Fix: build failure with -fno-common
[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c
index f88df7406ea567049321b6c508fdc5b249a4ff35..d3c28883c74bea2416d9afb8a5f0db7c87c03f91 100644 (file)
@@ -27,7 +27,6 @@
 #include <sys/types.h>
 #include <unistd.h>
 #include <urcu/compiler.h>
-#include <lttng/ust-error.h>
 #include <signal.h>
 
 #include <common/common.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"
 
+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);
 
@@ -250,7 +254,8 @@ static struct ust_registry_session *get_session_registry(
        case LTTNG_BUFFER_PER_UID:
        {
                struct buffer_reg_uid *reg_uid = buffer_reg_uid_find(
-                               ua_sess->tracing_id, ua_sess->bits_per_long, ua_sess->uid);
+                               ua_sess->tracing_id, ua_sess->bits_per_long,
+                               ua_sess->real_credentials.uid);
                if (!reg_uid) {
                        goto error;
                }
@@ -740,6 +745,10 @@ 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,
@@ -747,6 +756,8 @@ 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);
@@ -754,8 +765,19 @@ 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;
        }
@@ -765,23 +787,15 @@ 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;
 }
@@ -1099,7 +1113,7 @@ struct ust_app_event *alloc_ust_app_event(char *name,
        /* 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;
        }
 
@@ -1260,7 +1274,7 @@ error:
  * Return an ust_app_event object or NULL on error.
  */
 static struct ust_app_event *find_ust_app_event(struct lttng_ht *ht,
-               char *name, struct lttng_filter_bytecode *filter,
+               const char *name, const struct lttng_filter_bytecode *filter,
                int loglevel_value,
                const struct lttng_event_exclusion *exclusion)
 {
@@ -1321,7 +1335,7 @@ int create_ust_channel_context(struct ust_app_channel *ua_chan,
                         * continue normally.
                         */
                        ret = 0;
-                       DBG3("UST app disable event failed. Application is dead.");
+                       DBG3("UST app add context failed. Application is dead.");
                }
                goto error;
        }
@@ -1683,6 +1697,7 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
        pthread_mutex_unlock(&app->sock_lock);
        if (ret < 0) {
                if (ret != -EPIPE && ret != -LTTNG_UST_ERR_EXITING) {
+                       abort();
                        ERR("Error ustctl create event %s for app pid: %d with ret %d",
                                        ua_event->attr.name, app->pid, ret);
                } else {
@@ -1795,11 +1810,6 @@ static void shadow_copy_event(struct ust_app_event *ua_event,
 static void shadow_copy_channel(struct ust_app_channel *ua_chan,
                struct ltt_ust_channel *uchan)
 {
-       struct lttng_ht_iter iter;
-       struct ltt_ust_event *uevent;
-       struct ltt_ust_context *uctx;
-       struct ust_app_event *ua_event;
-
        DBG2("UST app shadow copy of channel %s started", ua_chan->name);
 
        strncpy(ua_chan->name, uchan->name, sizeof(ua_chan->name));
@@ -1826,34 +1836,6 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
        ua_chan->enabled = uchan->enabled;
        ua_chan->tracing_channel_id = uchan->id;
 
-       cds_list_for_each_entry(uctx, &uchan->ctx_list, list) {
-               struct ust_app_ctx *ua_ctx = alloc_ust_app_ctx(&uctx->ctx);
-
-               if (ua_ctx == NULL) {
-                       continue;
-               }
-               lttng_ht_node_init_ulong(&ua_ctx->node,
-                               (unsigned long) ua_ctx->ctx.ctx);
-               lttng_ht_add_ulong(ua_chan->ctx, &ua_ctx->node);
-               cds_list_add_tail(&ua_ctx->list, &ua_chan->ctx_list);
-       }
-
-       /* Copy all events from ltt ust channel to ust app channel */
-       cds_lfht_for_each_entry(uchan->events->ht, &iter.iter, uevent, node.node) {
-               ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
-                               uevent->filter, uevent->attr.loglevel, uevent->exclusion);
-               if (ua_event == NULL) {
-                       DBG2("UST event %s not found on shadow copy channel",
-                                       uevent->attr.name);
-                       ua_event = alloc_ust_app_event(uevent->attr.name, &uevent->attr);
-                       if (ua_event == NULL) {
-                               continue;
-                       }
-                       shadow_copy_event(ua_event, uevent);
-                       add_unique_ust_app_event(ua_chan, ua_event);
-               }
-       }
-
        DBG3("UST app shadow copy of channel %s done", ua_chan->name);
 }
 
