);
+               if (ret < 0) {
+                       /* Somehow, the session daemon is not responding anymore. */
+                       goto end_nosignal;
+               }
+               break;
+       }
+       case LTTNG_CONSUMER_CREATE_TRACE_CHUNK:
+       {
+               const struct lttng_credentials credentials = {
+                       .uid = LTTNG_OPTIONAL_INIT_VALUE(msg.u.create_trace_chunk.credentials.value.uid),
+                       .gid = LTTNG_OPTIONAL_INIT_VALUE(msg.u.create_trace_chunk.credentials.value.gid),
+               };
+               const bool is_local_trace =
+                               !msg.u.create_trace_chunk.relayd_id.is_set;
+               const uint64_t relayd_id =
+                               msg.u.create_trace_chunk.relayd_id.value;
+               const char *chunk_override_name =
+                               *msg.u.create_trace_chunk.override_name ?
+                                       msg.u.create_trace_chunk.override_name :
+                                       NULL;
+               struct lttng_directory_handle *chunk_directory_handle = NULL;
+
+               /*
+                * The session daemon will only provide a chunk directory file
+                * descriptor for local traces.
+                */
+               if (is_local_trace) {
+                       int chunk_dirfd;
+
+                       /* Acnowledge the reception of the command. */
+                       ret = consumer_send_status_msg(sock,
+                                       LTTCOMM_CONSUMERD_SUCCESS);
+                       if (ret < 0) {
+                               /* Somehow, the session daemon is not responding anymore. */
+                               goto end_nosignal;
+                       }
+
+                       /*
+                        * Receive trace chunk domain dirfd.
+                        */
+                       ret = lttcomm_recv_fds_unix_sock(sock, &chunk_dirfd, 1);
+                       if (ret != sizeof(chunk_dirfd)) {
+                               ERR("Failed to receive trace chunk domain directory file descriptor");
+                               goto error_fatal;
+                       }
+
+                       DBG("Received trace chunk domain directory fd (%d)",
+                                       chunk_dirfd);
+                       chunk_directory_handle = lttng_directory_handle_create_from_dirfd(
+                                       chunk_dirfd);
+                       if (!chunk_directory_handle) {
+                               ERR("Failed to initialize chunk domain directory handle from directory file descriptor");
+                               if (close(chunk_dirfd)) {
+                                       PERROR("Failed to close chunk directory file descriptor");
+                               }
+                               goto error_fatal;
+                       }
+               }
+
+               ret_code = lttng_consumer_create_trace_chunk(
+                               !is_local_trace ? &relayd_id : NULL,
+                               msg.u.create_trace_chunk.session_id,
+                               msg.u.create_trace_chunk.chunk_id,
+                               (time_t) msg.u.create_trace_chunk
+                                               .creation_timestamp,
+                               chunk_override_name,
+                               msg.u.create_trace_chunk.credentials.is_set ?
+                                               &credentials :
+                                               NULL,
+                               chunk_directory_handle);
+               lttng_directory_handle_put(chunk_directory_handle);
+               goto end_msg_sessiond;
+       }
+       case LTTNG_CONSUMER_CLOSE_TRACE_CHUNK:
+       {
+               enum lttng_trace_chunk_command_type close_command =
+                               msg.u.close_trace_chunk.close_command.value;
+               const uint64_t relayd_id =
+                               msg.u.close_trace_chunk.relayd_id.value;
+               struct lttcomm_consumer_close_trace_chunk_reply reply;
+               char closed_trace_chunk_path[LTTNG_PATH_MAX];
+               int ret;
+
+               ret_code = lttng_consumer_close_trace_chunk(
+                               msg.u.close_trace_chunk.relayd_id.is_set ?
+                                               &relayd_id :
+                                               NULL,
+                               msg.u.close_trace_chunk.session_id,
+                               msg.u.close_trace_chunk.chunk_id,
+                               (time_t) msg.u.close_trace_chunk.close_timestamp,
+                               msg.u.close_trace_chunk.close_command.is_set ?
+                                               &close_command :
+                                               NULL, closed_trace_chunk_path);
+               reply.ret_code = ret_code;
+               reply.path_length = strlen(closed_trace_chunk_path) + 1;
+               ret = lttcomm_send_unix_sock(sock, &reply, sizeof(reply));
+               if (ret != sizeof(reply)) {
+                       goto error_fatal;
+               }
+               ret = lttcomm_send_unix_sock(sock, closed_trace_chunk_path,
+                               reply.path_length);
+               if (ret != reply.path_length) {
+                       goto error_fatal;
+               }
+               goto end_nosignal;
+       }
+       case LTTNG_CONSUMER_TRACE_CHUNK_EXISTS:
+       {
+               const uint64_t relayd_id =
+                               msg.u.trace_chunk_exists.relayd_id.value;
+
+               ret_code = lttng_consumer_trace_chunk_exists(
+                               msg.u.trace_chunk_exists.relayd_id.is_set ?
+                                               &relayd_id : NULL,
+                               msg.u.trace_chunk_exists.session_id,
+                               msg.u.trace_chunk_exists.chunk_id);
+               goto end_msg_sessiond;
+       }
+       case LTTNG_CONSUMER_OPEN_CHANNEL_PACKETS:
+       {
+               const uint64_t key = msg.u.open_channel_packets.key;
+               struct lttng_consumer_channel *channel =
+                               consumer_find_channel(key);
+
+               if (channel) {
+                       pthread_mutex_lock(&channel->lock);
+                       ret_code = lttng_consumer_open_channel_packets(channel);
+                       pthread_mutex_unlock(&channel->lock);
+               } else {
+                       /*
+                        * The channel could have disappeared in per-pid
+                        * buffering mode.
+                        */
+                       DBG("Channel %" PRIu64 " not found", key);
+                       ret_code = LTTCOMM_CONSUMERD_CHAN_NOT_FOUND;
+               }
+
+               health_code_update();
+               goto end_msg_sessiond;
+       }
+       default:
+               break;
+       }
+
+end_nosignal:
+       /*
+        * Return 1 to indicate success since the 0 value can be a socket
+        * shutdown during the recv() or send() call.
+        */
+       ret = 1;
+       goto end;
+
+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;
+       }
+       ret = 1;
+       goto end;
+
+end_channel_error:
        if (channel) {
                /*
                 * Free channel here since no one has a reference to it. We don't
@@ -1552,53 +2206,54 @@ end_channel_error:
                /* Stop everything if session daemon can not be notified. */
                goto error_fatal;
        }
-       rcu_read_unlock();
-
-       health_code_update();
+       ret = 1;
+       goto end;
 
