Cleanup: Extract `ust_app_synchronize_all_channels()` function
[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c
index 8c9277cae225ea80e9df7bf106d304a529e71769..50d2f1932657e56f7863e5b23fd3ef8b48cad87d 100644 (file)
@@ -1,23 +1,12 @@
 /*
- * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
- * Copyright (C) 2016 Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
+ * Copyright (C) 2016 Jérémie Galarneau <jeremie.galarneau@efficios.com>
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License, version 2 only,
- * as published by the Free Software Foundation.
+ * SPDX-License-Identifier: GPL-2.0-only
  *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
 #define _LGPL_SOURCE
-#include <errno.h>
 #include <inttypes.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <urcu/compiler.h>
-#include <lttng/ust-error.h>
 #include <signal.h>
 
+#include <common/bytecode/bytecode.h>
+#include <common/compat/errno.h>
 #include <common/common.h>
+#include <common/hashtable/utils.h>
+#include <lttng/event-rule/event-rule.h>
+#include <lttng/event-rule/event-rule-internal.h>
+#include <lttng/event-rule/tracepoint.h>
+#include <lttng/condition/condition.h>
+#include <lttng/condition/on-event-internal.h>
+#include <lttng/condition/on-event.h>
+#include <lttng/trigger/trigger-internal.h>
 #include <common/sessiond-comm/sessiond-comm.h>
 
 #include "buffer-registry.h"
 #include "health-sessiond.h"
 #include "ust-app.h"
 #include "ust-consumer.h"
-#include "ust-ctl.h"
+#include "lttng-ust-ctl.h"
+#include "lttng-ust-error.h"
 #include "utils.h"
 #include "session.h"
 #include "lttng-sessiond.h"
 #include "notification-thread-commands.h"
 #include "rotate.h"
+#include "event.h"
+
+struct lttng_ht *ust_app_ht;
+struct lttng_ht *ust_app_ht_by_sock;
+struct lttng_ht *ust_app_ht_by_notify_sock;
 
 static
 int ust_app_flush_app_session(struct ust_app *app, struct ust_app_session *ua_sess);
@@ -84,7 +88,7 @@ static uint64_t get_next_session_id(void)
 
 static void copy_channel_attr_to_ustctl(
                struct ustctl_consumer_channel_attr *attr,
-               struct lttng_ust_channel_attr *uattr)
+               struct lttng_ust_abi_channel_attr *uattr)
 {
        /* Copy event attributes since the layout is different. */
        attr->subbuf_size = uattr->subbuf_size;
@@ -124,7 +128,7 @@ static int ht_match_ust_app_event(struct cds_lfht_node *node, const void *_key)
 
        /* Event loglevel. */
        if (ev_loglevel_value != key->loglevel_type) {
-               if (event->attr.loglevel_type == LTTNG_UST_LOGLEVEL_ALL
+               if (event->attr.loglevel_type == LTTNG_UST_ABI_LOGLEVEL_ALL
                                && key->loglevel_type == 0 &&
                                ev_loglevel_value == -1) {
                        /*
@@ -161,7 +165,7 @@ static int ht_match_ust_app_event(struct cds_lfht_node *node, const void *_key)
                /* 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) {
+                                       event->exclusion->count * LTTNG_UST_ABI_SYM_NAME_LEN) != 0) {
                        goto no_match;
                }
        }
@@ -251,7 +255,7 @@ static struct ust_registry_session *get_session_registry(
        {
                struct buffer_reg_uid *reg_uid = buffer_reg_uid_find(
                                ua_sess->tracing_id, ua_sess->bits_per_long,
-                               ua_sess->real_credentials.uid);
+                               lttng_credentials_get_uid(&ua_sess->real_credentials));
                if (!reg_uid) {
                        goto error;
                }
@@ -319,6 +323,51 @@ void delete_ust_app_event(int sock, struct ust_app_event *ua_event,
        free(ua_event);
 }
 
+/*
+ * Delayed reclaim of a ust_app_event_notifier_rule object. This MUST be called
+ * through a call_rcu().
+ */
+static
+void free_ust_app_event_notifier_rule_rcu(struct rcu_head *head)
+{
+       struct ust_app_event_notifier_rule *obj = caa_container_of(
+                       head, struct ust_app_event_notifier_rule, rcu_head);
+
+       free(obj);
+}
+
+/*
+ * Delete ust app event notifier rule safely.
+ */
+static void delete_ust_app_event_notifier_rule(int sock,
+               struct ust_app_event_notifier_rule *ua_event_notifier_rule,
+               struct ust_app *app)
+{
+       int ret;
+
+       assert(ua_event_notifier_rule);
+
+       if (ua_event_notifier_rule->exclusion != NULL) {
+               free(ua_event_notifier_rule->exclusion);
+       }
+
+       if (ua_event_notifier_rule->obj != NULL) {
+               pthread_mutex_lock(&app->sock_lock);
+               ret = ustctl_release_object(sock, ua_event_notifier_rule->obj);
+               pthread_mutex_unlock(&app->sock_lock);
+               if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("Failed to release event notifier object: app = '%s' (ppid %d), ret = %d",
+                                       app->name, (int) app->ppid, ret);
+               }
+
+               free(ua_event_notifier_rule->obj);
+       }
+
+       lttng_trigger_put(ua_event_notifier_rule->trigger);
+       call_rcu(&ua_event_notifier_rule->rcu_head,
+                       free_ust_app_event_notifier_rule_rcu);
+}
+
 /*
  * Release ust data object of the given stream.
  *
@@ -391,7 +440,7 @@ void save_per_pid_lost_discarded_counters(struct ust_app_channel *ua_chan)
        struct ltt_session *session;
        struct ltt_ust_channel *uchan;
 
-       if (ua_chan->attr.type != LTTNG_UST_CHAN_PER_CPU) {
+       if (ua_chan->attr.type != LTTNG_UST_ABI_CHAN_PER_CPU) {
                return;
        }
 
@@ -531,7 +580,7 @@ int ust_app_register_done(struct ust_app *app)
        return ret;
 }
 
-int ust_app_release_object(struct ust_app *app, struct lttng_ust_object_data *data)
+int ust_app_release_object(struct ust_app *app, struct lttng_ust_abi_object_data *data)
 {
        int ret, sock;
 
@@ -741,6 +790,10 @@ error:
  * nullified. The session lock MUST be held unless the application is
  * in the destroy path.
  *
+ * Do not hold the registry lock while communicating with the consumerd, because
+ * doing so causes inter-process deadlocks between consumerd and sessiond with
+ * the metadata request notification.
+ *
  * Return 0 on success else a negative value.
  */
 static int close_metadata(struct ust_registry_session *registry,
@@ -748,6 +801,8 @@ static int close_metadata(struct ust_registry_session *registry,
 {
        int ret;
        struct consumer_socket *socket;
+       uint64_t metadata_key;
+       bool registry_was_already_closed;
 
        assert(registry);
        assert(consumer);
@@ -755,8 +810,19 @@ static int close_metadata(struct ust_registry_session *registry,
        rcu_read_lock();
 
        pthread_mutex_lock(&registry->lock);
+       metadata_key = registry->metadata_key;
+       registry_was_already_closed = registry->metadata_closed;
+       if (metadata_key != 0) {
+               /*
+                * 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;
+       }
+       pthread_mutex_unlock(&registry->lock);
 
-       if (!registry->metadata_key || registry->metadata_closed) {
+       if (metadata_key == 0 || registry_was_already_closed) {
                ret = 0;
                goto end;
        }
@@ -766,23 +832,15 @@ static int close_metadata(struct ust_registry_session *registry,
                        consumer);
        if (!socket) {
                ret = -1;
-               goto error;
+               goto end;
        }
 
-       ret = consumer_close_metadata(socket, registry->metadata_key);
+       ret = consumer_close_metadata(socket, metadata_key);
        if (ret < 0) {
-               goto error;
+               goto end;
        }
 
-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:
-       pthread_mutex_unlock(&registry->lock);
        rcu_read_unlock();
        return ret;
 }
@@ -895,6 +953,9 @@ void delete_ust_app(struct ust_app *app)
 {
        int ret, sock;
        struct ust_app_session *ua_sess, *tmp_ua_sess;
+       struct lttng_ht_iter iter;
+       struct ust_app_event_notifier_rule *event_notifier_rule;
+       bool event_notifier_write_fd_is_open;
 
        /*
         * The session list lock must be held during this function to guarantee
@@ -914,9 +975,54 @@ void delete_ust_app(struct ust_app *app)
                rcu_read_unlock();
        }
 
+       /* Remove the event notifier rules associated with this app. */
+       rcu_read_lock();
+       cds_lfht_for_each_entry (app->token_to_event_notifier_rule_ht->ht,
+                       &iter.iter, event_notifier_rule, node.node) {
+               ret = lttng_ht_del(app->token_to_event_notifier_rule_ht, &iter);
+               assert(!ret);
+
+               delete_ust_app_event_notifier_rule(
+                               app->sock, event_notifier_rule, app);
+       }
+
+       rcu_read_unlock();
+
        ht_cleanup_push(app->sessions);
        ht_cleanup_push(app->ust_sessions_objd);
        ht_cleanup_push(app->ust_objd);
+       ht_cleanup_push(app->token_to_event_notifier_rule_ht);
+
+       /*
+        * This could be NULL if the event notifier setup failed (e.g the app
+        * was killed or the tracer does not support this feature).
+        */
+       if (app->event_notifier_group.object) {
+               enum lttng_error_code ret_code;
+               const int event_notifier_read_fd = lttng_pipe_get_readfd(
+                               app->event_notifier_group.event_pipe);
+
+               ret_code = notification_thread_command_remove_tracer_event_source(
+                               notification_thread_handle,
+                               event_notifier_read_fd);
+               if (ret_code != LTTNG_OK) {
+                       ERR("Failed to remove application tracer event source from notification thread");
+               }
+
+               ustctl_release_object(sock, app->event_notifier_group.object);
+               free(app->event_notifier_group.object);
+       }
+
+       event_notifier_write_fd_is_open = lttng_pipe_is_write_open(
+                       app->event_notifier_group.event_pipe);
+       lttng_pipe_destroy(app->event_notifier_group.event_pipe);
+       /*
+        * Release the file descriptors reserved for the event notifier pipe.
+        * The app could be destroyed before the write end of the pipe could be
+        * passed to the application (and closed). In that case, both file
+        * descriptors must be released.
+        */
+       lttng_fd_put(LTTNG_FD_APPS, event_notifier_write_fd_is_open ? 2 : 1);
 
        /*
         * Wait until we have deleted the application from the sock hash table
@@ -1003,7 +1109,7 @@ struct ust_app_session *alloc_ust_app_session(void)
 
        ua_sess->handle = -1;
        ua_sess->channels = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
-       ua_sess->metadata_attr.type = LTTNG_UST_CHAN_METADATA;
+       ua_sess->metadata_attr.type = LTTNG_UST_ABI_CHAN_METADATA;
        pthread_mutex_init(&ua_sess->lock, NULL);
 
        return ua_sess;
@@ -1016,9 +1122,9 @@ error_free:
  * Alloc new UST app channel.
  */
 static
-struct ust_app_channel *alloc_ust_app_channel(char *name,
+struct ust_app_channel *alloc_ust_app_channel(const char *name,
                struct ust_app_session *ua_sess,
-               struct lttng_ust_channel_attr *attr)
+               struct lttng_ust_abi_channel_attr *attr)
 {
        struct ust_app_channel *ua_chan;
 
@@ -1056,7 +1162,7 @@ struct ust_app_channel *alloc_ust_app_channel(char *name,
                ua_chan->attr.blocking_timeout = attr->u.s.blocking_timeout;
        }
        /* By default, the channel is a per cpu channel. */
-       ua_chan->attr.type = LTTNG_UST_CHAN_PER_CPU;
+       ua_chan->attr.type = LTTNG_UST_ABI_CHAN_PER_CPU;
 
        DBG3("UST app channel %s allocated", ua_chan->name);
 
@@ -1093,14 +1199,14 @@ error:
  */
 static
 struct ust_app_event *alloc_ust_app_event(char *name,
-               struct lttng_ust_event *attr)
+               struct lttng_ust_abi_event *attr)
 {
        struct ust_app_event *ua_event;
 
        /* Init most of the default value by allocating and zeroing */
        ua_event = zmalloc(sizeof(struct ust_app_event));
        if (ua_event == NULL) {
-               PERROR("malloc");
+               PERROR("Failed to allocate ust_app_event structure");
                goto error;
        }
 
@@ -1122,6 +1228,65 @@ error:
        return NULL;
 }
 
+/*
+ * Allocate a new UST app event notifier rule.
+ */
+static struct ust_app_event_notifier_rule *alloc_ust_app_event_notifier_rule(
+               struct lttng_trigger *trigger)
+{
+       enum lttng_event_rule_generate_exclusions_status
+                       generate_exclusion_status;
+       struct ust_app_event_notifier_rule *ua_event_notifier_rule;
+       struct lttng_condition *condition = NULL;
+       const struct lttng_event_rule *event_rule = NULL;
+
+       ua_event_notifier_rule = zmalloc(sizeof(struct ust_app_event_notifier_rule));
+       if (ua_event_notifier_rule == NULL) {
+               PERROR("Failed to allocate ust_app_event_notifier_rule structure");
+               goto error;
+       }
+
+       ua_event_notifier_rule->enabled = 1;
+       ua_event_notifier_rule->token = lttng_trigger_get_tracer_token(trigger);
+       lttng_ht_node_init_u64(&ua_event_notifier_rule->node,
+                       ua_event_notifier_rule->token);
+
+       condition = lttng_trigger_get_condition(trigger);
+       assert(condition);
+       assert(lttng_condition_get_type(condition) == LTTNG_CONDITION_TYPE_ON_EVENT);
+
+       assert(LTTNG_CONDITION_STATUS_OK == lttng_condition_on_event_get_rule(condition, &event_rule));
+       assert(event_rule);
+
+       /* Acquire the event notifier's reference to the trigger. */
+       lttng_trigger_get(trigger);
+
+       ua_event_notifier_rule->trigger = trigger;
+       ua_event_notifier_rule->filter = lttng_event_rule_get_filter_bytecode(event_rule);
+       generate_exclusion_status = lttng_event_rule_generate_exclusions(
+                       event_rule, &ua_event_notifier_rule->exclusion);
+       switch (generate_exclusion_status) {
+       case LTTNG_EVENT_RULE_GENERATE_EXCLUSIONS_STATUS_OK:
+       case LTTNG_EVENT_RULE_GENERATE_EXCLUSIONS_STATUS_NONE:
+               break;
+       default:
+               /* Error occured. */
+               ERR("Failed to generate exclusions from trigger while allocating an event notifier rule");
+               goto error_put_trigger;
+       }
+
+       DBG3("UST app event notifier rule allocated: token = %" PRIu64,
+                       ua_event_notifier_rule->token);
+
+       return ua_event_notifier_rule;
+
+error_put_trigger:
+       lttng_trigger_put(trigger);
+error:
+       free(ua_event_notifier_rule);
+       return NULL;
+}
+
 /*
  * Alloc new UST app context.
  */
@@ -1139,8 +1304,8 @@ struct ust_app_ctx *alloc_ust_app_ctx(struct lttng_ust_context_attr *uctx)
 
        if (uctx) {
                memcpy(&ua_ctx->ctx, uctx, sizeof(ua_ctx->ctx));
-               if (uctx->ctx == LTTNG_UST_CONTEXT_APP_CONTEXT) {
-                       char *provider_name = NULL, *ctx_name = NULL;
+               if (uctx->ctx == LTTNG_UST_ABI_CONTEXT_APP_CONTEXT) {
+                       char *provider_name = NULL, *ctx_name = NULL;
 
