Set event exclusions in the target when event is created
[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c
index 225d3f86a81a3837b4acbf9ed23c5d3cf01a9416..d8adccde214925f2f9cd68d20ef65dadc3617951 100644 (file)
@@ -17,6 +17,7 @@
 
 #define _GNU_SOURCE
 #include <errno.h>
+#include <inttypes.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <urcu/compiler.h>
 #include <lttng/ust-error.h>
+#include <signal.h>
 
 #include <common/common.h>
 #include <common/sessiond-comm/sessiond-comm.h>
 
+#include "buffer-registry.h"
 #include "fd-limit.h"
-#include "health.h"
+#include "health-sessiond.h"
 #include "ust-app.h"
 #include "ust-consumer.h"
 #include "ust-ctl.h"
+#include "utils.h"
 
-/* Next available channel key. */
-static unsigned long next_channel_key;
+/* Next available channel key. Access under next_channel_key_lock. */
+static uint64_t _next_channel_key;
+static pthread_mutex_t next_channel_key_lock = PTHREAD_MUTEX_INITIALIZER;
+
+/* Next available session ID. Access under next_session_id_lock. */
+static uint64_t _next_session_id;
+static pthread_mutex_t next_session_id_lock = PTHREAD_MUTEX_INITIALIZER;
 
 /*
- * Return the atomically incremented value of next_channel_key.
+ * Return the incremented value of next_channel_key.
  */
-static inline unsigned long get_next_channel_key(void)
+static uint64_t get_next_channel_key(void)
 {
-       return uatomic_add_return(&next_channel_key, 1);
+       uint64_t ret;
+
+       pthread_mutex_lock(&next_channel_key_lock);
+       ret = ++_next_channel_key;
+       pthread_mutex_unlock(&next_channel_key_lock);
+       return ret;
 }
 
 /*
- * Return the consumer socket from the given consumer output with the right
- * bitness. On error, returns NULL.
- *
- * The caller MUST acquire a rcu read side lock and keep it until the socket
- * object reference is not needed anymore.
+ * Return the atomically incremented value of next_session_id.
  */
-static struct consumer_socket *find_consumer_socket_by_bitness(int bits,
-               struct consumer_output *consumer)
+static uint64_t get_next_session_id(void)
 {
-       int consumer_fd;
-       struct consumer_socket *socket = NULL;
-
-       switch (bits) {
-       case 64:
-               consumer_fd = uatomic_read(&ust_consumerd64_fd);
-               break;
-       case 32:
-               consumer_fd = uatomic_read(&ust_consumerd32_fd);
-               break;
-       default:
-               assert(0);
-               goto end;
-       }
+       uint64_t ret;
 
-       socket = consumer_find_socket(consumer_fd, consumer);
-       if (!socket) {
-               ERR("Consumer socket fd %d not found in consumer obj %p",
-                               consumer_fd, consumer);
-       }
+       pthread_mutex_lock(&next_session_id_lock);
+       ret = ++_next_session_id;
+       pthread_mutex_unlock(&next_session_id_lock);
+       return ret;
+}
 
-end:
-       return socket;
+static void copy_channel_attr_to_ustctl(
+               struct ustctl_consumer_channel_attr *attr,
+               struct lttng_ust_channel_attr *uattr)
+{
+       /* Copy event attributes since the layout is different. */
+       attr->subbuf_size = uattr->subbuf_size;
+       attr->num_subbuf = uattr->num_subbuf;
+       attr->overwrite = uattr->overwrite;
+       attr->switch_timer_interval = uattr->switch_timer_interval;
+       attr->read_timer_interval = uattr->read_timer_interval;
+       attr->output = uattr->output;
 }
 
 /*
@@ -99,7 +104,7 @@ static int ht_match_ust_app_event(struct cds_lfht_node *node, const void *_key)
        event = caa_container_of(node, struct ust_app_event, node.node);
        key = _key;
 
-       /* Match the 3 elements of the key: name, filter and loglevel. */
+       /* Match the 4 elements of the key: name, filter, loglevel, exclusions */
 
        /* Event name */
        if (strncmp(event->attr.name, key->name, sizeof(event->attr.name)) != 0) {
@@ -135,6 +140,21 @@ static int ht_match_ust_app_event(struct cds_lfht_node *node, const void *_key)
                }
        }
 
+       /* One of the exclusions is NULL, fail. */
+       if ((key->exclusion && !event->exclusion) || (!key->exclusion && event->exclusion)) {
+               goto no_match;
+       }
+
+       if (key->exclusion && event->exclusion) {
+               /* Both exclusions exists, check count followed by the names. */
+               if (event->exclusion->count != key->exclusion->count ||
+                               memcmp(event->exclusion->names, key->exclusion->names,
+                                       event->exclusion->count * LTTNG_UST_SYM_NAME_LEN) != 0) {
+                       goto no_match;
+               }
+       }
+
+
        /* Match. */
        return 1;
 
@@ -161,6 +181,7 @@ static void add_unique_ust_app_event(struct ust_app_channel *ua_chan,
        key.name = event->attr.name;
        key.filter = event->filter;
        key.loglevel = event->attr.loglevel;
+       key.exclusion = event->exclusion;
 
        node_ptr = cds_lfht_add_unique(ht->ht,
                        ht->hash_fct(event->node.key, lttng_ht_seed),
@@ -190,6 +211,48 @@ static void close_notify_sock_rcu(struct rcu_head *head)
        free(obj);
 }
 
+/*
+ * Return the session registry according to the buffer type of the given
+ * session.
+ *
+ * A registry per UID object MUST exists before calling this function or else
+ * it assert() if not found. RCU read side lock must be acquired.
+ */
+static struct ust_registry_session *get_session_registry(
+               struct ust_app_session *ua_sess)
+{
+       struct ust_registry_session *registry = NULL;
+
+       assert(ua_sess);
+
+       switch (ua_sess->buffer_type) {
+       case LTTNG_BUFFER_PER_PID:
+       {
+               struct buffer_reg_pid *reg_pid = buffer_reg_pid_find(ua_sess->id);
+               if (!reg_pid) {
+                       goto error;
+               }
+               registry = reg_pid->registry->reg.ust;
+               break;
+       }
+       case LTTNG_BUFFER_PER_UID:
+       {
+               struct buffer_reg_uid *reg_uid = buffer_reg_uid_find(
+                               ua_sess->tracing_id, ua_sess->bits_per_long, ua_sess->uid);
+               if (!reg_uid) {
+                       goto error;
+               }
+               registry = reg_uid->registry->reg.ust;
+               break;
+       }
+       default:
+               assert(0);
+       };
+
+error:
+       return registry;
+}
+
 /*
  * Delete ust context safely. RCU read lock must be held before calling
  * this function.
@@ -224,7 +287,8 @@ void delete_ust_app_event(int sock, struct ust_app_event *ua_event)
        assert(ua_event);
 
        free(ua_event->filter);
-
+       if (ua_event->exclusion != NULL)
+               free(ua_event->exclusion);
        if (ua_event->obj != NULL) {
                ret = ustctl_release_object(sock, ua_event->obj);
                if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
@@ -237,13 +301,13 @@ void delete_ust_app_event(int sock, struct ust_app_event *ua_event)
 }
 
 /*
- * Delete ust app stream safely. RCU read lock must be held before calling
- * this function.
+ * Release ust data object of the given stream.
+ *
+ * Return 0 on success or else a negative value.
  */
-static
-void delete_ust_app_stream(int sock, struct ust_app_stream *stream)
+static int release_ust_app_stream(int sock, struct ust_app_stream *stream)
 {
-       int ret;
+       int ret = 0;
 
        assert(stream);
 
@@ -256,9 +320,40 @@ void delete_ust_app_stream(int sock, struct ust_app_stream *stream)
                lttng_fd_put(LTTNG_FD_APPS, 2);
                free(stream->obj);
        }
+
+       return ret;
+}
+
+/*
+ * Delete ust app stream safely. RCU read lock must be held before calling
+ * this function.
+ */
+static
+void delete_ust_app_stream(int sock, struct ust_app_stream *stream)
+{
+       assert(stream);
+
+       (void) release_ust_app_stream(sock, stream);
        free(stream);
 }
 
+/*
+ * We need to execute ht_destroy outside of RCU read-side critical
+ * section and outside of call_rcu thread, so we postpone its execution
+ * using ht_cleanup_push. It is simpler than to change the semantic of
+ * the many callers of delete_ust_app_session().
+ */
+static
+void delete_ust_app_channel_rcu(struct rcu_head *head)
+{
+       struct ust_app_channel *ua_chan =
+               caa_container_of(head, struct ust_app_channel, rcu_head);
+
+       ht_cleanup_push(ua_chan->ctx);
+       ht_cleanup_push(ua_chan->events);
+       free(ua_chan);
+}
+
 /*
  * Delete ust app channel safely. RCU read lock must be held before calling
  * this function.
@@ -272,6 +367,7 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan,
        struct ust_app_event *ua_event;
        struct ust_app_ctx *ua_ctx;
        struct ust_app_stream *stream, *stmp;
+       struct ust_registry_session *registry;
 
        assert(ua_chan);
 
@@ -285,11 +381,11 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan,
 
        /* Wipe context */
        cds_lfht_for_each_entry(ua_chan->ctx->ht, &iter.iter, ua_ctx, node.node) {
+               cds_list_del(&ua_ctx->list);
                ret = lttng_ht_del(ua_chan->ctx, &iter);
                assert(!ret);
                delete_ust_app_ctx(sock, ua_ctx);
        }
-       lttng_ht_destroy(ua_chan->ctx);
 
        /* Wipe events */
        cds_lfht_for_each_entry(ua_chan->events->ht, &iter.iter, ua_event,
@@ -298,10 +394,14 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan,
                assert(!ret);
                delete_ust_app_event(sock, ua_event);
        }
-       lttng_ht_destroy(ua_chan->events);
 
-       /* Wipe and free registry. */
-       ust_registry_channel_destroy(&ua_chan->session->registry, &ua_chan->registry);
+       if (ua_chan->session->buffer_type == LTTNG_BUFFER_PER_PID) {
+               /* Wipe and free registry from session registry. */
+               registry = get_session_registry(ua_chan->session);
+               if (registry) {
+                       ust_registry_channel_del_free(registry, ua_chan->key);
+               }
+       }
 
        if (ua_chan->obj != NULL) {
                /* Remove channel from application UST object descriptor. */
@@ -312,41 +412,125 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan,
                        ERR("UST app sock %d release channel obj failed with ret %d",
                                        sock, ret);
                }
-               lttng_fd_put(LTTNG_FD_APPS, 2);
+               lttng_fd_put(LTTNG_FD_APPS, 1);
                free(ua_chan->obj);
        }
-       free(ua_chan);
+       call_rcu(&ua_chan->rcu_head, delete_ust_app_channel_rcu);
 }
 
 /*
- * For a given application and session, push metadata to consumer. The session
- * lock MUST be acquired here before calling this.
+ * Push metadata to consumer socket.
  *
- * Return 0 on success else a negative error.
+ * The socket lock MUST be acquired.
+ * The ust app session lock MUST be acquired.
+ *
+ * On success, return the len of metadata pushed or else a negative value.
  */
-static int push_metadata(struct ust_app *app, struct ust_app_session *ua_sess)
+ssize_t ust_app_push_metadata(struct ust_registry_session *registry,
+               struct consumer_socket *socket, int send_zero_data)
 {
        int ret;
        char *metadata_str = NULL;
        size_t len, offset;
-       struct consumer_socket *socket;
+       ssize_t ret_val;
 
-       assert(app);
-       assert(ua_sess);
+       assert(registry);
+       assert(socket);
 
-       if (!ua_sess->consumer || !ua_sess->metadata) {
-               /* No consumer means no stream associated so just return gracefully. */
-               ret = 0;
+       /*
+        * On a push metadata error either the consumer is dead or the metadata
+        * channel has been destroyed because its endpoint might have died (e.g:
+        * relayd). If so, the metadata closed flag is set to 1 so we deny pushing
+        * metadata again which is not valid anymore on the consumer side.
+        *
+        * The ust app session mutex locked allows us to make this check without
+        * the registry lock.
+        */
+       if (registry->metadata_closed) {
+               return -EPIPE;
+       }
+
+       pthread_mutex_lock(&registry->lock);
+
+       offset = registry->metadata_len_sent;
+       len = registry->metadata_len - registry->metadata_len_sent;
+       if (len == 0) {
+               DBG3("No metadata to push for metadata key %" PRIu64,
+                               registry->metadata_key);
+               ret_val = len;
+               if (send_zero_data) {
+                       DBG("No metadata to push");
+                       goto push_data;
+               }
                goto end;
        }
 
+       /* Allocate only what we have to send. */
+       metadata_str = zmalloc(len);
+       if (!metadata_str) {
+               PERROR("zmalloc ust app metadata string");
+               ret_val = -ENOMEM;
+               goto error;
+       }
+       /* Copy what we haven't send out. */
+       memcpy(metadata_str, registry->metadata + offset, len);
+       registry->metadata_len_sent += len;
+
+push_data:
+       pthread_mutex_unlock(&registry->lock);
+       ret = consumer_push_metadata(socket, registry->metadata_key,
+                       metadata_str, len, offset);
+       if (ret < 0) {
+               ret_val = ret;
+               goto error_push;
+       }
+
+       free(metadata_str);
+       return len;
+
+end:
+error:
+       pthread_mutex_unlock(&registry->lock);
+error_push:
+       free(metadata_str);
+       return ret_val;
+}
+
+/*
+ * For a given application and session, push metadata to consumer. The session
+ * lock MUST be acquired here before calling this.
+ * Either sock or consumer is required : if sock is NULL, the default
+ * socket to send the metadata is retrieved from consumer, if sock
+ * is not NULL we use it to send the metadata.
+ *
+ * Return 0 on success else a negative error.
+ */
+static int push_metadata(struct ust_registry_session *registry,
+               struct consumer_output *consumer)
+{
+       int ret_val;
+       ssize_t ret;
+       struct consumer_socket *socket;
+
+       assert(registry);
+       assert(consumer);
+
        rcu_read_lock();
 