-       return 1;
 error_fatal:
-       rcu_read_unlock();
        /* This will issue a consumer stop. */
-       return -1;
+       ret = -1;
+       goto end;
+
+end:
+       rcu_read_unlock();
+       health_code_update();
+       return ret;
 }
 
-/*
- * 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)
+void lttng_ustctl_flush_buffer(struct lttng_consumer_stream *stream,
+               int producer_active)
 {
        assert(stream);
        assert(stream->ustream);
 
-       return ustctl_get_mmap_read_offset(stream->ustream, off);
+       ustctl_flush_buffer(stream->ustream, producer_active);
 }
 
 /*
- * Wrapper over the mmap() read offset from ust-ctl library. Since this can be
- * compiled out, we isolate it in this library.
+ * Take a snapshot for a specific stream.
+ *
+ * Returns 0 on success, < 0 on error
  */
-void *lttng_ustctl_get_mmap_base(struct lttng_consumer_stream *stream)
+int lttng_ustconsumer_take_snapshot(struct lttng_consumer_stream *stream)
 {
        assert(stream);
        assert(stream->ustream);
 
-       return ustctl_get_mmap_base(stream->ustream);
+       return ustctl_snapshot(stream->ustream);
 }
 
 /*
- * Take a snapshot for a specific fd
+ * Sample consumed and produced positions for a specific stream.
  *
- * Returns 0 on success, < 0 on error
+ * Returns 0 on success, < 0 on error.
  */
-int lttng_ustconsumer_take_snapshot(struct lttng_consumer_stream *stream)
+int lttng_ustconsumer_sample_snapshot_positions(
+               struct lttng_consumer_stream *stream)
 {
        assert(stream);
        assert(stream->ustream);
 
-       return ustctl_snapshot(stream->ustream);
+       return ustctl_snapshot_sample_positions(stream->ustream);
 }
 
 /*
@@ -1640,6 +2295,14 @@ void lttng_ustconsumer_flush_buffer(struct lttng_consumer_stream *stream,
        ustctl_flush_buffer(stream->ustream, producer);
 }
 
+void lttng_ustconsumer_clear_buffer(struct lttng_consumer_stream *stream)
+{
+       assert(stream);
+       assert(stream->ustream);
+
+       ustctl_clear_buffer(stream->ustream);
+}
+
 int lttng_ustconsumer_get_current_timestamp(
                struct lttng_consumer_stream *stream, uint64_t *ts)
 {
@@ -1650,28 +2313,88 @@ int lttng_ustconsumer_get_current_timestamp(
        return ustctl_get_current_timestamp(stream->ustream, ts);
 }
 
+int lttng_ustconsumer_get_sequence_number(
+               struct lttng_consumer_stream *stream, uint64_t *seq)
+{
+       assert(stream);
+       assert(stream->ustream);
+       assert(seq);
+
+       return ustctl_get_sequence_number(stream->ustream, seq);
+}
+
 /*
- * Called when the stream signal the consumer that it has hang up.
+ * Called when the stream signals the consumer that it has hung up.
  */
 void lttng_ustconsumer_on_stream_hangup(struct lttng_consumer_stream *stream)
 {
        assert(stream);
        assert(stream->ustream);
 