                        provider_name = strdup(uctx->u.app_ctx.provider_name);
                        ctx_name = strdup(uctx->u.app_ctx.ctx_name);
@@ -1163,50 +1328,51 @@ error:
 }
 
 /*
- * Allocate a filter and copy the given original filter.
+ * Create a liblttng-ust filter bytecode from given bytecode.
  *
  * Return allocated filter or NULL on error.
  */
-static struct lttng_filter_bytecode *copy_filter_bytecode(
-               struct lttng_filter_bytecode *orig_f)
+static struct lttng_ust_abi_filter_bytecode *create_ust_filter_bytecode_from_bytecode(
+               const struct lttng_bytecode *orig_f)
 {
-       struct lttng_filter_bytecode *filter = NULL;
+       struct lttng_ust_abi_filter_bytecode *filter = NULL;
 
-       /* Copy filter bytecode */
+       /* Copy filter bytecode. */
        filter = zmalloc(sizeof(*filter) + orig_f->len);
        if (!filter) {
-               PERROR("zmalloc alloc filter bytecode");
+               PERROR("Failed to allocate lttng_ust_filter_bytecode: bytecode len = %" PRIu32 " bytes", orig_f->len);
                goto error;
        }
 
+       assert(sizeof(struct lttng_bytecode) ==
+                       sizeof(struct lttng_ust_abi_filter_bytecode));
        memcpy(filter, orig_f, sizeof(*filter) + orig_f->len);
-
 error:
        return filter;
 }
 
 /*
- * Create a liblttng-ust filter bytecode from given bytecode.
+ * Create a liblttng-ust capture bytecode from given bytecode.
  *
  * Return allocated filter or NULL on error.
  */
-static struct lttng_ust_filter_bytecode *create_ust_bytecode_from_bytecode(
-               struct lttng_filter_bytecode *orig_f)
+static struct lttng_ust_abi_capture_bytecode *
+create_ust_capture_bytecode_from_bytecode(const struct lttng_bytecode *orig_f)
 {
-       struct lttng_ust_filter_bytecode *filter = NULL;
+       struct lttng_ust_abi_capture_bytecode *capture = NULL;
 
-       /* Copy filter bytecode */
-       filter = zmalloc(sizeof(*filter) + orig_f->len);
-       if (!filter) {
-               PERROR("zmalloc alloc ust filter bytecode");
+       /* Copy capture bytecode. */
+       capture = zmalloc(sizeof(*capture) + orig_f->len);
+       if (!capture) {
+               PERROR("Failed to allocate lttng_ust_abi_capture_bytecode: bytecode len = %" PRIu32 " bytes", orig_f->len);
                goto error;
        }
 
-       assert(sizeof(struct lttng_filter_bytecode) ==
-                       sizeof(struct lttng_ust_filter_bytecode));
-       memcpy(filter, orig_f, sizeof(*filter) + orig_f->len);
+       assert(sizeof(struct lttng_bytecode) ==
+                       sizeof(struct lttng_ust_abi_capture_bytecode));
+       memcpy(capture, orig_f, sizeof(*capture) + orig_f->len);
 error:
-       return filter;
+       return capture;
 }
 
 /*
@@ -1261,7 +1427,7 @@ error:
  * Return an ust_app_event object or NULL on error.
  */
 static struct ust_app_event *find_ust_app_event(struct lttng_ht *ht,
-               const char *name, const struct lttng_filter_bytecode *filter,
+               const char *name, const struct lttng_bytecode *filter,
                int loglevel_value,
                const struct lttng_event_exclusion *exclusion)
 {
@@ -1294,6 +1460,35 @@ end:
        return event;
 }
 
+/*
+ * Look-up an event notifier rule based on its token id.
+ *
+ * Must be called with the RCU read lock held.
+ * Return an ust_app_event_notifier_rule object or NULL on error.
+ */
+static struct ust_app_event_notifier_rule *find_ust_app_event_notifier_rule(
+               struct lttng_ht *ht, uint64_t token)
+{
+       struct lttng_ht_iter iter;
+       struct lttng_ht_node_u64 *node;
+       struct ust_app_event_notifier_rule *event_notifier_rule = NULL;
+
+       assert(ht);
+
+       lttng_ht_lookup(ht, &token, &iter);
+       node = lttng_ht_iter_get_node_u64(&iter);
+       if (node == NULL) {
+               DBG2("UST app event notifier rule token not found: token = %" PRIu64,
+                               token);
+               goto end;
+       }
+
+       event_notifier_rule = caa_container_of(
+                       node, struct ust_app_event_notifier_rule, node);
+end:
+       return event_notifier_rule;
+}
+
 /*
  * Create the channel context on the tracer.
  *
@@ -1340,33 +1535,82 @@ error:
 /*
  * Set the filter on the tracer.
  */
-static
-int set_ust_event_filter(struct ust_app_event *ua_event,
-               struct ust_app *app)
+static int set_ust_object_filter(struct ust_app *app,
+               const struct lttng_bytecode *bytecode,
+               struct lttng_ust_abi_object_data *ust_object)
 {
        int ret;
-       struct lttng_ust_filter_bytecode *ust_bytecode = NULL;
+       struct lttng_ust_abi_filter_bytecode *ust_bytecode = NULL;
 
        health_code_update();
 
-       if (!ua_event->filter) {
-               ret = 0;
+       ust_bytecode = create_ust_filter_bytecode_from_bytecode(bytecode);
+       if (!ust_bytecode) {
+               ret = -LTTNG_ERR_NOMEM;
+               goto error;
+       }
+       pthread_mutex_lock(&app->sock_lock);
+       ret = ustctl_set_filter(app->sock, ust_bytecode,
+                       ust_object);
+       pthread_mutex_unlock(&app->sock_lock);
+       if (ret < 0) {
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app set object filter failed: object = %p of app pid = %d, ret = %d",
+                                       ust_object, 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("Failed to set UST app object filter. Application is dead.");
+               }
                goto error;
        }
 
-       ust_bytecode = create_ust_bytecode_from_bytecode(ua_event->filter);
+       DBG2("UST filter successfully set: object = %p", ust_object);
+
+error:
+       health_code_update();
+       free(ust_bytecode);
+       return ret;
+}
+
+/*
+ * Set a capture bytecode for the passed object.
+ * The sequence number enforces the ordering at runtime and on reception of
+ * the captured payloads.
+ */
+static int set_ust_capture(struct ust_app *app,
+               const struct lttng_bytecode *bytecode,
+               unsigned int capture_seqnum,
+               struct lttng_ust_abi_object_data *ust_object)
+{
+       int ret;
+       struct lttng_ust_abi_capture_bytecode *ust_bytecode = NULL;
+
+       health_code_update();
+
+       ust_bytecode = create_ust_capture_bytecode_from_bytecode(bytecode);
        if (!ust_bytecode) {
                ret = -LTTNG_ERR_NOMEM;
                goto error;
        }
+
+       /*
+        * Set the sequence number to ensure the capture of fields is ordered.
+        */
+       ust_bytecode->seqnum = capture_seqnum;
+
        pthread_mutex_lock(&app->sock_lock);
-       ret = ustctl_set_filter(app->sock, ust_bytecode,
-                       ua_event->obj);
+       ret = ustctl_set_capture(app->sock, ust_bytecode,
+                       ust_object);
        pthread_mutex_unlock(&app->sock_lock);
        if (ret < 0) {
                if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
-                       ERR("UST app event %s filter failed for app (pid: %d) "
-                                       "with ret %d", ua_event->attr.name, app->pid, ret);
+                       ERR("UST app set object capture failed: object = %p of app pid = %d, ret = %d",
+                                       ust_object, app->pid, ret);
                } else {
                        /*
                         * This is normal behavior, an application can die during the
@@ -1374,12 +1618,13 @@ int set_ust_event_filter(struct ust_app_event *ua_event,
                         * continue normally.
                         */
                        ret = 0;
-                       DBG3("UST app filter event failed. Application is dead.");
+                       DBG3("Failed to set UST app object capture. Application is dead.");
                }
+
                goto error;
        }
 
-       DBG2("UST filter set successfully for event %s", ua_event->name);
+       DBG2("UST capture successfully set: object = %p", ust_object);
 
 error:
        health_code_update();
@@ -1388,12 +1633,12 @@ error:
 }
 
 static
-struct lttng_ust_event_exclusion *create_ust_exclusion_from_exclusion(
-               struct lttng_event_exclusion *exclusion)
+struct lttng_ust_abi_event_exclusion *create_ust_exclusion_from_exclusion(
+               const struct lttng_event_exclusion *exclusion)
 {
-       struct lttng_ust_event_exclusion *ust_exclusion = NULL;
-       size_t exclusion_alloc_size = sizeof(struct lttng_ust_event_exclusion) +
-               LTTNG_UST_SYM_NAME_LEN * exclusion->count;
+       struct lttng_ust_abi_event_exclusion *ust_exclusion = NULL;
+       size_t exclusion_alloc_size = sizeof(struct lttng_ust_abi_event_exclusion) +
+               LTTNG_UST_ABI_SYM_NAME_LEN * exclusion->count;
 
        ust_exclusion = zmalloc(exclusion_alloc_size);
        if (!ust_exclusion) {
@@ -1402,7 +1647,7 @@ struct lttng_ust_event_exclusion *create_ust_exclusion_from_exclusion(
        }
 
        assert(sizeof(struct lttng_event_exclusion) ==
-                       sizeof(struct lttng_ust_event_exclusion));
+                       sizeof(struct lttng_ust_abi_event_exclusion));
        memcpy(ust_exclusion, exclusion, exclusion_alloc_size);
 end:
        return ust_exclusion;
@@ -1411,33 +1656,30 @@ end:
 /*
  * Set event exclusions on the tracer.
  */
-static
-int set_ust_event_exclusion(struct ust_app_event *ua_event,
-               struct ust_app *app)
+static int set_ust_object_exclusions(struct ust_app *app,
+               const struct lttng_event_exclusion *exclusions,
+               struct lttng_ust_abi_object_data *ust_object)
 {
        int ret;
-       struct lttng_ust_event_exclusion *ust_exclusion = NULL;
+       struct lttng_ust_abi_event_exclusion *ust_exclusions = NULL;
 
-       health_code_update();
+       assert(exclusions && exclusions->count > 0);
 
-       if (!ua_event->exclusion || !ua_event->exclusion->count) {
-               ret = 0;
-               goto error;
-       }
+       health_code_update();
 
-       ust_exclusion = create_ust_exclusion_from_exclusion(
-                       ua_event->exclusion);
-       if (!ust_exclusion) {
+       ust_exclusions = create_ust_exclusion_from_exclusion(
+                       exclusions);
+       if (!ust_exclusions) {
                ret = -LTTNG_ERR_NOMEM;
                goto error;
        }
        pthread_mutex_lock(&app->sock_lock);
-       ret = ustctl_set_exclusion(app->sock, ust_exclusion, ua_event->obj);
+       ret = ustctl_set_exclusion(app->sock, ust_exclusions, ust_object);
        pthread_mutex_unlock(&app->sock_lock);
        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);
+                       ERR("Failed to set UST app exclusions for object %p of app (pid: %d) "
+                                       "with ret %d", ust_object, app->pid, ret);
                } else {
                        /*
                         * This is normal behavior, an application can die during the
@@ -1445,37 +1687,36 @@ int set_ust_event_exclusion(struct ust_app_event *ua_event,
                         * continue normally.
                         */
                        ret = 0;
-                       DBG3("UST app event exclusion failed. Application is dead.");
+                       DBG3("Failed to set UST app object exclusions. Application is dead.");
                }
                goto error;
        }
 
-       DBG2("UST exclusion set successfully for event %s", ua_event->name);
+       DBG2("UST exclusions set successfully for object %p", ust_object);
 
 error:
        health_code_update();
-       free(ust_exclusion);
+       free(ust_exclusions);
        return ret;
 }
 
 /*
  * Disable the specified event on to UST tracer for the UST session.
  */
-static int disable_ust_event(struct ust_app *app,
-               struct ust_app_session *ua_sess, struct ust_app_event *ua_event)
+static int disable_ust_object(struct ust_app *app,
+               struct lttng_ust_abi_object_data *object)
 {
        int ret;
 
        health_code_update();
 
        pthread_mutex_lock(&app->sock_lock);
-       ret = ustctl_disable(app->sock, ua_event->obj);
+       ret = ustctl_disable(app->sock, object);
        pthread_mutex_unlock(&app->sock_lock);
        if (ret < 0) {
                if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
-                       ERR("UST app event %s disable failed for app (pid: %d) "
-                                       "and session handle %d with ret %d",
-                                       ua_event->attr.name, app->pid, ua_sess->handle, ret);
+                       ERR("Failed to disable UST app object %p app (pid: %d) with ret %d",
+                                       object, app->pid, ret);
                } else {
                        /*
                         * This is normal behavior, an application can die during the
@@ -1483,13 +1724,13 @@ static int disable_ust_event(struct ust_app *app,
                         * continue normally.
                         */
                        ret = 0;
-                       DBG3("UST app disable event failed. Application is dead.");
+                       DBG3("Failed to disable UST app object. Application is dead.");
                }
                goto error;
        }
 
