Move UST registry into sessiond and implement notifiers
[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c
index 397a2dfab29b5f2106f1a235a4ce1a7bfb7f0a7b..371f1600bb16a9eebcdc96c211e1dd9a96471b3f 100644 (file)
 #include "ust-consumer.h"
 #include "ust-ctl.h"
 
+/* Next available channel key. */
+static unsigned long next_channel_key;
+
+/*
+ * Return the atomically incremented value of next_channel_key.
+ */
+static inline unsigned long get_next_channel_key(void)
+{
+       return uatomic_add_return(&next_channel_key, 1);
+}
+
+/*
+ * Return the consumer socket from the given consumer output with the right
+ * bitness. On error, returns NULL.
+ *
+ * The caller MUST acquire a rcu read side lock and keep it until the socket
+ * object reference is not needed anymore.
+ */
+static struct consumer_socket *find_consumer_socket_by_bitness(int bits,
+               struct consumer_output *consumer)
+{
+       int consumer_fd;
+       struct consumer_socket *socket = NULL;
+
+       switch (bits) {
+       case 64:
+               consumer_fd = uatomic_read(&ust_consumerd64_fd);
+               break;
+       case 32:
+               consumer_fd = uatomic_read(&ust_consumerd32_fd);
+               break;
+       default:
+               assert(0);
+               goto end;
+       }
+
+       socket = consumer_find_socket(consumer_fd, consumer);
+
+end:
+       return socket;
+}
+
 /*
  * Match function for the hash table lookup.
  *
@@ -100,16 +142,18 @@ no_match:
  * Unique add of an ust app event in the given ht. This uses the custom
  * ht_match_ust_app_event match function and the event name as hash.
  */
-static void add_unique_ust_app_event(struct lttng_ht *ht,
+static void add_unique_ust_app_event(struct ust_app_channel *ua_chan,
                struct ust_app_event *event)
 {
        struct cds_lfht_node *node_ptr;
        struct ust_app_ht_key key;
+       struct lttng_ht *ht;
 
-       assert(ht);
-       assert(ht->ht);
+       assert(ua_chan);
+       assert(ua_chan->events);
        assert(event);
 
+       ht = ua_chan->events;
        key.name = event->attr.name;
        key.filter = event->filter;
        key.loglevel = event->attr.loglevel;
@@ -127,8 +171,16 @@ static void add_unique_ust_app_event(struct lttng_ht *ht,
 static
 void delete_ust_app_ctx(int sock, struct ust_app_ctx *ua_ctx)
 {
+       int ret;
+
+       assert(ua_ctx);
+
        if (ua_ctx->obj) {
-               ustctl_release_object(sock, ua_ctx->obj);
+               ret = ustctl_release_object(sock, ua_ctx->obj);
+               if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app sock %d release ctx obj handle %d failed with ret %d",
+                                       sock, ua_ctx->obj->handle, ret);
+               }
                free(ua_ctx->obj);
        }
        free(ua_ctx);
@@ -141,10 +193,18 @@ void delete_ust_app_ctx(int sock, struct ust_app_ctx *ua_ctx)
 static
 void delete_ust_app_event(int sock, struct ust_app_event *ua_event)
 {
+       int ret;
+
+       assert(ua_event);
+
        free(ua_event->filter);
 
        if (ua_event->obj != NULL) {
-               ustctl_release_object(sock, ua_event->obj);
+               ret = ustctl_release_object(sock, ua_event->obj);
+               if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app sock %d release event obj failed with ret %d",
+                                       sock, ret);
+               }
                free(ua_event->obj);
        }
        free(ua_event);
@@ -157,8 +217,16 @@ void delete_ust_app_event(int sock, struct ust_app_event *ua_event)
 static
 void delete_ust_app_stream(int sock, struct ust_app_stream *stream)
 {
+       int ret;
+
+       assert(stream);
+
        if (stream->obj) {
-               ustctl_release_object(sock, stream->obj);
+               ret = ustctl_release_object(sock, stream->obj);
+               if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app sock %d release stream obj failed with ret %d",
+                                       sock, ret);
+               }
                lttng_fd_put(LTTNG_FD_APPS, 2);
                free(stream->obj);
        }
@@ -170,7 +238,8 @@ void delete_ust_app_stream(int sock, struct ust_app_stream *stream)
  * this function.
  */
 static
-void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan)
+void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan,
+               struct ust_app *app)
 {
        int ret;
        struct lttng_ht_iter iter;
@@ -178,6 +247,10 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan)
        struct ust_app_ctx *ua_ctx;
        struct ust_app_stream *stream, *stmp;
 
+       assert(ua_chan);
+
+       DBG3("UST app deleting channel %s", ua_chan->name);
+
        /* Wipe stream */
        cds_list_for_each_entry_safe(stream, stmp, &ua_chan->streams.head, list) {
                cds_list_del(&stream->list);
@@ -201,8 +274,18 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan)
        }
        lttng_ht_destroy(ua_chan->events);
 
+       /* Wipe and free registry. */
+       ust_registry_channel_destroy(&ua_chan->session->registry, &ua_chan->registry);
+
        if (ua_chan->obj != NULL) {
-               ustctl_release_object(sock, ua_chan->obj);
+               /* Remove channel from application UST object descriptor. */
+               iter.iter.node = &ua_chan->ust_objd_node.node;
+               lttng_ht_del(app->ust_objd, &iter);
+               ret = ustctl_release_object(sock, ua_chan->obj);
+               if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app sock %d release channel obj failed with ret %d",
+                                       sock, ret);
+               }
                lttng_fd_put(LTTNG_FD_APPS, 2);
                free(ua_chan->obj);
        }
@@ -214,36 +297,33 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan)
  * this function.
  */
 static
-void delete_ust_app_session(int sock, struct ust_app_session *ua_sess)
+void delete_ust_app_session(int sock, struct ust_app_session *ua_sess,
+               struct ust_app *app)
 {
        int ret;
        struct lttng_ht_iter iter;
        struct ust_app_channel *ua_chan;
 
        if (ua_sess->metadata) {
-               if (ua_sess->metadata->stream_obj) {
-                       ustctl_release_object(sock, ua_sess->metadata->stream_obj);
-                       lttng_fd_put(LTTNG_FD_APPS, 2);
-                       free(ua_sess->metadata->stream_obj);
-               }
-               if (ua_sess->metadata->obj) {
-                       ustctl_release_object(sock, ua_sess->metadata->obj);
-                       lttng_fd_put(LTTNG_FD_APPS, 2);
-                       free(ua_sess->metadata->obj);
-               }
-               trace_ust_destroy_metadata(ua_sess->metadata);
+               delete_ust_app_channel(sock, ua_sess->metadata, app);
        }
 
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
                ret = lttng_ht_del(ua_sess->channels, &iter);
                assert(!ret);
-               delete_ust_app_channel(sock, ua_chan);
+               delete_ust_app_channel(sock, ua_chan, app);
        }
        lttng_ht_destroy(ua_sess->channels);
 
+       ust_registry_session_destroy(&ua_sess->registry);
+
        if (ua_sess->handle != -1) {
-               ustctl_release_handle(sock, ua_sess->handle);
+               ret = ustctl_release_handle(sock, ua_sess->handle);
+               if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app sock %d release session handle failed with ret %d",
+                                       sock, ret);
+               }
        }
        free(ua_sess);
 }
@@ -270,7 +350,7 @@ void delete_ust_app(struct ust_app *app)
        cds_list_for_each_entry_safe(ua_sess, tmp_ua_sess, &app->teardown_head,
                        teardown_node) {
                /* Free every object in the session and the session. */
-               delete_ust_app_session(sock, ua_sess);
+               delete_ust_app_session(sock, ua_sess, app);
        }
 
        /*
@@ -313,11 +393,38 @@ void delete_ust_app_rcu(struct rcu_head *head)
        delete_ust_app(app);
 }
 
+/*
+ * Delete the session from the application ht and delete the data structure by
+ * freeing every object inside and releasing them.
+ */
+static void destroy_app_session(struct ust_app *app,
+               struct ust_app_session *ua_sess)
+{
+       int ret;
+       struct lttng_ht_iter iter;
+
+       assert(app);
+       assert(ua_sess);
+
+       iter.iter.node = &ua_sess->node.node;
+       ret = lttng_ht_del(app->sessions, &iter);
+       if (ret) {
+               /* Already scheduled for teardown. */
+               goto end;
+       }
+
+       /* Once deleted, free the data structure. */
+       delete_ust_app_session(app->sock, ua_sess, app);
+
+end:
+       return;
+}
+
 /*
  * Alloc new UST app session.
  */
 static
-struct ust_app_session *alloc_ust_app_session(void)
+struct ust_app_session *alloc_ust_app_session(struct ust_app *app)
 {
        struct ust_app_session *ua_sess;
 