-       ustctl_flush_buffer(stream->ustream, 0);
+       pthread_mutex_lock(&stream->lock);
+       if (!stream->quiescent) {
+               ustctl_flush_buffer(stream->ustream, 0);
+               stream->quiescent = true;
+       }
+       pthread_mutex_unlock(&stream->lock);
        stream->hangup_flush_done = 1;
 }
 
 void lttng_ustconsumer_del_channel(struct lttng_consumer_channel *chan)
 {
+       int i;
+
        assert(chan);
        assert(chan->uchan);
+       assert(chan->buffer_credentials.is_set);
 
        if (chan->switch_timer_enabled == 1) {
                consumer_timer_switch_stop(chan);
        }
+       for (i = 0; i < chan->nr_stream_fds; i++) {
+               int ret;
+
+               ret = close(chan->stream_fds[i]);
+               if (ret) {
+                       PERROR("close");
+               }
+               if (chan->shm_path[0]) {
+                       char shm_path[PATH_MAX];
+
+                       ret = get_stream_shm_path(shm_path, chan->shm_path, i);
+                       if (ret) {
+                               ERR("Cannot get stream shm path");
+                       }
+                       ret = run_as_unlink(shm_path,
+                                       lttng_credentials_get_uid(LTTNG_OPTIONAL_GET_PTR(
+                                                       chan->buffer_credentials)),
+                                       lttng_credentials_get_gid(LTTNG_OPTIONAL_GET_PTR(
+                                                       chan->buffer_credentials)));
+                       if (ret) {
+                               PERROR("unlink %s", shm_path);
+                       }
+               }
+       }
+}
+
+void lttng_ustconsumer_free_channel(struct lttng_consumer_channel *chan)
+{
+       assert(chan);
+       assert(chan->uchan);
+       assert(chan->buffer_credentials.is_set);
+
        consumer_metadata_cache_destroy(chan);
        ustctl_destroy_channel(chan->uchan);
+       /* Try to rmdir all directories under shm_path root. */
+       if (chan->root_shm_path[0]) {
+               (void) run_as_rmdir_recursive(chan->root_shm_path,
+                               lttng_credentials_get_uid(LTTNG_OPTIONAL_GET_PTR(
+                                               chan->buffer_credentials)),
+                               lttng_credentials_get_gid(LTTNG_OPTIONAL_GET_PTR(
+                                               chan->buffer_credentials)),
+                               LTTNG_DIRECTORY_HANDLE_SKIP_NON_EMPTY_FLAG);
+       }
+       free(chan->stream_fds);
 }
 
 void lttng_ustconsumer_del_stream(struct lttng_consumer_stream *stream)
@@ -1701,67 +2424,20 @@ int lttng_ustconsumer_close_wakeup_fd(struct lttng_consumer_stream *stream)
        return ustctl_stream_close_wakeup_fd(stream->ustream);
 }
 
-/*
- * Populate index values of a UST stream. Values are set in big endian order.
- *
- * Return 0 on success or else a negative value.
- */
-static int get_index_values(struct ctf_packet_index *index,
-               struct ustctl_consumer_stream *ustream)
+static
+void metadata_stream_reset_cache_consumed_position(
+               struct lttng_consumer_stream *stream)
 {
-       int ret;
-
-       ret = ustctl_get_timestamp_begin(ustream, &index->timestamp_begin);
-       if (ret < 0) {
-               PERROR("ustctl_get_timestamp_begin");
-               goto error;
-       }
-       index->timestamp_begin = htobe64(index->timestamp_begin);
-
-       ret = ustctl_get_timestamp_end(ustream, &index->timestamp_end);
-       if (ret < 0) {
-               PERROR("ustctl_get_timestamp_end");
-               goto error;
-       }
-       index->timestamp_end = htobe64(index->timestamp_end);
-
-       ret = ustctl_get_events_discarded(ustream, &index->events_discarded);
-       if (ret < 0) {
-               PERROR("ustctl_get_events_discarded");
-               goto error;
-       }
-       index->events_discarded = htobe64(index->events_discarded);
-
-       ret = ustctl_get_content_size(ustream, &index->content_size);
-       if (ret < 0) {
-               PERROR("ustctl_get_content_size");
-               goto error;
-       }
-       index->content_size = htobe64(index->content_size);
-
-       ret = ustctl_get_packet_size(ustream, &index->packet_size);
-       if (ret < 0) {
-               PERROR("ustctl_get_packet_size");
-               goto error;
-       }
-       index->packet_size = htobe64(index->packet_size);
-
-       ret = ustctl_get_stream_id(ustream, &index->stream_id);
-       if (ret < 0) {
-               PERROR("ustctl_get_stream_id");
-               goto error;
-       }
-       index->stream_id = htobe64(index->stream_id);
-
-error:
-       return ret;
+       DBG("Reset metadata cache of session %" PRIu64,
+                       stream->chan->session_id);
+       stream->ust_metadata_pushed = 0;
 }
 