+       /*
+        * Means that no metadata was assigned to the session. This can happens if
+        * no start has been done previously.
+        */
+       if (!registry->metadata_key) {
+               ret_val = 0;
+               goto end_rcu_unlock;
+       }
+
        /* Get consumer socket to use to push the metadata.*/
-       socket = find_consumer_socket_by_bitness(app->bits_per_long,
-                       ua_sess->consumer);
+       socket = consumer_find_socket_by_bitness(registry->bits_per_long,
+                       consumer);
        if (!socket) {
-               ret = -1;
+               ret_val = -1;
                goto error_rcu_unlock;
        }
 
@@ -361,54 +545,26 @@ static int push_metadata(struct ust_app *app, struct ust_app_session *ua_sess)
         * ability to reorder the metadata it receives.
         */
        pthread_mutex_lock(socket->lock);
-       pthread_mutex_lock(&ua_sess->registry.lock);
-
-       offset = ua_sess->registry.metadata_len_sent;
-       len = ua_sess->registry.metadata_len - ua_sess->registry.metadata_len_sent;
-       if (len == 0) {
-               DBG3("No metadata to push for session id %d", ua_sess->id);
-               ret = 0;
-               goto error_reg_unlock;
-       }
-       assert(len > 0);
-
-       /* Allocate only what we have to send. */
-       metadata_str = zmalloc(len);
-       if (!metadata_str) {
-               PERROR("zmalloc ust app metadata string");
-               ret = -ENOMEM;
-               goto error_reg_unlock;
-       }
-       /* Copy what we haven't send out. */
-       memcpy(metadata_str, ua_sess->registry.metadata + offset, len);
-
-       pthread_mutex_unlock(&ua_sess->registry.lock);
-
-       ret = ust_consumer_push_metadata(socket, ua_sess, metadata_str, len,
-                       offset);
+       ret = ust_app_push_metadata(registry, socket, 0);
+       pthread_mutex_unlock(socket->lock);
        if (ret < 0) {
-               pthread_mutex_unlock(socket->lock);
+               ret_val = ret;
                goto error_rcu_unlock;
        }
 
-       /* Update len sent of the registry. */
-       pthread_mutex_lock(&ua_sess->registry.lock);
-       ua_sess->registry.metadata_len_sent += len;
-       pthread_mutex_unlock(&ua_sess->registry.lock);
-       pthread_mutex_unlock(socket->lock);
-
        rcu_read_unlock();
-       free(metadata_str);
        return 0;
 
-error_reg_unlock:
-       pthread_mutex_unlock(&ua_sess->registry.lock);
-       pthread_mutex_unlock(socket->lock);
 error_rcu_unlock:
+       /*
+        * On error, flag the registry that the metadata is closed. We were unable
+        * to push anything and this means that either the consumer is not
+        * responding or the metadata cache has been destroyed on the consumer.
+        */
+       registry->metadata_closed = 1;
+end_rcu_unlock:
        rcu_read_unlock();
-       free(metadata_str);
-end:
-       return ret;
+       return ret_val;
 }
 
 /*
@@ -419,45 +575,63 @@ end:
  *
  * Return 0 on success else a negative value.
  */
-static int close_metadata(struct ust_app *app, struct ust_app_session *ua_sess)
+static int close_metadata(struct ust_registry_session *registry,
+               struct consumer_output *consumer)
 {
        int ret;
        struct consumer_socket *socket;
 
-       assert(app);
-       assert(ua_sess);
+       assert(registry);
+       assert(consumer);
 
-       /* Ignore if no metadata. Valid since it can be called on unregister. */
-       if (!ua_sess->metadata) {
+       rcu_read_lock();
+
+       if (!registry->metadata_key || registry->metadata_closed) {
                ret = 0;
-               goto error;
+               goto end;
        }
 
-       rcu_read_lock();
-
        /* Get consumer socket to use to push the metadata.*/
-       socket = find_consumer_socket_by_bitness(app->bits_per_long,
-                       ua_sess->consumer);
+       socket = consumer_find_socket_by_bitness(registry->bits_per_long,
+                       consumer);
        if (!socket) {
                ret = -1;
-               goto error_rcu_unlock;
+               goto error;
        }
 
-       ret = ust_consumer_close_metadata(socket, ua_sess->metadata);
+       ret = consumer_close_metadata(socket, registry->metadata_key);
        if (ret < 0) {
-               goto error_rcu_unlock;
+               goto error;
        }
 
-error_rcu_unlock:
-       /* Destroy metadata on our side since we must not use it anymore. */
-       delete_ust_app_channel(-1, ua_sess->metadata, app);
-       ua_sess->metadata = NULL;
-
-       rcu_read_unlock();
 error:
+       /*
+        * Metadata closed. Even on error this means that the consumer is not
+        * responding or not found so either way a second close should NOT be emit
+        * for this registry.
+        */
+       registry->metadata_closed = 1;
+end:
+       rcu_read_unlock();
        return ret;
 }
 
+/*
+ * We need to execute ht_destroy outside of RCU read-side critical
+ * section and outside of call_rcu thread, so we postpone its execution
+ * using ht_cleanup_push. It is simpler than to change the semantic of
+ * the many callers of delete_ust_app_session().
+ */
+static
+void delete_ust_app_session_rcu(struct rcu_head *head)
+{
+       struct ust_app_session *ua_sess =
+               caa_container_of(head, struct ust_app_session, rcu_head);
+
+       ht_cleanup_push(ua_sess->channels);
+       free(ua_sess);
+}
+
 /*
  * Delete ust app session safely. RCU read lock must be held before calling
  * this function.
@@ -469,15 +643,28 @@ void delete_ust_app_session(int sock, struct ust_app_session *ua_sess,
        int ret;
        struct lttng_ht_iter iter;
        struct ust_app_channel *ua_chan;
+       struct ust_registry_session *registry;
 
        assert(ua_sess);
 
-       if (ua_sess->metadata) {
+       pthread_mutex_lock(&ua_sess->lock);
+
+       registry = get_session_registry(ua_sess);
+       if (registry && !registry->metadata_closed) {
                /* Push metadata for application before freeing the application. */
-               (void) push_metadata(app, ua_sess);
+               (void) push_metadata(registry, ua_sess->consumer);
 
-               /* And ask to close it for this session. */
-               (void) close_metadata(app, ua_sess);
+               /*
+                * Don't ask to close metadata for global per UID buffers. Close
+                * metadata only on destroy trace session in this case. Also, the
+                * previous push metadata could have flag the metadata registry to
+                * close so don't send a close command if closed.
+                */
+               if (ua_sess->buffer_type != LTTNG_BUFFER_PER_UID &&
+                               !registry->metadata_closed) {
+                       /* And ask to close it for this session registry. */
+                       (void) close_metadata(registry, ua_sess->consumer);
+               }
        }
 
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
@@ -486,9 +673,15 @@ void delete_ust_app_session(int sock, struct ust_app_session *ua_sess,
                assert(!ret);
                delete_ust_app_channel(sock, ua_chan, app);
        }
-       lttng_ht_destroy(ua_sess->channels);
 
-       ust_registry_session_destroy(&ua_sess->registry);
+       /* In case of per PID, the registry is kept in the session. */
+       if (ua_sess->buffer_type == LTTNG_BUFFER_PER_PID) {
+               struct buffer_reg_pid *reg_pid = buffer_reg_pid_find(ua_sess->id);
+               if (reg_pid) {
+                       buffer_reg_pid_remove(reg_pid);
+                       buffer_reg_pid_destroy(reg_pid);
+               }
+       }
 
        if (ua_sess->handle != -1) {
                ret = ustctl_release_handle(sock, ua_sess->handle);
@@ -497,12 +690,16 @@ void delete_ust_app_session(int sock, struct ust_app_session *ua_sess,
                                        sock, ret);
                }
        }
-       free(ua_sess);
+       pthread_mutex_unlock(&ua_sess->lock);
+
+       call_rcu(&ua_sess->rcu_head, delete_ust_app_session_rcu);
 }
 
 /*
  * Delete a traceable application structure from the global list. Never call
  * this function outside of a call_rcu call.
+ *
+ * RCU read side lock should _NOT_ be held when calling this function.
  */
 static
 void delete_ust_app(struct ust_app *app)
@@ -510,21 +707,22 @@ void delete_ust_app(struct ust_app *app)
        int ret, sock;
        struct ust_app_session *ua_sess, *tmp_ua_sess;
 
-       rcu_read_lock();
-
        /* Delete ust app sessions info */
        sock = app->sock;
        app->sock = -1;
 
-       lttng_ht_destroy(app->sessions);
-
        /* Wipe sessions */
        cds_list_for_each_entry_safe(ua_sess, tmp_ua_sess, &app->teardown_head,
                        teardown_node) {
                /* Free every object in the session and the session. */
+               rcu_read_lock();
                delete_ust_app_session(sock, ua_sess, app);
+               rcu_read_unlock();
        }
 
+       ht_cleanup_push(app->sessions);
+       ht_cleanup_push(app->ust_objd);
+
        /*
         * Wait until we have deleted the application from the sock hash table
         * before closing this socket, otherwise an application could re-use the
@@ -546,8 +744,6 @@ void delete_ust_app(struct ust_app *app)
 
        DBG2("UST app pid %d deleted", app->pid);
        free(app);
-
-       rcu_read_unlock();
 }
 
 /*
@@ -610,21 +806,9 @@ struct ust_app_session *alloc_ust_app_session(struct ust_app *app)
        ua_sess->handle = -1;
        ua_sess->channels = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
        pthread_mutex_init(&ua_sess->lock, NULL);
-       if (ust_registry_session_init(&ua_sess->registry, app,
-                       app->bits_per_long,
-                       app->uint8_t_alignment,
-                       app->uint16_t_alignment,
-                       app->uint32_t_alignment,
-                       app->uint64_t_alignment,
-                       app->long_alignment,
-                       app->byte_order)) {
-               goto error;
-       }
 
        return ua_sess;
 
-error:
-       free(ua_sess);
 error_free:
        return NULL;
 }
@@ -652,15 +836,14 @@ struct ust_app_channel *alloc_ust_app_channel(char *name,
 
        ua_chan->enabled = 1;
        ua_chan->handle = -1;
+       ua_chan->session = ua_sess;
        ua_chan->key = get_next_channel_key();
        ua_chan->ctx = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        ua_chan->events = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
        lttng_ht_node_init_str(&ua_chan->node, ua_chan->name);
 
        CDS_INIT_LIST_HEAD(&ua_chan->streams.head);
-
-       /* Initialize UST registry. */
-       ust_registry_channel_init(&ua_sess->registry, &ua_chan->registry);
+       CDS_INIT_LIST_HEAD(&ua_chan->ctx_list);
 
        /* Copy attributes */
        if (attr) {
@@ -752,6 +935,8 @@ struct ust_app_ctx *alloc_ust_app_ctx(struct lttng_ust_context *uctx)
                goto error;
        }
 
+       CDS_INIT_LIST_HEAD(&ua_ctx->list);
+
        if (uctx) {
                memcpy(&ua_ctx->ctx, uctx, sizeof(ua_ctx->ctx));
        }
@@ -789,8 +974,7 @@ error:
  * Find an ust_app using the sock and return it. RCU read side lock must be
  * held before calling this helper function.
  */
-static
-struct ust_app *find_app_by_sock(int sock)
+struct ust_app *ust_app_find_by_sock(int sock)
 {
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;
@@ -838,7 +1022,8 @@ error:
  * Return an ust_app_event object or NULL on error.
  */
 static struct ust_app_event *find_ust_app_event(struct lttng_ht *ht,
-               char *name, struct lttng_ust_filter_bytecode *filter, int loglevel)
+               char *name, struct lttng_ust_filter_bytecode *filter, int loglevel,
+               const struct lttng_event_exclusion *exclusion)
 {
        struct lttng_ht_iter iter;
        struct lttng_ht_node_str *node;
@@ -852,6 +1037,8 @@ static struct ust_app_event *find_ust_app_event(struct lttng_ht *ht,
        key.name = name;
        key.filter = filter;
        key.loglevel = loglevel;
+       /* lttng_event_exclusion and lttng_ust_event_exclusion structures are similar */
+       key.exclusion = (struct lttng_ust_event_exclusion *)exclusion;
 
        /* Lookup using the event name as hash and a custom match fct. */
        cds_lfht_lookup(ht->ht, ht->hash_fct((void *) name, lttng_ht_seed),
@@ -887,6 +1074,12 @@ int create_ust_channel_context(struct ust_app_channel *ua_chan,
                        ERR("UST app create channel context failed for app (pid: %d) "
                                        "with ret %d", app->pid, ret);
                } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
                        DBG3("UST app disable event failed. Application is dead.");
                }
                goto error;
@@ -925,6 +1118,12 @@ int set_ust_event_filter(struct ust_app_event *ua_event,
                        ERR("UST app event %s filter failed for app (pid: %d) "
                                        "with ret %d", ua_event->attr.name, app->pid, ret);
                } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
                        DBG3("UST app filter event failed. Application is dead.");
                }
                goto error;
@@ -937,6 +1136,47 @@ error:
        return ret;
 }
 