@@ -325,15 +432,28 @@ struct ust_app_session *alloc_ust_app_session(void)
        ua_sess = zmalloc(sizeof(struct ust_app_session));
        if (ua_sess == NULL) {
                PERROR("malloc");
-               goto error;
+               goto error_free;
        }
 
        ua_sess->handle = -1;
        ua_sess->channels = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
+       pthread_mutex_init(&ua_sess->lock, NULL);
+       if (ust_registry_session_init(&ua_sess->registry, app,
+                       app->bits_per_long,
+                       app->uint8_t_alignment,
+                       app->uint16_t_alignment,
+                       app->uint32_t_alignment,
+                       app->uint64_t_alignment,
+                       app->long_alignment,
+                       app->byte_order)) {
+               goto error;
+       }
 
        return ua_sess;
 
 error:
+       free(ua_sess);
+error_free:
        return NULL;
 }
 
@@ -342,7 +462,8 @@ error:
  */
 static
 struct ust_app_channel *alloc_ust_app_channel(char *name,
-               struct lttng_ust_channel *attr)
+               struct ust_app_session *ua_sess,
+               struct lttng_ust_channel_attr *attr)
 {
        struct ust_app_channel *ua_chan;
 
@@ -359,16 +480,28 @@ struct ust_app_channel *alloc_ust_app_channel(char *name,
 
        ua_chan->enabled = 1;
        ua_chan->handle = -1;
+       ua_chan->key = get_next_channel_key();
        ua_chan->ctx = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        ua_chan->events = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
        lttng_ht_node_init_str(&ua_chan->node, ua_chan->name);
 
        CDS_INIT_LIST_HEAD(&ua_chan->streams.head);
 
+       /* Initialize UST registry. */
+       ust_registry_channel_init(&ua_sess->registry, &ua_chan->registry);
+
        /* Copy attributes */
        if (attr) {
-               memcpy(&ua_chan->attr, attr, sizeof(ua_chan->attr));
+               /* Translate from lttng_ust_channel to ustctl_consumer_channel_attr. */
+               ua_chan->attr.subbuf_size = attr->subbuf_size;
+               ua_chan->attr.num_subbuf = attr->num_subbuf;
+               ua_chan->attr.overwrite = attr->overwrite;
+               ua_chan->attr.switch_timer_interval = attr->switch_timer_interval;
+               ua_chan->attr.read_timer_interval = attr->read_timer_interval;
+               ua_chan->attr.output = attr->output;
        }
+       /* By default, the channel is a per cpu channel. */
+       ua_chan->attr.type = LTTNG_UST_CHAN_PER_CPU;
 
        DBG3("UST app channel %s allocated", ua_chan->name);
 
@@ -378,6 +511,28 @@ error:
        return NULL;
 }
 
+/*
+ * Allocate and initialize a UST app stream.
+ *
+ * Return newly allocated stream pointer or NULL on error.
+ */
+struct ust_app_stream *ust_app_alloc_stream(void)
+{
+       struct ust_app_stream *stream = NULL;
+
+       stream = zmalloc(sizeof(*stream));
+       if (stream == NULL) {
+               PERROR("zmalloc ust app stream");
+               goto error;
+       }
+
+       /* Zero could be a valid value for a handle so flag it to -1. */
+       stream->handle = -1;
+
+error:
+       return stream;
+}
+
 /*
  * Alloc new UST app event.
  */
@@ -481,6 +636,29 @@ error:
        return NULL;
 }
 
+/*
+ * Find an ust_app using the notify sock and return it. RCU read side lock must
+ * be held before calling this helper function.
+ */
+static struct ust_app *find_app_by_notify_sock(int sock)
+{
+       struct lttng_ht_node_ulong *node;
+       struct lttng_ht_iter iter;
+
+       lttng_ht_lookup(ust_app_ht_by_notify_sock, (void *)((unsigned long) sock),
+                       &iter);
+       node = lttng_ht_iter_get_node_ulong(&iter);
+       if (node == NULL) {
+               DBG2("UST app find by notify sock %d not found", sock);
+               goto error;
+       }
+
+       return caa_container_of(node, struct ust_app, notify_sock_n);
+
+error:
+       return NULL;
+}
+
 /*
  * Lookup for an ust app event based on event name, filter bytecode and the
  * event loglevel.
@@ -519,6 +697,8 @@ end:
 
 /*
  * Create the channel context on the tracer.
+ *
+ * Called with UST app session lock held.
  */
 static
 int create_ust_channel_context(struct ust_app_channel *ua_chan,
@@ -526,20 +706,27 @@ int create_ust_channel_context(struct ust_app_channel *ua_chan,
 {
        int ret;
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        ret = ustctl_add_context(app->sock, &ua_ctx->ctx,
                        ua_chan->obj, &ua_ctx->obj);
        if (ret < 0) {
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app create channel context failed for app (pid: %d) "
+                                       "with ret %d", app->pid, ret);
+               } else {
+                       DBG3("UST app disable event failed. Application is dead.");
+               }
                goto error;
        }
 
        ua_ctx->handle = ua_ctx->obj->handle;
 
-       DBG2("UST app context created successfully for channel %s", ua_chan->name);
+       DBG2("UST app context handle %d created successfully for channel %s",
+                       ua_ctx->handle, ua_chan->name);
 
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -552,7 +739,7 @@ int set_ust_event_filter(struct ust_app_event *ua_event,
 {
        int ret;
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        if (!ua_event->filter) {
                ret = 0;
@@ -562,13 +749,19 @@ int set_ust_event_filter(struct ust_app_event *ua_event,
        ret = ustctl_set_filter(app->sock, ua_event->filter,
                        ua_event->obj);
        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);
+               } else {
+                       DBG3("UST app filter event failed. Application is dead.");
+               }
                goto error;
        }
 
        DBG2("UST filter set successfully for event %s", ua_event->name);
 
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -580,13 +773,17 @@ static int disable_ust_event(struct ust_app *app,
 {
        int ret;
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        ret = ustctl_disable(app->sock, ua_event->obj);
        if (ret < 0) {
-               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);
+               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);
+               } else {
+                       DBG3("UST app disable event failed. Application is dead.");
+               }
                goto error;
        }
 
@@ -594,7 +791,7 @@ static int disable_ust_event(struct ust_app *app,
                        ua_event->attr.name, app->pid);
 
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -606,13 +803,17 @@ static int disable_ust_channel(struct ust_app *app,
 {
        int ret;
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        ret = ustctl_disable(app->sock, ua_chan->obj);
        if (ret < 0) {
-               ERR("UST app channel %s disable failed for app (pid: %d) "
-                               "and session handle %d with ret %d",
-                               ua_chan->name, app->pid, ua_sess->handle, ret);
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app channel %s disable failed for app (pid: %d) "
+                                       "and session handle %d with ret %d",
+                                       ua_chan->name, app->pid, ua_sess->handle, ret);
+               } else {
+                       DBG3("UST app disable channel failed. Application is dead.");
+               }
                goto error;
        }
 
@@ -620,7 +821,7 @@ static int disable_ust_channel(struct ust_app *app,
                        ua_chan->name, app->pid);
 
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -632,13 +833,17 @@ static int enable_ust_channel(struct ust_app *app,
 {
        int ret;
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        ret = ustctl_enable(app->sock, ua_chan->obj);
        if (ret < 0) {
-               ERR("UST app channel %s enable failed for app (pid: %d) "
-                               "and session handle %d with ret %d",
-                               ua_chan->name, app->pid, ua_sess->handle, ret);
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app channel %s enable failed for app (pid: %d) "
+                                       "and session handle %d with ret %d",
+                                       ua_chan->name, app->pid, ua_sess->handle, ret);
+               } else {
+                       DBG3("UST app enable channel failed. Application is dead.");
+               }
                goto error;
        }
 
@@ -648,7 +853,7 @@ static int enable_ust_channel(struct ust_app *app,
                        ua_chan->name, app->pid);
 
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -660,13 +865,17 @@ static int enable_ust_event(struct ust_app *app,
 {
        int ret;
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        ret = ustctl_enable(app->sock, ua_event->obj);
        if (ret < 0) {
-               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);
+               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);
+               } else {
+                       DBG3("UST app enable event failed. Application is dead.");
+               }
                goto error;
        }
 
@@ -674,179 +883,100 @@ static int enable_ust_event(struct ust_app *app,
                        ua_event->attr.name, app->pid);
 