-       DBG2("UST app event %s disabled successfully for app (pid: %d)",
-                       ua_event->attr.name, app->pid);
+       DBG2("UST app object %p disabled successfully for app (pid: %d)",
+                       object, app->pid);
 
 error:
        health_code_update();
@@ -1577,21 +1818,20 @@ error:
 /*
  * Enable the specified event on to UST tracer for the UST session.
  */
-static int enable_ust_event(struct ust_app *app,
-               struct ust_app_session *ua_sess, struct ust_app_event *ua_event)
+static int enable_ust_object(
+               struct ust_app *app, struct lttng_ust_abi_object_data *ust_object)
 {
        int ret;
 
        health_code_update();
 
        pthread_mutex_lock(&app->sock_lock);
-       ret = ustctl_enable(app->sock, ua_event->obj);
+       ret = ustctl_enable(app->sock, ust_object);
        pthread_mutex_unlock(&app->sock_lock);
        if (ret < 0) {
                if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
-                       ERR("UST app event %s enable failed for app (pid: %d) "
-                                       "and session handle %d with ret %d",
-                                       ua_event->attr.name, app->pid, ua_sess->handle, ret);
+                       ERR("UST app enable failed for object %p app (pid: %d) with ret %d",
+                                       ust_object, app->pid, ret);
                } else {
                        /*
                         * This is normal behavior, an application can die during the
@@ -1599,13 +1839,13 @@ static int enable_ust_event(struct ust_app *app,
                         * continue normally.
                         */
                        ret = 0;
-                       DBG3("UST app enable event failed. Application is dead.");
+                       DBG3("Failed to enable UST app object. Application is dead.");
                }
                goto error;
        }
 
-       DBG2("UST app event %s enabled successfully for app (pid: %d)",
-                       ua_event->attr.name, app->pid);
+       DBG2("UST app object %p enabled successfully for app (pid: %d)",
+                       ust_object, app->pid);
 
 error:
        health_code_update();
@@ -1701,14 +1941,14 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
 
        ua_event->handle = ua_event->obj->handle;
 
-       DBG2("UST app event %s created successfully for pid:%d",
-                       ua_event->attr.name, app->pid);
+       DBG2("UST app event %s created successfully for pid:%d object: %p",
+                       ua_event->attr.name, app->pid, ua_event->obj);
 
        health_code_update();
 
        /* Set filter if one is present. */
        if (ua_event->filter) {
-               ret = set_ust_event_filter(ua_event, app);
+               ret = set_ust_object_filter(app, ua_event->filter, ua_event->obj);
                if (ret < 0) {
                        goto error;
                }
@@ -1716,7 +1956,7 @@ 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);
+               ret = set_ust_object_exclusions(app, ua_event->exclusion, ua_event->obj);
                if (ret < 0) {
                        goto error;
                }
@@ -1728,7 +1968,7 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
                 * We now need to explicitly enable the event, since it
                 * is now disabled at creation.
                 */
-               ret = enable_ust_event(app, ua_sess, ua_event);
+               ret = enable_ust_object(app, ua_event->obj);
                if (ret < 0) {
                        /*
                         * If we hit an EPERM, something is wrong with our enable call. If
@@ -1755,100 +1995,314 @@ error:
        return ret;
 }
 
-/*
- * Copy data between an UST app event and a LTT event.
- */
-static void shadow_copy_event(struct ust_app_event *ua_event,
-               struct ltt_ust_event *uevent)
+static int init_ust_event_notifier_from_event_rule(
+               const struct lttng_event_rule *rule,
+               struct lttng_ust_abi_event_notifier *event_notifier)
 {
-       size_t exclusion_alloc_size;
+       enum lttng_event_rule_status status;
+       enum lttng_ust_abi_loglevel_type ust_loglevel_type = LTTNG_UST_ABI_LOGLEVEL_ALL;
+       int loglevel = -1, ret = 0;
+       const char *pattern;
 
-       strncpy(ua_event->name, uevent->attr.name, sizeof(ua_event->name));
-       ua_event->name[sizeof(ua_event->name) - 1] = '\0';
+       /* For now only LTTNG_EVENT_RULE_TYPE_TRACEPOINT are supported. */
+       assert(lttng_event_rule_get_type(rule) ==
+                       LTTNG_EVENT_RULE_TYPE_TRACEPOINT);
 
-       ua_event->enabled = uevent->enabled;
+       memset(event_notifier, 0, sizeof(*event_notifier));
 
-       /* Copy event attributes */
-       memcpy(&ua_event->attr, &uevent->attr, sizeof(ua_event->attr));
+       if (lttng_event_rule_targets_agent_domain(rule)) {
+               /*
+                * Special event for agents
+                * The actual meat of the event is in the filter that will be
+                * attached later on.
+                * Set the default values for the agent event.
+                */
+               pattern = event_get_default_agent_ust_name(
+                               lttng_event_rule_get_domain_type(rule));
+               loglevel = 0;
+               ust_loglevel_type = LTTNG_UST_ABI_LOGLEVEL_ALL;
+       } else {
+               const struct lttng_log_level_rule *log_level_rule;
 
-       /* Copy filter bytecode */
-       if (uevent->filter) {
-               ua_event->filter = copy_filter_bytecode(uevent->filter);
-               /* Filter might be NULL here in case of ENONEM. */
-       }
+               status = lttng_event_rule_tracepoint_get_pattern(rule, &pattern);
+               if (status != LTTNG_EVENT_RULE_STATUS_OK) {
+                       /* At this point, this is a fatal error. */
+                       abort();
+               }
 
-       /* Copy exclusion data */
-       if (uevent->exclusion) {
-               exclusion_alloc_size = sizeof(struct lttng_event_exclusion) +
-                               LTTNG_UST_SYM_NAME_LEN * uevent->exclusion->count;
-               ua_event->exclusion = zmalloc(exclusion_alloc_size);
-               if (ua_event->exclusion == NULL) {
-                       PERROR("malloc");
+               status = lttng_event_rule_tracepoint_get_log_level_rule(
+                               rule, &log_level_rule);
+               if (status == LTTNG_EVENT_RULE_STATUS_UNSET) {
+                       ust_loglevel_type = LTTNG_UST_ABI_LOGLEVEL_ALL;
+               } else if (status == LTTNG_EVENT_RULE_STATUS_OK) {
+                       enum lttng_log_level_rule_status llr_status;
+
+                       switch (lttng_log_level_rule_get_type(log_level_rule)) {
+                       case LTTNG_LOG_LEVEL_RULE_TYPE_EXACTLY:
+                               ust_loglevel_type = LTTNG_UST_ABI_LOGLEVEL_SINGLE;
+                               llr_status = lttng_log_level_rule_exactly_get_level(
+                                               log_level_rule, &loglevel);
+                               break;
+                       case LTTNG_LOG_LEVEL_RULE_TYPE_AT_LEAST_AS_SEVERE_AS:
+                               ust_loglevel_type = LTTNG_UST_ABI_LOGLEVEL_RANGE;
+                               llr_status = lttng_log_level_rule_at_least_as_severe_as_get_level(
+                                               log_level_rule, &loglevel);
+                               break;
+                       default:
+                               abort();
+                       }
+
+                       assert(llr_status == LTTNG_LOG_LEVEL_RULE_STATUS_OK);
                } else {
-                       memcpy(ua_event->exclusion, uevent->exclusion,
-                                       exclusion_alloc_size);
+                       /* At this point this is a fatal error. */
+                       abort();
                }
        }
+
+       event_notifier->event.instrumentation = LTTNG_UST_ABI_TRACEPOINT;
+       ret = lttng_strncpy(event_notifier->event.name, pattern,
+                       LTTNG_UST_ABI_SYM_NAME_LEN - 1);
+       if (ret) {
+               ERR("Failed to copy event rule pattern to notifier: pattern = '%s' ",
+                               pattern);
+               goto end;
+       }
+
+       event_notifier->event.loglevel_type = ust_loglevel_type;
+       event_notifier->event.loglevel = loglevel;
+end:
+       return ret;
 }
 
 /*
- * Copy data between an UST app channel and a LTT channel.
+ * Create the specified event notifier against the user space tracer of a
+ * given application.
  */
-static void shadow_copy_channel(struct ust_app_channel *ua_chan,
-               struct ltt_ust_channel *uchan)
+static int create_ust_event_notifier(struct ust_app *app,
+               struct ust_app_event_notifier_rule *ua_event_notifier_rule)
 {
-       DBG2("UST app shadow copy of channel %s started", ua_chan->name);
+       int ret = 0;
+       enum lttng_condition_status condition_status;
+       const struct lttng_condition *condition = NULL;
+       struct lttng_ust_abi_event_notifier event_notifier;
+       const struct lttng_event_rule *event_rule = NULL;
+       unsigned int capture_bytecode_count = 0, i;
+       enum lttng_condition_status cond_status;
 
-       strncpy(ua_chan->name, uchan->name, sizeof(ua_chan->name));
-       ua_chan->name[sizeof(ua_chan->name) - 1] = '\0';
+       health_code_update();
+       assert(app->event_notifier_group.object);
 
-       ua_chan->tracefile_size = uchan->tracefile_size;
-       ua_chan->tracefile_count = uchan->tracefile_count;
+       condition = lttng_trigger_get_const_condition(
+                       ua_event_notifier_rule->trigger);
+       assert(condition);
+       assert(lttng_condition_get_type(condition) == LTTNG_CONDITION_TYPE_ON_EVENT);
 
-       /* 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;
-       ua_chan->attr.overwrite = uchan->attr.overwrite;
-       ua_chan->attr.switch_timer_interval = uchan->attr.switch_timer_interval;
-       ua_chan->attr.read_timer_interval = uchan->attr.read_timer_interval;
-       ua_chan->monitor_timer_interval = uchan->monitor_timer_interval;
-       ua_chan->attr.output = uchan->attr.output;
-       ua_chan->attr.blocking_timeout = uchan->attr.u.s.blocking_timeout;
+       condition_status = lttng_condition_on_event_get_rule(
+                       condition, &event_rule);
+       assert(condition_status == LTTNG_CONDITION_STATUS_OK);
 
-       /*
-        * Note that the attribute channel type is not set since the channel on the
-        * tracing registry side does not have this information.
-        */
+       assert(event_rule);
+       assert(lttng_event_rule_get_type(event_rule) == LTTNG_EVENT_RULE_TYPE_TRACEPOINT);
 
-       ua_chan->enabled = uchan->enabled;
-       ua_chan->tracing_channel_id = uchan->id;
+       init_ust_event_notifier_from_event_rule(event_rule, &event_notifier);
+       event_notifier.event.token = ua_event_notifier_rule->token;
 
-       DBG3("UST app shadow copy of channel %s done", ua_chan->name);
-}
+       /* Create UST event notifier against the tracer. */
+       pthread_mutex_lock(&app->sock_lock);
+       ret = ustctl_create_event_notifier(app->sock, &event_notifier,
+                       app->event_notifier_group.object,
+                       &ua_event_notifier_rule->obj);
+       pthread_mutex_unlock(&app->sock_lock);
+       if (ret < 0) {
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("Error ustctl create event notifier: name = '%s', app = '%s' (ppid: %d), ret = %d",
+                                       event_notifier.event.name, app->name,
+                                       app->ppid, 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 notifier failed (application is dead): app = '%s' (ppid = %d)",
+                                       app->name, app->ppid);
+               }
 
-/*
- * Copy data between a UST app session and a regular LTT session.
- */
-static void shadow_copy_session(struct ust_app_session *ua_sess,
-               struct ltt_ust_session *usess, struct ust_app *app)
-{
-       struct tm *timeinfo;
-       char datetime[16];
-       int ret;
-       char tmp_shm_path[PATH_MAX];
+               goto error;
+       }
 
-       timeinfo = localtime(&app->registration_time);
-       strftime(datetime, sizeof(datetime), "%Y%m%d-%H%M%S", timeinfo);
+       ua_event_notifier_rule->handle = ua_event_notifier_rule->obj->handle;
 
-       DBG2("Shadow copy of session handle %d", ua_sess->handle);
+       DBG2("UST app event notifier %s created successfully: app = '%s' (ppid: %d), object: %p",
+                       event_notifier.event.name, app->name, app->ppid,
+                       ua_event_notifier_rule->obj);
 