+/*
+ * Set event exclusions on the tracer.
+ */
+static
+int set_ust_event_exclusion(struct ust_app_event *ua_event,
+               struct ust_app *app)
+{
+       int ret;
+
+       health_code_update();
+
+       if (!ua_event->exclusion || !ua_event->exclusion->count) {
+               ret = 0;
+               goto error;
+       }
+
+       ret = ustctl_set_exclusion(app->sock, ua_event->exclusion,
+                       ua_event->obj);
+       if (ret < 0) {
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app event %s exclusions failed for app (pid: %d) "
+                                       "with ret %d", ua_event->attr.name, app->pid, ret);
+               } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
+                       DBG3("UST app event exclusion failed. Application is dead.");
+               }
+               goto error;
+       }
+
+       DBG2("UST exclusion set successfully for event %s", ua_event->name);
+
+error:
+       health_code_update();
+       return ret;
+}
+
 /*
  * Disable the specified event on to UST tracer for the UST session.
  */
@@ -954,6 +1194,12 @@ static int disable_ust_event(struct ust_app *app,
                                        "and session handle %d with ret %d",
                                        ua_event->attr.name, app->pid, ua_sess->handle, ret);
                } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
                        DBG3("UST app disable event failed. Application is dead.");
                }
                goto error;
@@ -984,6 +1230,12 @@ static int disable_ust_channel(struct ust_app *app,
                                        "and session handle %d with ret %d",
                                        ua_chan->name, app->pid, ua_sess->handle, ret);
                } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
                        DBG3("UST app disable channel failed. Application is dead.");
                }
                goto error;
@@ -1014,6 +1266,12 @@ static int enable_ust_channel(struct ust_app *app,
                                        "and session handle %d with ret %d",
                                        ua_chan->name, app->pid, ua_sess->handle, ret);
                } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
                        DBG3("UST app enable channel failed. Application is dead.");
                }
                goto error;
@@ -1046,6 +1304,12 @@ static int enable_ust_event(struct ust_app *app,
                                        "and session handle %d with ret %d",
                                        ua_event->attr.name, app->pid, ua_sess->handle, ret);
                } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
                        DBG3("UST app enable event failed. Application is dead.");
                }
                goto error;
@@ -1060,69 +1324,24 @@ error:
 }
 
 /*
- * Create the specified channel onto the UST tracer for a UST session. This
- * MUST be called with UST app session lock held.
+ * Send channel and stream buffer to application.
  *
  * Return 0 on success. On error, a negative value is returned.
  */
-static int create_ust_channel(struct ust_app *app,
-               struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan,
-               struct consumer_output *consumer)
+static int send_channel_pid_to_ust(struct ust_app *app,
+               struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan)
 {
        int ret;
-       unsigned int nb_fd = 0;
-       struct consumer_socket *socket;
        struct ust_app_stream *stream, *stmp;
 
        assert(app);
        assert(ua_sess);
        assert(ua_chan);
-       assert(consumer);
-
-       rcu_read_lock();
-       health_code_update();
-
-       /* Get the right consumer socket for the application. */
-       socket = find_consumer_socket_by_bitness(app->bits_per_long, consumer);
-       if (!socket) {
-               ret = -1;
-               goto error;
-       }
-
-       health_code_update();
-
-       /*
-        * Ask consumer to create channel. The consumer will return the number of
-        * stream we have to expect.
-        */
-       ret = ust_consumer_ask_channel(ua_sess, ua_chan, consumer, socket);
-       if (ret < 0) {
-               goto error;
-       }
-
-       /*
-        * Compute the number of fd needed before receiving them. It must be 2 per
-        * stream (2 being the default value here).
-        */
-       nb_fd = DEFAULT_UST_STREAM_FD_NUM * ua_chan->expected_stream_count;
-
-       /* Reserve the amount of file descriptor we need. */
-       ret = lttng_fd_get(LTTNG_FD_APPS, nb_fd);
-       if (ret < 0) {
-               ERR("Exhausted number of available FD upon create channel");
-               goto error_fd_get;
-       }
 
        health_code_update();
 
-       /*
-        * Now get the channel from the consumer. This call wil populate the stream
-        * list of that channel and set the ust object.
-        */
-       ret = ust_consumer_get_channel(socket, ua_chan);
-       if (ret < 0) {
-               goto error_destroy;
-       }
+       DBG("UST app sending channel %s to UST app sock %d", ua_chan->name,
+                       app->sock);
 
        /* Send channel to the application. */
        ret = ust_consumer_send_channel_to_ust(app, ua_sess, ua_chan);
@@ -1142,41 +1361,11 @@ static int create_ust_channel(struct ust_app *app,
                cds_list_del(&stream->list);
                delete_ust_app_stream(-1, stream);
        }
-
        /* Flag the channel that it is sent to the application. */
        ua_chan->is_sent = 1;
-       /* Assign session to channel. */
-       ua_chan->session = ua_sess;
-       /* Initialize ust objd object using the received handle and add it. */
-       lttng_ht_node_init_ulong(&ua_chan->ust_objd_node, ua_chan->handle);
-       lttng_ht_add_unique_ulong(app->ust_objd, &ua_chan->ust_objd_node);
 
-       health_code_update();
-
-       /* If channel is not enabled, disable it on the tracer */
-       if (!ua_chan->enabled) {
-               ret = disable_ust_channel(app, ua_sess, ua_chan);
-               if (ret < 0) {
-                       goto error;
-               }
-       }
-
-       rcu_read_unlock();
-       return 0;
-
-error_destroy:
-       lttng_fd_put(LTTNG_FD_APPS, nb_fd);
-error_fd_get:
-       /*
-        * Initiate a destroy channel on the consumer since we had an error
-        * handling it on our side. The return value is of no importance since we
-        * already have a ret value set by the previous error that we need to
-        * return.
-        */
-       (void) ust_consumer_destroy_channel(socket, ua_chan);
 error:
        health_code_update();
-       rcu_read_unlock();
        return ret;
 }
 
@@ -1201,6 +1390,12 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
                        ERR("Error ustctl create event %s for app pid: %d with ret %d",
                                        ua_event->attr.name, app->pid, ret);
                } else {
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       ret = 0;
                        DBG3("UST app create event failed. Application is dead.");
                }
                goto error;
@@ -1221,6 +1416,14 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
                }
        }
 
+       /* Set exclusions for the event */
+       if (ua_event->exclusion) {
+               ret = set_ust_event_exclusion(ua_event, app);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
+
        /* If event not enabled, disable it on the tracer */
        if (ua_event->enabled == 0) {
                ret = disable_ust_event(app, ua_sess, ua_event);
@@ -1256,6 +1459,8 @@ error:
 static void shadow_copy_event(struct ust_app_event *ua_event,
                struct ltt_ust_event *uevent)
 {
+       size_t exclusion_alloc_size;
+
        strncpy(ua_event->name, uevent->attr.name, sizeof(ua_event->name));
        ua_event->name[sizeof(ua_event->name) - 1] = '\0';
 
@@ -1269,6 +1474,16 @@ static void shadow_copy_event(struct ust_app_event *ua_event,
                ua_event->filter = alloc_copy_ust_app_filter(uevent->filter);
                /* Filter might be NULL here in case of ENONEM. */
        }
+
+       /* Copy exclusion data */
+       if (uevent->exclusion) {
+               exclusion_alloc_size = sizeof(struct lttng_ust_event_exclusion) +
+                               LTTNG_UST_SYM_NAME_LEN * uevent->exclusion->count;
+               ua_event->exclusion = zmalloc(exclusion_alloc_size);
+               if (ua_event->exclusion) {
+                       memcpy(ua_event->exclusion, uevent->exclusion, exclusion_alloc_size);
+               }
+       }
 }
 
 /*
@@ -1288,6 +1503,9 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
        strncpy(ua_chan->name, uchan->name, sizeof(ua_chan->name));
        ua_chan->name[sizeof(ua_chan->name) - 1] = '\0';
 
+       ua_chan->tracefile_size = uchan->tracefile_size;
+       ua_chan->tracefile_count = uchan->tracefile_count;
+
        /* Copy event attributes since the layout is different. */
        ua_chan->attr.subbuf_size = uchan->attr.subbuf_size;
        ua_chan->attr.num_subbuf = uchan->attr.num_subbuf;
@@ -1301,8 +1519,9 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
         */
 
        ua_chan->enabled = uchan->enabled;
+       ua_chan->tracing_channel_id = uchan->id;
 
-       cds_lfht_for_each_entry(uchan->ctx->ht, &iter.iter, uctx, node.node) {
+       cds_list_for_each_entry(uctx, &uchan->ctx_list, list) {
                ua_ctx = alloc_ust_app_ctx(&uctx->ctx);
                if (ua_ctx == NULL) {
                        continue;
@@ -1310,12 +1529,13 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
                lttng_ht_node_init_ulong(&ua_ctx->node,
                                (unsigned long) ua_ctx->ctx.ctx);
                lttng_ht_add_unique_ulong(ua_chan->ctx, &ua_ctx->node);
+               cds_list_add_tail(&ua_ctx->list, &ua_chan->ctx_list);
        }
 
        /* Copy all events from ltt ust channel to ust app channel */
        cds_lfht_for_each_entry(uchan->events->ht, &iter.iter, uevent, node.node) {
                ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
-                               uevent->filter, uevent->attr.loglevel);
+                               uevent->filter, uevent->attr.loglevel, uevent->exclusion);
                if (ua_event == NULL) {
                        DBG2("UST event %s not found on shadow copy channel",
                                        uevent->attr.name);
@@ -1353,20 +1573,39 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
 
        DBG2("Shadow copy of session handle %d", ua_sess->handle);
 
-       ua_sess->id = usess->id;
-       ua_sess->uid = usess->uid;
-       ua_sess->gid = usess->gid;
-
-       ret = snprintf(ua_sess->path, PATH_MAX, "%s-%d-%s/", app->name, app->pid,
-                       datetime);
+       ua_sess->tracing_id = usess->id;
+       ua_sess->id = get_next_session_id();
+       ua_sess->uid = app->uid;
+       ua_sess->gid = app->gid;
+       ua_sess->euid = usess->uid;
+       ua_sess->egid = usess->gid;
+       ua_sess->buffer_type = usess->buffer_type;
+       ua_sess->bits_per_long = app->bits_per_long;
+       /* There is only one consumer object per session possible. */
+       ua_sess->consumer = usess->consumer;
+       ua_sess->output_traces = usess->output_traces;
+       ua_sess->live_timer_interval = usess->live_timer_interval;
+
+       switch (ua_sess->buffer_type) {
+       case LTTNG_BUFFER_PER_PID:
+               ret = snprintf(ua_sess->path, sizeof(ua_sess->path),
+                               DEFAULT_UST_TRACE_PID_PATH "/%s-%d-%s", app->name, app->pid,
+                               datetime);
+               break;
+       case LTTNG_BUFFER_PER_UID:
+               ret = snprintf(ua_sess->path, sizeof(ua_sess->path),
+                               DEFAULT_UST_TRACE_UID_PATH, ua_sess->uid, app->bits_per_long);
+               break;
+       default:
+               assert(0);
+               goto error;
+       }
        if (ret < 0) {
                PERROR("asprintf UST shadow copy session");
-               /* TODO: We cannot return an error from here.. */
                assert(0);
+               goto error;
        }
 
-       /* TODO: support all UST domain */
-
        /* Iterate over all channels in global domain. */
        cds_lfht_for_each_entry(usess->domain_global.channels->ht, &iter.iter,
                        uchan, node.node) {
@@ -1396,6 +1635,9 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
 
                lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
        }
+
+error:
+       return;
 }
 
 /*
@@ -1406,7 +1648,7 @@ void __lookup_session_by_app(struct ltt_ust_session *usess,
                        struct ust_app *app, struct lttng_ht_iter *iter)
 {
        /* Get right UST app session from app */
-       lttng_ht_lookup(app->sessions, (void *)((unsigned long) usess->id), iter);
+       lttng_ht_lookup(app->sessions, &usess->id, iter);
 }
 
 /*
@@ -1417,10 +1659,10 @@ static struct ust_app_session *lookup_session_by_app(
                struct ltt_ust_session *usess, struct ust_app *app)
 {
        struct lttng_ht_iter iter;
-       struct lttng_ht_node_ulong *node;
+       struct lttng_ht_node_u64 *node;
 
        __lookup_session_by_app(usess, app, &iter);
-       node = lttng_ht_iter_get_node_ulong(&iter);
+       node = lttng_ht_iter_get_node_u64(&iter);
        if (node == NULL) {
                goto error;
        }
@@ -1431,6 +1673,119 @@ error:
        return NULL;
 }
 