 error:
-       health_code_update(&health_thread_cmd);
-       return ret;
-}
-
-/*
- * Open metadata onto the UST tracer for a UST session.
- */
-static int open_ust_metadata(struct ust_app *app,
-               struct ust_app_session *ua_sess)
-{
-       int ret;
-       struct lttng_ust_channel_attr uattr;
-
-       health_code_update(&health_thread_cmd);
-
-       uattr.overwrite = ua_sess->metadata->attr.overwrite;
-       uattr.subbuf_size = ua_sess->metadata->attr.subbuf_size;
-       uattr.num_subbuf = ua_sess->metadata->attr.num_subbuf;
-       uattr.switch_timer_interval =
-               ua_sess->metadata->attr.switch_timer_interval;
-       uattr.read_timer_interval =
-               ua_sess->metadata->attr.read_timer_interval;
-       uattr.output = ua_sess->metadata->attr.output;
-
-       /* We are going to receive 2 fds, we need to reserve them. */
-       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
-       if (ret < 0) {
-               ERR("Exhausted number of available FD upon metadata open");
-               goto error;
-       }
-       /* UST tracer metadata creation */
-       ret = ustctl_open_metadata(app->sock, ua_sess->handle, &uattr,
-                       &ua_sess->metadata->obj);
-       if (ret < 0) {
-               ERR("UST app open metadata failed for app pid:%d with ret %d",
-                               app->pid, ret);
-               goto error;
-       }
-
-       ua_sess->metadata->handle = ua_sess->metadata->obj->handle;
-
-error:
-       health_code_update(&health_thread_cmd);
-       return ret;
-}
-
-/*
- * Create metadata stream onto the UST tracer for a given session.
- */
-static int create_ust_metadata_stream(struct ust_app *app,
-               struct ust_app_session *ua_sess)
-{
-       int ret;
-
-       health_code_update(&health_thread_cmd);
-
-       /* We are going to receive 2 fds, we need to reserve them. */
-       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
-       if (ret < 0) {
-               ERR("Exhausted number of available FD upon metadata stream create");
-               goto error;
-       }
-       ret = ustctl_create_stream(app->sock, ua_sess->metadata->obj,
-                       &ua_sess->metadata->stream_obj);
-       if (ret < 0) {
-               lttng_fd_put(LTTNG_FD_APPS, 2);
-               ERR("UST create metadata stream failed");
-               goto error;
-       }
-
-error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
 /*
- * Create stream onto the UST tracer for a given channel.
+ * Create the specified channel onto the UST tracer for a UST session.
+ * Called with UST app session lock held.
  *
- * Return -ENOENT if no more stream is available for this channel.
- * On success, return 0.
- * On error, return a negative value.
+ * Return 0 on success. On error, a negative value is returned.
  */
-static int create_ust_stream(struct ust_app *app,
-               struct ust_app_channel *ua_chan, struct ust_app_stream *stream)
+static int create_ust_channel(struct ust_app *app,
+               struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan,
+               struct consumer_output *consumer)
 {
        int ret;
+       unsigned int nb_fd = 0;
+       struct consumer_socket *socket;
+       struct ust_app_stream *stream, *stmp;
 
        assert(app);
+       assert(ua_sess);
        assert(ua_chan);
-       assert(ua_chan->obj);
-       assert(stream);
+       assert(consumer);
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
-       /* We are going to receive 2 fds, we need to reserve them. */
-       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
-       if (ret < 0) {
-               ERR("Exhausted number of available FD on stream creation");
-               /* Just to make sure we never return -ENOENT. */
+       /* Get the right consumer socket for the application. */
+       socket = find_consumer_socket_by_bitness(app->bits_per_long, consumer);
+       if (!socket) {
                ret = -1;
                goto error;
        }
 
+       health_code_update();
+
        /*
-        * Set the stream name before creating it. On error, we don't have to
-        * delete it on the tracer side.
+        * Ask consumer to create channel. The consumer will return the number of
+        * stream we have to expect.
         */
-       ret = snprintf(stream->name, sizeof(stream->name), "%s_%u",
-                       ua_chan->name, ua_chan->streams.count);
+       ret = ust_consumer_ask_channel(ua_sess, ua_chan, consumer, socket);
        if (ret < 0) {
-               /* Without the stream name we can't continue using it. */
-               PERROR("snprintf UST create stream");
-               /* Just to make sure we never return -ENOENT. */
-               ret = -1;
                goto error;
        }
 
-       ret = ustctl_create_stream(app->sock, ua_chan->obj, &stream->obj);
+       /*
+        * Compute the number of fd needed before receiving them. It must be 2 per
+        * stream.
+        */
+       nb_fd = DEFAULT_UST_STREAM_FD_NUM * ua_chan->expected_stream_count;
+
+       /* Reserve the amount of file descriptor we need. */
+       ret = lttng_fd_get(LTTNG_FD_APPS, nb_fd);
        if (ret < 0) {
-               lttng_fd_put(LTTNG_FD_APPS, 2);
-               /* Indicates that there is no more stream for that channel. */
-               if (ret != -LTTNG_UST_ERR_NOENT) {
-                       ERR("UST create metadata stream failed (ret: %d)", ret);
-               }
-               goto error;
+               ERR("Exhausted number of available FD upon create channel");
+               goto error_fd_get;
        }
 
-       /* Set stream handle with the returned value. */
-       stream->handle = stream->obj->handle;
-
-error:
-       health_code_update(&health_thread_cmd);
-       return ret;
-}
-
-/*
- * Create the specified channel onto the UST tracer for a UST session.
- */
-static int create_ust_channel(struct ust_app *app,
-               struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan)
-{
-       int ret;
-
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
-       /* TODO: remove cast and use lttng-ust-abi.h */
-
-       /* We are going to receive 2 fds, we need to reserve them. */
-       ret = lttng_fd_get(LTTNG_FD_APPS, 2);
+       /*
+        * Now get the channel from the consumer. This call wil populate the stream
+        * list of that channel and set the ust object.
+        */
+       ret = ust_consumer_get_channel(socket, ua_chan);
        if (ret < 0) {
-               ERR("Exhausted number of available FD upon create channel");
-               goto error;
+               goto error_destroy;
        }
 
-       health_code_update(&health_thread_cmd);
-
-       ret = ustctl_create_channel(app->sock, ua_sess->handle,
-                       (struct lttng_ust_channel_attr *)&ua_chan->attr, &ua_chan->obj);
+       /* Send channel to the application. */
+       ret = ust_consumer_send_channel_to_ust(app, ua_sess, ua_chan);
        if (ret < 0) {
-               ERR("Creating channel %s for app (pid: %d, sock: %d) "
-                               "and session handle %d with ret %d",
-                               ua_chan->name, app->pid, app->sock,
-                               ua_sess->handle, ret);
-               lttng_fd_put(LTTNG_FD_APPS, 2);
                goto error;
        }
 
-       ua_chan->handle = ua_chan->obj->handle;
+       /* Send all streams to application. */
+       cds_list_for_each_entry_safe(stream, stmp, &ua_chan->streams.head, list) {
+               ret = ust_consumer_send_stream_to_ust(app, ua_chan, stream);
+               if (ret < 0) {
+                       goto error;
+               }
+               /* We don't need the stream anymore once sent to the tracer. */
+               cds_list_del(&stream->list);
+               delete_ust_app_stream(-1, stream);
+       }
 
-       DBG2("UST app channel %s created successfully for pid:%d and sock:%d",
-                       ua_chan->name, app->pid, app->sock);
+       /* Flag the channel that it is sent to the application. */
+       ua_chan->is_sent = 1;
+       /* Assign session to channel. */
+       ua_chan->session = ua_sess;
+       /* Initialize ust objd object using the received handle and add it. */
+       lttng_ht_node_init_ulong(&ua_chan->ust_objd_node, ua_chan->handle);
+       lttng_ht_add_unique_ulong(app->ust_objd, &ua_chan->ust_objd_node);
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        /* If channel is not enabled, disable it on the tracer */
        if (!ua_chan->enabled) {
@@ -856,13 +986,27 @@ static int create_ust_channel(struct ust_app *app,
                }
        }
 
+       return 0;
+
+error_destroy:
+       lttng_fd_put(LTTNG_FD_APPS, nb_fd);
+error_fd_get:
+       /*
+        * Initiate a destroy channel on the consumer since we had an error
+        * handling it on our side. The return value is of no importance since we
+        * already have a ret value set by the previous error that we need to
+        * return.
+        */
+       (void) ust_consumer_destroy_channel(socket, ua_chan);
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
 /*
  * Create the specified event onto the UST tracer for a UST session.
+ *
+ * Should be called with session mutex held.
  */
 static
 int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
@@ -870,14 +1014,18 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
 {
        int ret = 0;
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        /* Create UST event on tracer */
        ret = ustctl_create_event(app->sock, &ua_event->attr, ua_chan->obj,
                        &ua_event->obj);
        if (ret < 0) {
-               ERR("Error ustctl create event %s for app pid: %d with ret %d",
-                               ua_event->attr.name, app->pid, ret);
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("Error ustctl create event %s for app pid: %d with ret %d",
+                                       ua_event->attr.name, app->pid, ret);
+               } else {
+                       DBG3("UST app create event failed. Application is dead.");
+               }
                goto error;
        }
 
@@ -886,7 +1034,7 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
        DBG2("UST app event %s created successfully for pid:%d",
                        ua_event->attr.name, app->pid);
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        /* Set filter if one is present. */
        if (ua_event->filter) {
@@ -921,7 +1069,7 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
        }
 
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -962,8 +1110,18 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
 
        strncpy(ua_chan->name, uchan->name, sizeof(ua_chan->name));
        ua_chan->name[sizeof(ua_chan->name) - 1] = '\0';
-       /* Copy event attributes */
-       memcpy(&ua_chan->attr, &uchan->attr, sizeof(ua_chan->attr));
+
+       /* 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->attr.output = uchan->attr.output;
+       /*
+        * 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;
 
@@ -989,7 +1147,7 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
                                continue;
                        }
                        shadow_copy_event(ua_event, uevent);
-                       add_unique_ust_app_event(ua_chan->events, ua_event);
+                       add_unique_ust_app_event(ua_chan, ua_event);
                }
        }
 