@@ -1863,29 +1845,22 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
 static void shadow_copy_session(struct ust_app_session *ua_sess,
                struct ltt_ust_session *usess, struct ust_app *app)
 {
-       struct lttng_ht_node_str *ua_chan_node;
-       struct lttng_ht_iter iter;
-       struct ltt_ust_channel *uchan;
-       struct ust_app_channel *ua_chan;
-       time_t rawtime;
        struct tm *timeinfo;
        char datetime[16];
        int ret;
        char tmp_shm_path[PATH_MAX];
 
-       /* Get date and time for unique app path */
-       time(&rawtime);
-       timeinfo = localtime(&rawtime);
+       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();
-       ua_sess->uid = app->uid;
-       ua_sess->gid = app->gid;
-       ua_sess->euid = usess->uid;
-       ua_sess->egid = usess->gid;
+       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;
        ua_sess->bits_per_long = app->bits_per_long;
 
@@ -1906,7 +1881,9 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
                break;
        case LTTNG_BUFFER_PER_UID:
                ret = snprintf(ua_sess->path, sizeof(ua_sess->path),
-                               DEFAULT_UST_TRACE_UID_PATH, ua_sess->uid, app->bits_per_long);
+                               DEFAULT_UST_TRACE_UID_PATH,
+                               ua_sess->real_credentials.uid,
+                               app->bits_per_long);
                break;
        default:
                assert(0);
@@ -1928,12 +1905,12 @@ 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:
@@ -1949,37 +1926,6 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
                        sizeof(ua_sess->shm_path) - strlen(ua_sess->shm_path) - 1);
                ua_sess->shm_path[sizeof(ua_sess->shm_path) - 1] = '\0';
        }
-
-       /* Iterate over all channels in global domain. */
-       cds_lfht_for_each_entry(usess->domain_global.channels->ht, &iter.iter,
-                       uchan, node.node) {
-               struct lttng_ht_iter uiter;
-
-               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) {
-                       /* Session exist. Contiuing. */
-                       continue;
-               }
-
-               DBG2("Channel %s not found on shadow session copy, creating it",
-                               uchan->name);
-               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);
-       }
        return;
 
 error:
@@ -1990,7 +1936,7 @@ error:
  * Lookup sesison wrapper.
  */
 static
-void __lookup_session_by_app(struct ltt_ust_session *usess,
+void __lookup_session_by_app(const struct ltt_ust_session *usess,
                        struct ust_app *app, struct lttng_ht_iter *iter)
 {
        /* Get right UST app session from app */
@@ -2002,7 +1948,7 @@ void __lookup_session_by_app(struct ltt_ust_session *usess,
  * id.
  */
 static struct ust_app_session *lookup_session_by_app(
-               struct ltt_ust_session *usess, struct ust_app *app)
+               const struct ltt_ust_session *usess, struct ust_app *app)
 {
        struct lttng_ht_iter iter;
        struct lttng_ht_node_u64 *node;
@@ -2057,10 +2003,11 @@ static int setup_buffer_reg_pid(struct ust_app_session *ua_sess,
                        app->bits_per_long, app->uint8_t_alignment,
                        app->uint16_t_alignment, app->uint32_t_alignment,
                        app->uint64_t_alignment, app->long_alignment,
-                       app->byte_order, app->version.major,
-                       app->version.minor, reg_pid->root_shm_path,
-                       reg_pid->shm_path,
-                       ua_sess->euid, ua_sess->egid);
+                       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, ua_sess->tracing_id,
+                       app->uid);
        if (ret < 0) {
                /*
                 * reg_pid->registry->reg.ust is NULL upon error, so we need to
@@ -2127,7 +2074,8 @@ 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
@@ -2529,7 +2477,7 @@ static int do_consumer_create_channel(struct ltt_ust_session *usess,
         * stream we have to expect.
         */
        ret = ust_consumer_ask_channel(ua_sess, ua_chan, usess->consumer, socket,
-                       registry, trace_archive_id);
+                       registry, usess->current_trace_chunk);
        if (ret < 0) {
                goto error_ask;
        }
@@ -2912,7 +2860,7 @@ static int create_channel_per_uid(struct ust_app *app,
         */
        ret = do_consumer_create_channel(usess, ua_sess, ua_chan,
                        app->bits_per_long, reg_uid->registry->reg.ust,
-                       session->current_archive_id);
+                       session->most_recent_chunk_id.value);
        if (ret < 0) {
                ERR("Error creating UST channel \"%s\" on the consumer daemon",
                                ua_chan->name);
@@ -2949,10 +2897,9 @@ static int create_channel_per_uid(struct ust_app *app,
 