+/*
+ * Setup buffer registry per PID for the given session and application. If none
+ * is found, a new one is created, added to the global registry and
+ * initialized. If regp is valid, it's set with the newly created object.
+ *
+ * Return 0 on success or else a negative value.
+ */
+static int setup_buffer_reg_pid(struct ust_app_session *ua_sess,
+               struct ust_app *app, struct buffer_reg_pid **regp)
+{
+       int ret = 0;
+       struct buffer_reg_pid *reg_pid;
+
+       assert(ua_sess);
+       assert(app);
+
+       rcu_read_lock();
+
+       reg_pid = buffer_reg_pid_find(ua_sess->id);
+       if (!reg_pid) {
+               /*
+                * This is the create channel path meaning that if there is NO
+                * registry available, we have to create one for this session.
+                */
+               ret = buffer_reg_pid_create(ua_sess->id, &reg_pid);
+               if (ret < 0) {
+                       goto error;
+               }
+               buffer_reg_pid_add(reg_pid);
+       } else {
+               goto end;
+       }
+
+       /* Initialize registry. */
+       ret = ust_registry_session_init(&reg_pid->registry->reg.ust, app,
+                       app->bits_per_long, app->uint8_t_alignment,
+                       app->uint16_t_alignment, app->uint32_t_alignment,
+                       app->uint64_t_alignment, app->long_alignment,
+                       app->byte_order, app->version.major,
+                       app->version.minor);
+       if (ret < 0) {
+               goto error;
+       }
+
+       DBG3("UST app buffer registry per PID created successfully");
+
+end:
+       if (regp) {
+               *regp = reg_pid;
+       }
+error:
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * Setup buffer registry per UID for the given session and application. If none
+ * is found, a new one is created, added to the global registry and
+ * initialized. If regp is valid, it's set with the newly created object.
+ *
+ * Return 0 on success or else a negative value.
+ */
+static int setup_buffer_reg_uid(struct ltt_ust_session *usess,
+               struct ust_app *app, struct buffer_reg_uid **regp)
+{
+       int ret = 0;
+       struct buffer_reg_uid *reg_uid;
+
+       assert(usess);
+       assert(app);
+
+       rcu_read_lock();
+
+       reg_uid = buffer_reg_uid_find(usess->id, app->bits_per_long, app->uid);
+       if (!reg_uid) {
+               /*
+                * This is the create channel path meaning that if there is NO
+                * registry available, we have to create one for this session.
+                */
+               ret = buffer_reg_uid_create(usess->id, app->bits_per_long, app->uid,
+                               LTTNG_DOMAIN_UST, &reg_uid);
+               if (ret < 0) {
+                       goto error;
+               }
+               buffer_reg_uid_add(reg_uid);
+       } else {
+               goto end;
+       }
+
+       /* Initialize registry. */
+       ret = ust_registry_session_init(&reg_uid->registry->reg.ust, NULL,
+                       app->bits_per_long, app->uint8_t_alignment,
+                       app->uint16_t_alignment, app->uint32_t_alignment,
+                       app->uint64_t_alignment, app->long_alignment,
+                       app->byte_order, app->version.major,
+                       app->version.minor);
+       if (ret < 0) {
+               goto error;
+       }
+       /* Add node to teardown list of the session. */
+       cds_list_add(&reg_uid->lnode, &usess->buffer_reg_uid_list);
+
+       DBG3("UST app buffer registry per UID created successfully");
+
+end:
+       if (regp) {
+               *regp = reg_uid;
+       }
+error:
+       rcu_read_unlock();
+       return ret;
+}
+
 /*
  * Create a session on the tracer side for the given app.
  *
@@ -1457,7 +1812,7 @@ static int create_ust_app_session(struct ltt_ust_session *usess,
 
        ua_sess = lookup_session_by_app(usess, app);
        if (ua_sess == NULL) {
-               DBG2("UST app pid: %d session id %d not found, creating it",
+               DBG2("UST app pid: %d session id %" PRIu64 " not found, creating it",
                                app->pid, usess->id);
                ua_sess = alloc_ust_app_session(app);
                if (ua_sess == NULL) {
@@ -1469,6 +1824,27 @@ static int create_ust_app_session(struct ltt_ust_session *usess,
                created = 1;
        }
 
+       switch (usess->buffer_type) {
+       case LTTNG_BUFFER_PER_PID:
+               /* Init local registry. */
+               ret = setup_buffer_reg_pid(ua_sess, app, NULL);
+               if (ret < 0) {
+                       goto error;
+               }
+               break;
+       case LTTNG_BUFFER_PER_UID:
+               /* Look for a global registry. If none exists, create one. */
+               ret = setup_buffer_reg_uid(usess, app, NULL);
+               if (ret < 0) {
+                       goto error;
+               }
+               break;
+       default:
+               assert(0);
+               ret = -EINVAL;
+               goto error;
+       }
+
        health_code_update();
 
        if (ua_sess->handle == -1) {
@@ -1479,6 +1855,13 @@ static int create_ust_app_session(struct ltt_ust_session *usess,
                                                app->pid, ret);
                        } else {
                                DBG("UST app creating session failed. Application is dead");
+                               /*
+                                * This is normal behavior, an application can die during the
+                                * creation process. Don't report an error so the execution can
+                                * continue normally. This will get flagged ENOTCONN and the
+                                * caller will handle it.
+                                */
+                               ret = 0;
                        }
                        delete_ust_app_session(-1, ua_sess, app);
                        if (ret != -ENOMEM) {
@@ -1494,20 +1877,13 @@ static int create_ust_app_session(struct ltt_ust_session *usess,
                ua_sess->handle = ret;
 
                /* Add ust app session to app's HT */
-               lttng_ht_node_init_ulong(&ua_sess->node, (unsigned long) ua_sess->id);
-               lttng_ht_add_unique_ulong(app->sessions, &ua_sess->node);
+               lttng_ht_node_init_u64(&ua_sess->node,
+                               ua_sess->tracing_id);
+               lttng_ht_add_unique_u64(app->sessions, &ua_sess->node);
 
                DBG2("UST app session created successfully with handle %d", ret);
        }
 
-       /*
-        * Assign consumer if not already set. For one application, there is only
-        * one possible consumer has of now.
-        */
-       if (!ua_sess->consumer) {
-               ua_sess->consumer = usess->consumer;
-       }
-
        *ua_sess_ptr = ua_sess;
        if (is_created) {
                *is_created = created;
@@ -1524,7 +1900,7 @@ error:
 /*
  * Create a context for the channel on the tracer.
  *
- * Called with UST app session lock held.
+ * Called with UST app session lock held and a RCU read side lock.
  */
 static
 int create_ust_app_channel_context(struct ust_app_session *ua_sess,
@@ -1554,6 +1930,7 @@ int create_ust_app_channel_context(struct ust_app_session *ua_sess,
 
        lttng_ht_node_init_ulong(&ua_ctx->node, (unsigned long) ua_ctx->ctx.ctx);
        lttng_ht_add_unique_ulong(ua_chan->ctx, &ua_ctx->node);
+       cds_list_add_tail(&ua_ctx->list, &ua_chan->ctx_list);
 
        ret = create_ust_channel_context(ua_chan, ua_ctx, app);
        if (ret < 0) {
@@ -1626,7 +2003,8 @@ error:
 }
 
 /*
- * Lookup ust app channel for session and enable it on the tracer side.
+ * Lookup ust app channel for session and enable it on the tracer side. This
+ * MUST be called with a RCU read side lock acquired.
  */
 static int enable_ust_app_channel(struct ust_app_session *ua_sess,
                struct ltt_ust_channel *uchan, struct ust_app *app)
@@ -1639,8 +2017,8 @@ static int enable_ust_app_channel(struct ust_app_session *ua_sess,
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
        ua_chan_node = lttng_ht_iter_get_node_str(&iter);
        if (ua_chan_node == NULL) {
-               DBG2("Unable to find channel %s in ust session id %u",
-                               uchan->name, ua_sess->id);
+               DBG2("Unable to find channel %s in ust session id %" PRIu64,
+                               uchan->name, ua_sess->tracing_id);
                goto error;
        }
 
@@ -1656,63 +2034,604 @@ error:
 }
 
 /*
- * Create UST app channel and create it on the tracer. Set ua_chanp of the
- * newly created channel if not NULL.
+ * Ask the consumer to create a channel and get it if successful.
  *
- * Called with UST app session lock held.
+ * Return 0 on success or else a negative value.
  */
-static int create_ust_app_channel(struct ust_app_session *ua_sess,
-               struct ltt_ust_channel *uchan, struct ust_app *app,
-               struct consumer_output *consumer, enum lttng_ust_chan_type type,
-               struct ust_app_channel **ua_chanp)
+static int do_consumer_create_channel(struct ltt_ust_session *usess,
+               struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan,
+               int bitness, struct ust_registry_session *registry)
 {
-       int ret = 0;
-       struct lttng_ht_iter iter;
-       struct lttng_ht_node_str *ua_chan_node;
-       struct ust_app_channel *ua_chan;
+       int ret;
+       unsigned int nb_fd = 0;
+       struct consumer_socket *socket;
 
-       /* Lookup channel in the ust app session */
-       lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
-       ua_chan_node = lttng_ht_iter_get_node_str(&iter);
-       if (ua_chan_node != NULL) {
-               ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
-               goto end;
-       }
+       assert(usess);
+       assert(ua_sess);
+       assert(ua_chan);
+       assert(registry);
 
-       ua_chan = alloc_ust_app_channel(uchan->name, ua_sess, &uchan->attr);
-       if (ua_chan == NULL) {
-               /* Only malloc can fail here */
-               ret = -ENOMEM;
+       rcu_read_lock();
+       health_code_update();
+
+       /* Get the right consumer socket for the application. */
+       socket = consumer_find_socket_by_bitness(bitness, usess->consumer);
+       if (!socket) {
+               ret = -EINVAL;
                goto error;
        }
-       shadow_copy_channel(ua_chan, uchan);
 
-       /* Set channel type. */
-       ua_chan->attr.type = type;
+       health_code_update();
 
-       ret = create_ust_channel(app, ua_sess, ua_chan, consumer);
+       /* Need one fd for the channel. */
+       ret = lttng_fd_get(LTTNG_FD_APPS, 1);
        if (ret < 0) {
+               ERR("Exhausted number of available FD upon create channel");
                goto error;
        }
 
-       DBG2("UST app create channel %s for PID %d completed", ua_chan->name,
-                       app->pid);
+       /*
+        * Ask consumer to create channel. The consumer will return the number of
+        * stream we have to expect.
+        */
+       ret = ust_consumer_ask_channel(ua_sess, ua_chan, usess->consumer, socket,
+                       registry);
+       if (ret < 0) {
+               goto error_ask;
+       }
 
-       /* Only add the channel if successful on the tracer side. */
-       lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
+       /*
+        * Compute the number of fd needed before receiving them. It must be 2 per
+        * stream (2 being the default value here).
+        */
+       nb_fd = DEFAULT_UST_STREAM_FD_NUM * ua_chan->expected_stream_count;
 
-end:
-       if (ua_chanp) {
-               *ua_chanp = ua_chan;
+       /* Reserve the amount of file descriptor we need. */
+       ret = lttng_fd_get(LTTNG_FD_APPS, nb_fd);
+       if (ret < 0) {
+               ERR("Exhausted number of available FD upon create channel");
+               goto error_fd_get_stream;
        }
 