@@ -1046,13 +1204,19 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
 
                DBG2("Channel %s not found on shadow session copy, creating it",
                                uchan->name);
-               ua_chan = alloc_ust_app_channel(uchan->name, &uchan->attr);
+               ua_chan = alloc_ust_app_channel(uchan->name, ua_sess, &uchan->attr);
                if (ua_chan == NULL) {
                        /* malloc failed FIXME: Might want to do handle ENOMEM .. */
                        continue;
                }
-
                shadow_copy_channel(ua_chan, uchan);
+               /*
+                * The concept of metadata channel does not exist on the tracing
+                * registry side of the session daemon so this can only be a per CPU
+                * channel and not metadata.
+                */
+               ua_chan->attr.type = LTTNG_UST_CHAN_PER_CPU;
+
                lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
        }
 }
@@ -1112,13 +1276,13 @@ static int create_ust_app_session(struct ltt_ust_session *usess,
        assert(app);
        assert(ua_sess_ptr);
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        ua_sess = lookup_session_by_app(usess, app);
        if (ua_sess == NULL) {
                DBG2("UST app pid: %d session id %d not found, creating it",
                                app->pid, usess->id);
-               ua_sess = alloc_ust_app_session();
+               ua_sess = alloc_ust_app_session(app);
                if (ua_sess == NULL) {
                        /* Only malloc can failed so something is really wrong */
                        ret = -ENOMEM;
@@ -1128,13 +1292,18 @@ static int create_ust_app_session(struct ltt_ust_session *usess,
                created = 1;
        }
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        if (ua_sess->handle == -1) {
                ret = ustctl_create_session(app->sock);
                if (ret < 0) {
-                       ERR("Creating session for app pid %d", app->pid);
-                       delete_ust_app_session(-1, ua_sess);
+                       if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                               ERR("Creating session for app pid %d with ret %d",
+                                               app->pid, ret);
+                       } else {
+                               DBG("UST app creating session failed. Application is dead");
+                       }
+                       delete_ust_app_session(-1, ua_sess, app);
                        if (ret != -ENOMEM) {
                                /*
                                 * Tracer is probably gone or got an internal error so let's
@@ -1162,12 +1331,14 @@ static int create_ust_app_session(struct ltt_ust_session *usess,
        ret = 0;
 
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
 /*
  * Create a context for the channel on the tracer.
+ *
+ * Called with UST app session lock held.
  */
 static
 int create_ust_app_channel_context(struct ust_app_session *ua_sess,
@@ -1209,6 +1380,8 @@ error:
 
 /*
  * Enable on the tracer side a ust app event for the session and channel.
+ *
+ * Called with UST app session lock held.
  */
 static
 int enable_ust_app_event(struct ust_app_session *ua_sess,
@@ -1299,9 +1472,12 @@ error:
 /*
  * Create UST app channel and create it on the tracer. Set ua_chanp of the
  * newly created channel if not NULL.
+ *
+ * Called with UST app session lock held.
  */
 static int create_ust_app_channel(struct ust_app_session *ua_sess,
                struct ltt_ust_channel *uchan, struct ust_app *app,
+               struct consumer_output *consumer, enum lttng_ust_chan_type type,
                struct ust_app_channel **ua_chanp)
 {
        int ret = 0;
@@ -1317,7 +1493,7 @@ static int create_ust_app_channel(struct ust_app_session *ua_sess,
                goto end;
        }
 
-       ua_chan = alloc_ust_app_channel(uchan->name, &uchan->attr);
+       ua_chan = alloc_ust_app_channel(uchan->name, ua_sess, &uchan->attr);
        if (ua_chan == NULL) {
                /* Only malloc can fail here */
                ret = -ENOMEM;
@@ -1325,19 +1501,20 @@ static int create_ust_app_channel(struct ust_app_session *ua_sess,
        }
        shadow_copy_channel(ua_chan, uchan);
 
-       ret = create_ust_channel(app, ua_sess, ua_chan);
+       /* Set channel type. */
+       ua_chan->attr.type = type;
+
+       ret = create_ust_channel(app, ua_sess, ua_chan, consumer);
        if (ret < 0) {
-               /* Not found previously means that it does not exist on the tracer */
-               assert(ret != -LTTNG_UST_ERR_EXIST);
                goto error;
        }
 
-       /* Only add the channel if successful on the tracer side. */
-       lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
-
        DBG2("UST app create channel %s for PID %d completed", ua_chan->name,
                        app->pid);
 
+       /* Only add the channel if successful on the tracer side. */
+       lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
+
 end:
        if (ua_chanp) {
                *ua_chanp = ua_chan;
@@ -1347,12 +1524,14 @@ end:
        return 0;
 
 error:
-       delete_ust_app_channel(-1, ua_chan);
+       delete_ust_app_channel(ua_chan->is_sent ? app->sock : -1, ua_chan, app);
        return ret;
 }
 
 /*
  * Create UST app event and create it on the tracer side.
+ *
+ * Called with ust app session mutex held.
  */
 static
 int create_ust_app_event(struct ust_app_session *ua_sess,
@@ -1387,7 +1566,7 @@ int create_ust_app_event(struct ust_app_session *ua_sess,
                goto error;
        }
 
-       add_unique_ust_app_event(ua_chan->events, ua_event);
+       add_unique_ust_app_event(ua_chan, ua_event);
 
        DBG2("UST app create event %s for PID %d completed", ua_event->name,
                        app->pid);
@@ -1403,62 +1582,55 @@ error:
 
 /*
  * Create UST metadata and open it on the tracer side.
+ *
+ * Called with UST app session lock held.
  */
 static int create_ust_app_metadata(struct ust_app_session *ua_sess,
-               char *pathname, struct ust_app *app)
+               struct ust_app *app, struct consumer_output *consumer)
 {
        int ret = 0;
+       struct ust_app_channel *metadata;
 
-       if (ua_sess->metadata == NULL) {
-               /* Allocate UST metadata */
-               ua_sess->metadata = trace_ust_create_metadata(pathname);
-               if (ua_sess->metadata == NULL) {
-                       /* malloc() failed */
-                       goto error;
-               }
-
-               ret = open_ust_metadata(app, ua_sess);
-               if (ret < 0) {
-                       DBG3("Opening metadata failed. Cleaning up memory");
-
-                       /* Cleanup failed metadata struct */
-                       free(ua_sess->metadata);
-                       /*
-                        * This is very important because delete_ust_app_session check if
-                        * the pointer is null or not in order to delete the metadata.
-                        */
-                       ua_sess->metadata = NULL;
-                       goto error;
-               }
+       assert(ua_sess);
+       assert(app);
 
-               DBG2("UST metadata opened for app pid %d", app->pid);
+       if (ua_sess->metadata) {
+               /* Already exist. Return success. */
+               goto end;
        }
 
-       /* Open UST metadata stream */
-       if (ua_sess->metadata->stream_obj == NULL) {
-               ret = create_ust_metadata_stream(app, ua_sess);
-               if (ret < 0) {
-                       goto error;
-               }
+       /* Allocate UST metadata */
+       metadata = alloc_ust_app_channel(DEFAULT_METADATA_NAME, ua_sess, NULL);
+       if (!metadata) {
+               /* malloc() failed */
+               ret = -ENOMEM;
+               goto error;
+       }
 
-               ret = snprintf(ua_sess->metadata->pathname, PATH_MAX,
-                               "%s/metadata", ua_sess->path);
-               if (ret < 0) {
-                       PERROR("asprintf UST create stream");
-                       goto error;
-               }
+       /* Set default attributes for metadata. */
+       metadata->attr.overwrite = DEFAULT_CHANNEL_OVERWRITE;
+       metadata->attr.subbuf_size = default_get_metadata_subbuf_size();
+       metadata->attr.num_subbuf = DEFAULT_METADATA_SUBBUF_NUM;
+       metadata->attr.switch_timer_interval = DEFAULT_CHANNEL_SWITCH_TIMER;
+       metadata->attr.read_timer_interval = DEFAULT_CHANNEL_READ_TIMER;
+       metadata->attr.output = LTTNG_UST_MMAP;
+       metadata->attr.type = LTTNG_UST_CHAN_METADATA;
 
-               DBG2("UST metadata stream object created for app pid %d",
-                               app->pid);
-       } else {
-               ERR("Attempting to create stream without metadata opened");
-               goto error;
+       ret = create_ust_channel(app, ua_sess, metadata, consumer);
+       if (ret < 0) {
+               goto error_create;
        }
 
-       return 0;
+       ua_sess->metadata = metadata;
 
+       DBG2("UST metadata opened for app pid %d", app->pid);
+
+end:
+       return 0;
+error_create:
+       delete_ust_app_channel(metadata->is_sent ? app->sock : -1, metadata, app);
 error:
-       return -1;
+       return ret;
 }
 
 /*
@@ -1477,14 +1649,12 @@ struct ust_app *ust_app_find_by_pid(pid_t pid)
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;
 
-       rcu_read_lock();
        lttng_ht_lookup(ust_app_ht, (void *)((unsigned long) pid), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
                DBG2("UST app no found with pid %d", pid);
                goto error;
        }
-       rcu_read_unlock();
 
        DBG2("Found UST app by pid %d", pid);
 