        notification_ret = notification_thread_command_add_channel(
                        notification_thread_handle, session->name,
-                       ua_sess->euid, ua_sess->egid,
-                       ua_chan->name,
-                       ua_chan->key,
-                       LTTNG_DOMAIN_UST,
+                       ua_sess->effective_credentials.uid,
+                       ua_sess->effective_credentials.gid, ua_chan->name,
+                       ua_chan->key, LTTNG_DOMAIN_UST,
                        ua_chan->attr.subbuf_size * ua_chan->attr.num_subbuf);
        if (notification_ret != LTTNG_OK) {
                ret = - (int) notification_ret;
@@ -3026,7 +2973,7 @@ static int create_channel_per_pid(struct ust_app *app,
        /* Create and get channel on the consumer side. */
        ret = do_consumer_create_channel(usess, ua_sess, ua_chan,
                        app->bits_per_long, registry,
-                       session->current_archive_id);
+                       session->most_recent_chunk_id.value);
        if (ret < 0) {
                ERR("Error creating UST channel \"%s\" on the consumer daemon",
                        ua_chan->name);
@@ -3050,10 +2997,9 @@ static int create_channel_per_pid(struct ust_app *app,
 
        cmd_ret = notification_thread_command_add_channel(
                        notification_thread_handle, session->name,
-                       ua_sess->euid, ua_sess->egid,
-                       ua_chan->name,
-                       ua_chan->key,
-                       LTTNG_DOMAIN_UST,
+                       ua_sess->effective_credentials.uid,
+                       ua_sess->effective_credentials.gid, ua_chan->name,
+                       ua_chan->key, LTTNG_DOMAIN_UST,
                        ua_chan->attr.subbuf_size * ua_chan->attr.num_subbuf);
        if (cmd_ret != LTTNG_OK) {
                ret = - (int) cmd_ret;
@@ -3075,7 +3021,7 @@ error:
 
 /*
  * From an already allocated ust app channel, create the channel buffers if
- * need and send it to the application. This MUST be called with a RCU read
+ * needed and send them to the application. This MUST be called with a RCU read
  * side lock acquired.
  *
  * Called with UST app session lock held.
@@ -3083,7 +3029,7 @@ error:
  * Return 0 on success or else a negative value. Returns -ENOTCONN if
  * the application exited concurrently.
  */
-static int do_create_channel(struct ust_app *app,
+static int ust_app_channel_send(struct ust_app *app,
                struct ltt_ust_session *usess, struct ust_app_session *ua_sess,
                struct ust_app_channel *ua_chan)
 {
@@ -3091,6 +3037,7 @@ static int do_create_channel(struct ust_app *app,
 
        assert(app);
        assert(usess);
+       assert(usess->active);
        assert(ua_sess);
        assert(ua_chan);
 