-       ua_sess->tracing_id = usess->id;
-       ua_sess->id = get_next_session_id();
-       ua_sess->real_credentials.uid = app->uid;
-       ua_sess->real_credentials.gid = app->gid;
-       ua_sess->effective_credentials.uid = usess->uid;
-       ua_sess->effective_credentials.gid = usess->gid;
-       ua_sess->buffer_type = usess->buffer_type;
+       health_code_update();
+
+       /* Set filter if one is present. */
+       if (ua_event_notifier_rule->filter) {
+               ret = set_ust_object_filter(app, ua_event_notifier_rule->filter,
+                               ua_event_notifier_rule->obj);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
+
+       /* Set exclusions for the event. */
+       if (ua_event_notifier_rule->exclusion) {
+               ret = set_ust_object_exclusions(app,
+                               ua_event_notifier_rule->exclusion,
+                               ua_event_notifier_rule->obj);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
+
+       /* Set the capture bytecodes. */
+       cond_status = lttng_condition_on_event_get_capture_descriptor_count(
+                       condition, &capture_bytecode_count);
+       assert(cond_status == LTTNG_CONDITION_STATUS_OK);
+
+       for (i = 0; i < capture_bytecode_count; i++) {
+               const struct lttng_bytecode *capture_bytecode =
+                               lttng_condition_on_event_get_capture_bytecode_at_index(
+                                               condition, i);
+
+               ret = set_ust_capture(app, capture_bytecode, i,
+                               ua_event_notifier_rule->obj);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
+
+       /*
+        * We now need to explicitly enable the event, since it
+        * is disabled at creation.
+        */
+       ret = enable_ust_object(app, ua_event_notifier_rule->obj);
+       if (ret < 0) {
+               /*
+                * If we hit an EPERM, something is wrong with our enable call.
+                * If we get an EEXIST, there is a problem on the tracer side
+                * since we just created it.
+                */
+               switch (ret) {
+               case -LTTNG_UST_ERR_PERM:
+                       /* Code flow problem. */
+                       abort();
+               case -LTTNG_UST_ERR_EXIST:
+                       /* It's OK for our use case. */
+                       ret = 0;
+                       break;
+               default:
+                       break;
+               }
+
+               goto error;
+       }
+
+       ua_event_notifier_rule->enabled = true;
+
+error:
+       health_code_update();
+       return ret;
+}
+
+/*
+ * Copy data between an UST app event and a LTT event.
+ */
+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';
+
+       ua_event->enabled = uevent->enabled;
+
+       /* Copy event attributes */
+       memcpy(&ua_event->attr, &uevent->attr, sizeof(ua_event->attr));
+
+       /* Copy filter bytecode */
+       if (uevent->filter) {
+               ua_event->filter = lttng_bytecode_copy(uevent->filter);
+               /* Filter might be NULL here in case of ENONEM. */
+       }
+
+       /* Copy exclusion data */
+       if (uevent->exclusion) {
+               exclusion_alloc_size = sizeof(struct lttng_event_exclusion) +
+                               LTTNG_UST_ABI_SYM_NAME_LEN * uevent->exclusion->count;
+               ua_event->exclusion = zmalloc(exclusion_alloc_size);
+               if (ua_event->exclusion == NULL) {
+                       PERROR("malloc");
+               } else {
+                       memcpy(ua_event->exclusion, uevent->exclusion,
+                                       exclusion_alloc_size);
+               }
+       }
+}
+
+/*
+ * Copy data between an UST app channel and a LTT channel.
+ */
+static void shadow_copy_channel(struct ust_app_channel *ua_chan,
+               struct ltt_ust_channel *uchan)
+{
+       DBG2("UST app shadow copy of channel %s started", ua_chan->name);
+
+       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;
+       ua_chan->attr.overwrite = uchan->attr.overwrite;
+       ua_chan->attr.switch_timer_interval = uchan->attr.switch_timer_interval;
+       ua_chan->attr.read_timer_interval = uchan->attr.read_timer_interval;
+       ua_chan->monitor_timer_interval = uchan->monitor_timer_interval;
+       ua_chan->attr.output = uchan->attr.output;
+       ua_chan->attr.blocking_timeout = uchan->attr.u.s.blocking_timeout;
+
+       /*
+        * Note that the attribute channel type is not set since the channel on the
+        * tracing registry side does not have this information.
+        */
+
+       ua_chan->enabled = uchan->enabled;
+       ua_chan->tracing_channel_id = uchan->id;
+
+       DBG3("UST app shadow copy of channel %s done", ua_chan->name);
+}
+
+/*
+ * Copy data between a UST app session and a regular LTT session.
+ */
+static void shadow_copy_session(struct ust_app_session *ua_sess,
+               struct ltt_ust_session *usess, struct ust_app *app)
+{
+       struct tm *timeinfo;
+       char datetime[16];
+       int ret;
+       char tmp_shm_path[PATH_MAX];
+
+       timeinfo = localtime(&app->registration_time);
+       strftime(datetime, sizeof(datetime), "%Y%m%d-%H%M%S", timeinfo);
+
+       DBG2("Shadow copy of session handle %d", ua_sess->handle);
+
+       ua_sess->tracing_id = usess->id;
+       ua_sess->id = get_next_session_id();
+       LTTNG_OPTIONAL_SET(&ua_sess->real_credentials.uid, app->uid);
+       LTTNG_OPTIONAL_SET(&ua_sess->real_credentials.gid, app->gid);
+       LTTNG_OPTIONAL_SET(&ua_sess->effective_credentials.uid, usess->uid);
+       LTTNG_OPTIONAL_SET(&ua_sess->effective_credentials.gid, 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. */
@@ -1869,7 +2323,7 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
        case LTTNG_BUFFER_PER_UID:
                ret = snprintf(ua_sess->path, sizeof(ua_sess->path),
                                DEFAULT_UST_TRACE_UID_PATH,
-                               ua_sess->real_credentials.uid,
+                               lttng_credentials_get_uid(&ua_sess->real_credentials),
                                app->bits_per_long);
                break;
        default:
@@ -1892,12 +2346,12 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
                switch (ua_sess->buffer_type) {
                case LTTNG_BUFFER_PER_PID:
                        ret = snprintf(tmp_shm_path, sizeof(tmp_shm_path),
-                                       DEFAULT_UST_TRACE_PID_PATH "/%s-%d-%s",
+                                       "/" DEFAULT_UST_TRACE_PID_PATH "/%s-%d-%s",
                                        app->name, app->pid, datetime);
                        break;
                case LTTNG_BUFFER_PER_UID:
                        ret = snprintf(tmp_shm_path, sizeof(tmp_shm_path),
-                                       DEFAULT_UST_TRACE_UID_PATH,
+                                       "/" DEFAULT_UST_TRACE_UID_PATH,
                                        app->uid, app->bits_per_long);
                        break;
                default:
@@ -1992,8 +2446,10 @@ static int setup_buffer_reg_pid(struct ust_app_session *ua_sess,
                        app->uint64_t_alignment, app->long_alignment,
                        app->byte_order, app->version.major, app->version.minor,
                        reg_pid->root_shm_path, reg_pid->shm_path,
-                       ua_sess->effective_credentials.uid,
-                       ua_sess->effective_credentials.gid);
+                       lttng_credentials_get_uid(&ua_sess->effective_credentials),
+                       lttng_credentials_get_gid(&ua_sess->effective_credentials),
+                       ua_sess->tracing_id,
+                       app->uid);
        if (ret < 0) {
                /*
                 * reg_pid->registry->reg.ust is NULL upon error, so we need to
@@ -2060,7 +2516,8 @@ static int setup_buffer_reg_uid(struct ltt_ust_session *usess,
                        app->uint64_t_alignment, app->long_alignment,
                        app->byte_order, app->version.major,
                        app->version.minor, reg_uid->root_shm_path,
-                       reg_uid->shm_path, usess->uid, usess->gid);
+                       reg_uid->shm_path, usess->uid, usess->gid,
+                       ua_sess->tracing_id, app->uid);
        if (ret < 0) {
                /*
                 * reg_uid->registry->reg.ust is NULL upon error, so we need to
@@ -2227,14 +2684,14 @@ static int ht_match_ust_app_ctx(struct cds_lfht_node *node, const void *_key)
        }
 
        switch(key->ctx) {
-       case LTTNG_UST_CONTEXT_PERF_THREAD_COUNTER:
+       case LTTNG_UST_ABI_CONTEXT_PERF_THREAD_COUNTER:
                if (strncmp(key->u.perf_counter.name,
                                ctx->ctx.u.perf_counter.name,
                                sizeof(key->u.perf_counter.name))) {
                        goto no_match;
                }
                break;
-       case LTTNG_UST_CONTEXT_APP_CONTEXT:
+       case LTTNG_UST_ABI_CONTEXT_APP_CONTEXT:
                if (strcmp(key->u.app_ctx.provider_name,
                                ctx->ctx.u.app_ctx.provider_name) ||
                                strcmp(key->u.app_ctx.ctx_name,
@@ -2291,7 +2748,7 @@ end:
  */
 static
 int create_ust_app_channel_context(struct ust_app_channel *ua_chan,
-               struct lttng_ust_context_attr *uctx,
+               struct lttng_ust_context_attr *uctx,
                struct ust_app *app)
 {
        int ret = 0;
@@ -2336,7 +2793,7 @@ int enable_ust_app_event(struct ust_app_session *ua_sess,
 {
        int ret;
 
-       ret = enable_ust_event(app, ua_sess, ua_event);
+       ret = enable_ust_object(app, ua_event->obj);
        if (ret < 0) {
                goto error;
        }
@@ -2355,7 +2812,7 @@ static int disable_ust_app_event(struct ust_app_session *ua_sess,
 {
        int ret;
 
-       ret = disable_ust_event(app, ua_sess, ua_event);
+       ret = disable_ust_object(app, ua_event->obj);
        if (ret < 0) {
                goto error;
        }
@@ -2556,12 +3013,12 @@ error:
  *
  * Return 0 on success or else a negative value.
  */
-static int duplicate_channel_object(struct buffer_reg_channel *reg_chan,
+static int duplicate_channel_object(struct buffer_reg_channel *buf_reg_chan,
                struct ust_app_channel *ua_chan)
 {
        int ret;
 
-       assert(reg_chan);
+       assert(buf_reg_chan);
        assert(ua_chan);
 
        /* Need two fds for the channel. */
@@ -2572,10 +3029,10 @@ static int duplicate_channel_object(struct buffer_reg_channel *reg_chan,
        }
 
        /* Duplicate object for stream once the original is in the registry. */
-       ret = ustctl_duplicate_ust_object_data(&ua_chan->obj, reg_chan->obj.ust);
+       ret = ustctl_duplicate_ust_object_data(&ua_chan->obj, buf_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);
+                               buf_reg_chan->obj.ust, ua_chan->obj, ret);
                goto error;
        }
        ua_chan->handle = ua_chan->obj->handle;
@@ -2594,14 +3051,14 @@ error_fd_get:
  *
  * Return 0 on success or else a negative value.
  */
-static int setup_buffer_reg_streams(struct buffer_reg_channel *reg_chan,
+static int setup_buffer_reg_streams(struct buffer_reg_channel *buf_reg_chan,
                struct ust_app_channel *ua_chan,
                struct ust_app *app)
 {
        int ret = 0;
        struct ust_app_stream *stream, *stmp;
 
-       assert(reg_chan);
+       assert(buf_reg_chan);
        assert(ua_chan);
 
        DBG2("UST app setup buffer registry stream");
@@ -2621,7 +3078,7 @@ static int setup_buffer_reg_streams(struct buffer_reg_channel *reg_chan,
                 */
                reg_stream->obj.ust = stream->obj;
                stream->obj = NULL;
-               buffer_reg_stream_add(reg_stream, reg_chan);
+               buffer_reg_stream_add(reg_stream, buf_reg_chan);
 
                /* We don't need the streams anymore. */
                cds_list_del(&stream->list);
@@ -2644,7 +3101,7 @@ 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;
+       struct buffer_reg_channel *buf_reg_chan = NULL;
 
        assert(reg_sess);
        assert(ua_chan);
@@ -2652,14 +3109,14 @@ static int create_buffer_reg_channel(struct buffer_reg_session *reg_sess,
        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);
+       ret = buffer_reg_channel_create(ua_chan->tracing_channel_id, &buf_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;
-       reg_chan->num_subbuf = ua_chan->attr.num_subbuf;
+       assert(buf_reg_chan);
+       buf_reg_chan->consumer_key = ua_chan->key;
+       buf_reg_chan->subbuf_size = ua_chan->attr.subbuf_size;
+       buf_reg_chan->num_subbuf = ua_chan->attr.num_subbuf;
 
        /* Create and add a channel registry to session. */
        ret = ust_registry_channel_add(reg_sess->reg.ust,
@@ -2667,17 +3124,17 @@ static int create_buffer_reg_channel(struct buffer_reg_session *reg_sess,
        if (ret < 0) {
                goto error;
        }
-       buffer_reg_channel_add(reg_sess, reg_chan);
+       buffer_reg_channel_add(reg_sess, buf_reg_chan);
 
        if (regp) {
-               *regp = reg_chan;
+               *regp = buf_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);
+       buffer_reg_channel_destroy(buf_reg_chan, LTTNG_DOMAIN_UST);
 error_create:
        return ret;
 }
@@ -2689,32 +3146,32 @@ error_create:
  * 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,
+               struct ust_app_channel *ua_chan, struct buffer_reg_channel *buf_reg_chan,
                struct ust_app *app)
 {
        int ret;
 
        assert(reg_sess);
-       assert(reg_chan);
+       assert(buf_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, app);
+       ret = setup_buffer_reg_streams(buf_reg_chan, ua_chan, app);
        if (ret < 0) {
                goto error;
        }
 
-       reg_chan->obj.ust = ua_chan->obj;
+       buf_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);
+       buffer_reg_channel_remove(reg_sess, buf_reg_chan);
+       buffer_reg_channel_destroy(buf_reg_chan, LTTNG_DOMAIN_UST);
        return ret;
 }
 
@@ -2723,21 +3180,21 @@ error:
  *
  * Return 0 on success else a negative value.
  */
-static int send_channel_uid_to_ust(struct buffer_reg_channel *reg_chan,
+static int send_channel_uid_to_ust(struct buffer_reg_channel *buf_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(buf_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);
+       ret = duplicate_channel_object(buf_reg_chan, ua_chan);
        if (ret < 0) {
                goto error;
        }
@@ -2754,8 +3211,8 @@ static int send_channel_uid_to_ust(struct buffer_reg_channel *reg_chan,
        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) {
+       pthread_mutex_lock(&buf_reg_chan->stream_list_lock);
+       cds_list_for_each_entry(reg_stream, &buf_reg_chan->streams, lnode) {
                struct ust_app_stream stream;
 
                ret = duplicate_stream_object(reg_stream, &stream);
@@ -2781,7 +3238,7 @@ static int send_channel_uid_to_ust(struct buffer_reg_channel *reg_chan,
        ua_chan->is_sent = 1;
 
 error_stream_unlock:
-       pthread_mutex_unlock(&reg_chan->stream_list_lock);
+       pthread_mutex_unlock(&buf_reg_chan->stream_list_lock);
 error:
        return ret;
 }
@@ -2800,10 +3257,10 @@ static int create_channel_per_uid(struct ust_app *app,
 {
        int ret;
        struct buffer_reg_uid *reg_uid;
-       struct buffer_reg_channel *reg_chan;
+       struct buffer_reg_channel *buf_reg_chan;
        struct ltt_session *session = NULL;
        enum lttng_error_code notification_ret;
-       struct ust_registry_channel *chan_reg;
+       struct ust_registry_channel *ust_reg_chan;
 
        assert(app);
        assert(usess);
@@ -2820,14 +3277,14 @@ static int create_channel_per_uid(struct ust_app *app,
         */
        assert(reg_uid);
 