@@ -1495,89 +1665,99 @@ error:
        return NULL;
 }
 
-/*
- * Using pid and uid (of the app), allocate a new ust_app struct and
- * add it to the global traceable app list.
- *
- * On success, return 0, else return malloc -ENOMEM, or -EINVAL if app
- * bitness is not supported.
- */
-int ust_app_register(struct ust_register_msg *msg, int sock)
+struct ust_app *ust_app_create(struct ust_register_msg *msg, int sock)
 {
-       struct ust_app *lta;
-       int ret;
+       struct ust_app *lta = NULL;
+
+       assert(msg);
+       assert(sock >= 0);
+
+       DBG3("UST app creating application for socket %d", sock);
 
        if ((msg->bits_per_long == 64 &&
                                (uatomic_read(&ust_consumerd64_fd) == -EINVAL))
                        || (msg->bits_per_long == 32 &&
                                (uatomic_read(&ust_consumerd32_fd) == -EINVAL))) {
                ERR("Registration failed: application \"%s\" (pid: %d) has "
-                       "%d-bit long, but no consumerd for this long size is available.\n",
-                       msg->name, msg->pid, msg->bits_per_long);
-               ret = close(sock);
-               if (ret) {
-                       PERROR("close");
-               }
-               lttng_fd_put(LTTNG_FD_APPS, 1);
-               return -EINVAL;
-       }
-       if (msg->major != LTTNG_UST_COMM_MAJOR) {
-               ERR("Registration failed: application \"%s\" (pid: %d) has "
-                       "communication protocol version %u.%u, but sessiond supports 2.x.\n",
-                       msg->name, msg->pid, msg->major, msg->minor);
-               ret = close(sock);
-               if (ret) {
-                       PERROR("close");
-               }
-               lttng_fd_put(LTTNG_FD_APPS, 1);
-               return -EINVAL;
+                               "%d-bit long, but no consumerd for this size is available.\n",
+                               msg->name, msg->pid, msg->bits_per_long);
+               goto error;
        }
+
        lta = zmalloc(sizeof(struct ust_app));
        if (lta == NULL) {
                PERROR("malloc");
-               return -ENOMEM;
+               goto error;
        }
 
        lta->ppid = msg->ppid;
        lta->uid = msg->uid;
        lta->gid = msg->gid;
        lta->compatible = 0;  /* Not compatible until proven */
+
        lta->bits_per_long = msg->bits_per_long;
+       lta->uint8_t_alignment = msg->uint8_t_alignment;
+       lta->uint16_t_alignment = msg->uint16_t_alignment;
+       lta->uint32_t_alignment = msg->uint32_t_alignment;
+       lta->uint64_t_alignment = msg->uint64_t_alignment;
+       lta->long_alignment = msg->long_alignment;
+       lta->byte_order = msg->byte_order;
+
        lta->v_major = msg->major;
        lta->v_minor = msg->minor;
        strncpy(lta->name, msg->name, sizeof(lta->name));
-       lta->name[16] = '\0';
+       lta->name[LTTNG_UST_ABI_PROCNAME_LEN] = '\0';
        lta->sessions = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
+       lta->ust_objd = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
+       lta->notify_sock = -1;
+       lta->compatible = 1;
 
        lta->pid = msg->pid;
-       lttng_ht_node_init_ulong(&lta->pid_n, (unsigned long)lta->pid);
+       lttng_ht_node_init_ulong(&lta->pid_n, (unsigned long) lta->pid);
        lta->sock = sock;
-       lttng_ht_node_init_ulong(&lta->sock_n, (unsigned long)lta->sock);
+       lttng_ht_node_init_ulong(&lta->sock_n, (unsigned long) lta->sock);
 
        CDS_INIT_LIST_HEAD(&lta->teardown_head);
 
+error:
+       return lta;
+}
+
+void ust_app_add(struct ust_app *app)
+{
+       assert(app);
+       assert(app->notify_sock >= 0);
+
        rcu_read_lock();
 
        /*
         * On a re-registration, we want to kick out the previous registration of
         * that pid
         */
-       lttng_ht_add_replace_ulong(ust_app_ht, &lta->pid_n);
+       lttng_ht_add_replace_ulong(ust_app_ht, &app->pid_n);
 
        /*
         * The socket _should_ be unique until _we_ call close. So, a add_unique
         * for the ust_app_ht_by_sock is used which asserts fail if the entry was
         * already in the table.
         */
-       lttng_ht_add_unique_ulong(ust_app_ht_by_sock, &lta->sock_n);
+       lttng_ht_add_unique_ulong(ust_app_ht_by_sock, &app->sock_n);
 
-       rcu_read_unlock();
+       /* Add application to the notify socket hash table. */
+       lttng_ht_node_init_ulong(&app->notify_sock_n, app->notify_sock);
+       lttng_ht_add_unique_ulong(ust_app_ht_by_notify_sock, &app->notify_sock_n);
 
-       DBG("App registered with pid:%d ppid:%d uid:%d gid:%d sock:%d name:%s"
-                       " (version %d.%d)", lta->pid, lta->ppid, lta->uid, lta->gid,
-                       lta->sock, lta->name, lta->v_major, lta->v_minor);
+       DBG("App registered with pid:%d ppid:%d uid:%d gid:%d sock:%d name:%s "
+                       "(version %d.%d)", app->pid, app->ppid, app->uid, app->gid,
+                       app->sock, app->name, app->v_major, app->v_minor);
 
-       return 0;
+       rcu_read_unlock();
+}
+
+int ust_app_version(struct ust_app *app)
+{
+       assert(app);
+       return ustctl_tracer_version(app->sock, &app->version);
 }
 
 /*
@@ -1599,27 +1779,25 @@ void ust_app_unregister(int sock)
        /* Get the node reference for a call_rcu */
        lttng_ht_lookup(ust_app_ht_by_sock, (void *)((unsigned long) sock), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
-       if (node == NULL) {
-               ERR("Unable to find app by sock %d", sock);
-               goto error;
-       }
+       assert(node);
 
        lta = caa_container_of(node, struct ust_app, sock_n);
-
        DBG("PID %d unregistering with sock %d", lta->pid, sock);
 
        /* Remove application from PID hash table */
        ret = lttng_ht_del(ust_app_ht_by_sock, &iter);
        assert(!ret);
 
-       /* Assign second node for deletion */
-       iter.iter.node = &lta->pid_n.node;
+       /* Remove application from notify hash table */
+       iter.iter.node = &lta->notify_sock_n.node;
+       ret = lttng_ht_del(ust_app_ht_by_notify_sock, &iter);
 
        /*
         * Ignore return value since the node might have been removed before by an
         * add replace during app registration because the PID can be reassigned by
         * the OS.
         */
+       iter.iter.node = &lta->pid_n.node;
        ret = lttng_ht_del(ust_app_ht, &iter);
        if (ret) {
                DBG3("Unregister app by PID %d failed. This can happen on pid reuse",
@@ -1645,7 +1823,6 @@ void ust_app_unregister(int sock)
        /* Free memory */
        call_rcu(&lta->pid_n.head, delete_ust_app_rcu);
 
-error:
        rcu_read_unlock();
        return;
 }
@@ -1688,7 +1865,7 @@ int ust_app_list_events(struct lttng_event **events)
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                struct lttng_ust_tracepoint_iter uiter;
 
-               health_code_update(&health_thread_cmd);
+               health_code_update();
 
                if (!app->compatible) {
                        /*
@@ -1699,14 +1876,28 @@ int ust_app_list_events(struct lttng_event **events)
                }
                handle = ustctl_tracepoint_list(app->sock);
                if (handle < 0) {
-                       ERR("UST app list events getting handle failed for app pid %d",
-                                       app->pid);
+                       if (handle != -EPIPE && handle != -LTTNG_UST_ERR_EXITING) {
+                               ERR("UST app list events getting handle failed for app pid %d",
+                                               app->pid);
+                       }
                        continue;
                }
 
                while ((ret = ustctl_tracepoint_list_get(app->sock, handle,
                                        &uiter)) != -LTTNG_UST_ERR_NOENT) {
-                       health_code_update(&health_thread_cmd);
+                       /* Handle ustctl error. */
+                       if (ret < 0) {
+                               free(tmp_event);
+                               if (ret != -LTTNG_UST_ERR_EXITING || ret != -EPIPE) {
+                                       ERR("UST app tp list get failed for app %d with ret %d",
+                                                       app->sock, ret);
+                               } else {
+                                       DBG3("UST app tp list get failed. Application is dead");
+                               }
+                               goto rcu_error;
+                       }
+
+                       health_code_update();
                        if (count >= nbmem) {
                                /* In case the realloc fails, we free the memory */
                                void *ptr;
@@ -1740,7 +1931,7 @@ int ust_app_list_events(struct lttng_event **events)
 rcu_error:
        rcu_read_unlock();
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -1768,7 +1959,7 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                struct lttng_ust_field_iter uiter;
 