@@ -3135,16 +3082,14 @@ error:
 }
 
 /*
- * Create UST app channel and create it on the tracer. Set ua_chanp of the
- * newly created channel if not NULL.
+ * Create UST app channel and return it through ua_chanp if not NULL.
  *
  * Called with UST app session lock and RCU read-side lock held.
  *
- * Return 0 on success or else a negative value. Returns -ENOTCONN if
- * the application exited concurrently.
+ * Return 0 on success or else a negative value.
  */
-static int create_ust_app_channel(struct ust_app_session *ua_sess,
-               struct ltt_ust_channel *uchan, struct ust_app *app,
+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,
                struct ust_app_channel **ua_chanp)
 {
@@ -3165,21 +3110,13 @@ static int create_ust_app_channel(struct ust_app_session *ua_sess,
        if (ua_chan == NULL) {
                /* Only malloc can fail here */
                ret = -ENOMEM;
-               goto error_alloc;
+               goto error;
        }
        shadow_copy_channel(ua_chan, uchan);
 
        /* Set channel type. */
        ua_chan->attr.type = type;
 
-       ret = do_create_channel(app, usess, ua_sess, ua_chan);
-       if (ret < 0) {
-               goto error;
-       }
-
-       DBG2("UST app create channel %s for PID %d completed", ua_chan->name,
-                       app->pid);
-
        /* Only add the channel if successful on the tracer side. */
        lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
 end:
@@ -3191,8 +3128,6 @@ end:
        return 0;
 
 error:
-       delete_ust_app_channel(ua_chan->is_sent ? app->sock : -1, ua_chan, app);
-error_alloc:
        return ret;
 }
 
@@ -3209,18 +3144,9 @@ int create_ust_app_event(struct ust_app_session *ua_sess,
        int ret = 0;
        struct ust_app_event *ua_event;
 
-       /* Get event node */
-       ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
-                       uevent->filter, uevent->attr.loglevel, uevent->exclusion);
-       if (ua_event != NULL) {
-               ret = -EEXIST;
-               goto end;
-       }
-
-       /* Does not exist so create one */
        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;
        }
@@ -3229,8 +3155,19 @@ 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;
        }
 
@@ -3323,7 +3260,7 @@ static int create_ust_app_metadata(struct ust_app_session *ua_sess,
         * consumer.
         */
        ret = ust_consumer_ask_channel(ua_sess, metadata, consumer, socket,
-                       registry, session->current_archive_id);
+                       registry, session->current_trace_chunk);
        if (ret < 0) {
                /* Nullify the metadata key so we don't try to close it later on. */
                registry->metadata_key = 0;
@@ -3463,6 +3400,8 @@ void ust_app_add(struct ust_app *app)
        assert(app);
        assert(app->notify_sock >= 0);
 
+       app->registration_time = time(NULL);
+
        rcu_read_lock();
 
        /*
@@ -4003,12 +3942,7 @@ int ust_app_disable_channel_glb(struct ltt_ust_session *usess,
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
 
-       if (usess == NULL || uchan == NULL) {
-               ERR("Disabling UST global channel with NULL values");
-               ret = -1;
-               goto error;
-       }
-
+       assert(usess->active);
        DBG2("UST app disabling channel %s from global domain for session id %" PRIu64,
                        uchan->name, usess->id);
 
@@ -4048,8 +3982,6 @@ int ust_app_disable_channel_glb(struct ltt_ust_session *usess,
        }
 
        rcu_read_unlock();
-
-error:
        return ret;
 }
 
@@ -4064,12 +3996,7 @@ int ust_app_enable_channel_glb(struct ltt_ust_session *usess,
        struct ust_app *app;
        struct ust_app_session *ua_sess;
 
-       if (usess == NULL || uchan == NULL) {
-               ERR("Adding UST global channel to NULL values");
-               ret = -1;
-               goto error;
-       }
-
+       assert(usess->active);
        DBG2("UST app enabling channel %s to global domain for session id %" PRIu64,
                        uchan->name, usess->id);
 
@@ -4098,8 +4025,6 @@ int ust_app_enable_channel_glb(struct ltt_ust_session *usess,
        }
 
        rcu_read_unlock();
-
-error:
        return ret;
 }
 
@@ -4117,6 +4042,7 @@ int ust_app_disable_event_glb(struct ltt_ust_session *usess,
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;
 