-       /* Everything went well. */
-       return 0;
-
-error:
-       delete_ust_app_channel(ua_chan->is_sent ? app->sock : -1, ua_chan, app);
-       return ret;
-}
+       health_code_update();
+
+       /*
+        * Now get the channel from the consumer. This call wil populate the stream
+        * list of that channel and set the ust objects.
+        */
+       if (usess->consumer->enabled) {
+               ret = ust_consumer_get_channel(socket, ua_chan);
+               if (ret < 0) {
+                       goto error_destroy;
+               }
+       }
+
+       rcu_read_unlock();
+       return 0;
+
+error_destroy:
+       lttng_fd_put(LTTNG_FD_APPS, nb_fd);
+error_fd_get_stream:
+       /*
+        * Initiate a destroy channel on the consumer since we had an error
+        * handling it on our side. The return value is of no importance since we
+        * already have a ret value set by the previous error that we need to
+        * return.
+        */
+       (void) ust_consumer_destroy_channel(socket, ua_chan);
+error_ask:
+       lttng_fd_put(LTTNG_FD_APPS, 1);
+error:
+       health_code_update();
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * Duplicate the ust data object of the ust app stream and save it in the
+ * buffer registry stream.
+ *
+ * Return 0 on success or else a negative value.
+ */
+static int duplicate_stream_object(struct buffer_reg_stream *reg_stream,
+               struct ust_app_stream *stream)
+{
+       int ret;
+
+       assert(reg_stream);
+       assert(stream);
+
+       /* Reserve the amount of file descriptor we need. */
+       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
+       if (ret < 0) {
+               ERR("Exhausted number of available FD upon duplicate stream");
+               goto error;
+       }
+
+       /* Duplicate object for stream once the original is in the registry. */
+       ret = ustctl_duplicate_ust_object_data(&stream->obj,
+                       reg_stream->obj.ust);
+       if (ret < 0) {
+               ERR("Duplicate stream obj from %p to %p failed with ret %d",
+                               reg_stream->obj.ust, stream->obj, ret);
+               lttng_fd_put(LTTNG_FD_APPS, 2);
+               goto error;
+       }
+       stream->handle = stream->obj->handle;
+
+error:
+       return ret;
+}
+
+/*
+ * Duplicate the ust data object of the ust app. channel and save it in the
+ * buffer registry channel.
+ *
+ * Return 0 on success or else a negative value.
+ */
+static int duplicate_channel_object(struct buffer_reg_channel *reg_chan,
+               struct ust_app_channel *ua_chan)
+{
+       int ret;
+
+       assert(reg_chan);
+       assert(ua_chan);
+
+       /* Need two fds for the channel. */
+       ret = lttng_fd_get(LTTNG_FD_APPS, 1);
+       if (ret < 0) {
+               ERR("Exhausted number of available FD upon duplicate channel");
+               goto error_fd_get;
+       }
+
+       /* Duplicate object for stream once the original is in the registry. */
+       ret = ustctl_duplicate_ust_object_data(&ua_chan->obj, reg_chan->obj.ust);
+       if (ret < 0) {
+               ERR("Duplicate channel obj from %p to %p failed with ret: %d",
+                               reg_chan->obj.ust, ua_chan->obj, ret);
+               goto error;
+       }
+       ua_chan->handle = ua_chan->obj->handle;
+
+       return 0;
+
+error:
+       lttng_fd_put(LTTNG_FD_APPS, 1);
+error_fd_get:
+       return ret;
+}
+
+/*
+ * For a given channel buffer registry, setup all streams of the given ust
+ * application channel.
+ *
+ * Return 0 on success or else a negative value.
+ */
+static int setup_buffer_reg_streams(struct buffer_reg_channel *reg_chan,
+               struct ust_app_channel *ua_chan)
+{
+       int ret = 0;
+       struct ust_app_stream *stream, *stmp;
+
+       assert(reg_chan);
+       assert(ua_chan);
+
+       DBG2("UST app setup buffer registry stream");
+
+       /* Send all streams to application. */
+       cds_list_for_each_entry_safe(stream, stmp, &ua_chan->streams.head, list) {
+               struct buffer_reg_stream *reg_stream;
+
+               ret = buffer_reg_stream_create(&reg_stream);
+               if (ret < 0) {
+                       goto error;
+               }
+
+               /*
+                * Keep original pointer and nullify it in the stream so the delete
+                * stream call does not release the object.
+                */
+               reg_stream->obj.ust = stream->obj;
+               stream->obj = NULL;
+               buffer_reg_stream_add(reg_stream, reg_chan);
+
+               /* We don't need the streams anymore. */
+               cds_list_del(&stream->list);
+               delete_ust_app_stream(-1, stream);
+       }
+
+error:
+       return ret;
+}
+
+/*
+ * Create a buffer registry channel for the given session registry and
+ * application channel object. If regp pointer is valid, it's set with the
+ * created object. Important, the created object is NOT added to the session
+ * registry hash table.
+ *
+ * Return 0 on success else a negative value.
+ */
+static int create_buffer_reg_channel(struct buffer_reg_session *reg_sess,
+               struct ust_app_channel *ua_chan, struct buffer_reg_channel **regp)
+{
+       int ret;
+       struct buffer_reg_channel *reg_chan = NULL;
+
+       assert(reg_sess);
+       assert(ua_chan);
+
+       DBG2("UST app creating buffer registry channel for %s", ua_chan->name);
+
+       /* Create buffer registry channel. */
+       ret = buffer_reg_channel_create(ua_chan->tracing_channel_id, &reg_chan);
+       if (ret < 0) {
+               goto error_create;
+       }
+       assert(reg_chan);
+       reg_chan->consumer_key = ua_chan->key;
+       reg_chan->subbuf_size = ua_chan->attr.subbuf_size;
+
+       /* Create and add a channel registry to session. */
+       ret = ust_registry_channel_add(reg_sess->reg.ust,
+                       ua_chan->tracing_channel_id);
+       if (ret < 0) {
+               goto error;
+       }
+       buffer_reg_channel_add(reg_sess, reg_chan);
+
+       if (regp) {
+               *regp = reg_chan;
+       }
+
+       return 0;
+
+error:
+       /* Safe because the registry channel object was not added to any HT. */
+       buffer_reg_channel_destroy(reg_chan, LTTNG_DOMAIN_UST);
+error_create:
+       return ret;
+}
+
+/*
+ * Setup buffer registry channel for the given session registry and application
+ * channel object. If regp pointer is valid, it's set with the created object.
+ *
+ * Return 0 on success else a negative value.
+ */
+static int setup_buffer_reg_channel(struct buffer_reg_session *reg_sess,
+               struct ust_app_channel *ua_chan, struct buffer_reg_channel *reg_chan)
+{
+       int ret;
+
+       assert(reg_sess);
+       assert(reg_chan);
+       assert(ua_chan);
+       assert(ua_chan->obj);
+
+       DBG2("UST app setup buffer registry channel for %s", ua_chan->name);
+
+       /* Setup all streams for the registry. */
+       ret = setup_buffer_reg_streams(reg_chan, ua_chan);
+       if (ret < 0) {
+               goto error;
+       }
+
+       reg_chan->obj.ust = ua_chan->obj;
+       ua_chan->obj = NULL;
+
+       return 0;
+
+error:
+       buffer_reg_channel_remove(reg_sess, reg_chan);
+       buffer_reg_channel_destroy(reg_chan, LTTNG_DOMAIN_UST);
+       return ret;
+}
+
+/*
+ * Send buffer registry channel to the application.
+ *
+ * Return 0 on success else a negative value.
+ */
+static int send_channel_uid_to_ust(struct buffer_reg_channel *reg_chan,
+               struct ust_app *app, struct ust_app_session *ua_sess,
+               struct ust_app_channel *ua_chan)
+{
+       int ret;
+       struct buffer_reg_stream *reg_stream;
+
+       assert(reg_chan);
+       assert(app);
+       assert(ua_sess);
+       assert(ua_chan);
+
+       DBG("UST app sending buffer registry channel to ust sock %d", app->sock);
+
+       ret = duplicate_channel_object(reg_chan, ua_chan);
+       if (ret < 0) {
+               goto error;
+       }
+
+       /* Send channel to the application. */
+       ret = ust_consumer_send_channel_to_ust(app, ua_sess, ua_chan);
+       if (ret < 0) {
+               goto error;
+       }
+
+       health_code_update();
+
+       /* Send all streams to application. */
+       pthread_mutex_lock(&reg_chan->stream_list_lock);
+       cds_list_for_each_entry(reg_stream, &reg_chan->streams, lnode) {
+               struct ust_app_stream stream;
+
+               ret = duplicate_stream_object(reg_stream, &stream);
+               if (ret < 0) {
+                       goto error_stream_unlock;
+               }
+
+               ret = ust_consumer_send_stream_to_ust(app, ua_chan, &stream);
+               if (ret < 0) {
+                       (void) release_ust_app_stream(-1, &stream);
+                       goto error_stream_unlock;
+               }
+
+               /*
+                * The return value is not important here. This function will output an
+                * error if needed.
+                */
+               (void) release_ust_app_stream(-1, &stream);
+       }
+       ua_chan->is_sent = 1;
+
+error_stream_unlock:
+       pthread_mutex_unlock(&reg_chan->stream_list_lock);
+error:
+       return ret;
+}
+
+/*
+ * Create and send to the application the created buffers with per UID buffers.
+ *
+ * Return 0 on success else a negative value.
+ */
+static int create_channel_per_uid(struct ust_app *app,
+               struct ltt_ust_session *usess, struct ust_app_session *ua_sess,
+               struct ust_app_channel *ua_chan)
+{
+       int ret;
+       struct buffer_reg_uid *reg_uid;
+       struct buffer_reg_channel *reg_chan;
+
+       assert(app);
+       assert(usess);
+       assert(ua_sess);
+       assert(ua_chan);
+
+       DBG("UST app creating channel %s with per UID buffers", ua_chan->name);
+
+       reg_uid = buffer_reg_uid_find(usess->id, app->bits_per_long, app->uid);
+       /*
+        * The session creation handles the creation of this global registry
+        * object. If none can be find, there is a code flow problem or a
+        * teardown race.
+        */
+       assert(reg_uid);
+
+       reg_chan = buffer_reg_channel_find(ua_chan->tracing_channel_id,
+                       reg_uid);
+       if (!reg_chan) {
+               /* Create the buffer registry channel object. */
+               ret = create_buffer_reg_channel(reg_uid->registry, ua_chan, &reg_chan);
+               if (ret < 0) {
+                       goto error;
+               }
+               assert(reg_chan);
+
+               /*
+                * Create the buffers on the consumer side. This call populates the
+                * ust app channel object with all streams and data object.
+                */
+               ret = do_consumer_create_channel(usess, ua_sess, ua_chan,
+                               app->bits_per_long, reg_uid->registry->reg.ust);
+               if (ret < 0) {
+                       /*
+                        * Let's remove the previously created buffer registry channel so
+                        * it's not visible anymore in the session registry.
+                        */
+                       ust_registry_channel_del_free(reg_uid->registry->reg.ust,
+                                       ua_chan->tracing_channel_id);
+                       buffer_reg_channel_remove(reg_uid->registry, reg_chan);
+                       buffer_reg_channel_destroy(reg_chan, LTTNG_DOMAIN_UST);
+                       goto error;
+               }
+
+               /*
+                * Setup the streams and add it to the session registry.
+                */
+               ret = setup_buffer_reg_channel(reg_uid->registry, ua_chan, reg_chan);
+               if (ret < 0) {
+                       goto error;
+               }
+
+       }
+
+       /* Send buffers to the application. */
+       ret = send_channel_uid_to_ust(reg_chan, app, ua_sess, ua_chan);
+       if (ret < 0) {
+               goto error;
+       }
+
+error:
+       return ret;
+}
+
+/*
+ * Create and send to the application the created buffers with per PID buffers.
+ *
+ * Return 0 on success else a negative value.
+ */
+static int create_channel_per_pid(struct ust_app *app,
+               struct ltt_ust_session *usess, struct ust_app_session *ua_sess,
+               struct ust_app_channel *ua_chan)
+{
+       int ret;
+       struct ust_registry_session *registry;
+
+       assert(app);
+       assert(usess);
+       assert(ua_sess);
+       assert(ua_chan);
+
+       DBG("UST app creating channel %s with per PID buffers", ua_chan->name);
+
+       rcu_read_lock();
+
+       registry = get_session_registry(ua_sess);
+       assert(registry);
+
+       /* Create and add a new channel registry to session. */
+       ret = ust_registry_channel_add(registry, ua_chan->key);
+       if (ret < 0) {
+               goto error;
+       }
+
+       /* Create and get channel on the consumer side. */
+       ret = do_consumer_create_channel(usess, ua_sess, ua_chan,
+                       app->bits_per_long, registry);
+       if (ret < 0) {
+               goto error;
+       }
+
+       ret = send_channel_pid_to_ust(app, ua_sess, ua_chan);
+       if (ret < 0) {
+               goto error;
+       }
+
+error:
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * From an already allocated ust app channel, create the channel buffers if
+ * need and send it to the application. This MUST be called with a RCU read
+ * side lock acquired.
+ *
+ * Return 0 on success or else a negative value.
+ */
+static int do_create_channel(struct ust_app *app,
+               struct ltt_ust_session *usess, struct ust_app_session *ua_sess,
+               struct ust_app_channel *ua_chan)
+{
+       int ret;
+
+       assert(app);
+       assert(usess);
+       assert(ua_sess);
+       assert(ua_chan);
+
+       /* Handle buffer type before sending the channel to the application. */
+       switch (usess->buffer_type) {
+       case LTTNG_BUFFER_PER_UID:
+       {
+               ret = create_channel_per_uid(app, usess, ua_sess, ua_chan);
+               if (ret < 0) {
+                       goto error;
+               }
+               break;
+       }
+       case LTTNG_BUFFER_PER_PID:
+       {
+               ret = create_channel_per_pid(app, usess, ua_sess, ua_chan);
+               if (ret < 0) {
+                       goto error;
+               }
+               break;
+       }
+       default:
+               assert(0);
+               ret = -EINVAL;
+               goto error;
+       }
+
+       /* Initialize ust objd object using the received handle and add it. */
+       lttng_ht_node_init_ulong(&ua_chan->ust_objd_node, ua_chan->handle);
+       lttng_ht_add_unique_ulong(app->ust_objd, &ua_chan->ust_objd_node);
+
+       /* If channel is not enabled, disable it on the tracer */
+       if (!ua_chan->enabled) {
+               ret = disable_ust_channel(app, ua_sess, ua_chan);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
+
+error:
+       return ret;
+}
+
+/*
+ * Create UST app channel and create it on the tracer. Set ua_chanp of the
+ * newly created channel if not NULL.
+ *
+ * Called with UST app session lock and RCU read-side lock held.
+ *
+ * Return 0 on success or else a negative value.
+ */
+static int create_ust_app_channel(struct ust_app_session *ua_sess,
+               struct ltt_ust_channel *uchan, struct ust_app *app,
+               enum lttng_ust_chan_type type, struct ltt_ust_session *usess,
+               struct ust_app_channel **ua_chanp)
+{
+       int ret = 0;
+       struct lttng_ht_iter iter;
+       struct lttng_ht_node_str *ua_chan_node;
+       struct ust_app_channel *ua_chan;
+
+       /* Lookup channel in the ust app session */
+       lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
+       ua_chan_node = lttng_ht_iter_get_node_str(&iter);
+       if (ua_chan_node != NULL) {
+               ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
+               goto end;
+       }
+
+       ua_chan = alloc_ust_app_channel(uchan->name, ua_sess, &uchan->attr);
+       if (ua_chan == NULL) {
+               /* Only malloc can fail here */
+               ret = -ENOMEM;
+               goto error_alloc;
+       }
+       shadow_copy_channel(ua_chan, uchan);
+
+       /* Set channel type. */
+       ua_chan->attr.type = type;
+
+       ret = do_create_channel(app, usess, ua_sess, ua_chan);
+       if (ret < 0) {
+               goto error;
+       }
+
+       DBG2("UST app create channel %s for PID %d completed", ua_chan->name,
+                       app->pid);
+
+       /* Only add the channel if successful on the tracer side. */
+       lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
+
+end:
+       if (ua_chanp) {
+               *ua_chanp = ua_chan;
+       }
+
+       /* Everything went well. */
+       return 0;
+
+error:
+       delete_ust_app_channel(ua_chan->is_sent ? app->sock : -1, ua_chan, app);
+error_alloc:
+       return ret;
+}
 