 /*
  * Write up to one packet from the metadata cache to the channel.
  *
- * Returns the number of bytes pushed in the cache, or a negative value
- * on error.
+ * Returns the number of bytes pushed from the cache into the ring buffer, or a
+ * negative value on error.
  */
 static
 int commit_one_metadata_packet(struct lttng_consumer_stream *stream)
@@ -1770,28 +2446,66 @@ int commit_one_metadata_packet(struct lttng_consumer_stream *stream)
        int ret;
 
        pthread_mutex_lock(&stream->chan->metadata_cache->lock);
-       if (stream->chan->metadata_cache->contiguous
-                       == stream->ust_metadata_pushed) {
-               ret = 0;
-               goto end;
+       if (stream->chan->metadata_cache->max_offset ==
+           stream->ust_metadata_pushed) {
+               /*
+                * In the context of a user space metadata channel, a
+                * change in version can be detected in two ways:
+                *   1) During the pre-consume of the `read_subbuffer` loop,
+                *   2) When populating the metadata ring buffer (i.e. here).
+                *
+                * This function is invoked when there is no metadata
+                * available in the ring-buffer. If all data was consumed
+                * up to the size of the metadata cache, there is no metadata
+                * to insert in the ring-buffer.
+                *
+                * However, the metadata version could still have changed (a
+                * regeneration without any new data will yield the same cache
+                * size).
+                *
+                * The cache's version is checked for a version change and the
+                * consumed position is reset if one occurred.
+                *
+                * This check is only necessary for the user space domain as
+                * it has to manage the cache explicitly. If this reset was not
+                * performed, no metadata would be consumed (and no reset would
+                * occur as part of the pre-consume) until the metadata size
+                * exceeded the cache size.
+                */
+               if (stream->metadata_version !=
+                               stream->chan->metadata_cache->version) {
+                       metadata_stream_reset_cache_consumed_position(stream);
+                       consumer_stream_metadata_set_version(stream,
+                                       stream->chan->metadata_cache->version);
+               } else {
+                       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->chan->metadata_cache->max_offset
                        - stream->ust_metadata_pushed);
        assert(write_len != 0);
        if (write_len < 0) {
                ERR("Writing one metadata packet");
-               ret = -1;
+               ret = write_len;
                goto end;
        }
        stream->ust_metadata_pushed += write_len;
 
-       assert(stream->chan->metadata_cache->contiguous >=
+       assert(stream->chan->metadata_cache->max_offset >=
                        stream->ust_metadata_pushed);
        ret = write_len;
 
+       /*
+        * Switch packet (but don't open the next one) on every commit of
+        * a metadata packet. Since the subbuffer is fully filled (with padding,
+        * if needed), the stream is "quiescent" after this commit.
+        */
+       ustctl_flush_buffer(stream->ustream, 1);
+       stream->quiescent = true;
 end:
        pthread_mutex_unlock(&stream->chan->metadata_cache->lock);
        return ret;
@@ -1802,58 +2516,74 @@ end:
  * Sync metadata meaning request them to the session daemon and snapshot to the
  * metadata thread can consumer them.
  *
- * Metadata stream lock MUST be acquired.
+ * Metadata stream lock is held here, but we need to release it when
+ * interacting with sessiond, else we cause a deadlock with live
+ * awaiting on metadata to be pushed out.
  *
- * Return 0 if new metadatda is available, EAGAIN if the metadata stream
- * is empty or a negative value on error.
+ * The RCU read side lock must be held by the caller.
  */
-int lttng_ustconsumer_sync_metadata(struct lttng_consumer_local_data *ctx,
-               struct lttng_consumer_stream *metadata)
+enum sync_metadata_status lttng_ustconsumer_sync_metadata(
+               struct lttng_consumer_local_data *ctx,
+               struct lttng_consumer_stream *metadata_stream)
 {
        int ret;
-       int retry = 0;
+       enum sync_metadata_status status;
+       struct lttng_consumer_channel *metadata_channel;
 
        assert(ctx);
-       assert(metadata);
+       assert(metadata_stream);
 
+       metadata_channel = metadata_stream->chan;
+       pthread_mutex_unlock(&metadata_stream->lock);
        /*
         * Request metadata from the sessiond, but don't wait for the flush
         * because we locked the metadata thread.
         */
-       ret = lttng_ustconsumer_request_metadata(ctx, metadata->chan, 0, 0);
+       ret = lttng_ustconsumer_request_metadata(ctx, metadata_channel, 0, 0);
+       pthread_mutex_lock(&metadata_stream->lock);
        if (ret < 0) {
+               status = SYNC_METADATA_STATUS_ERROR;
                goto end;
        }
 
-       ret = commit_one_metadata_packet(metadata);
-       if (ret <= 0) {
+       /*
+        * The metadata stream and channel can be deleted while the
+        * metadata stream lock was released. The streamed is checked
+        * for deletion before we use it further.
+        *
+        * Note that it is safe to access a logically-deleted stream since its
+        * existence is still guaranteed by the RCU read side lock. However,
+        * it should no longer be used. The close/deletion of the metadata
+        * channel and stream already guarantees that all metadata has been
+        * consumed. Therefore, there is nothing left to do in this function.
+        */
+       if (consumer_stream_is_deleted(metadata_stream)) {
+               DBG("Metadata stream %" PRIu64 " was deleted during the metadata synchronization",
+                               metadata_stream->key);
+               status = SYNC_METADATA_STATUS_NO_DATA;
                goto end;
-       } else if (ret > 0) {
-               retry = 1;
        }
 