+       assert(usess->active);
        DBG("UST app disabling event %s for all apps in channel "
                        "%s for session id %" PRIu64,
                        uevent->attr.name, uchan->name, usess->id);
@@ -4165,107 +4091,77 @@ int ust_app_disable_event_glb(struct ltt_ust_session *usess,
        }
 
        rcu_read_unlock();
-
        return ret;
 }
 
-/*
- * For a specific UST session, create the channel for all registered apps.
- */
-int ust_app_create_channel_glb(struct ltt_ust_session *usess,
-               struct ltt_ust_channel *uchan)
+/* The ua_sess lock must be held by the caller.  */
+static
+int ust_app_channel_create(struct ltt_ust_session *usess,
+               struct ust_app_session *ua_sess,
+               struct ltt_ust_channel *uchan, struct ust_app *app,
+               struct ust_app_channel **_ua_chan)
 {
-       int ret = 0, created;
-       struct lttng_ht_iter iter;
-       struct ust_app *app;
-       struct ust_app_session *ua_sess = NULL;
-
-       /* Very wrong code flow */
-       assert(usess);
-       assert(uchan);
-
-       DBG2("UST app adding channel %s to UST domain for session id %" PRIu64,
-                       uchan->name, usess->id);
+       int ret = 0;
+       struct ust_app_channel *ua_chan = NULL;
 
-       rcu_read_lock();
+       assert(ua_sess);
+       ASSERT_LOCKED(ua_sess->lock);
 
-       /* For every registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
-               if (!app->compatible) {
-                       /*
-                        * TODO: In time, we should notice the caller of this error by
-                        * telling him that this is a version error.
-                        */
-                       continue;
-               }
-               if (!trace_ust_pid_tracker_lookup(usess, app->pid)) {
-                       /* Skip. */
-                       continue;
-               }
+       if (!strncmp(uchan->name, DEFAULT_METADATA_NAME,
+                    sizeof(uchan->name))) {
+               copy_channel_attr_to_ustctl(&ua_sess->metadata_attr,
+                       &uchan->attr);
+               ret = 0;
+       } else {
+               struct ltt_ust_context *uctx = NULL;
 
                /*
-                * 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.
+                * Create channel onto application and synchronize its
+                * configuration.
                 */
-               ret = find_or_create_ust_app_session(usess, app, &ua_sess, &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.
-                                */
-                               ret = 0;        /* Not an error. */
-                               continue;
-                       case -ENOMEM:
-                       default:
-                               goto error_rcu_unlock;
-                       }
-               }
-               assert(ua_sess);
-
-               pthread_mutex_lock(&ua_sess->lock);
-
-               if (ua_sess->deleted) {
-                       pthread_mutex_unlock(&ua_sess->lock);
-                       continue;
-               }
-
-               if (!strncmp(uchan->name, DEFAULT_METADATA_NAME,
-                                       sizeof(uchan->name))) {
-                       copy_channel_attr_to_ustctl(&ua_sess->metadata_attr, &uchan->attr);
-                       ret = 0;
+               ret = ust_app_channel_allocate(ua_sess, uchan,
+                       LTTNG_UST_CHAN_PER_CPU, usess,
+                       &ua_chan);
+               if (ret == 0) {
+                       ret = ust_app_channel_send(app, usess,
+                               ua_sess, ua_chan);
                } else {
-                       /* Create channel onto application. We don't need the chan ref. */
-                       ret = create_ust_app_channel(ua_sess, uchan, app,
-                                       LTTNG_UST_CHAN_PER_CPU, usess, NULL);
+                       goto end;
                }
-               pthread_mutex_unlock(&ua_sess->lock);
-               if (ret < 0) {
-                       /* Cleanup the created session if it's the case. */
-                       if (created) {
-                               destroy_app_session(app, ua_sess);
-                       }
-                       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.
-                                */
-                               ret = 0;        /* Not an error. */
-                               continue;
-                       case -ENOMEM:
-                       default:
-                               goto error_rcu_unlock;
+
+               /* Add contexts. */
+               cds_list_for_each_entry(uctx, &uchan->ctx_list, list) {
+                       ret = create_ust_app_channel_context(ua_chan,
+                               &uctx->ctx, app);
+                       if (ret) {
+                               goto end;
                        }
                }
        }
-
-error_rcu_unlock:
-       rcu_read_unlock();
+       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.
+                        */
+                       ret = 0;        /* Not an error. */
+                       break;
+               case -ENOMEM:
+               default:
+                       break;
+               }
+       }
+end:
+       if (ret == 0 && _ua_chan) {
+               /*
+                * Only return the application's channel on success. Note
+                * that the channel can still be part of the application's
+                * channel hashtable on error.
+                */
+               *_ua_chan = ua_chan;
+       }
        return ret;
 }
 