 /*
  * Create UST app event and create it on the tracer side.
@@ -1729,7 +2648,7 @@ int create_ust_app_event(struct ust_app_session *ua_sess,
 
        /* Get event node */
        ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
-                       uevent->filter, uevent->attr.loglevel);
+                       uevent->filter, uevent->attr.loglevel, uevent->exclusion);
        if (ua_event != NULL) {
                ret = -EEXIST;
                goto end;
@@ -1769,22 +2688,28 @@ error:
 /*
  * Create UST metadata and open it on the tracer side.
  *
- * Called with UST app session lock held.
+ * Called with UST app session lock held and RCU read side lock.
  */
 static int create_ust_app_metadata(struct ust_app_session *ua_sess,
-               struct ust_app *app, struct consumer_output *consumer)
+               struct ust_app *app, struct consumer_output *consumer,
+               struct ustctl_consumer_channel_attr *attr)
 {
        int ret = 0;
        struct ust_app_channel *metadata;
        struct consumer_socket *socket;
+       struct ust_registry_session *registry;
 
        assert(ua_sess);
        assert(app);
        assert(consumer);
 
-       if (ua_sess->metadata) {
-               /* Already exist. Return success. */
-               goto end;
+       registry = get_session_registry(ua_sess);
+       assert(registry);
+
+       /* Metadata already exists for this registry or it was closed previously */
+       if (registry->metadata_key || registry->metadata_closed) {
+               ret = 0;
+               goto error;
        }
 
        /* Allocate UST metadata */
@@ -1795,30 +2720,54 @@ static int create_ust_app_metadata(struct ust_app_session *ua_sess,
                goto error;
        }
 
-       /* Set default attributes for metadata. */
-       metadata->attr.overwrite = DEFAULT_CHANNEL_OVERWRITE;
-       metadata->attr.subbuf_size = default_get_metadata_subbuf_size();
-       metadata->attr.num_subbuf = DEFAULT_METADATA_SUBBUF_NUM;
-       metadata->attr.switch_timer_interval = DEFAULT_UST_CHANNEL_SWITCH_TIMER;
-       metadata->attr.read_timer_interval = DEFAULT_UST_CHANNEL_READ_TIMER;
-       metadata->attr.output = LTTNG_UST_MMAP;
-       metadata->attr.type = LTTNG_UST_CHAN_METADATA;
+       if (!attr) {
+               /* Set default attributes for metadata. */
+               metadata->attr.overwrite = DEFAULT_CHANNEL_OVERWRITE;
+               metadata->attr.subbuf_size = default_get_metadata_subbuf_size();
+               metadata->attr.num_subbuf = DEFAULT_METADATA_SUBBUF_NUM;
+               metadata->attr.switch_timer_interval = DEFAULT_METADATA_SWITCH_TIMER;
+               metadata->attr.read_timer_interval = DEFAULT_METADATA_READ_TIMER;
+               metadata->attr.output = LTTNG_UST_MMAP;
+               metadata->attr.type = LTTNG_UST_CHAN_METADATA;
+       } else {
+               memcpy(&metadata->attr, attr, sizeof(metadata->attr));
+               metadata->attr.output = LTTNG_UST_MMAP;
+               metadata->attr.type = LTTNG_UST_CHAN_METADATA;
+       }
+
+       /* Need one fd for the channel. */
+       ret = lttng_fd_get(LTTNG_FD_APPS, 1);
+       if (ret < 0) {
+               ERR("Exhausted number of available FD upon create metadata");
+               goto error;
+       }
 
        /* Get the right consumer socket for the application. */
-       socket = find_consumer_socket_by_bitness(app->bits_per_long, consumer);
+       socket = consumer_find_socket_by_bitness(app->bits_per_long, consumer);
        if (!socket) {
                ret = -EINVAL;
                goto error_consumer;
        }
 
+       /*
+        * Keep metadata key so we can identify it on the consumer side. Assign it
+        * to the registry *before* we ask the consumer so we avoid the race of the
+        * consumer requesting the metadata and the ask_channel call on our side
+        * did not returned yet.
+        */
+       registry->metadata_key = metadata->key;
+
        /*
         * Ask the metadata channel creation to the consumer. The metadata object
         * will be created by the consumer and kept their. However, the stream is
         * never added or monitored until we do a first push metadata to the
         * consumer.
         */
-       ret = ust_consumer_ask_channel(ua_sess, metadata, consumer, socket);
+       ret = ust_consumer_ask_channel(ua_sess, metadata, consumer, socket,
+                       registry);
        if (ret < 0) {
+               /* Nullify the metadata key so we don't try to close it later on. */
+               registry->metadata_key = 0;
                goto error_consumer;
        }
 
@@ -1828,18 +2777,18 @@ static int create_ust_app_metadata(struct ust_app_session *ua_sess,
         * because after this point, if an error occurs, the only way the stream
         * can be deleted is to be monitored in the consumer.
         */
-       ret = ust_consumer_setup_metadata(socket, metadata);
+       ret = consumer_setup_metadata(socket, metadata->key);
        if (ret < 0) {
+               /* Nullify the metadata key so we don't try to close it later on. */
+               registry->metadata_key = 0;
                goto error_consumer;
        }
 
-       ua_sess->metadata = metadata;
-
-       DBG2("UST metadata created for app pid %d", app->pid);
+       DBG2("UST metadata with key %" PRIu64 " created for app pid %d",
+                       metadata->key, app->pid);
 
-end:
-       return 0;
 error_consumer:
+       lttng_fd_put(LTTNG_FD_APPS, 1);
        delete_ust_app_channel(-1, metadata, app);
 error:
        return ret;
@@ -1924,7 +2873,7 @@ struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
 
        lta->v_major = msg->major;
        lta->v_minor = msg->minor;
-       lta->sessions = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
+       lta->sessions = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        lta->ust_objd = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        lta->notify_sock = -1;
 
@@ -2061,6 +3010,8 @@ void ust_app_unregister(int sock)
        /* Remove sessions so they are not visible during deletion.*/
        cds_lfht_for_each_entry(lta->sessions->ht, &iter.iter, ua_sess,
                        node.node) {
+               struct ust_registry_session *registry;
+
                ret = lttng_ht_del(lta->sessions, &iter);
                if (ret) {
                        /* The session was already removed so scheduled for teardown. */
@@ -2084,8 +3035,23 @@ void ust_app_unregister(int sock)
                 * The close metadata below nullifies the metadata pointer in the
                 * session so the delete session will NOT push/close a second time.
                 */
-               (void) push_metadata(lta, ua_sess);
-               (void) close_metadata(lta, ua_sess);
+               registry = get_session_registry(ua_sess);
+               if (registry && !registry->metadata_closed) {
+                       /* Push metadata for application before freeing the application. */
+                       (void) push_metadata(registry, ua_sess->consumer);
+
+                       /*
+                        * Don't ask to close metadata for global per UID buffers. Close
+                        * metadata only on destroy trace session in this case. Also, the
+                        * previous push metadata could have flag the metadata registry to
+                        * close so don't send a close command if closed.
+                        */
+                       if (ua_sess->buffer_type != LTTNG_BUFFER_PER_UID &&
+                                       !registry->metadata_closed) {
+                               /* And ask to close it for this session registry. */
+                               (void) close_metadata(registry, ua_sess->consumer);
+                       }
+               }
 
                cds_list_add(&ua_sess->teardown_node, &lta->teardown_head);
                pthread_mutex_unlock(&ua_sess->lock);
@@ -2164,6 +3130,12 @@ int ust_app_list_events(struct lttng_event **events)
                                                        app->sock, ret);
                                } else {
                                        DBG3("UST app tp list get failed. Application is dead");
+                                       /*
+                                        * This is normal behavior, an application can die during the
+                                        * creation process. Don't report an error so the execution can
+                                        * continue normally. Continue normal execution.
+                                        */
+                                       break;
                                }
                                goto rcu_error;
                        }
@@ -2258,6 +3230,12 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
                                                        app->sock, ret);
                                } else {
                                        DBG3("UST app tp list field failed. Application is dead");
+                                       /*
+                                        * This is normal behavior, an application can die during the
+                                        * creation process. Don't report an error so the execution can
+                                        * continue normally.
+                                        */
+                                       break;
                                }
                                goto rcu_error;
                        }
@@ -2307,6 +3285,8 @@ error:
 
 /*
  * Free and clean all traceable apps of the global list.
+ *
+ * Should _NOT_ be called with RCU read-side lock held.
  */
 void ust_app_clean_list(void)
 {
@@ -2337,13 +3317,12 @@ void ust_app_clean_list(void)
                ret = lttng_ht_del(ust_app_ht_by_notify_sock, &iter);
                assert(!ret);
        }
+       rcu_read_unlock();
 
        /* Destroy is done only when the ht is empty */
-       lttng_ht_destroy(ust_app_ht);
-       lttng_ht_destroy(ust_app_ht_by_sock);
-       lttng_ht_destroy(ust_app_ht_by_notify_sock);
-
-       rcu_read_unlock();
+       ht_cleanup_push(ust_app_ht);
+       ht_cleanup_push(ust_app_ht_by_sock);
+       ht_cleanup_push(ust_app_ht_by_notify_sock);
 }
 
 /*
@@ -2375,7 +3354,7 @@ int ust_app_disable_channel_glb(struct ltt_ust_session *usess,
                goto error;
        }
 
-       DBG2("UST app disabling channel %s from global domain for session id %d",
+       DBG2("UST app disabling channel %s from global domain for session id %" PRIu64,
                        uchan->name, usess->id);
 
        rcu_read_lock();
@@ -2436,7 +3415,7 @@ int ust_app_enable_channel_glb(struct ltt_ust_session *usess,
                goto error;
        }
 
-       DBG2("UST app enabling channel %s to global domain for session id %d",
+       DBG2("UST app enabling channel %s to global domain for session id %" PRIu64,
                        uchan->name, usess->id);
 
        rcu_read_lock();
@@ -2484,7 +3463,8 @@ int ust_app_disable_event_glb(struct ltt_ust_session *usess,
        struct ust_app_event *ua_event;
 
        DBG("UST app disabling event %s for all apps in channel "
-                       "%s for session id %d", uevent->attr.name, uchan->name, usess->id);
+                       "%s for session id %" PRIu64,
+                       uevent->attr.name, uchan->name, usess->id);
 
        rcu_read_lock();
 
@@ -2507,7 +3487,7 @@ int ust_app_disable_event_glb(struct ltt_ust_session *usess,
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
                ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
                if (ua_chan_node == NULL) {
-                       DBG2("Channel %s not found in session id %d for app pid %d."
+                       DBG2("Channel %s not found in session id %" PRIu64 " for app pid %d."
                                        "Skipping", uchan->name, usess->id, app->pid);
                        continue;
                }
@@ -2550,7 +3530,7 @@ int ust_app_disable_all_event_glb(struct ltt_ust_session *usess,
        struct ust_app_event *ua_event;
 
        DBG("UST app disabling all event for all apps in channel "
-                       "%s for session id %d", uchan->name, usess->id);
+                       "%s for session id %" PRIu64, uchan->name, usess->id);
 
        rcu_read_lock();
 
@@ -2608,7 +3588,7 @@ int ust_app_create_channel_glb(struct ltt_ust_session *usess,
        assert(usess);
        assert(uchan);
 
-       DBG2("UST app adding channel %s to global domain for session id %d",
+       DBG2("UST app adding channel %s to UST domain for session id %" PRIu64,
                        uchan->name, usess->id);
 
        rcu_read_lock();
@@ -2645,9 +3625,17 @@ int ust_app_create_channel_glb(struct ltt_ust_session *usess,
                assert(ua_sess);
 
                pthread_mutex_lock(&ua_sess->lock);
-               /* Create channel onto application. We don't need the chan ref. */
-               ret = create_ust_app_channel(ua_sess, uchan, app, usess->consumer,
-                               LTTNG_UST_CHAN_PER_CPU, NULL);
+               if (!strncmp(uchan->name, DEFAULT_METADATA_NAME,
+                                       sizeof(uchan->name))) {
+                       struct ustctl_consumer_channel_attr attr;
+                       copy_channel_attr_to_ustctl(&attr, &uchan->attr);
+                       ret = create_ust_app_metadata(ua_sess, app, usess->consumer,
+                                       &attr);
+               } else {
+                       /* Create channel onto application. We don't need the chan ref. */
+                       ret = create_ust_app_channel(ua_sess, uchan, app,
+                                       LTTNG_UST_CHAN_PER_CPU, usess, NULL);
+               }
                pthread_mutex_unlock(&ua_sess->lock);
                if (ret < 0) {
                        if (ret == -ENOMEM) {
@@ -2680,7 +3668,7 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;
 
-       DBG("UST app enabling event %s for all apps for session id %d",
+       DBG("UST app enabling event %s for all apps for session id %" PRIu64,
                        uevent->attr.name, usess->id);
 