-               health_code_update(&health_thread_cmd);
+               health_code_update();
 
                if (!app->compatible) {
                        /*
@@ -1779,14 +1970,28 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
                }
                handle = ustctl_tracepoint_field_list(app->sock);
                if (handle < 0) {
-                       ERR("UST app list event fields getting handle failed for app pid %d",
-                                       app->pid);
+                       if (handle != -EPIPE && handle != -LTTNG_UST_ERR_EXITING) {
+                               ERR("UST app list field getting handle failed for app pid %d",
+                                               app->pid);
+                       }
                        continue;
                }
 
                while ((ret = ustctl_tracepoint_field_list_get(app->sock, handle,
                                        &uiter)) != -LTTNG_UST_ERR_NOENT) {
-                       health_code_update(&health_thread_cmd);
+                       /* Handle ustctl error. */
+                       if (ret < 0) {
+                               free(tmp_event);
+                               if (ret != -LTTNG_UST_ERR_EXITING || ret != -EPIPE) {
+                                       ERR("UST app tp list field failed for app %d with ret %d",
+                                                       app->sock, ret);
+                               } else {
+                                       DBG3("UST app tp list field failed. Application is dead");
+                               }
+                               goto rcu_error;
+                       }
+
+                       health_code_update();
                        if (count >= nbmem) {
                                /* In case the realloc fails, we free the memory */
                                void *ptr;
@@ -1825,7 +2030,7 @@ int ust_app_list_event_fields(struct lttng_event_field **fields)
 rcu_error:
        rcu_read_unlock();
 error:
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return ret;
 }
 
@@ -1869,6 +2074,7 @@ void ust_app_ht_alloc(void)
 {
        ust_app_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        ust_app_ht_by_sock = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
+       ust_app_ht_by_notify_sock = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
 }
 
 /*
@@ -2159,8 +2365,11 @@ int ust_app_create_channel_glb(struct ltt_ust_session *usess,
                }
                assert(ua_sess);
 
+               pthread_mutex_lock(&ua_sess->lock);
                /* Create channel onto application. We don't need the chan ref. */
-               ret = create_ust_app_channel(ua_sess, uchan, app, NULL);
+               ret = create_ust_app_channel(ua_sess, uchan, app, usess->consumer,
+                               LTTNG_UST_CHAN_PER_CPU, NULL);
+               pthread_mutex_unlock(&ua_sess->lock);
                if (ret < 0) {
                        if (ret == -ENOMEM) {
                                /* No more memory is a fatal error. Stop right now. */
@@ -2168,7 +2377,7 @@ int ust_app_create_channel_glb(struct ltt_ust_session *usess,
                        }
                        /* Cleanup the created session if it's the case. */
                        if (created) {
-                               delete_ust_app_session(app->sock, ua_sess);
+                               destroy_app_session(app, ua_sess);
                        }
                }
        }
@@ -2218,6 +2427,8 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
                        continue;
                }
 
+               pthread_mutex_lock(&ua_sess->lock);
+
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
                ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
@@ -2232,13 +2443,16 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
                if (ua_event == NULL) {
                        DBG3("UST app enable event %s not found for app PID %d."
                                        "Skipping app", uevent->attr.name, app->pid);
-                       continue;
+                       goto next_app;
                }
 
                ret = enable_ust_app_event(ua_sess, ua_event, app);
                if (ret < 0) {
+                       pthread_mutex_unlock(&ua_sess->lock);
                        goto error;
                }
+       next_app:
+               pthread_mutex_unlock(&ua_sess->lock);
        }
 
 error:
@@ -2280,6 +2494,7 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
                        continue;
                }
 
+               pthread_mutex_lock(&ua_sess->lock);
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
                ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
@@ -2289,6 +2504,7 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
 
                ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
+               pthread_mutex_unlock(&ua_sess->lock);
                if (ret < 0) {
                        if (ret != -LTTNG_UST_ERR_EXIST) {
                                /* Possible value at this point: -ENOMEM. If so, we stop! */
@@ -2311,11 +2527,7 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
 int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
 {
        int ret = 0;
-       struct lttng_ht_iter iter;
        struct ust_app_session *ua_sess;
-       struct ust_app_channel *ua_chan;
-       struct ust_app_stream *ustream;
-       struct consumer_socket *socket;
 
        DBG("Starting tracing for ust app pid %d", app->pid);
 
@@ -2331,6 +2543,8 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                goto end;
        }
 
+       pthread_mutex_lock(&ua_sess->lock);
+
        /* Upon restart, we skip the setup, already done */
        if (ua_sess->started) {
                goto skip_setup;
@@ -2344,110 +2558,55 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                if (ret < 0) {
                        if (ret != -EEXIST) {
                                ERR("Trace directory creation error");
-                               ret = -1;
-                               goto error_rcu_unlock;
+                               goto error_unlock;
                        }
                }
        }
 
-       ret = create_ust_app_metadata(ua_sess, usess->pathname, app);
+       /* Create the metadata for the application. */
+       ret = create_ust_app_metadata(ua_sess, app, usess->consumer);
        if (ret < 0) {
-               ret = LTTNG_ERR_UST_META_FAIL;
-               goto error_rcu_unlock;
+               goto error_unlock;
        }
 
-       /* For each channel */
-       cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
-                       node.node) {
-               /* Create all streams */
-               while (1) {
-                       /* Create UST stream */
-                       ustream = zmalloc(sizeof(*ustream));
-                       if (ustream == NULL) {
-                               PERROR("zmalloc ust stream");
-                               goto error_rcu_unlock;
-                       }
-
-                       health_code_update(&health_thread_cmd);
-
-                       ret = create_ust_stream(app, ua_chan, ustream);
-                       if (ret < 0) {
-                               /* Free unused memory after this point. */
-                               free(ustream);
-                               if (ret == -LTTNG_UST_ERR_NOENT) {
-                                       /* Got all streams. Continue normal execution. */
-                                       break;
-                               }
-                               /* Error at this point. Stop everything. */
-                               ret = LTTNG_ERR_UST_STREAM_FAIL;
-                               goto error_rcu_unlock;
-                       }
-
-                       health_code_update(&health_thread_cmd);
-
-                       /* Order is important this is why a list is used. */
-                       cds_list_add_tail(&ustream->list, &ua_chan->streams.head);
-                       ua_chan->streams.count++;
-
-                       DBG2("UST stream %d ready (handle: %d)", ua_chan->streams.count,
-                                       ustream->handle);
-               }
-
-               health_code_update(&health_thread_cmd);
-       }
-
-       switch (app->bits_per_long) {
-       case 64:
-               socket = consumer_find_socket(uatomic_read(&ust_consumerd64_fd),
-                               usess->consumer);
-               if (socket == NULL) {
-                       goto skip_setup;
-               }
-               break;
-       case 32:
-               socket = consumer_find_socket(uatomic_read(&ust_consumerd32_fd),
-                               usess->consumer);
-               if (socket == NULL) {
-                       goto skip_setup;
-               }
-               break;
-       default:
-               ret = -EINVAL;
-               goto error_rcu_unlock;
-       }
-
-       /* Setup UST consumer socket and send fds to it */
-       ret = ust_consumer_send_session(ua_sess, usess->consumer, socket);
-       if (ret < 0) {
-               goto error_rcu_unlock;
-       }
-
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
 skip_setup:
        /* This start the UST tracing */
        ret = ustctl_start_session(app->sock, ua_sess->handle);
        if (ret < 0) {
-               ERR("Error starting tracing for app pid: %d (ret: %d)", app->pid, ret);
-               goto error_rcu_unlock;
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("Error starting tracing for app pid: %d (ret: %d)",
+                                       app->pid, ret);
+               } else {
+                       DBG("UST app start session failed. Application is dead.");
+               }
+               goto error_unlock;
        }
 
        /* Indicate that the session has been started once */
        ua_sess->started = 1;
 
-       health_code_update(&health_thread_cmd);
+       pthread_mutex_unlock(&ua_sess->lock);
+
+       health_code_update();
 
        /* Quiescent wait after starting trace */
-       ustctl_wait_quiescent(app->sock);
+       ret = ustctl_wait_quiescent(app->sock);
+       if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+               ERR("UST app wait quiescent failed for app pid %d ret %d",
+                               app->pid, ret);
+       }
 
 end:
        rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return 0;
 
-error_rcu_unlock:
+error_unlock:
+       pthread_mutex_unlock(&ua_sess->lock);
        rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return -1;
 }
 
@@ -2484,52 +2643,75 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
                goto error_rcu_unlock;
        }
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        /* This inhibits UST tracing */
        ret = ustctl_stop_session(app->sock, ua_sess->handle);
        if (ret < 0) {
-               ERR("Error stopping tracing for app pid: %d (ret: %d)", app->pid, ret);
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("Error stopping tracing for app pid: %d (ret: %d)",
+                                       app->pid, ret);
+               } else {
+                       DBG("UST app stop session failed. Application is dead.");
+               }
                goto error_rcu_unlock;
        }
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        /* Quiescent wait after stopping trace */
-       ustctl_wait_quiescent(app->sock);
+       ret = ustctl_wait_quiescent(app->sock);
+       if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+               ERR("UST app wait quiescent failed for app pid %d ret %d",
+                               app->pid, ret);
+       }
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
        /* Flushing buffers */
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
-               health_code_update(&health_thread_cmd);
+               health_code_update();
+               assert(ua_chan->is_sent);
                ret = ustctl_sock_flush_buffer(app->sock, ua_chan->obj);
                if (ret < 0) {
-                       ERR("UST app PID %d channel %s flush failed with ret %d",
-                                       app->pid, ua_chan->name, ret);
+                       if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                               ERR("UST app PID %d channel %s flush failed with ret %d",
+                                               app->pid, ua_chan->name, ret);
+                       } else {
+                               DBG3("UST app failed to flush %s. Application is dead.",
+                                               ua_chan->name);
+                               /* No need to continue. */
+                               goto end;
+                       }
                        /* Continuing flushing all buffers */
                        continue;
                }
        }
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
 