-       ustctl_flush_buffer(metadata->ustream, 1);
-       ret = ustctl_snapshot(metadata->ustream);
+       ret = commit_one_metadata_packet(metadata_stream);
        if (ret < 0) {
-               if (errno != EAGAIN) {
-                       ERR("Sync metadata, taking UST snapshot");
-                       goto end;
-               }
-               DBG("No new metadata when syncing them.");
-               /* No new metadata, exit. */
-               ret = ENODATA;
+               status = SYNC_METADATA_STATUS_ERROR;
+               goto end;
+       } else if (ret > 0) {
+               status = SYNC_METADATA_STATUS_NEW_DATA;
+       } else /* ret == 0 */ {
+               status = SYNC_METADATA_STATUS_NO_DATA;
                goto end;
        }
 
-       /*
-        * After this flush, we still need to extract metadata.
-        */
-       if (retry) {
-               ret = EAGAIN;
+       ret = ustctl_snapshot(metadata_stream->ustream);
+       if (ret < 0) {
+               ERR("Failed to take a snapshot of the metadata ring-buffer positions, ret = %d", ret);
+               status = SYNC_METADATA_STATUS_ERROR;
+               goto end;
        }
 
 end:
-       return ret;
+       return status;
 }
 
 /*
@@ -1907,41 +2637,20 @@ end:
        return ret;
 }
 
-/*
- * Read subbuffer from the given stream.
- *
- * Stream lock MUST be acquired.
- *
- * Return 0 on success else a negative value.
- */
-int lttng_ustconsumer_read_subbuffer(struct lttng_consumer_stream *stream,
-               struct lttng_consumer_local_data *ctx)
+static int consumer_stream_ust_on_wake_up(struct lttng_consumer_stream *stream)
 {
-       unsigned long len, subbuf_size, padding;
-       int err, write_index = 1;
-       long ret = 0;
-       struct ustctl_consumer_stream *ustream;
-       struct ctf_packet_index index;
-
-       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;
+       int ret = 0;
 
        /*
-        * We can consume the 1 byte written into the wait_fd by UST. Don't trigger
-        * error if we cannot read this one byte (read returns 0), or if the error
-        * is EAGAIN or EWOULDBLOCK.
+        * We can consume the 1 byte written into the wait_fd by
+        * UST. Don't trigger error if we cannot read this one byte
+        * (read returns 0), or if the error is EAGAIN or EWOULDBLOCK.
         *
-        * This is only done when the stream is monitored by a thread, before the
-        * flush is done after a hangup and if the stream is not flagged with data
-        * since there might be nothing to consume in the wait fd but still have
-        * data available flagged by the consumer wake up pipe.
+        * This is only done when the stream is monitored by a thread,
+        * before the flush is done after a hangup and if the stream
+        * is not flagged with data since there might be nothing to
+        * consume in the wait fd but still have data available
+        * flagged by the consumer wake up pipe.
         */
        if (stream->monitor && !stream->hangup_flush_done && !stream->has_data) {
                char dummy;
@@ -1950,118 +2659,309 @@ int lttng_ustconsumer_read_subbuffer(struct lttng_consumer_stream *stream,
                readlen = lttng_read(stream->wait_fd, &dummy, 1);
                if (readlen < 0 && 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) {
-                       ret = commit_one_metadata_packet(stream);
-                       if (ret <= 0) {
-                               goto end;
-                       }
-                       ustctl_flush_buffer(stream->ustream, 1);
-                       goto retry;
-               }
+       return ret;
+}
 
-               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);
+static int extract_common_subbuffer_info(struct lttng_consumer_stream *stream,
+               struct stream_subbuffer *subbuf)
+{
+       int ret;
+
+       ret = ustctl_get_subbuf_size(
+                       stream->ustream, &subbuf->info.data.subbuf_size);
+       if (ret) {
                goto end;
        }
-       assert(stream->chan->output == CONSUMER_CHANNEL_MMAP);
 