        /*
@@ -2718,7 +3706,7 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
 
                /* Get event node */
                ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
-                               uevent->filter, uevent->attr.loglevel);
+                               uevent->filter, uevent->attr.loglevel, uevent->exclusion);
                if (ua_event == NULL) {
                        DBG3("UST app enable event %s not found for app PID %d."
                                        "Skipping app", uevent->attr.name, app->pid);
@@ -2753,7 +3741,7 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
 
-       DBG("UST app creating event %s for all apps for session id %d",
+       DBG("UST app creating event %s for all apps for session id %" PRIu64,
                        uevent->attr.name, usess->id);
 
        rcu_read_lock();
@@ -2803,6 +3791,7 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
 /*
  * Start tracing for a specific UST session and app.
  */
+static
 int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
 {
        int ret = 0;
@@ -2833,7 +3822,7 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
        if (usess->consumer->type == CONSUMER_DST_LOCAL &&
                        strlen(usess->consumer->dst.trace_path) > 0) {
                ret = run_as_mkdir_recursive(usess->consumer->dst.trace_path,
-                               S_IRWXU | S_IRWXG, usess->uid, usess->gid);
+                               S_IRWXU | S_IRWXG, ua_sess->euid, ua_sess->egid);
                if (ret < 0) {
                        if (ret != -EEXIST) {
                                ERR("Trace directory creation error");
@@ -2842,8 +3831,11 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                }
        }
 
-       /* Create the metadata for the application. */
-       ret = create_ust_app_metadata(ua_sess, app, usess->consumer);
+       /*
+        * Create the metadata for the application. This returns gracefully if a
+        * metadata was already set for the session.
+        */
+       ret = create_ust_app_metadata(ua_sess, app, usess->consumer, NULL);
        if (ret < 0) {
                goto error_unlock;
        }
@@ -2859,6 +3851,13 @@ skip_setup:
                                        app->pid, ret);
                } else {
                        DBG("UST app start session failed. Application is dead.");
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       pthread_mutex_unlock(&ua_sess->lock);
+                       goto end;
                }
                goto error_unlock;
        }
@@ -2892,12 +3891,12 @@ error_unlock:
 /*
  * Stop tracing for a specific UST session and app.
  */
+static
 int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
 {
        int ret = 0;
-       struct lttng_ht_iter iter;
        struct ust_app_session *ua_sess;
-       struct ust_app_channel *ua_chan;
+       struct ust_registry_session *registry;
 
        DBG("Stopping tracing for ust app pid %d", app->pid);
 
@@ -2934,6 +3933,12 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
                                        app->pid, ret);
                } else {
                        DBG("UST app stop session failed. Application is dead.");
+                       /*
+                        * This is normal behavior, an application can die during the
+                        * creation process. Don't report an error so the execution can
+                        * continue normally.
+                        */
+                       goto end_unlock;
                }
                goto error_rcu_unlock;
        }
@@ -2949,6 +3954,56 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
 
        health_code_update();
 
+       registry = get_session_registry(ua_sess);
+       assert(registry);
+
+       if (!registry->metadata_closed) {
+               /* Push metadata for application before freeing the application. */
+               (void) push_metadata(registry, ua_sess->consumer);
+       }
+
+end_unlock:
+       pthread_mutex_unlock(&ua_sess->lock);
+end_no_session:
+       rcu_read_unlock();
+       health_code_update();
+       return 0;
+
+error_rcu_unlock:
+       pthread_mutex_unlock(&ua_sess->lock);
+       rcu_read_unlock();
+       health_code_update();
+       return -1;
+}
+
+/*
+ * Flush buffers for a specific UST session and app.
+ */
+static
+int ust_app_flush_trace(struct ltt_ust_session *usess, struct ust_app *app)
+{
+       int ret = 0;
+       struct lttng_ht_iter iter;
+       struct ust_app_session *ua_sess;
+       struct ust_app_channel *ua_chan;
+
+       DBG("Flushing buffers for ust app pid %d", app->pid);
+
+       rcu_read_lock();
+
+       if (!app->compatible) {
+               goto end_no_session;
+       }
+
+       ua_sess = lookup_session_by_app(usess, app);
+       if (ua_sess == NULL) {
+               goto end_no_session;
+       }
+
+       pthread_mutex_lock(&ua_sess->lock);
+
+       health_code_update();
+
        /* Flushing buffers */
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
@@ -2962,8 +4017,11 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
                        } else {
                                DBG3("UST app failed to flush %s. Application is dead.",
                                                ua_chan->name);
-                               /* No need to continue. */
-                               break;
+                               /*
+                                * This is normal behavior, an application can die during the
+                                * creation process. Don't report an error so the execution can
+                                * continue normally.
+                                */
                        }
                        /* Continuing flushing all buffers */
                        continue;
@@ -2972,22 +4030,11 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
 
        health_code_update();
 
-       ret = push_metadata(app, ua_sess);
-       if (ret < 0) {
-               goto error_rcu_unlock;
-       }
-
        pthread_mutex_unlock(&ua_sess->lock);
 end_no_session:
        rcu_read_unlock();
        health_code_update();
        return 0;
-
-error_rcu_unlock:
-       pthread_mutex_unlock(&ua_sess->lock);
-       rcu_read_unlock();
-       health_code_update();
-       return -1;
 }
 
 /*
@@ -2998,7 +4045,7 @@ static int destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
        int ret;
        struct ust_app_session *ua_sess;
        struct lttng_ht_iter iter;
-       struct lttng_ht_node_ulong *node;
+       struct lttng_ht_node_u64 *node;
 
        DBG("Destroy tracing for ust app pid %d", app->pid);
 
@@ -3009,7 +4056,7 @@ static int destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
        }
 
        __lookup_session_by_app(usess, app, &iter);
-       node = lttng_ht_iter_get_node_ulong(&iter);
+       node = lttng_ht_iter_get_node_u64(&iter);
        if (node == NULL) {
                /* Session is being or is deleted. */
                goto end;
@@ -3075,12 +4122,64 @@ int ust_app_stop_trace_all(struct ltt_ust_session *usess)
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                ret = ust_app_stop_trace(usess, app);
                if (ret < 0) {
-                       ERR("UST app stop trace failed with ret %d", ret);
                        /* Continue to next apps even on error */
                        continue;
                }
        }
 
+       /* Flush buffers and push metadata (for UID buffers). */
+       switch (usess->buffer_type) {
+       case LTTNG_BUFFER_PER_UID:
+       {
+               struct buffer_reg_uid *reg;
+
+               /* Flush all per UID buffers associated to that session. */
+               cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
+                       struct ust_registry_session *ust_session_reg;
+                       struct buffer_reg_channel *reg_chan;
+                       struct consumer_socket *socket;
+
+                       /* Get consumer socket to use to push the metadata.*/
+                       socket = consumer_find_socket_by_bitness(reg->bits_per_long,
+                                       usess->consumer);
+                       if (!socket) {
+                               /* Ignore request if no consumer is found for the session. */
+                               continue;
+                       }
+
+                       cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
+                                       reg_chan, node.node) {
+                               /*
+                                * The following call will print error values so the return
+                                * code is of little importance because whatever happens, we
+                                * have to try them all.
+                                */
+                               (void) consumer_flush_channel(socket, reg_chan->consumer_key);
+                       }
+
+                       ust_session_reg = reg->registry->reg.ust;
+                       if (!ust_session_reg->metadata_closed) {
+                               /* Push metadata. */
+                               (void) push_metadata(ust_session_reg, usess->consumer);
+                       }
+               }
+
+               break;
+       }
+       case LTTNG_BUFFER_PER_PID:
+               cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+                       ret = ust_app_flush_trace(usess, app);
+                       if (ret < 0) {
+                               /* Continue to next apps even on error */
+                               continue;
+                       }
+               }
+               break;
+       default:
+               assert(0);
+               break;
+       }
+
        rcu_read_unlock();
 
        return 0;
@@ -3118,7 +4217,7 @@ int ust_app_destroy_trace_all(struct ltt_ust_session *usess)
 void ust_app_global_update(struct ltt_ust_session *usess, int sock)
 {
        int ret = 0;
-       struct lttng_ht_iter iter, uiter, iter_ctx;
+       struct lttng_ht_iter iter, uiter;
        struct ust_app *app;
        struct ust_app_session *ua_sess = NULL;
        struct ust_app_channel *ua_chan;
@@ -3128,12 +4227,12 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
        assert(usess);
        assert(sock >= 0);
 
-       DBG2("UST app global update for app sock %d for session id %d", sock,
+       DBG2("UST app global update for app sock %d for session id %" PRIu64, sock,
                        usess->id);
 
        rcu_read_lock();
 
-       app = find_app_by_sock(sock);
+       app = ust_app_find_by_sock(sock);
        if (app == NULL) {
                /*
                 * Application can be unregistered before so this is possible hence
@@ -3163,18 +4262,38 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
         */
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
-               ret = create_ust_channel(app, ua_sess, ua_chan, usess->consumer);
-               if (ret < 0) {
-                       /*
-                        * Stop everything. On error, the application failed, no more file
-                        * descriptor are available or ENOMEM so stopping here is the only
-                        * thing we can do for now.
-                        */
-                       goto error_unlock;
+               /*
+                * For a metadata channel, handle it differently.
+                */
+               if (!strncmp(ua_chan->name, DEFAULT_METADATA_NAME,
+                                       sizeof(ua_chan->name))) {
+                       ret = create_ust_app_metadata(ua_sess, app, usess->consumer,
+                                       &ua_chan->attr);
+                       if (ret < 0) {
+                               goto error_unlock;
+                       }
+                       /* Remove it from the hash table and continue!. */
+                       ret = lttng_ht_del(ua_sess->channels, &iter);
+                       assert(!ret);
+                       delete_ust_app_channel(-1, ua_chan, app);
+                       continue;
+               } else {
+                       ret = do_create_channel(app, usess, ua_sess, ua_chan);
+                       if (ret < 0) {
+                               /*
+                                * Stop everything. On error, the application failed, no more
+                                * file descriptor are available or ENOMEM so stopping here is
+                                * the only thing we can do for now.
+                                */
+                               goto error_unlock;
+                       }
                }
 
-               cds_lfht_for_each_entry(ua_chan->ctx->ht, &iter_ctx.iter, ua_ctx,
-                               node.node) {
+               /*
+                * Add context using the list so they are enabled in the same order the
+                * user added them.
+                */
+               cds_list_for_each_entry(ua_ctx, &ua_chan->ctx_list, list) {
                        ret = create_ust_channel_context(ua_chan, ua_ctx, app);
                        if (ret < 0) {
                                goto error_unlock;
@@ -3313,7 +4432,7 @@ int ust_app_enable_event_pid(struct ltt_ust_session *usess,
        ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
 
        ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
-                       uevent->filter, uevent->attr.loglevel);
+                       uevent->filter, uevent->attr.loglevel, uevent->exclusion);
        if (ua_event == NULL) {
                ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
                if (ret < 0) {
@@ -3531,10 +4650,13 @@ static int reply_ust_register_channel(int sock, int sobjd, int cobjd,
 {
        int ret, ret_code = 0;
        uint32_t chan_id, reg_count;
+       uint64_t chan_reg_key;
        enum ustctl_channel_header type;
        struct ust_app *app;
        struct ust_app_channel *ua_chan;
        struct ust_app_session *ua_sess;
+       struct ust_registry_session *registry;
+       struct ust_registry_channel *chan_reg;
 
        rcu_read_lock();
 
@@ -3544,48 +4666,62 @@ static int reply_ust_register_channel(int sock, int sobjd, int cobjd,
                DBG("Application socket %d is being teardown. Abort event notify",
                                sock);
                ret = 0;
+               free(fields);
                goto error_rcu_unlock;
        }
 
-       /* Lookup channel by UST object descriptor. Should always be found. */
+       /* Lookup channel by UST object descriptor. */
        ua_chan = find_channel_by_objd(app, cobjd);
-       assert(ua_chan);
+       if (!ua_chan) {
+               DBG("Application channel is being teardown. Abort event notify");
+               ret = 0;
+               free(fields);
+               goto error_rcu_unlock;
+       }
+
        assert(ua_chan->session);
        ua_sess = ua_chan->session;
-       assert(ua_sess);
 
-       pthread_mutex_lock(&ua_sess->registry.lock);
-
-       if (ust_registry_is_max_id(ua_chan->session->registry.used_channel_id)) {
-               ret_code = -1;
-               chan_id = -1U;
-               type = -1;
-               goto reply;
-       }
+       /* Get right session registry depending on the session buffer type. */
+       registry = get_session_registry(ua_sess);
+       assert(registry);
 
-       /* Don't assign ID to metadata. */
-       if (ua_chan->attr.type == LTTNG_UST_CHAN_METADATA) {
-               chan_id = -1U;
+       /* Depending on the buffer type, a different channel key is used. */
+       if (ua_sess->buffer_type == LTTNG_BUFFER_PER_UID) {
+               chan_reg_key = ua_chan->tracing_channel_id;
        } else {
-               chan_id = ust_registry_get_next_chan_id(&ua_chan->session->registry);
+               chan_reg_key = ua_chan->key;
        }
 