+       assert(ua_sess->metadata->is_sent);
        /* Flush all buffers before stopping */
        ret = ustctl_sock_flush_buffer(app->sock, ua_sess->metadata->obj);
        if (ret < 0) {
-               ERR("UST app PID %d metadata flush failed with ret %d", app->pid,
-                               ret);
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app PID %d metadata flush failed with ret %d", app->pid,
+                                       ret);
+                       goto error_rcu_unlock;
+               } else {
+                       DBG3("UST app failed to flush metadata. Application is dead.");
+               }
        }
 
 end:
        rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return 0;
 
 error_rcu_unlock:
        rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return -1;
 }
 
@@ -2538,11 +2720,10 @@ error_rcu_unlock:
  */
 static int destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
 {
+       int ret;
        struct ust_app_session *ua_sess;
-       struct lttng_ust_object_data obj;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;
-       int ret;
 
        DBG("Destroy tracing for ust app pid %d", app->pid);
 
@@ -2559,28 +2740,22 @@ static int destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
                goto end;
        }
        ua_sess = caa_container_of(node, struct ust_app_session, node);
-       ret = lttng_ht_del(app->sessions, &iter);
-       if (ret) {
-               /* Already scheduled for teardown. */
-               goto end;
-       }
 
-       obj.handle = ua_sess->handle;
-       obj.shm_fd = -1;
-       obj.wait_fd = -1;
-       obj.memory_map_size = 0;
-       health_code_update(&health_thread_cmd);
-       ustctl_release_object(app->sock, &obj);
+       health_code_update();
+       destroy_app_session(app, ua_sess);
 
-       health_code_update(&health_thread_cmd);
-       delete_ust_app_session(app->sock, ua_sess);
+       health_code_update();
 
        /* Quiescent wait after stopping trace */
-       ustctl_wait_quiescent(app->sock);
+       ret = ustctl_wait_quiescent(app->sock);
+       if (ret < 0 && ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+               ERR("UST app wait quiescent failed for app pid %d ret %d",
+                               app->pid, ret);
+       }
 
 end:
        rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
+       health_code_update();
        return 0;
 }
 
@@ -2676,6 +2851,7 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
        struct ust_app_ctx *ua_ctx;
 
        assert(usess);
+       assert(sock >= 0);
 
        DBG2("UST app global update for app sock %d for session id %d", sock,
                        usess->id);
@@ -2684,7 +2860,7 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
 
        app = find_app_by_sock(sock);
        if (app == NULL) {
-               ERR("Failed to update app sock %d", sock);
+               ERR("Failed to find app sock %d", sock);
                goto error;
        }
 
@@ -2699,25 +2875,30 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
        }
        assert(ua_sess);
 
+       pthread_mutex_lock(&ua_sess->lock);
+
        /*
-        * We can iterate safely here over all UST app session sicne the create ust
+        * We can iterate safely here over all UST app session since the create ust
         * app session above made a shadow copy of the UST global domain from the
         * ltt ust session.
         */
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
-               ret = create_ust_channel(app, ua_sess, ua_chan);
+               ret = create_ust_channel(app, ua_sess, ua_chan, usess->consumer);
                if (ret < 0) {
-                       /* FIXME: Should we quit here or continue... */
-                       continue;
+                       /*
+                        * Stop everything. On error, the application failed, no more file
+                        * descriptor are available or ENOMEM so stopping here is the only
+                        * thing we can do for now.
+                        */
+                       goto error_unlock;
                }
 
                cds_lfht_for_each_entry(ua_chan->ctx->ht, &iter_ctx.iter, ua_ctx,
                                node.node) {
                        ret = create_ust_channel_context(ua_chan, ua_ctx, app);
                        if (ret < 0) {
-                               /* FIXME: Should we quit here or continue... */
-                               continue;
+                               goto error_unlock;
                        }
                }
 
@@ -2727,12 +2908,13 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
                                node.node) {
                        ret = create_ust_event(app, ua_sess, ua_chan, ua_event);
                        if (ret < 0) {
-                               /* FIXME: Should we quit here or continue... */
-                               continue;
+                               goto error_unlock;
                        }
                }
        }
 
+       pthread_mutex_unlock(&ua_sess->lock);
+
        if (usess->start_trace) {
                ret = ust_app_start_trace(usess, app);
                if (ret < 0) {
@@ -2742,7 +2924,16 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
                DBG2("UST trace started for app pid %d", app->pid);
        }
 
+       /* Everything went well at this point. */
+       rcu_read_unlock();
+       return;
+
+error_unlock:
+       pthread_mutex_unlock(&ua_sess->lock);
 error:
+       if (ua_sess) {
+               destroy_app_session(app, ua_sess);
+       }
        rcu_read_unlock();
        return;
 }
@@ -2775,19 +2966,21 @@ int ust_app_add_ctx_channel_glb(struct ltt_ust_session *usess,
                        continue;
                }
 
+               pthread_mutex_lock(&ua_sess->lock);
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
                ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
                if (ua_chan_node == NULL) {
-                       continue;
+                       goto next_app;
                }
                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel,
                                node);
-
                ret = create_ust_app_channel_context(ua_sess, ua_chan, &uctx->ctx, app);
                if (ret < 0) {
-                       continue;
+                       goto next_app;
                }
+       next_app:
+               pthread_mutex_unlock(&ua_sess->lock);
        }
 
        rcu_read_unlock();
@@ -2816,20 +3009,22 @@ int ust_app_enable_event_pid(struct ltt_ust_session *usess,
        if (app == NULL) {
                ERR("UST app enable event per PID %d not found", pid);
                ret = -1;
-               goto error;
+               goto end;
        }
 
        if (!app->compatible) {
                ret = 0;
-               goto error;
+               goto end;
        }
 
        ua_sess = lookup_session_by_app(usess, app);
        if (!ua_sess) {
                /* The application has problem or is probably dead. */
-               goto error;
+               ret = 0;
+               goto end;
        }
 
+       pthread_mutex_lock(&ua_sess->lock);
        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
        ua_chan_node = lttng_ht_iter_get_node_str(&iter);
@@ -2843,16 +3038,18 @@ int ust_app_enable_event_pid(struct ltt_ust_session *usess,
        if (ua_event == NULL) {
                ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
                if (ret < 0) {
-                       goto error;
+                       goto end_unlock;
                }
        } else {
                ret = enable_ust_app_event(ua_sess, ua_event, app);
                if (ret < 0) {
-                       goto error;
+                       goto end_unlock;
                }
        }
 
-error:
+end_unlock:
+       pthread_mutex_unlock(&ua_sess->lock);
+end:
        rcu_read_unlock();
        return ret;
 }
@@ -2920,49 +3117,6 @@ error:
        return ret;
 }
 
-/*
- * Validate version of UST apps and set the compatible bit.
- */
-int ust_app_validate_version(int sock)
-{
-       int ret;
-       struct ust_app *app;
-
-       rcu_read_lock();
-
-       app = find_app_by_sock(sock);
-       assert(app);
-
-       health_code_update(&health_thread_cmd);
-
-       ret = ustctl_tracer_version(sock, &app->version);
-       if (ret < 0) {
-               goto error;
-       }
-
-       /* Validate version */
-       if (app->version.major != UST_APP_MAJOR_VERSION) {
-               goto error;
-       }
-
-       DBG2("UST app PID %d is compatible with internal major version %d "
-                       "(supporting == %d)", app->pid, app->version.major,
-                       UST_APP_MAJOR_VERSION);
-       app->compatible = 1;
-       rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
-       return 0;
-
-error:
-       DBG2("UST app PID %d is not compatible with internal major version %d "
-                       "(supporting == %d)", app->pid, app->version.major,
-                       UST_APP_MAJOR_VERSION);
-       app->compatible = 0;
-       rcu_read_unlock();
-       health_code_update(&health_thread_cmd);
-       return -1;
-}
-
 /*
  * Calibrate registered applications.
  */
@@ -2983,7 +3137,7 @@ int ust_app_calibrate_glb(struct lttng_ust_calibrate *calibrate)
                        continue;
                }
 
-               health_code_update(&health_thread_cmd);
+               health_code_update();
 
                ret = ustctl_calibrate(app->sock, calibrate);
                if (ret < 0) {
@@ -2993,7 +3147,6 @@ int ust_app_calibrate_glb(struct lttng_ust_calibrate *calibrate)
                                ret = 0;
                                break;
                        default:
-                               /* TODO: Report error to user */
                                DBG2("Calibrate app PID %d returned with error %d",
                                                app->pid, ret);
                                break;
@@ -3005,7 +3158,294 @@ int ust_app_calibrate_glb(struct lttng_ust_calibrate *calibrate)
 
        rcu_read_unlock();
 