@@ -4283,6 +4179,7 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
        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);
 
@@ -4368,6 +4265,7 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
 
+       assert(usess->active);
        DBG("UST app creating event %s for all apps for session id %" PRIu64,
                        uevent->attr.name, usess->id);
 
@@ -4417,7 +4315,6 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
        }
 
        rcu_read_unlock();
-
        return ret;
 }
 
@@ -4454,48 +4351,16 @@ 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 directories if consumer is LOCAL and has a path defined. */
-       if (usess->consumer->type == CONSUMER_DST_LOCAL &&
-                       usess->consumer->dst.session_root_path[0] != '\0') {
-               char *tmp_path;
-
-               tmp_path = zmalloc(LTTNG_PATH_MAX);
-               if (!tmp_path) {
-                       ERR("Alloc tmp_path");
-                       goto error_unlock;
-               }
-               ret = snprintf(tmp_path, LTTNG_PATH_MAX, "%s%s%s",
-                               usess->consumer->dst.session_root_path,
-                               usess->consumer->chunk_path,
-                               usess->consumer->subdir);
-               if (ret >= LTTNG_PATH_MAX) {
-                       ERR("Local destination path exceeds the maximal allowed length of %i bytes (needs %i bytes) with path = \"%s%s%s\"",
-                                       LTTNG_PATH_MAX, ret,
-                                       usess->consumer->dst.session_root_path,
-                                       usess->consumer->chunk_path,
-                                       usess->consumer->subdir);
-                       free(tmp_path);
-                       goto error_unlock;
-               }
-
-               DBG("Creating directory path for local tracing: \"%s\"",
-                               tmp_path);
-               ret = run_as_mkdir_recursive(tmp_path, S_IRWXU | S_IRWXG,
-                               ua_sess->euid, ua_sess->egid);
-               free(tmp_path);
-               if (ret < 0) {
-                       if (errno != EEXIST) {
-                               ERR("Trace directory creation error");
-                               goto error_unlock;
-                       }
-               }
-       }
-
        /*
         * Create the metadata for the application. This returns gracefully if a
         * metadata was already set for the session.
@@ -4508,7 +4373,7 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
        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);
@@ -4531,6 +4396,7 @@ skip_setup:
 
        /* Indicate that the session has been started once */
        ua_sess->started = 1;
+       ua_sess->enabled = 1;
 
        pthread_mutex_unlock(&ua_sess->lock);
 
@@ -4620,6 +4486,7 @@ 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);
@@ -4990,7 +4857,6 @@ end:
  */
 int ust_app_start_trace_all(struct ltt_ust_session *usess)
 {
-       int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;
 
@@ -5013,11 +4879,7 @@ int ust_app_start_trace_all(struct ltt_ust_session *usess)
        (void) ust_app_clear_quiescent_session(usess);
 
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
-               ret = ust_app_start_trace(usess, app);
-               if (ret < 0) {
-                       /* Continue to next apps even on error */
-                       continue;
-               }
+               ust_app_global_update(usess, app);
        }
 
        rcu_read_unlock();
@@ -5086,92 +4948,147 @@ int ust_app_destroy_trace_all(struct ltt_ust_session *usess)
        return 0;
 }
 