-       reg_count = ust_registry_get_event_count(&ua_chan->registry);
-       if (reg_count < 31) {
-               type = USTCTL_CHANNEL_HEADER_COMPACT;
+       pthread_mutex_lock(&registry->lock);
+
+       chan_reg = ust_registry_channel_find(registry, chan_reg_key);
+       assert(chan_reg);
+
+       if (!chan_reg->register_done) {
+               reg_count = ust_registry_get_event_count(chan_reg);
+               if (reg_count < 31) {
+                       type = USTCTL_CHANNEL_HEADER_COMPACT;
+               } else {
+                       type = USTCTL_CHANNEL_HEADER_LARGE;
+               }
+
+               chan_reg->nr_ctx_fields = nr_fields;
+               chan_reg->ctx_fields = fields;
+               chan_reg->header_type = type;
        } else {
-               type = USTCTL_CHANNEL_HEADER_LARGE;
+               /* Get current already assigned values. */
+               type = chan_reg->header_type;
+               free(fields);
+               /* Set to NULL so the error path does not do a double free. */
+               fields = NULL;
        }
-
-       ua_chan->registry.nr_ctx_fields = nr_fields;
-       ua_chan->registry.ctx_fields = fields;
-       ua_chan->registry.chan_id = chan_id;
-       ua_chan->registry.header_type = type;
+       /* Channel id is set during the object creation. */
+       chan_id = chan_reg->chan_id;
 
        /* Append to metadata */
-       if (!ret_code) {
-               ret_code = ust_metadata_channel_statedump(&ua_chan->session->registry,
-                               &ua_chan->registry);
+       if (!chan_reg->metadata_dumped) {
+               ret_code = ust_metadata_channel_statedump(registry, chan_reg);
                if (ret_code) {
                        ERR("Error appending channel metadata (errno = %d)", ret_code);
                        goto reply;
@@ -3593,8 +4729,9 @@ static int reply_ust_register_channel(int sock, int sobjd, int cobjd,
        }
 
 reply:
-       DBG3("UST app replying to register channel with id %u, type: %d, ret: %d",
-                       chan_id, type, ret_code);
+       DBG3("UST app replying to register channel key %" PRIu64
+                       " with id %u, type: %d, ret: %d", chan_reg_key, chan_id, type,
+                       ret_code);
 
        ret = ustctl_reply_register_channel(sock, chan_id, type, ret_code);
        if (ret < 0) {
@@ -3606,10 +4743,16 @@ reply:
                goto error;
        }
 
+       /* This channel registry registration is completed. */
+       chan_reg->register_done = 1;
+
 error:
-       pthread_mutex_unlock(&ua_sess->registry.lock);
+       pthread_mutex_unlock(&registry->lock);
 error_rcu_unlock:
        rcu_read_unlock();
+       if (ret) {
+               free(fields);
+       }
        return ret;
 }
 
@@ -3628,9 +4771,11 @@ static int add_event_ust_registry(int sock, int sobjd, int cobjd, char *name,
 {
        int ret, ret_code;
        uint32_t event_id = 0;
+       uint64_t chan_reg_key;
        struct ust_app *app;
        struct ust_app_channel *ua_chan;
        struct ust_app_session *ua_sess;
+       struct ust_registry_session *registry;
 
        rcu_read_lock();
 
@@ -3640,20 +4785,46 @@ static int add_event_ust_registry(int sock, int sobjd, int cobjd, char *name,
                DBG("Application socket %d is being teardown. Abort event notify",
                                sock);
                ret = 0;
+               free(sig);
+               free(fields);
+               free(model_emf_uri);
                goto error_rcu_unlock;
        }
 
-       /* Lookup channel by UST object descriptor. Should always be found. */
+       /* Lookup channel by UST object descriptor. */
        ua_chan = find_channel_by_objd(app, cobjd);
-       assert(ua_chan);
+       if (!ua_chan) {
+               DBG("Application channel is being teardown. Abort event notify");
+               ret = 0;
+               free(sig);
+               free(fields);
+               free(model_emf_uri);
+               goto error_rcu_unlock;
+       }
+
        assert(ua_chan->session);
        ua_sess = ua_chan->session;
 
-       pthread_mutex_lock(&ua_sess->registry.lock);
+       registry = get_session_registry(ua_sess);
+       assert(registry);
+
+       if (ua_sess->buffer_type == LTTNG_BUFFER_PER_UID) {
+               chan_reg_key = ua_chan->tracing_channel_id;
+       } else {
+               chan_reg_key = ua_chan->key;
+       }
+
+       pthread_mutex_lock(&registry->lock);
 
-       ret_code = ust_registry_create_event(&ua_sess->registry,
-                       &ua_chan->registry, sobjd, cobjd, name, sig, nr_fields, fields,
-                       loglevel, model_emf_uri, &event_id);
+       /*
+        * From this point on, this call acquires the ownership of the sig, fields
+        * and model_emf_uri meaning any free are done inside it if needed. These
+        * three variables MUST NOT be read/write after this.
+        */
+       ret_code = ust_registry_create_event(registry, chan_reg_key,
+                       sobjd, cobjd, name, sig, nr_fields, fields, loglevel,
+                       model_emf_uri, ua_sess->buffer_type, &event_id,
+                       app);
 
        /*
         * The return value is returned to ustctl so in case of an error, the
@@ -3674,10 +4845,11 @@ static int add_event_ust_registry(int sock, int sobjd, int cobjd, char *name,
                goto error;
        }
 
-       DBG3("UST registry event %s has been added successfully", name);
+       DBG3("UST registry event %s with id %" PRId32 " added successfully",
+                       name, event_id);
 
 error:
-       pthread_mutex_unlock(&ua_sess->registry.lock);
+       pthread_mutex_unlock(&registry->lock);
 error_rcu_unlock:
        rcu_read_unlock();
        return ret;
@@ -3726,7 +4898,12 @@ int ust_app_recv_notify(int sock)
                        goto error;
                }
 
-               /* Add event to the UST registry coming from the notify socket. */
+               /*
+                * Add event to the UST registry coming from the notify socket. This
+                * call will free if needed the sig, fields and model_emf_uri. This
+                * code path loses the ownsership of these variables and transfer them
+                * to the this function.
+                */
                ret = add_event_ust_registry(sock, sobjd, cobjd, name, sig, nr_fields,
                                fields, loglevel, model_emf_uri);
                if (ret < 0) {
@@ -3754,6 +4931,11 @@ int ust_app_recv_notify(int sock)
                        goto error;
                }
 
+               /*
+                * The fields ownership are transfered to this function call meaning
+                * that if needed it will be freed. After this, it's invalid to access
+                * fields or clean it up.
+                */
                ret = reply_ust_register_channel(sock, sobjd, cobjd, nr_fields,
                                fields);
                if (ret < 0) {
@@ -3847,3 +5029,235 @@ close_socket:
                call_rcu(&obj->head, close_notify_sock_rcu);
        }
 }
+
+/*
+ * Destroy a ust app data structure and free its memory.
+ */
+void ust_app_destroy(struct ust_app *app)
+{
+       if (!app) {
+               return;
+       }
+
+       call_rcu(&app->pid_n.head, delete_ust_app_rcu);
+}
+
+/*
+ * Take a snapshot for a given UST session. The snapshot is sent to the given
+ * output.
+ *
+ * Return 0 on success or else a negative value.
+ */
+int ust_app_snapshot_record(struct ltt_ust_session *usess,
+               struct snapshot_output *output, int wait, unsigned int nb_streams)
+{
+       int ret = 0;
+       struct lttng_ht_iter iter;
+       struct ust_app *app;
+       char pathname[PATH_MAX];
+       uint64_t max_stream_size = 0;
+
+       assert(usess);
+       assert(output);
+
+       rcu_read_lock();
+
+       /*
+        * Compute the maximum size of a single stream if a max size is asked by
+        * the caller.
+        */
+       if (output->max_size > 0 && nb_streams > 0) {
+               max_stream_size = output->max_size / nb_streams;
+       }
+
+       switch (usess->buffer_type) {
+       case LTTNG_BUFFER_PER_UID:
+       {
+               struct buffer_reg_uid *reg;
+
+               cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
+                       struct buffer_reg_channel *reg_chan;
+                       struct consumer_socket *socket;
+
+                       /* Get consumer socket to use to push the metadata.*/
+                       socket = consumer_find_socket_by_bitness(reg->bits_per_long,
+                                       usess->consumer);
+                       if (!socket) {
+                               ret = -EINVAL;
+                               goto error;
+                       }
+
+                       memset(pathname, 0, sizeof(pathname));
+                       ret = snprintf(pathname, sizeof(pathname),
+                                       DEFAULT_UST_TRACE_DIR "/" DEFAULT_UST_TRACE_UID_PATH,
+                                       reg->uid, reg->bits_per_long);
+                       if (ret < 0) {
+                               PERROR("snprintf snapshot path");
+                               goto error;
+                       }
+
+                       /* Add the UST default trace dir to path. */
+                       cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
+                                       reg_chan, node.node) {
+
+                               /*
+                                * Make sure the maximum stream size is not lower than the
+                                * subbuffer size or else it's an error since we won't be able to
+                                * snapshot anything.
+                                */
+                               if (max_stream_size &&
+                                               reg_chan->subbuf_size > max_stream_size) {
+                                       ret = -EINVAL;
+                                       DBG3("UST app snapshot record maximum stream size %" PRIu64
+                                                       " is smaller than subbuffer size of %zu",
+                                                       max_stream_size, reg_chan->subbuf_size);
+                                       goto error;
+                               }
+                               ret = consumer_snapshot_channel(socket, reg_chan->consumer_key, output, 0,
+                                               usess->uid, usess->gid, pathname, wait,
+                                               max_stream_size);
+                               if (ret < 0) {
+                                       goto error;
+                               }
+                       }
+                       ret = consumer_snapshot_channel(socket, reg->registry->reg.ust->metadata_key, output,
+                                       1, usess->uid, usess->gid, pathname, wait,
+                                       max_stream_size);
+                       if (ret < 0) {
+                               goto error;
+                       }
+               }
+               break;
+       }
+       case LTTNG_BUFFER_PER_PID:
+       {
+               cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+                       struct consumer_socket *socket;
+                       struct lttng_ht_iter chan_iter;
+                       struct ust_app_channel *ua_chan;
+                       struct ust_app_session *ua_sess;
+                       struct ust_registry_session *registry;
+
+                       ua_sess = lookup_session_by_app(usess, app);
+                       if (!ua_sess) {
+                               /* Session not associated with this app. */
+                               continue;
+                       }
+
+                       /* Get the right consumer socket for the application. */
+                       socket = consumer_find_socket_by_bitness(app->bits_per_long,
+                                       output->consumer);
+                       if (!socket) {
+                               ret = -EINVAL;
+                               goto error;
+                       }
+
+                       /* Add the UST default trace dir to path. */
+                       memset(pathname, 0, sizeof(pathname));
+                       ret = snprintf(pathname, sizeof(pathname), DEFAULT_UST_TRACE_DIR "/%s",
+                                       ua_sess->path);
+                       if (ret < 0) {
+                               PERROR("snprintf snapshot path");
+                               goto error;
+                       }
+
+                       cds_lfht_for_each_entry(ua_sess->channels->ht, &chan_iter.iter,
+                                       ua_chan, node.node) {
+                               /*
+                                * Make sure the maximum stream size is not lower than the
+                                * subbuffer size or else it's an error since we won't be able to
+                                * snapshot anything.
+                                */
+                               if (max_stream_size &&
+                                               ua_chan->attr.subbuf_size > max_stream_size) {
+                                       ret = -EINVAL;
+                                       DBG3("UST app snapshot record maximum stream size %" PRIu64
+                                                       " is smaller than subbuffer size of %" PRIu64,
+                                                       max_stream_size, ua_chan->attr.subbuf_size);
+                                       goto error;
+                               }
+
+                               ret = consumer_snapshot_channel(socket, ua_chan->key, output, 0,
+                                               ua_sess->euid, ua_sess->egid, pathname, wait,
+                                               max_stream_size);
+                               if (ret < 0) {
+                                       goto error;
+                               }
+                       }
+
+                       registry = get_session_registry(ua_sess);
+                       assert(registry);
+                       ret = consumer_snapshot_channel(socket, registry->metadata_key, output,
+                                       1, ua_sess->euid, ua_sess->egid, pathname, wait,
+                                       max_stream_size);
+                       if (ret < 0) {
+                               goto error;
+                       }
+               }
+               break;
+       }
+       default:
+               assert(0);
+               break;
+       }
+
+error:
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * Return the number of streams for a UST session.
+ */
+unsigned int ust_app_get_nb_stream(struct ltt_ust_session *usess)
+{
+       unsigned int ret = 0;
+       struct ust_app *app;
+       struct lttng_ht_iter iter;
+
+       assert(usess);
+
+       switch (usess->buffer_type) {
+       case LTTNG_BUFFER_PER_UID:
+       {
+               struct buffer_reg_uid *reg;
+
+               cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
+                       struct buffer_reg_channel *reg_chan;
+
+                       cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
+                                       reg_chan, node.node) {
+                               ret += reg_chan->stream_count;
+                       }
+               }
+               break;
+       }
+       case LTTNG_BUFFER_PER_PID:
+       {
+               rcu_read_lock();
+               cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+                       struct ust_app_channel *ua_chan;
+                       struct ust_app_session *ua_sess;
+                       struct lttng_ht_iter chan_iter;
+
+                       ua_sess = lookup_session_by_app(usess, app);
+                       if (!ua_sess) {
+                               /* Session not associated with this app. */
+                               continue;
+                       }
+
+                       cds_lfht_for_each_entry(ua_sess->channels->ht, &chan_iter.iter,
+                                       ua_chan, node.node) {
+                               ret += ua_chan->streams.count;
+                       }
+               }
+               rcu_read_unlock();
+               break;
+       }
+       default:
+               assert(0);
+               break;
+       }
+
+       return ret;
+}
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