-       if (!stream->metadata_flag) {
-               index.offset = htobe64(stream->out_fd_offset);
-               ret = get_index_values(&index, ustream);
-               if (ret < 0) {
+       ret = ustctl_get_padded_subbuf_size(
+                       stream->ustream, &subbuf->info.data.padded_subbuf_size);
+       if (ret) {
+               goto end;
+       }
+
+end:
+       return ret;
+}
+
+static int extract_metadata_subbuffer_info(struct lttng_consumer_stream *stream,
+               struct stream_subbuffer *subbuf)
+{
+       int ret;
+
+       ret = extract_common_subbuffer_info(stream, subbuf);
+       if (ret) {
+               goto end;
+       }
+
+       subbuf->info.metadata.version = stream->metadata_version;
+
+end:
+       return ret;
+}
+
+static int extract_data_subbuffer_info(struct lttng_consumer_stream *stream,
+               struct stream_subbuffer *subbuf)
+{
+       int ret;
+
+       ret = extract_common_subbuffer_info(stream, subbuf);
+       if (ret) {
+               goto end;
+       }
+
+       ret = ustctl_get_packet_size(
+                       stream->ustream, &subbuf->info.data.packet_size);
+       if (ret < 0) {
+               PERROR("Failed to get sub-buffer packet size");
+               goto end;
+       }
+
+       ret = ustctl_get_content_size(
+                       stream->ustream, &subbuf->info.data.content_size);
+       if (ret < 0) {
+               PERROR("Failed to get sub-buffer content size");
+               goto end;
+       }
+
+       ret = ustctl_get_timestamp_begin(
+                       stream->ustream, &subbuf->info.data.timestamp_begin);
+       if (ret < 0) {
+               PERROR("Failed to get sub-buffer begin timestamp");
+               goto end;
+       }
+
+       ret = ustctl_get_timestamp_end(
+                       stream->ustream, &subbuf->info.data.timestamp_end);
+       if (ret < 0) {
+               PERROR("Failed to get sub-buffer end timestamp");
+               goto end;
+       }
+
+       ret = ustctl_get_events_discarded(
+                       stream->ustream, &subbuf->info.data.events_discarded);
+       if (ret) {
+               PERROR("Failed to get sub-buffer events discarded count");
+               goto end;
+       }
+
+       ret = ustctl_get_sequence_number(stream->ustream,
+                       &subbuf->info.data.sequence_number.value);
+       if (ret) {
+               /* May not be supported by older LTTng-modules. */
+               if (ret != -ENOTTY) {
+                       PERROR("Failed to get sub-buffer sequence number");
                        goto end;
                }
        } else {
-               write_index = 0;
+               subbuf->info.data.sequence_number.is_set = true;
        }
 
-       /* Get the full padded subbuffer size */
-       err = ustctl_get_padded_subbuf_size(ustream, &len);
-       assert(err == 0);
+       ret = ustctl_get_stream_id(
+                       stream->ustream, &subbuf->info.data.stream_id);
+       if (ret < 0) {
+               PERROR("Failed to get stream id");
+               goto end;
+       }
 
-       /* Get subbuffer data size (without padding) */
-       err = ustctl_get_subbuf_size(ustream, &subbuf_size);
-       assert(err == 0);
+       ret = ustctl_get_instance_id(stream->ustream,
+                       &subbuf->info.data.stream_instance_id.value);
+       if (ret) {
+               /* May not be supported by older LTTng-modules. */
+               if (ret != -ENOTTY) {
+                       PERROR("Failed to get stream instance id");
+                       goto end;
+               }
+       } else {
+               subbuf->info.data.stream_instance_id.is_set = true;
+       }
+end:
+       return ret;
+}
 
-       /* Make sure we don't get a subbuffer size bigger than the padded */
-       assert(len >= subbuf_size);
+static int get_next_subbuffer_common(struct lttng_consumer_stream *stream,
+               struct stream_subbuffer *subbuffer)
+{
+       int ret;
+       const char *addr;
 
-       padding = len - subbuf_size;
-       /* write the subbuffer to the tracefile */
-       ret = lttng_consumer_on_read_subbuffer_mmap(ctx, stream, subbuf_size, padding, &index);
-       /*
-        * 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);
-               write_index = 0;
+       ret = stream->read_subbuffer_ops.extract_subbuffer_info(
+                       stream, subbuffer);
+       if (ret) {
+               goto end;
        }
-       err = ustctl_put_next_subbuf(ustream);
-       assert(err == 0);
 
-       /*
-        * This will consumer the byte on the wait_fd if and only if there is not
-        * next subbuffer to be acquired.
-        */
-       if (!stream->metadata_flag) {
-               ret = notify_if_more_data(stream, ctx);
-               if (ret < 0) {
-                       goto end;
-               }
+       ret = get_current_subbuf_addr(stream, &addr);
+       if (ret) {
+               goto end;
        }
 
-       /* Write index if needed. */
-       if (!write_index) {
+       subbuffer->buffer.buffer = lttng_buffer_view_init(
+                       addr, 0, subbuffer->info.data.padded_subbuf_size);
+       assert(subbuffer->buffer.buffer.data != NULL);
+end:
+       return ret;
+}
+
+static int get_next_subbuffer(struct lttng_consumer_stream *stream,
+               struct stream_subbuffer *subbuffer)
+{
+       int ret;
+
+       ret = ustctl_get_next_subbuf(stream->ustream);
+       if (ret) {
                goto end;
        }
 