-       health_code_update(&health_thread_cmd);
+       health_code_update();
+
+       return ret;
+}
+
+/*
+ * Receive registration and populate the given msg structure.
+ *
+ * On success return 0 else a negative value returned by the ustctl call.
+ */
+int ust_app_recv_registration(int sock, struct ust_register_msg *msg)
+{
+       int ret;
+       uint32_t pid, ppid, uid, gid;
+
+       assert(msg);
+
+       ret = ustctl_recv_reg_msg(sock, &msg->type, &msg->major, &msg->minor,
+                       &pid, &ppid, &uid, &gid,
+                       &msg->bits_per_long,
+                       &msg->uint8_t_alignment,
+                       &msg->uint16_t_alignment,
+                       &msg->uint32_t_alignment,
+                       &msg->uint64_t_alignment,
+                       &msg->long_alignment,
+                       &msg->byte_order,
+                       msg->name);
+       if (ret < 0) {
+               switch (-ret) {
+               case EPIPE:
+               case ECONNRESET:
+               case LTTNG_UST_ERR_EXITING:
+                       DBG3("UST app recv reg message failed. Application died");
+                       break;
+               case LTTNG_UST_ERR_UNSUP_MAJOR:
+                       ERR("UST app recv reg unsupported version %d.%d. Supporting %d.%d",
+                                       msg->major, msg->minor, LTTNG_UST_ABI_MAJOR_VERSION,
+                                       LTTNG_UST_ABI_MINOR_VERSION);
+                       break;
+               default:
+                       ERR("UST app recv reg message failed with ret %d", ret);
+                       break;
+               }
+               goto error;
+       }
+       msg->pid = (pid_t) pid;
+       msg->ppid = (pid_t) ppid;
+       msg->uid = (uid_t) uid;
+       msg->gid = (gid_t) gid;
+
+error:
+       return ret;
+}
+
+static struct ust_app_channel *find_channel_by_objd(struct ust_app *app,
+               int objd)
+{
+       struct lttng_ht_node_ulong *node;
+       struct lttng_ht_iter iter;
+       struct ust_app_channel *ua_chan = NULL;
+
+       assert(app);
+
+       lttng_ht_lookup(app->ust_objd, (void *)((unsigned long) objd), &iter);
+       node = lttng_ht_iter_get_node_ulong(&iter);
+       if (node == NULL) {
+               DBG2("UST app channel find by objd %d not found", objd);
+               goto error;
+       }
+
+       ua_chan = caa_container_of(node, struct ust_app_channel, ust_objd_node);
+
+error:
+       return ua_chan;
+}
+
+static int reply_ust_register_channel(int sock, int sobjd, int cobjd,
+               size_t nr_fields, struct ustctl_field *fields)
+{
+       int ret, ret_code = 0;
+       uint32_t chan_id, reg_count;
+       enum ustctl_channel_header type;
+       struct ust_app *app;
+       struct ust_app_channel *ua_chan;
+       struct ust_app_session *ua_sess;
+
+       rcu_read_lock();
 
+       /* Lookup application. If not found, there is a code flow error. */
+       app = find_app_by_notify_sock(sock);
+       assert(app);
+
+       /* Lookup channel by UST object descriptor. Should always be found. */
+       ua_chan = find_channel_by_objd(app, cobjd);
+       assert(ua_chan);
+       assert(ua_chan->session);
+       ua_sess = ua_chan->session;
+       assert(ua_sess);
+
+       pthread_mutex_lock(&ua_sess->registry.lock);
+
+       if (ust_registry_is_max_id(ua_chan->session->registry.used_channel_id)) {
+               ret_code = -1;
+               chan_id = -1U;
+               type = -1;
+               goto reply;
+       }
+
+       /* Don't assign ID to metadata. */
+       if (ua_chan->attr.type == LTTNG_UST_CHAN_METADATA) {
+               chan_id = -1U;
+       } else {
+               chan_id = ust_registry_get_next_chan_id(&ua_chan->session->registry);
+       }
+
+       reg_count = ust_registry_get_event_count(&ua_chan->registry);
+       if (reg_count < 31) {
+               type = USTCTL_CHANNEL_HEADER_COMPACT;
+       } else {
+               type = USTCTL_CHANNEL_HEADER_LARGE;
+       }
+
+       ua_chan->registry.nr_ctx_fields = nr_fields;
+       ua_chan->registry.ctx_fields = fields;
+       ua_chan->registry.chan_id = chan_id;
+       ua_chan->registry.header_type = type;
+
+       /* Append to metadata */
+       if (!ret_code) {
+               ret_code = ust_metadata_channel_statedump(&ua_chan->session->registry,
+                               &ua_chan->registry);
+               if (ret_code) {
+                       ERR("Error appending channel metadata (errno = %d)", ret_code);
+                       goto reply;
+               }
+       }
+
+reply:
+       DBG3("UST app replying to register channel with id %u, type: %d, ret: %d",
+                       chan_id, type, ret_code);
+
+       ret = ustctl_reply_register_channel(sock, chan_id, type, ret_code);
+       if (ret < 0) {
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app reply channel failed with ret %d", ret);
+               } else {
+                       DBG3("UST app reply channel failed. Application died");
+               }
+               goto error;
+       }
+
+error:
+       pthread_mutex_unlock(&ua_sess->registry.lock);
+       rcu_read_unlock();
+       return ret;
+}
+
+static int add_event_ust_registry(int sock, int sobjd, int cobjd, char *name,
+               char *sig, size_t nr_fields, struct ustctl_field *fields, int loglevel,
+               char *model_emf_uri)
+{
+       int ret, ret_code;
+       uint32_t event_id = 0;
+       struct ust_app *app;
+       struct ust_app_channel *ua_chan;
+       struct ust_app_session *ua_sess;
+
+       rcu_read_lock();
+
+       /* Lookup application. If not found, there is a code flow error. */
+       app = find_app_by_notify_sock(sock);
+       assert(app);
+
+       /* Lookup channel by UST object descriptor. Should always be found. */
+       ua_chan = find_channel_by_objd(app, cobjd);
+       assert(ua_chan);
+       assert(ua_chan->session);
+       ua_sess = ua_chan->session;
+
+       pthread_mutex_lock(&ua_sess->registry.lock);
+
+       ret_code = ust_registry_create_event(&ua_sess->registry, &ua_chan->registry, sobjd, cobjd,
+                       name, sig, nr_fields, fields, loglevel, model_emf_uri, &event_id);
+
+       /*
+        * The return value is returned to ustctl so in case of an error, the
+        * application can be notified. In case of an error, it's important not to
+        * return a negative error or else the application will get closed.
+        */
+       ret = ustctl_reply_register_event(sock, event_id, ret_code);
+       if (ret < 0) {
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app reply event failed with ret %d", ret);
+               } else {
+                       DBG3("UST app reply event failed. Application died");
+               }
+               /*
+                * No need to wipe the create event since the application socket will
+                * get close on error hence cleaning up everything by itself.
+                */
+               goto error;
+       }
+
+error:
+       pthread_mutex_unlock(&ua_sess->registry.lock);
+       rcu_read_unlock();
+       return ret;
+}
+
+int ust_app_recv_notify(int sock)
+{
+       int ret;
+       enum ustctl_notify_cmd cmd;
+
+       DBG3("UST app receiving notify from sock %d", sock);
+
+       ret = ustctl_recv_notify(sock, &cmd);
+       if (ret < 0) {
+               if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       ERR("UST app recv notify failed with ret %d", ret);
+               } else {
+                       DBG3("UST app recv notify failed. Application died");
+               }
+               goto error;
+       }
+
+       switch (cmd) {
+       case USTCTL_NOTIFY_CMD_EVENT:
+       {
+               int sobjd, cobjd, loglevel;
+               char name[LTTNG_UST_SYM_NAME_LEN], *sig, *model_emf_uri;
+               size_t nr_fields;
+               struct ustctl_field *fields;
+
+               DBG2("UST app ustctl register event received");
+
+               ret = ustctl_recv_register_event(sock, &sobjd, &cobjd, name, &loglevel,
+                               &sig, &nr_fields, &fields, &model_emf_uri);
+               if (ret < 0) {
+                       if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                               ERR("UST app recv event failed with ret %d", ret);
+                       } else {
+                               DBG3("UST app recv event failed. Application died");
+                       }
+                       goto error;
+               }
+
+               /* Add event to the UST registry coming from the notify socket. */
+               ret = add_event_ust_registry(sock, sobjd, cobjd, name, sig, nr_fields,
+                               fields, loglevel, model_emf_uri);
+               if (ret < 0) {
+                       goto error;
+               }
+
+               break;
+       }
+       case USTCTL_NOTIFY_CMD_CHANNEL:
+       {
+               int sobjd, cobjd;
+               size_t nr_fields;
+               struct ustctl_field *fields;
+
+               DBG2("UST app ustctl register channel received");
+
+               ret = ustctl_recv_register_channel(sock, &sobjd, &cobjd, &nr_fields,
+                               &fields);
+               if (ret < 0) {
+                       if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                               ERR("UST app recv channel failed with ret %d", ret);
+                       } else {
+                               DBG3("UST app recv channel failed. Application died");
+                       }
+                       goto error;
+               }
+
+               ret = reply_ust_register_channel(sock, sobjd, cobjd, nr_fields,
+                               fields);
+               if (ret < 0) {
+                       goto error;
+               }
+
+               break;
+       }
+       default:
+               /* Should NEVER happen. */
+               assert(0);
+       }
+
+error:
        return ret;
 }
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