-       reg_chan = buffer_reg_channel_find(ua_chan->tracing_channel_id,
+       buf_reg_chan = buffer_reg_channel_find(ua_chan->tracing_channel_id,
                        reg_uid);
-       if (reg_chan) {
+       if (buf_reg_chan) {
                goto send_channel;
        }
 
        /* Create the buffer registry channel object. */
-       ret = create_buffer_reg_channel(reg_uid->registry, ua_chan, &reg_chan);
+       ret = create_buffer_reg_channel(reg_uid->registry, ua_chan, &buf_reg_chan);
        if (ret < 0) {
                ERR("Error creating the UST channel \"%s\" registry instance",
                                ua_chan->name);
@@ -2856,8 +3313,8 @@ static int create_channel_per_uid(struct ust_app *app,
                 */
                ust_registry_channel_del_free(reg_uid->registry->reg.ust,
                                ua_chan->tracing_channel_id, false);
-               buffer_reg_channel_remove(reg_uid->registry, reg_chan);
-               buffer_reg_channel_destroy(reg_chan, LTTNG_DOMAIN_UST);
+               buffer_reg_channel_remove(reg_uid->registry, buf_reg_chan);
+               buffer_reg_channel_destroy(buf_reg_chan, LTTNG_DOMAIN_UST);
                goto error;
        }
 
@@ -2865,7 +3322,7 @@ static int create_channel_per_uid(struct ust_app *app,
         * Setup the streams and add it to the session registry.
         */
        ret = setup_buffer_reg_channel(reg_uid->registry,
-                       ua_chan, reg_chan, app);
+                       ua_chan, buf_reg_chan, app);
        if (ret < 0) {
                ERR("Error setting up UST channel \"%s\"", ua_chan->name);
                goto error;
@@ -2873,17 +3330,18 @@ static int create_channel_per_uid(struct ust_app *app,
 
        /* Notify the notification subsystem of the channel's creation. */
        pthread_mutex_lock(&reg_uid->registry->reg.ust->lock);
-       chan_reg = ust_registry_channel_find(reg_uid->registry->reg.ust,
+       ust_reg_chan = ust_registry_channel_find(reg_uid->registry->reg.ust,
                        ua_chan->tracing_channel_id);
-       assert(chan_reg);
-       chan_reg->consumer_key = ua_chan->key;
-       chan_reg = NULL;
+       assert(ust_reg_chan);
+       ust_reg_chan->consumer_key = ua_chan->key;
+       ust_reg_chan = NULL;
        pthread_mutex_unlock(&reg_uid->registry->reg.ust->lock);
 
        notification_ret = notification_thread_command_add_channel(
                        notification_thread_handle, session->name,
-                       ua_sess->effective_credentials.uid,
-                       ua_sess->effective_credentials.gid, ua_chan->name,
+                       lttng_credentials_get_uid(&ua_sess->effective_credentials),
+                       lttng_credentials_get_gid(&ua_sess->effective_credentials),
+                       ua_chan->name,
                        ua_chan->key, LTTNG_DOMAIN_UST,
                        ua_chan->attr.subbuf_size * ua_chan->attr.num_subbuf);
        if (notification_ret != LTTNG_OK) {
@@ -2894,7 +3352,7 @@ static int create_channel_per_uid(struct ust_app *app,
 
 send_channel:
        /* Send buffers to the application. */
-       ret = send_channel_uid_to_ust(reg_chan, app, ua_sess, ua_chan);
+       ret = send_channel_uid_to_ust(buf_reg_chan, app, ua_sess, ua_chan);
        if (ret < 0) {
                if (ret != -ENOTCONN) {
                        ERR("Error sending channel to application");
@@ -2926,7 +3384,7 @@ static int create_channel_per_pid(struct ust_app *app,
        enum lttng_error_code cmd_ret;
        struct ltt_session *session = NULL;
        uint64_t chan_reg_key;
-       struct ust_registry_channel *chan_reg;
+       struct ust_registry_channel *ust_reg_chan;
 
        assert(app);
        assert(usess);
@@ -2975,15 +3433,16 @@ static int create_channel_per_pid(struct ust_app *app,
 
        chan_reg_key = ua_chan->key;
        pthread_mutex_lock(&registry->lock);
-       chan_reg = ust_registry_channel_find(registry, chan_reg_key);
-       assert(chan_reg);
-       chan_reg->consumer_key = ua_chan->key;
+       ust_reg_chan = ust_registry_channel_find(registry, chan_reg_key);
+       assert(ust_reg_chan);
+       ust_reg_chan->consumer_key = ua_chan->key;
        pthread_mutex_unlock(&registry->lock);
 
        cmd_ret = notification_thread_command_add_channel(
                        notification_thread_handle, session->name,
-                       ua_sess->effective_credentials.uid,
-                       ua_sess->effective_credentials.gid, ua_chan->name,
+                       lttng_credentials_get_uid(&ua_sess->effective_credentials),
+                       lttng_credentials_get_gid(&ua_sess->effective_credentials),
+                       ua_chan->name,
                        ua_chan->key, LTTNG_DOMAIN_UST,
                        ua_chan->attr.subbuf_size * ua_chan->attr.num_subbuf);
        if (cmd_ret != LTTNG_OK) {
@@ -3075,7 +3534,7 @@ error:
  */
 static int ust_app_channel_allocate(struct ust_app_session *ua_sess,
                struct ltt_ust_channel *uchan,
-               enum lttng_ust_chan_type type, struct ltt_ust_session *usess,
+               enum lttng_ust_abi_chan_type type, struct ltt_ust_session *usess,
                struct ust_app_channel **ua_chanp)
 {
        int ret = 0;
@@ -3119,6 +3578,7 @@ error:
 /*
  * Create UST app event and create it on the tracer side.
  *
+ * Must be called with the RCU read side lock held.
  * Called with ust app session mutex held.
  */
 static
@@ -3131,7 +3591,7 @@ int create_ust_app_event(struct ust_app_session *ua_sess,
 
        ua_event = alloc_ust_app_event(uevent->attr.name, &uevent->attr);
        if (ua_event == NULL) {
-               /* Only malloc can failed so something is really wrong */
+               /* Only failure mode of alloc_ust_app_event(). */
                ret = -ENOMEM;
                goto end;
        }
@@ -3140,15 +3600,26 @@ int create_ust_app_event(struct ust_app_session *ua_sess,
        /* Create it on the tracer side */
        ret = create_ust_event(app, ua_sess, ua_chan, ua_event);
        if (ret < 0) {
-               /* Not found previously means that it does not exist on the tracer */
-               assert(ret != -LTTNG_UST_ERR_EXIST);
+               /*
+                * Not found previously means that it does not exist on the
+                * tracer. If the application reports that the event existed,
+                * it means there is a bug in the sessiond or lttng-ust
+                * (or corruption, etc.)
+                */
+               if (ret == -LTTNG_UST_ERR_EXIST) {
+                       ERR("Tracer for application reported that an event being created already existed: "
+                                       "event_name = \"%s\", pid = %d, ppid = %d, uid = %d, gid = %d",
+                                       uevent->attr.name,
+                                       app->pid, app->ppid, app->uid,
+                                       app->gid);
+               }
                goto error;
        }
 
        add_unique_ust_app_event(ua_chan, ua_event);
 
-       DBG2("UST app create event %s for PID %d completed", ua_event->name,
-                       app->pid);
+       DBG2("UST app create event completed: app = '%s' (ppid: %d)",
+                       app->name, app->ppid);
 
 end:
        return ret;
@@ -3159,6 +3630,59 @@ error:
        return ret;
 }
 
+/*
+ * Create UST app event notifier rule and create it on the tracer side.
+ *
+ * Must be called with the RCU read side lock held.
+ * Called with ust app session mutex held.
+ */
+static
+int create_ust_app_event_notifier_rule(struct lttng_trigger *trigger,
+               struct ust_app *app)
+{
+       int ret = 0;
+       struct ust_app_event_notifier_rule *ua_event_notifier_rule;
+
+       ua_event_notifier_rule = alloc_ust_app_event_notifier_rule(trigger);
+       if (ua_event_notifier_rule == NULL) {
+               ret = -ENOMEM;
+               goto end;
+       }
+
+       /* Create it on the tracer side. */
+       ret = create_ust_event_notifier(app, ua_event_notifier_rule);
+       if (ret < 0) {
+               /*
+                * Not found previously means that it does not exist on the
+                * tracer. If the application reports that the event existed,
+                * it means there is a bug in the sessiond or lttng-ust
+                * (or corruption, etc.)
+                */
+               if (ret == -LTTNG_UST_ERR_EXIST) {
+                       ERR("Tracer for application reported that an event notifier being created already exists: "
+                                       "token = \"%" PRIu64 "\", pid = %d, ppid = %d, uid = %d, gid = %d",
+                                       lttng_trigger_get_tracer_token(trigger),
+                                       app->pid, app->ppid, app->uid,
+                                       app->gid);
+               }
+               goto error;
+       }
+
+       lttng_ht_add_unique_u64(app->token_to_event_notifier_rule_ht,
+                       &ua_event_notifier_rule->node);
+
+       DBG2("UST app create token event rule completed: app = '%s' (ppid: %d), token = %" PRIu64,
+                       app->name, app->ppid, lttng_trigger_get_tracer_token(trigger));
+
+end:
+       return ret;
+
+error:
+       /* The RCU read side lock is already being held by the caller. */
+       delete_ust_app_event_notifier_rule(-1, ua_event_notifier_rule, app);
+       return ret;
+}
+
 /*
  * Create UST metadata and open it on the tracer side.
  *
@@ -3302,7 +3826,9 @@ error:
  */
 struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
 {
+       int ret;
        struct ust_app *lta = NULL;
+       struct lttng_pipe *event_notifier_event_source_pipe = NULL;
 
        assert(msg);
        assert(sock >= 0);
@@ -3319,12 +3845,33 @@ struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
                goto error;
        }
 
+       /*
+        * Reserve the two file descriptors of the event source pipe. The write
+        * end will be closed once it is passed to the application, at which
+        * point a single 'put' will be performed.
+        */
+       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
+       if (ret) {
+               ERR("Failed to reserve two file descriptors for the event source pipe while creating a new application instance: app = '%s' (ppid: %d)",
+                               msg->name, (int) msg->ppid);
+               goto error;
+       }
+
+       event_notifier_event_source_pipe = lttng_pipe_open(FD_CLOEXEC);
+       if (!event_notifier_event_source_pipe) {
+               PERROR("Failed to open application event source pipe: '%s' (ppid = %d)",
+                               msg->name, msg->ppid);
+               goto error;
+       }
+
        lta = zmalloc(sizeof(struct ust_app));
        if (lta == NULL) {
                PERROR("malloc");
-               goto error;
+               goto error_free_pipe;
        }
 
+       lta->event_notifier_group.event_pipe = event_notifier_event_source_pipe;
+
        lta->ppid = msg->ppid;
        lta->uid = msg->uid;
        lta->gid = msg->gid;
@@ -3343,6 +3890,7 @@ struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
        lta->ust_objd = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        lta->ust_sessions_objd = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        lta->notify_sock = -1;
+       lta->token_to_event_notifier_rule_ht = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
 
        /* Copy name and make sure it's NULL terminated. */
        strncpy(lta->name, msg->name, sizeof(lta->name));
@@ -3362,8 +3910,13 @@ struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
        lttng_ht_node_init_ulong(&lta->sock_n, (unsigned long) lta->sock);
 
        CDS_INIT_LIST_HEAD(&lta->teardown_head);
-error:
        return lta;
+
+error_free_pipe:
+       lttng_pipe_destroy(event_notifier_event_source_pipe);
+       lttng_fd_put(LTTNG_FD_APPS, 2);
+error:
+       return NULL;
 }
 
 /*
@@ -3429,6 +3982,74 @@ int ust_app_version(struct ust_app *app)
        return ret;
 }
 
+/*
+ * Setup the base event notifier group.
+ *
+ * Return 0 on success else a negative value either an errno code or a
+ * LTTng-UST error code.
+ */
+int ust_app_setup_event_notifier_group(struct ust_app *app)
+{
+       int ret;
+       int event_pipe_write_fd;
+       struct lttng_ust_abi_object_data *event_notifier_group = NULL;
+       enum lttng_error_code lttng_ret;
+
+       assert(app);
+
+       /* Get the write side of the pipe. */
+       event_pipe_write_fd = lttng_pipe_get_writefd(
+                       app->event_notifier_group.event_pipe);
+
+       pthread_mutex_lock(&app->sock_lock);
+       ret = ustctl_create_event_notifier_group(app->sock,
+                       event_pipe_write_fd, &event_notifier_group);
+       pthread_mutex_unlock(&app->sock_lock);
+       if (ret < 0) {
+               if (ret != -LTTNG_UST_ERR_EXITING && ret != -EPIPE) {
+                       ERR("Failed to create application event notifier group: ret = %d, app socket fd = %d, event_pipe_write_fd = %d",
+                                       ret, app->sock, event_pipe_write_fd);
+               } else {
+                       DBG("Failed to create application event notifier group (application is dead): app socket fd = %d",
+                                       app->sock);
+               }
+
+               goto error;
+       }
+
+       ret = lttng_pipe_write_close(app->event_notifier_group.event_pipe);
+       if (ret) {
+               ERR("Failed to close write end of the application's event source pipe: app = '%s' (ppid = %d)",
+                               app->name, app->ppid);
+               goto error;
+       }
+
+       /*
+        * Release the file descriptor that was reserved for the write-end of
+        * the pipe.
+        */
+       lttng_fd_put(LTTNG_FD_APPS, 1);
+
+       lttng_ret = notification_thread_command_add_tracer_event_source(
+                       notification_thread_handle,
+                       lttng_pipe_get_readfd(app->event_notifier_group.event_pipe),
+                       LTTNG_DOMAIN_UST);
+       if (lttng_ret != LTTNG_OK) {
+               ERR("Failed to add tracer event source to notification thread");
+               ret = - 1;
+               goto error;
+       }
+
+       /* Assign handle only when the complete setup is valid. */
+       app->event_notifier_group.object = event_notifier_group;
+       return ret;
+
+error:
+       ustctl_release_object(app->sock, app->event_notifier_group.object);
+       free(app->event_notifier_group.object);
+       return ret;
+}
+
 /*
  * Unregister app by removing it from the global traceable app list and freeing
  * the data struct.
@@ -3571,7 +4192,7 @@ int ust_app_list_events(struct lttng_event **events)
        rcu_read_lock();
 