-       if (stream->chan->live_timer_interval && !stream->metadata_flag) {
+       ret = get_next_subbuffer_common(stream, subbuffer);
+       if (ret) {
+               goto end;
+       }
+end:
+       return ret;
+}
+
+static int get_next_subbuffer_metadata(struct lttng_consumer_stream *stream,
+               struct stream_subbuffer *subbuffer)
+{
+       int ret;
+       bool cache_empty;
+       bool got_subbuffer;
+       bool coherent;
+       bool buffer_empty;
+       unsigned long consumed_pos, produced_pos;
+
+       do {
+               ret = ustctl_get_next_subbuf(stream->ustream);
+               if (ret == 0) {
+                       got_subbuffer = true;
+               } else {
+                       got_subbuffer = false;
+                       if (ret != -EAGAIN) {
+                               /* Fatal error. */
+                               goto end;
+                       }
+               }
+
                /*
-                * In live, block until all the metadata is sent.
+                * Determine if the cache is empty and ensure that a sub-buffer
+                * is made available if the cache is not empty.
                 */
-               err = consumer_stream_sync_metadata(ctx, stream->session_id);
-               if (err < 0) {
-                       goto end;
+               if (!got_subbuffer) {
+                       ret = commit_one_metadata_packet(stream);
+                       if (ret < 0 && ret != -ENOBUFS) {
+                               goto end;
+                       } else if (ret == 0) {
+                               /* Not an error, the cache is empty. */
+                               cache_empty = true;
+                               ret = -ENODATA;
+                               goto end;
+                       } else {
+                               cache_empty = false;
+                       }
+               } else {
+                       pthread_mutex_lock(&stream->chan->metadata_cache->lock);
+                       cache_empty = stream->chan->metadata_cache->max_offset ==
+                                     stream->ust_metadata_pushed;
+                       pthread_mutex_unlock(&stream->chan->metadata_cache->lock);
                }
+       } while (!got_subbuffer);
+
+       /* Populate sub-buffer infos and view. */
+       ret = get_next_subbuffer_common(stream, subbuffer);
+       if (ret) {
+               goto end;
+       }
+
+       ret = lttng_ustconsumer_sample_snapshot_positions(stream);
+       if (ret < 0) {
+               /*
+                * -EAGAIN is not expected since we got a sub-buffer and haven't
+                * pushed the consumption position yet (on put_next).
+                */
+               PERROR("Failed to take a snapshot of metadata buffer positions");
+               goto end;
        }
 
-       assert(!stream->metadata_flag);
-       err = consumer_stream_write_index(stream, &index);
-       if (err < 0) {
+       ret = lttng_ustconsumer_get_consumed_snapshot(stream, &consumed_pos);
+       if (ret) {
+               PERROR("Failed to get metadata consumed position");
+               goto end;
+       }
+
+       ret = lttng_ustconsumer_get_produced_snapshot(stream, &produced_pos);
+       if (ret) {
+               PERROR("Failed to get metadata produced position");
                goto end;
        }
 
+       /* Last sub-buffer of the ring buffer ? */
+       buffer_empty = (consumed_pos + stream->max_sb_size) == produced_pos;
+
+       /*
+        * The sessiond registry lock ensures that coherent units of metadata
+        * are pushed to the consumer daemon at once. Hence, if a sub-buffer is
+        * acquired, the cache is empty, and it is the only available sub-buffer
+        * available, it is safe to assume that it is "coherent".
+        */
+       coherent = got_subbuffer && cache_empty && buffer_empty;
+
+       LTTNG_OPTIONAL_SET(&subbuffer->info.metadata.coherent, coherent);
+end:
+       return ret;
+}
+
+static int put_next_subbuffer(struct lttng_consumer_stream *stream,
+               struct stream_subbuffer *subbuffer)
+{
+       const int ret = ustctl_put_next_subbuf(stream->ustream);
+
+       assert(ret == 0);
+       return ret;
+}
+
+static int signal_metadata(struct lttng_consumer_stream *stream,
+               struct lttng_consumer_local_data *ctx)
+{
+       return pthread_cond_broadcast(&stream->metadata_rdv) ? -errno : 0;
+}
+
+static int lttng_ustconsumer_set_stream_ops(
+               struct lttng_consumer_stream *stream)
+{
+       int ret = 0;
+
+       stream->read_subbuffer_ops.on_wake_up = consumer_stream_ust_on_wake_up;
+       if (stream->metadata_flag) {
+               stream->read_subbuffer_ops.get_next_subbuffer =
+                               get_next_subbuffer_metadata;
+               stream->read_subbuffer_ops.extract_subbuffer_info =
+                               extract_metadata_subbuffer_info;
+               stream->read_subbuffer_ops.reset_metadata =
+                               metadata_stream_reset_cache_consumed_position;
+               if (stream->chan->is_live) {
+                       stream->read_subbuffer_ops.on_sleep = signal_metadata;
+                       ret = consumer_stream_enable_metadata_bucketization(
+                                       stream);
+                       if (ret) {
+                               goto end;
+                       }
+               }
+       } else {
+               stream->read_subbuffer_ops.get_next_subbuffer =
+                               get_next_subbuffer;
+               stream->read_subbuffer_ops.extract_subbuffer_info =
+                               extract_data_subbuffer_info;
+               stream->read_subbuffer_ops.on_sleep = notify_if_more_data;
+               if (stream->chan->is_live) {
+                       stream->read_subbuffer_ops.send_live_beacon =
+                                       consumer_flush_ust_index;
+               }
+       }
+
+       stream->read_subbuffer_ops.put_next_subbuffer = put_next_subbuffer;
 end:
        return ret;
 }
@@ -2077,28 +2977,19 @@ int lttng_ustconsumer_on_recv_stream(struct lttng_consumer_stream *stream)
 