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
-               struct lttng_ust_tracepoint_iter uiter;
+               struct lttng_ust_abi_tracepoint_iter uiter;
 
                health_code_update();
 
@@ -3654,9 +4275,9 @@ int ust_app_list_events(struct lttng_event **events)
                                nbmem = new_nbmem;
                                tmp_event = new_tmp_event;
                        }
-                       memcpy(tmp_event[count].name, uiter.name, LTTNG_UST_SYM_NAME_LEN);
+                       memcpy(tmp_event[count].name, uiter.name, LTTNG_UST_ABI_SYM_NAME_LEN);
                        tmp_event[count].loglevel = uiter.loglevel;
-                       tmp_event[count].type = (enum lttng_event_type) LTTNG_UST_TRACEPOINT;
+                       tmp_event[count].type = (enum lttng_event_type) LTTNG_UST_ABI_TRACEPOINT;
                        tmp_event[count].pid = app->pid;
                        tmp_event[count].enabled = -1;
                        count++;
@@ -3702,7 +4323,7 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
        rcu_read_lock();
 
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
-               struct lttng_ust_field_iter uiter;
+               struct lttng_ust_abi_field_iter uiter;
 
                health_code_update();
 
@@ -3786,12 +4407,12 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
                                tmp_event = new_tmp_event;
                        }
 
-                       memcpy(tmp_event[count].field_name, uiter.field_name, LTTNG_UST_SYM_NAME_LEN);
+                       memcpy(tmp_event[count].field_name, uiter.field_name, LTTNG_UST_ABI_SYM_NAME_LEN);
                        /* Mapping between these enums matches 1 to 1. */
                        tmp_event[count].type = (enum lttng_event_field_type) uiter.type;
                        tmp_event[count].nowrite = uiter.nowrite;
 
-                       memcpy(tmp_event[count].event.name, uiter.event_name, LTTNG_UST_SYM_NAME_LEN);
+                       memcpy(tmp_event[count].event.name, uiter.event_name, LTTNG_UST_ABI_SYM_NAME_LEN);
                        tmp_event[count].event.loglevel = uiter.loglevel;
                        tmp_event[count].event.type = LTTNG_EVENT_TRACEPOINT;
                        tmp_event[count].event.pid = app->pid;
@@ -3838,16 +4459,12 @@ void ust_app_clean_list(void)
        if (ust_app_ht_by_notify_sock) {
                cds_lfht_for_each_entry(ust_app_ht_by_notify_sock->ht, &iter.iter, app,
                                notify_sock_n.node) {
-                       struct cds_lfht_node *node;
-                       struct ust_app *app;
-
-                       node = cds_lfht_iter_get_node(&iter.iter);
-                       if (!node) {
-                               continue;
-                       }
+                       /*
+                        * Assert that all notifiers are gone as all triggers
+                        * are unregistered prior to this clean-up.
+                        */
+                       assert(lttng_ht_get_count(app->token_to_event_notifier_rule_ht) == 0);
 
-                       app = container_of(node, struct ust_app,
-                                       notify_sock_n.node);
                        ust_app_notify_sock_unregister(app->notify_sock);
                }
        }
@@ -4094,13 +4711,16 @@ int ust_app_channel_create(struct ltt_ust_session *usess,
                 * configuration.
                 */
                ret = ust_app_channel_allocate(ua_sess, uchan,
-                       LTTNG_UST_CHAN_PER_CPU, usess,
+                       LTTNG_UST_ABI_CHAN_PER_CPU, usess,
                        &ua_chan);
-               if (ret == 0) {
-                       ret = ust_app_channel_send(app, usess,
-                               ua_sess, ua_chan);
-               } else {
-                       goto end;
+               if (ret < 0) {
+                       goto error;
+               }
+
+               ret = ust_app_channel_send(app, usess,
+                       ua_sess, ua_chan);
+               if (ret) {
+                       goto error;
                }
 
                /* Add contexts. */
@@ -4108,10 +4728,12 @@ int ust_app_channel_create(struct ltt_ust_session *usess,
                        ret = create_ust_app_channel_context(ua_chan,
                                &uctx->ctx, app);
                        if (ret) {
-                               goto end;
+                               goto error;
                        }
                }
        }
+
+error:
        if (ret < 0) {
                switch (ret) {
                case -ENOTCONN:
@@ -4127,7 +4749,7 @@ int ust_app_channel_create(struct ltt_ust_session *usess,
                        break;
                }
        }
-end:
+
        if (ret == 0 && _ua_chan) {
                /*
                 * Only return the application's channel on success. Note
@@ -4140,97 +4762,28 @@ end:
 }
 
 /*
- * For a specific UST session, create the channel for all registered apps.
+ * Enable event for a specific session and channel on the tracer.
  */
-int ust_app_create_channel_glb(struct ltt_ust_session *usess,
-               struct ltt_ust_channel *uchan)
+int ust_app_enable_event_glb(struct ltt_ust_session *usess,
+               struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent)
 {
        int ret = 0;
-       struct cds_lfht_iter iter;
+       struct lttng_ht_iter iter, uiter;
+       struct lttng_ht_node_str *ua_chan_node;
        struct ust_app *app;
+       struct ust_app_session *ua_sess;
+       struct ust_app_channel *ua_chan;
+       struct ust_app_event *ua_event;
 
-       assert(usess);
        assert(usess->active);
-       assert(uchan);
+       DBG("UST app enabling event %s for all apps for session id %" PRIu64,
+                       uevent->attr.name, usess->id);
 
-       DBG2("UST app adding channel %s to UST domain for session id %" PRIu64,
-                       uchan->name, usess->id);
-
-       rcu_read_lock();
-       /* For every registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter, app, pid_n.node) {
-               struct ust_app_session *ua_sess;
-               int session_was_created = 0;
-
-               if (!app->compatible ||
-                               !trace_ust_pid_tracker_lookup(usess, app->pid)) {
-                       goto error_rcu_unlock;
-               }
-
-               /*
-                * Create session on the tracer side and add it to app session HT. Note
-                * that if session exist, it will simply return a pointer to the ust
-                * app session.
-                */
-               ret = find_or_create_ust_app_session(usess, app, &ua_sess,
-                               &session_was_created);
-               if (ret < 0) {
-                       switch (ret) {
-                       case -ENOTCONN:
-                               /*
-                                * The application's socket is not valid. Either a bad
-                                * socket or a timeout on it. We can't inform the caller
-                                * that for a specific app, the session failed so lets
-                                * continue here; it is not an error.
-                                */
-                               ret = 0;
-                               goto error_rcu_unlock;
-                       case -ENOMEM:
-                       default:
-                               goto error_rcu_unlock;
-                       }
-               }
-
-               if (ua_sess->deleted) {
-                       continue;
-               }
-               ret = ust_app_channel_create(usess, ua_sess, uchan, app, NULL);
-               if (ret) {
-                       if (session_was_created) {
-                               destroy_app_session(app, ua_sess);
-                       }
-                       goto error_rcu_unlock;
-               }
-       }
-
-error_rcu_unlock:
-       rcu_read_unlock();
-       return ret;
-}
-
-/*
- * Enable event for a specific session and channel on the tracer.
- */
-int ust_app_enable_event_glb(struct ltt_ust_session *usess,
-               struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent)
-{
-       int ret = 0;
-       struct lttng_ht_iter iter, uiter;
-       struct lttng_ht_node_str *ua_chan_node;
-       struct ust_app *app;
-       struct ust_app_session *ua_sess;
-       struct ust_app_channel *ua_chan;
-       struct ust_app_event *ua_event;
-
-       assert(usess->active);
-       DBG("UST app enabling event %s for all apps for session id %" PRIu64,
-                       uevent->attr.name, usess->id);
-
-       /*
-        * NOTE: At this point, this function is called only if the session and
-        * channel passed are already created for all apps. and enabled on the
-        * tracer also.
-        */
+       /*
+        * NOTE: At this point, this function is called only if the session and
+        * channel passed are already created for all apps. and enabled on the
+        * tracer also.
+        */
 
        rcu_read_lock();
 
@@ -4394,24 +4947,20 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                goto end;
        }
 
+       if (ua_sess->enabled) {
+               pthread_mutex_unlock(&ua_sess->lock);
+               goto end;
+       }
+
        /* Upon restart, we skip the setup, already done */
        if (ua_sess->started) {
                goto skip_setup;
        }
 
-       /*
-        * 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);
-       if (ret < 0) {
-               goto error_unlock;
-       }
-
        health_code_update();
 
 skip_setup:
-       /* This start the UST tracing */
+       /* This starts the UST tracing */
        pthread_mutex_lock(&app->sock_lock);
        ret = ustctl_start_session(app->sock, ua_sess->handle);
        pthread_mutex_unlock(&app->sock_lock);
@@ -4434,6 +4983,7 @@ skip_setup:
 
        /* Indicate that the session has been started once */
        ua_sess->started = 1;
+       ua_sess->enabled = 1;
 
        pthread_mutex_unlock(&ua_sess->lock);
 
@@ -4523,6 +5073,7 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
        }
 
        health_code_update();
+       ua_sess->enabled = 0;
 
        /* Quiescent wait after stopping trace */
        pthread_mutex_lock(&app->sock_lock);
@@ -4641,7 +5192,7 @@ int ust_app_flush_session(struct ltt_ust_session *usess)
                /* 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 buffer_reg_channel *buf_reg_chan;
                        struct consumer_socket *socket;
 
                        /* Get consumer socket to use to push the metadata.*/
@@ -4653,13 +5204,13 @@ int ust_app_flush_session(struct ltt_ust_session *usess)
                        }
 
                        cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
-                                       reg_chan, node.node) {
+                                       buf_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);
+                               (void) consumer_flush_channel(socket, buf_reg_chan->consumer_key);
                        }
 
                        ust_session_reg = reg->registry->reg.ust;
@@ -4788,7 +5339,7 @@ int ust_app_clear_quiescent_session(struct ltt_ust_session *usess)
                 */
                cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
                        struct consumer_socket *socket;
-                       struct buffer_reg_channel *reg_chan;
+                       struct buffer_reg_channel *buf_reg_chan;
 
                        /* Get associated consumer socket.*/
                        socket = consumer_find_socket_by_bitness(
@@ -4802,7 +5353,7 @@ int ust_app_clear_quiescent_session(struct ltt_ust_session *usess)
                        }
 
                        cds_lfht_for_each_entry(reg->registry->channels->ht,
-                                       &iter.iter, reg_chan, node.node) {
+                                       &iter.iter, buf_reg_chan, node.node) {
                                /*
                                 * The following call will print error values so
                                 * the return code is of little importance
@@ -4810,7 +5361,7 @@ int ust_app_clear_quiescent_session(struct ltt_ust_session *usess)
                                 * all.
                                 */
                                (void) consumer_clear_quiescent_channel(socket,
-                                               reg_chan->consumer_key);
+                                               buf_reg_chan->consumer_key);
                        }
                }
                break;
@@ -5040,39 +5591,165 @@ end:
        return ret;
 }
 
-/*
- * The caller must ensure that the application is compatible and is tracked
- * by the PID tracker.
- */
+/* Called with RCU read-side lock held. */
 static
-void ust_app_synchronize(struct ltt_ust_session *usess,
-               struct ust_app *app)
+void ust_app_synchronize_event_notifier_rules(struct ust_app *app)
 {
        int ret = 0;
-       struct cds_lfht_iter uchan_iter;
-       struct ltt_ust_channel *uchan;
-       struct ust_app_session *ua_sess = NULL;
+       enum lttng_error_code ret_code;
+       enum lttng_trigger_status t_status;
+       struct lttng_ht_iter app_trigger_iter;
+       struct lttng_triggers *triggers = NULL;
+       struct ust_app_event_notifier_rule *event_notifier_rule;
+       unsigned int count, i;
 
        /*
-        * The application's configuration should only be synchronized for
-        * active sessions.
+        * Currrently, registering or unregistering a trigger with an
+        * event rule condition causes a full synchronization of the event
+        * notifiers.
+        *
+        * The first step attempts to add an event notifier for all registered
+        * triggers that apply to the user space tracers. Then, the
+        * application's event notifiers rules are all checked against the list
+        * of registered triggers. Any event notifier that doesn't have a
+        * matching trigger can be assumed to have been disabled.
+        *
+        * All of this is inefficient, but is put in place to get the feature
+        * rolling as it is simpler at this moment. It will be optimized Soon™
+        * to allow the state of enabled
+        * event notifiers to be synchronized in a piece-wise way.
         */
-       assert(usess->active);
 
-       ret = find_or_create_ust_app_session(usess, app, &ua_sess, NULL);
-       if (ret < 0) {
-               /* Tracer is probably gone or ENOMEM. */
-               goto error;
+       /* Get all triggers using uid 0 (root) */
+       ret_code = notification_thread_command_list_triggers(
+                       notification_thread_handle, 0, &triggers);
+       if (ret_code != LTTNG_OK) {
+               ret = -1;
+               goto end;
        }
-       assert(ua_sess);
 
-       pthread_mutex_lock(&ua_sess->lock);
-       if (ua_sess->deleted) {
-               pthread_mutex_unlock(&ua_sess->lock);
+       assert(triggers);
+
+       t_status = lttng_triggers_get_count(triggers, &count);
+       if (t_status != LTTNG_TRIGGER_STATUS_OK) {
+               ret = -1;
                goto end;
        }
 
+       for (i = 0; i < count; i++) {
+               struct lttng_condition *condition;
+               struct lttng_event_rule *event_rule;
+               struct lttng_trigger *trigger;
+               const struct ust_app_event_notifier_rule *looked_up_event_notifier_rule;
+               enum lttng_condition_status condition_status;
+               uint64_t token;
+
+               trigger = lttng_triggers_borrow_mutable_at_index(triggers, i);
+               assert(trigger);
+
+               token = lttng_trigger_get_tracer_token(trigger);
+               condition = lttng_trigger_get_condition(trigger);
+
+               if (lttng_condition_get_type(condition) != LTTNG_CONDITION_TYPE_ON_EVENT) {
+                       /* Does not apply */
+                       continue;
+               }
+
+               condition_status = lttng_condition_on_event_borrow_rule_mutable(condition, &event_rule);
+               assert(condition_status == LTTNG_CONDITION_STATUS_OK);
+
+               if (lttng_event_rule_get_domain_type(event_rule) == LTTNG_DOMAIN_KERNEL) {
+                       /* Skip kernel related triggers. */
+                       continue;
+               }
+
+               /*
+                * Find or create the associated token event rule. The caller
+                * holds the RCU read lock, so this is safe to call without
+                * explicitly acquiring it here.
+                */
+               looked_up_event_notifier_rule = find_ust_app_event_notifier_rule(
+                               app->token_to_event_notifier_rule_ht, token);
+               if (!looked_up_event_notifier_rule) {
+                       ret = create_ust_app_event_notifier_rule(trigger, app);
+                       if (ret < 0) {
+                               goto end;
+                       }
+               }
+       }
+
        rcu_read_lock();
+       /* Remove all unknown event sources from the app. */
+       cds_lfht_for_each_entry (app->token_to_event_notifier_rule_ht->ht,
+                       &app_trigger_iter.iter, event_notifier_rule,
+                       node.node) {
+               const uint64_t app_token = event_notifier_rule->token;
+               bool found = false;
+
+               /*
+                * Check if the app event trigger still exists on the
+                * notification side.
+                */
+               for (i = 0; i < count; i++) {
+                       uint64_t notification_thread_token;
+                       const struct lttng_trigger *trigger =
+                                       lttng_triggers_get_at_index(
+                                                       triggers, i);
+
+                       assert(trigger);
+
+                       notification_thread_token =
+                                       lttng_trigger_get_tracer_token(trigger);
+
+                       if (notification_thread_token == app_token) {
+                               found = true;
+                               break;
+                       }
+               }
+
+               if (found) {
+                       /* Still valid. */
+                       continue;
+               }
+
+               /*
+                * This trigger was unregistered, disable it on the tracer's
+                * side.
+                */
+               ret = lttng_ht_del(app->token_to_event_notifier_rule_ht,
+                               &app_trigger_iter);
+               assert(ret == 0);
+
+               /* Callee logs errors. */
+               (void) disable_ust_object(app, event_notifier_rule->obj);
+
+               delete_ust_app_event_notifier_rule(
+                               app->sock, event_notifier_rule, app);
+       }
+
+       rcu_read_unlock();
+
+end:
+       lttng_triggers_destroy(triggers);
+       return;
+}
+
+/*
+ * RCU read lock must be held by the caller.
+ */
+static
+void ust_app_synchronize_all_channels(struct ltt_ust_session *usess,
+               struct ust_app_session *ua_sess,
+               struct ust_app *app)
+{
+       int ret = 0;
+       struct cds_lfht_iter uchan_iter;
+       struct ltt_ust_channel *uchan;
+
+       assert(usess);
+       assert(ua_sess);
+       assert(app);
+
        cds_lfht_for_each_entry(usess->domain_global.channels->ht, &uchan_iter,
                        uchan, node.node) {
                struct ust_app_channel *ua_chan;
@@ -5086,11 +5763,11 @@ void ust_app_synchronize(struct ltt_ust_session *usess,
                 * allocated (if necessary) and sent to the application, and
                 * all enabled contexts will be added to the channel.
                 */
-               ret = find_or_create_ust_app_channel(usess, ua_sess,
+               ret = find_or_create_ust_app_channel(usess, ua_sess,
                        app, uchan, &ua_chan);
                if (ret) {
                        /* Tracer is probably gone or ENOMEM. */
-                       goto error_unlock;
+                       goto end;
                }
 
                if (!ua_chan) {
@@ -5103,7 +5780,7 @@ void ust_app_synchronize(struct ltt_ust_session *usess,
                        ret = ust_app_channel_synchronize_event(ua_chan,
                                uevent, ua_sess, app);
                        if (ret) {
-                               goto error_unlock;
+                               goto end;
                        }
                }
 
@@ -5112,10 +5789,62 @@ void ust_app_synchronize(struct ltt_ust_session *usess,
                                enable_ust_app_channel(ua_sess, uchan, app) :
                                disable_ust_app_channel(ua_sess, ua_chan, app);
                        if (ret) {
-                               goto error_unlock;
+                               goto end;
                        }
                }
        }
+end:
+       return;
+}
+
+/*
+ * The caller must ensure that the application is compatible and is tracked
+ * by the process attribute trackers.
+ */
+static
+void ust_app_synchronize(struct ltt_ust_session *usess,
+               struct ust_app *app)
+{
+       int ret = 0;
+       struct ust_app_session *ua_sess = NULL;
+
+       /*
+        * The application's configuration should only be synchronized for
+        * active sessions.
+        */
+       assert(usess->active);
+
+       ret = find_or_create_ust_app_session(usess, app, &ua_sess, NULL);
+       if (ret < 0) {
+               /* Tracer is probably gone or ENOMEM. */
+               goto error;
+       }
+       assert(ua_sess);
+
+       pthread_mutex_lock(&ua_sess->lock);
+       if (ua_sess->deleted) {
+               pthread_mutex_unlock(&ua_sess->lock);
+               goto end;
+       }
+
+       rcu_read_lock();
+
+       ust_app_synchronize_all_channels(usess, ua_sess, app);
+
+       /*
+        * Create the metadata for the application. This returns gracefully if a
+        * metadata was already set for the session.
+        *
+        * The metadata channel must be created after the data channels as the
+        * consumer daemon assumes this ordering. When interacting with a relay
+        * daemon, the consumer will use this assumption to send the
+        * "STREAMS_SENT" message to the relay daemon.
+        */
+       ret = create_ust_app_metadata(ua_sess, app, usess->consumer);
+       if (ret < 0) {
+               goto error_unlock;
+       }
+
        rcu_read_unlock();
 
 end:
@@ -5162,7 +5891,14 @@ void ust_app_global_update(struct ltt_ust_session *usess, struct ust_app *app)
        if (!app->compatible) {
                return;
        }
-       if (trace_ust_pid_tracker_lookup(usess, app->pid)) {
+       if (trace_ust_id_tracker_lookup(LTTNG_PROCESS_ATTR_VIRTUAL_PROCESS_ID,
+                           usess, app->pid) &&
+                       trace_ust_id_tracker_lookup(
+                                       LTTNG_PROCESS_ATTR_VIRTUAL_USER_ID,
+                                       usess, app->uid) &&
+                       trace_ust_id_tracker_lookup(
+                                       LTTNG_PROCESS_ATTR_VIRTUAL_GROUP_ID,
+                                       usess, app->gid)) {
                /*
                 * Synchronize the application's internal tracing configuration
                 * and start tracing.
@@ -5174,6 +5910,30 @@ void ust_app_global_update(struct ltt_ust_session *usess, struct ust_app *app)
        }
 }
 
+/*
+ * Add all event notifiers to an application.
+ *
+ * Called with session lock held.
+ * Called with RCU read-side lock held.
+ */
+void ust_app_global_update_event_notifier_rules(struct ust_app *app)
+{
+       DBG2("UST application global event notifier rules update: app = '%s' (ppid: %d)",
+                       app->name, app->ppid);
+
+       if (!app->compatible) {
+               return;
+       }
+
+       if (app->event_notifier_group.object == NULL) {
+               WARN("UST app global update of event notifiers for app skipped since communication handle is null: app = '%s' (ppid: %d)",
+                               app->name, app->ppid);
+               return;
+       }
+
+       ust_app_synchronize_event_notifier_rules(app);
+}
+
 /*
  * Called with session lock held.
  */
@@ -5189,6 +5949,19 @@ void ust_app_global_update_all(struct ltt_ust_session *usess)
        rcu_read_unlock();
 }
 
+void ust_app_global_update_all_event_notifier_rules(void)
+{
+       struct lttng_ht_iter iter;
+       struct ust_app *app;
+
+       rcu_read_lock();
+       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+               ust_app_global_update_event_notifier_rules(app);
+       }
+
+       rcu_read_unlock();
+}
+
 /*
  * Add context to a specific channel for global UST domain.
  */
@@ -5367,7 +6140,7 @@ static int reply_ust_register_channel(int sock, int cobjd,
        struct ust_app_channel *ua_chan;
        struct ust_app_session *ua_sess;
        struct ust_registry_session *registry;
-       struct ust_registry_channel *chan_reg;
+       struct ust_registry_channel *ust_reg_chan;
 
        rcu_read_lock();
 
@@ -5408,30 +6181,30 @@ static int reply_ust_register_channel(int sock, int cobjd,
 
        pthread_mutex_lock(&registry->lock);
 
-       chan_reg = ust_registry_channel_find(registry, chan_reg_key);
-       assert(chan_reg);
+       ust_reg_chan = ust_registry_channel_find(registry, chan_reg_key);
+       assert(ust_reg_chan);
 
-       if (!chan_reg->register_done) {
+       if (!ust_reg_chan->register_done) {
                /*
                 * TODO: eventually use the registry event count for
                 * this channel to better guess header type for per-pid
                 * buffers.
                 */
                type = USTCTL_CHANNEL_HEADER_LARGE;
-               chan_reg->nr_ctx_fields = nr_fields;
-               chan_reg->ctx_fields = fields;
+               ust_reg_chan->nr_ctx_fields = nr_fields;
+               ust_reg_chan->ctx_fields = fields;
                fields = NULL;
-               chan_reg->header_type = type;
+               ust_reg_chan->header_type = type;
        } else {
                /* Get current already assigned values. */
-               type = chan_reg->header_type;
+               type = ust_reg_chan->header_type;
        }
        /* Channel id is set during the object creation. */
-       chan_id = chan_reg->chan_id;
+       chan_id = ust_reg_chan->chan_id;
 
        /* Append to metadata */
-       if (!chan_reg->metadata_dumped) {
-               ret_code = ust_metadata_channel_statedump(registry, chan_reg);
+       if (!ust_reg_chan->metadata_dumped) {
+               ret_code = ust_metadata_channel_statedump(registry, ust_reg_chan);
                if (ret_code) {
                        ERR("Error appending channel metadata (errno = %d)", ret_code);
                        goto reply;
@@ -5454,7 +6227,7 @@ reply:
        }
 
        /* This channel registry registration is completed. */
-       chan_reg->register_done = 1;
+       ust_reg_chan->register_done = 1;
 
 error:
        pthread_mutex_unlock(&registry->lock);
@@ -5677,7 +6450,7 @@ int ust_app_recv_notify(int sock)
        case USTCTL_NOTIFY_CMD_EVENT:
        {
                int sobjd, cobjd, loglevel_value;
-               char name[LTTNG_UST_SYM_NAME_LEN], *sig, *model_emf_uri;
+               char name[LTTNG_UST_ABI_SYM_NAME_LEN], *sig, *model_emf_uri;
                size_t nr_fields;
                struct ustctl_field *fields;
 
@@ -5744,7 +6517,7 @@ int ust_app_recv_notify(int sock)
        case USTCTL_NOTIFY_CMD_ENUM:
        {
                int sobjd;
-               char name[LTTNG_UST_SYM_NAME_LEN];
+               char name[LTTNG_UST_ABI_SYM_NAME_LEN];
                size_t nr_entries;
                struct ustctl_enum_entry *entries;
 
@@ -5883,7 +6656,7 @@ enum lttng_error_code ust_app_snapshot_record(
        enum lttng_error_code status = LTTNG_OK;
        struct lttng_ht_iter iter;
        struct ust_app *app;
-       char pathname[PATH_MAX];
+       char *trace_path = NULL;
 
        assert(usess);
        assert(output);
@@ -5896,8 +6669,10 @@ enum lttng_error_code ust_app_snapshot_record(
                struct buffer_reg_uid *reg;
 
                cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
-                       struct buffer_reg_channel *reg_chan;
+                       struct buffer_reg_channel *buf_reg_chan;
                        struct consumer_socket *socket;
+                       char pathname[PATH_MAX];
+                       size_t consumer_path_offset = 0;
 
                        if (!reg->registry->reg.ust->metadata_key) {
                                /* Skip since no metadata is present */
@@ -5913,26 +6688,29 @@ enum lttng_error_code ust_app_snapshot_record(
                        }
 
                        memset(pathname, 0, sizeof(pathname));
-                       /*
-                        * DEFAULT_UST_TRACE_UID_PATH already contains a path
-                        * separator.
-                        */
                        ret = snprintf(pathname, sizeof(pathname),
-                                       DEFAULT_UST_TRACE_DIR DEFAULT_UST_TRACE_UID_PATH,
+                                       DEFAULT_UST_TRACE_DIR "/" DEFAULT_UST_TRACE_UID_PATH,
                                        reg->uid, reg->bits_per_long);
                        if (ret < 0) {
                                PERROR("snprintf snapshot path");
                                status = LTTNG_ERR_INVALID;
                                goto error;
                        }
-
-                        /* Add the UST default trace dir to path. */
+                       /* Free path allowed on previous iteration. */
+                       free(trace_path);
+                       trace_path = setup_channel_trace_path(usess->consumer, pathname,
+                                               &consumer_path_offset);
+                       if (!trace_path) {
+                               status = LTTNG_ERR_INVALID;
+                               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) {
+                                       buf_reg_chan, node.node) {
                                status = consumer_snapshot_channel(socket,
-                                               reg_chan->consumer_key,
+                                               buf_reg_chan->consumer_key,
                                                output, 0, usess->uid,
-                                               usess->gid, pathname, wait,
+                                               usess->gid, &trace_path[consumer_path_offset], wait,
                                                nb_packets_per_stream);
                                if (status != LTTNG_OK) {
                                        goto error;
@@ -5940,7 +6718,8 @@ enum lttng_error_code ust_app_snapshot_record(
                        }
                        status = consumer_snapshot_channel(socket,
                                        reg->registry->reg.ust->metadata_key, output, 1,
-                                       usess->uid, usess->gid, pathname, wait, 0);
+                                       usess->uid, usess->gid, &trace_path[consumer_path_offset],
+                                       wait, 0);
                        if (status != LTTNG_OK) {
                                goto error;
                        }
@@ -5955,6 +6734,8 @@ enum lttng_error_code ust_app_snapshot_record(
                        struct ust_app_channel *ua_chan;
                        struct ust_app_session *ua_sess;
                        struct ust_registry_session *registry;
+                       char pathname[PATH_MAX];
+                       size_t consumer_path_offset = 0;
 