        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, NULL);
-               if (ret < 0) {
+       /*
+        * Don't create anything if this is set for streaming or if there is
+        * no current trace chunk on the parent channel.
+        */
+       if (stream->net_seq_idx == (uint64_t) -1ULL && stream->chan->monitor &&
+                       stream->chan->trace_chunk) {
+               ret = consumer_stream_create_output_files(stream, true);
+               if (ret) {
                        goto error;
                }
-               stream->out_fd = ret;
-               stream->tracefile_size_current = 0;
-
-               if (!stream->metadata_flag) {
-                       ret = index_create_file(stream->chan->pathname,
-                                       stream->name, stream->uid, stream->gid,
-                                       stream->chan->tracefile_size,
-                                       stream->tracefile_count_current);
-                       if (ret < 0) {
-                               goto error;
-                       }
-                       stream->index_fd = ret;
-               }
        }
+
+       lttng_ustconsumer_set_stream_ops(stream);
        ret = 0;
 
 error:
@@ -2131,7 +3022,7 @@ int lttng_ustconsumer_data_pending(struct lttng_consumer_stream *stream)
                uint64_t contiguous, pushed;
 
                /* Ease our life a bit. */
-               contiguous = stream->chan->metadata_cache->contiguous;
+               contiguous = stream->chan->metadata_cache->max_offset;
                pushed = stream->ust_metadata_pushed;
 
                /*
@@ -2177,7 +3068,7 @@ end:
  * Stop a given metadata channel timer if enabled and close the wait fd which
  * is the poll pipe of the metadata stream.
  *
- * This MUST be called with the metadata channel acquired.
+ * This MUST be called with the metadata channel lock acquired.
  */
 void lttng_ustconsumer_close_metadata(struct lttng_consumer_channel *metadata)
 {
@@ -2260,6 +3151,10 @@ void lttng_ustconsumer_close_stream_wakeup(struct lttng_consumer_stream *stream)
  * function or any of its callees. Timers have a very strict locking
  * semantic with respect to teardown. Failure to respect this semantic
  * introduces deadlocks.
+ *
+ * DON'T hold the metadata lock when calling this function, else this
+ * can cause deadlock involving consumer awaiting for metadata to be
+ * pushed out due to concurrent interaction with the session daemon.
  */
 int lttng_ustconsumer_request_metadata(struct lttng_consumer_local_data *ctx,
                struct lttng_consumer_channel *channel, int timer, int wait)
@@ -2267,7 +3162,7 @@ int lttng_ustconsumer_request_metadata(struct lttng_consumer_local_data *ctx,
        struct lttcomm_metadata_request_msg request;
        struct lttcomm_consumer_msg msg;
        enum lttcomm_return_code ret_code = LTTCOMM_CONSUMERD_SUCCESS;
-       uint64_t len, key, offset;
+       uint64_t len, key, offset, version;
        int ret;
 
        assert(channel);
@@ -2299,7 +3194,7 @@ int lttng_ustconsumer_request_metadata(struct lttng_consumer_local_data *ctx,
        request.key = channel->key;
 
        DBG("Sending metadata request to sessiond, session id %" PRIu64
-                       ", per-pid %" PRIu64 ", app UID %u and channek key %" PRIu64,
+                       ", per-pid %" PRIu64 ", app UID %u and channel key %" PRIu64,
                        request.session_id, request.session_id_per_pid, request.uid,
                        request.key);
 
@@ -2347,6 +3242,7 @@ int lttng_ustconsumer_request_metadata(struct lttng_consumer_local_data *ctx,
        len = msg.u.push_metadata.len;
        key = msg.u.push_metadata.key;
        offset = msg.u.push_metadata.target_offset;
+       version = msg.u.push_metadata.version;
 
        assert(key == channel->key);
        if (len == 0) {
@@ -2369,7 +3265,7 @@ int lttng_ustconsumer_request_metadata(struct lttng_consumer_local_data *ctx,
        health_code_update();
 
        ret = lttng_ustconsumer_recv_metadata(ctx->consumer_metadata_socket,
-                       key, offset, len, channel, timer, wait);
+                       key, offset, len, version, channel, timer, wait);
        if (ret >= 0) {
                /*
                 * Only send the status msg if the sessiond is alive meaning a positive
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