                        ua_sess = lookup_session_by_app(usess, app);
                        if (!ua_sess) {
@@ -5972,23 +6753,28 @@ enum lttng_error_code ust_app_snapshot_record(
 
                        /* Add the UST default trace dir to path. */
                        memset(pathname, 0, sizeof(pathname));
-                       ret = snprintf(pathname, sizeof(pathname), DEFAULT_UST_TRACE_DIR "%s",
+                       ret = snprintf(pathname, sizeof(pathname), DEFAULT_UST_TRACE_DIR "/%s",
                                        ua_sess->path);
                        if (ret < 0) {
                                status = LTTNG_ERR_INVALID;
                                PERROR("snprintf snapshot path");
                                goto error;
                        }
-
-                        cds_lfht_for_each_entry(ua_sess->channels->ht, &chan_iter.iter,
+                       /* Free path allowed on previous iteration. */
+                       free(trace_path);
+                       trace_path = setup_channel_trace_path(usess->consumer, pathname,
+                                       &consumer_path_offset);
+                       if (!trace_path) {
+                               status = LTTNG_ERR_INVALID;
+                               goto error;
+                       }
+                       cds_lfht_for_each_entry(ua_sess->channels->ht, &chan_iter.iter,
                                        ua_chan, node.node) {
                                status = consumer_snapshot_channel(socket,
                                                ua_chan->key, output, 0,
-                                               ua_sess->effective_credentials
-                                                               .uid,
-                                               ua_sess->effective_credentials
-                                                               .gid,
-                                               pathname, wait,
+                                               lttng_credentials_get_uid(&ua_sess->effective_credentials),
+                                               lttng_credentials_get_gid(&ua_sess->effective_credentials),
+                                               &trace_path[consumer_path_offset], wait,
                                                nb_packets_per_stream);
                                switch (status) {
                                case LTTNG_OK:
@@ -6007,9 +6793,9 @@ enum lttng_error_code ust_app_snapshot_record(
                        }
                        status = consumer_snapshot_channel(socket,
                                        registry->metadata_key, output, 1,
-                                       ua_sess->effective_credentials.uid,
-                                       ua_sess->effective_credentials.gid,
-                                       pathname, wait, 0);
+                                       lttng_credentials_get_uid(&ua_sess->effective_credentials),
+                                       lttng_credentials_get_gid(&ua_sess->effective_credentials),
+                                       &trace_path[consumer_path_offset], wait, 0);
                        switch (status) {
                        case LTTNG_OK:
                                break;
@@ -6027,6 +6813,7 @@ enum lttng_error_code ust_app_snapshot_record(
        }
 
 error:
+       free(trace_path);
        rcu_read_unlock();
        return status;
 }
@@ -6049,19 +6836,19 @@ uint64_t ust_app_get_size_one_more_packet_per_stream(
                struct buffer_reg_uid *reg;
 
                cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
-                       struct buffer_reg_channel *reg_chan;
+                       struct buffer_reg_channel *buf_reg_chan;
 
                        rcu_read_lock();
                        cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
-                                       reg_chan, node.node) {
-                               if (cur_nr_packets >= reg_chan->num_subbuf) {
+                                       buf_reg_chan, node.node) {
+                               if (cur_nr_packets >= buf_reg_chan->num_subbuf) {
                                        /*
                                         * Don't take channel into account if we
                                         * already grab all its packets.
                                         */
                                        continue;
                                }
-                               tot_size += reg_chan->subbuf_size * reg_chan->stream_count;
+                               tot_size += buf_reg_chan->subbuf_size * buf_reg_chan->stream_count;
                        }
                        rcu_read_unlock();
                }
@@ -6285,9 +7072,14 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                struct buffer_reg_uid *reg;
 
                cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
-                       struct buffer_reg_channel *reg_chan;
+                       struct buffer_reg_channel *buf_reg_chan;
                        struct consumer_socket *socket;
 
+                       if (!reg->registry->reg.ust->metadata_key) {
+                               /* Skip since no metadata is present */
+                               continue;
+                       }
+
                        /* Get consumer socket to use to push the metadata.*/
                        socket = consumer_find_socket_by_bitness(reg->bits_per_long,
                                        usess->consumer);
@@ -6298,9 +7090,9 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
 
                        /* Rotate the data channels. */
                        cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
-                                       reg_chan, node.node) {
+                                       buf_reg_chan, node.node) {
                                ret = consumer_rotate_channel(socket,
-                                               reg_chan->consumer_key,
+                                               buf_reg_chan->consumer_key,
                                                usess->uid, usess->gid,
                                                usess->consumer,
                                                /* is_metadata_channel */ false);
@@ -6358,10 +7150,8 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                                        ua_chan, node.node) {
                                ret = consumer_rotate_channel(socket,
                                                ua_chan->key,
-                                               ua_sess->effective_credentials
-                                                               .uid,
-                                               ua_sess->effective_credentials
-                                                               .gid,
+                                               lttng_credentials_get_uid(&ua_sess->effective_credentials),
+                                               lttng_credentials_get_gid(&ua_sess->effective_credentials),
                                                ua_sess->consumer,
                                                /* is_metadata_channel */ false);
                                if (ret < 0) {
@@ -6377,8 +7167,8 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                        (void) push_metadata(registry, usess->consumer);
                        ret = consumer_rotate_channel(socket,
                                        registry->metadata_key,
-                                       ua_sess->effective_credentials.uid,
-                                       ua_sess->effective_credentials.gid,
+                                       lttng_credentials_get_uid(&ua_sess->effective_credentials),
+                                       lttng_credentials_get_gid(&ua_sess->effective_credentials),
                                        ua_sess->consumer,
                                        /* is_metadata_channel */ true);
                        if (ret < 0) {
@@ -6422,7 +7212,7 @@ enum lttng_error_code ust_app_create_channel_subdirectories(
 
                cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
                        fmt_ret = asprintf(&pathname_index,
-                                      DEFAULT_UST_TRACE_DIR DEFAULT_UST_TRACE_UID_PATH "/" DEFAULT_INDEX_DIR,
+                                      DEFAULT_UST_TRACE_DIR "/" DEFAULT_UST_TRACE_UID_PATH "/" DEFAULT_INDEX_DIR,
                                       reg->uid, reg->bits_per_long);
                        if (fmt_ret < 0) {
                                ERR("Failed to format channel index directory");
@@ -6449,6 +7239,17 @@ enum lttng_error_code ust_app_create_channel_subdirectories(
        {
                struct ust_app *app;
 
+               /*
+                * Create the toplevel ust/ directory in case no apps are running.
+                */
+               chunk_status = lttng_trace_chunk_create_subdirectory(
+                               usess->current_trace_chunk,
+                               DEFAULT_UST_TRACE_DIR);
+               if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
+                       ret = LTTNG_ERR_CREATE_DIR_FAIL;
+                       goto error;
+               }
+
                cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app,
                                pid_n.node) {
                        struct ust_app_session *ua_sess;
@@ -6467,7 +7268,7 @@ enum lttng_error_code ust_app_create_channel_subdirectories(
                        }
 
                        fmt_ret = asprintf(&pathname_index,
-                                       DEFAULT_UST_TRACE_DIR "%s/" DEFAULT_INDEX_DIR,
+                                       DEFAULT_UST_TRACE_DIR "/%s/" DEFAULT_INDEX_DIR,
                                        ua_sess->path);
                        if (fmt_ret < 0) {
                                ERR("Failed to format channel index directory");
@@ -6498,3 +7299,274 @@ error:
        rcu_read_unlock();
        return ret;
 }
+
+/*
+ * Clear all the channels of a session.
+ *
+ * Return LTTNG_OK on success or else an LTTng error code.
+ */
+enum lttng_error_code ust_app_clear_session(struct ltt_session *session)
+{
+       int ret;
+       enum lttng_error_code cmd_ret = LTTNG_OK;
+       struct lttng_ht_iter iter;
+       struct ust_app *app;
+       struct ltt_ust_session *usess = session->ust_session;
+
+       assert(usess);
+
+       rcu_read_lock();
+
+       if (usess->active) {
+               ERR("Expecting inactive session %s (%" PRIu64 ")", session->name, session->id);
+               cmd_ret = LTTNG_ERR_FATAL;
+               goto end;
+       }
+
+       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 *buf_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) {
+                               cmd_ret = LTTNG_ERR_INVALID;
+                               goto error_socket;
+                       }
+
+                       /* Clear the data channels. */
+                       cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
+                                       buf_reg_chan, node.node) {
+                               ret = consumer_clear_channel(socket,
+                                               buf_reg_chan->consumer_key);
+                               if (ret < 0) {
+                                       goto error;
+                               }
+                       }
+
+                       (void) push_metadata(reg->registry->reg.ust, usess->consumer);
+
+                       /*
+                        * Clear the metadata channel.
+                        * Metadata channel is not cleared per se but we still need to
+                        * perform a rotation operation on it behind the scene.
+                        */
+                       ret = consumer_clear_channel(socket,
+                                       reg->registry->reg.ust->metadata_key);
+                       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,
+                                       usess->consumer);
+                       if (!socket) {
+                               cmd_ret = LTTNG_ERR_INVALID;
+                               goto error_socket;
+                       }
+
+                       registry = get_session_registry(ua_sess);
+                       if (!registry) {
+                               DBG("Application session is being torn down. Skip application.");
+                               continue;
+                       }
+
+                       /* Clear the data channels. */
+                       cds_lfht_for_each_entry(ua_sess->channels->ht, &chan_iter.iter,
+                                       ua_chan, node.node) {
+                               ret = consumer_clear_channel(socket, ua_chan->key);
+                               if (ret < 0) {
+                                       /* Per-PID buffer and application going away. */
+                                       if (ret == -LTTNG_ERR_CHAN_NOT_FOUND) {
+                                               continue;
+                                       }
+                                       goto error;
+                               }
+                       }
+
+                       (void) push_metadata(registry, usess->consumer);
+
+                       /*
+                        * Clear the metadata channel.
+                        * Metadata channel is not cleared per se but we still need to
+                        * perform rotation operation on it behind the scene.
+                        */
+                       ret = consumer_clear_channel(socket, registry->metadata_key);
+                       if (ret < 0) {
+                               /* Per-PID buffer and application going away. */
+                               if (ret == -LTTNG_ERR_CHAN_NOT_FOUND) {
+                                       continue;
+                               }
+                               goto error;
+                       }
+               }
+               break;
+       }
+       default:
+               assert(0);
+               break;
+       }
+
+       cmd_ret = LTTNG_OK;
+       goto end;
+
+error:
+       switch (-ret) {
+       case LTTCOMM_CONSUMERD_RELAYD_CLEAR_DISALLOWED:
+               cmd_ret = LTTNG_ERR_CLEAR_RELAY_DISALLOWED;
+               break;
+       default:
+               cmd_ret = LTTNG_ERR_CLEAR_FAIL_CONSUMER;
+       }
+
+error_socket:
+end:
+       rcu_read_unlock();
+       return cmd_ret;
+}
+
+/*
+ * This function skips the metadata channel as the begin/end timestamps of a
+ * metadata packet are useless.
+ *
+ * Moreover, opening a packet after a "clear" will cause problems for live
+ * sessions as it will introduce padding that was not part of the first trace
+ * chunk. The relay daemon expects the content of the metadata stream of
+ * successive metadata trace chunks to be strict supersets of one another.
+ *
+ * For example, flushing a packet at the beginning of the metadata stream of
+ * a trace chunk resulting from a "clear" session command will cause the
+ * size of the metadata stream of the new trace chunk to not match the size of
+ * the metadata stream of the original chunk. This will confuse the relay
+ * daemon as the same "offset" in a metadata stream will no longer point
+ * to the same content.
+ */
+enum lttng_error_code ust_app_open_packets(struct ltt_session *session)
+{
+       enum lttng_error_code ret = LTTNG_OK;
+       struct lttng_ht_iter iter;
+       struct ltt_ust_session *usess = session->ust_session;
+
+       assert(usess);
+
+       rcu_read_lock();
+
+       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 *buf_reg_chan;
+                       struct consumer_socket *socket;
+
+                       socket = consumer_find_socket_by_bitness(
+                                       reg->bits_per_long, usess->consumer);
+                       if (!socket) {
+                               ret = LTTNG_ERR_FATAL;
+                               goto error;
+                       }
+
+                       cds_lfht_for_each_entry(reg->registry->channels->ht,
+                                       &iter.iter, buf_reg_chan, node.node) {
+                               const int open_ret =
+                                               consumer_open_channel_packets(
+                                                       socket,
+                                                       buf_reg_chan->consumer_key);
+
+                               if (open_ret < 0) {
+                                       ret = LTTNG_ERR_UNK;
+                                       goto error;
+                               }
+                       }
+               }
+               break;
+       }
+       case LTTNG_BUFFER_PER_PID:
+       {
+               struct ust_app *app;
+
+               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, usess->consumer);
+                       if (!socket) {
+                               ret = LTTNG_ERR_FATAL;
+                               goto error;
+                       }
+
+                       registry = get_session_registry(ua_sess);
+                       if (!registry) {
+                               DBG("Application session is being torn down. Skip application.");
+                               continue;
+                       }
+
+                       cds_lfht_for_each_entry(ua_sess->channels->ht,
+                                       &chan_iter.iter, ua_chan, node.node) {
+                               const int open_ret =
+                                               consumer_open_channel_packets(
+                                                       socket,
+                                                       ua_chan->key);
+
+                               if (open_ret < 0) {
+                                       /*
+                                        * Per-PID buffer and application going
+                                        * away.
+                                        */
+                                       if (open_ret == -LTTNG_ERR_CHAN_NOT_FOUND) {
+                                               continue;
+                                       }
+
+                                       ret = LTTNG_ERR_UNK;
+                                       goto error;
+                               }
+                       }
+               }
+               break;
+       }
+       default:
+               abort();
+               break;
+       }
+
+error:
+       rcu_read_unlock();
+       return ret;
+}
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