+/* The ua_sess lock must be held by the caller. */
 static
-void ust_app_global_create(struct ltt_ust_session *usess, struct ust_app *app)
+int find_or_create_ust_app_channel(
+               struct ltt_ust_session *usess,
+               struct ust_app_session *ua_sess,
+               struct ust_app *app,
+               struct ltt_ust_channel *uchan,
+               struct ust_app_channel **ua_chan)
 {
        int ret = 0;
-       struct lttng_ht_iter iter, uiter;
+       struct lttng_ht_iter iter;
+       struct lttng_ht_node_str *ua_chan_node;
+
+       lttng_ht_lookup(ua_sess->channels, (void *) uchan->name, &iter);
+       ua_chan_node = lttng_ht_iter_get_node_str(&iter);
+       if (ua_chan_node) {
+               *ua_chan = caa_container_of(ua_chan_node,
+                       struct ust_app_channel, node);
+               goto end;
+       }
+
+       ret = ust_app_channel_create(usess, ua_sess, uchan, app, ua_chan);
+       if (ret) {
+               goto end;
+       }
+end:
+       return ret;
+}
+
+static
+int ust_app_channel_synchronize_event(struct ust_app_channel *ua_chan,
+               struct ltt_ust_event *uevent, struct ust_app_session *ua_sess,
+               struct ust_app *app)
+{
+       int ret = 0;
+       struct ust_app_event *ua_event = NULL;
+
+       ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
+               uevent->filter, uevent->attr.loglevel, uevent->exclusion);
+       if (!ua_event) {
+               ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
+               if (ret < 0) {
+                       goto end;
+               }
+       } else {
+               if (ua_event->enabled != uevent->enabled) {
+                       ret = uevent->enabled ?
+                               enable_ust_app_event(ua_sess, ua_event, app) :
+                               disable_ust_app_event(ua_sess, ua_event, app);
+               }
+       }
+
+end:
+       return ret;
+}
+
+/*
+ * The caller must ensure that the application is compatible and is tracked
+ * by the PID tracker.
+ */
+static
+void ust_app_synchronize(struct ltt_ust_session *usess,
+               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;
-       struct ust_app_channel *ua_chan;
-       struct ust_app_event *ua_event;
-       struct ust_app_ctx *ua_ctx;
-       int is_created = 0;
 
-       ret = find_or_create_ust_app_session(usess, app, &ua_sess, &is_created);
+       /*
+        * 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;
        }
-       if (!is_created) {
-               /* App session already created. */
-               goto end;
-       }
        assert(ua_sess);
 
        pthread_mutex_lock(&ua_sess->lock);
-
        if (ua_sess->deleted) {
                pthread_mutex_unlock(&ua_sess->lock);
                goto end;
        }
 
-       /*
-        * 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 = do_create_channel(app, usess, ua_sess, ua_chan);
-               if (ret < 0 && ret != -ENOTCONN) {
-                       /*
-                        * 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. The only exception is
-                        * -ENOTCONN, which indicates that the application
-                        * has exit.
-                        */
-                       goto error_unlock;
-               }
+       rcu_read_lock();
+       cds_lfht_for_each_entry(usess->domain_global.channels->ht, &uchan_iter,
+                       uchan, node.node) {
+               struct ust_app_channel *ua_chan;
+               struct cds_lfht_iter uevent_iter;
+               struct ltt_ust_event *uevent;
 
                /*
-                * Add context using the list so they are enabled in the same order the
-                * user added them.
+                * Search for a matching ust_app_channel. If none is found,
+                * create it. Creating the channel will cause the ua_chan
+                * structure to be allocated, the channel buffers to be
+                * allocated (if necessary) and sent to the application, and
+                * all enabled contexts will be added to the channel.
                 */
-               cds_list_for_each_entry(ua_ctx, &ua_chan->ctx_list, list) {
-                       ret = create_ust_channel_context(ua_chan, ua_ctx, app);
-                       if (ret < 0) {
-                               goto error_unlock;
-                       }
+               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;
                }
 
+               if (!ua_chan) {
+                       /* ua_chan will be NULL for the metadata channel */
+                       continue;
+               }
 
-               /* For each events */
-               cds_lfht_for_each_entry(ua_chan->events->ht, &uiter.iter, ua_event,
+               cds_lfht_for_each_entry(uchan->events->ht, &uevent_iter, uevent,
                                node.node) {
-                       ret = create_ust_event(app, ua_sess, ua_chan, ua_event);
-                       if (ret < 0) {
+                       ret = ust_app_channel_synchronize_event(ua_chan,
+                               uevent, ua_sess, app);
+                       if (ret) {
                                goto error_unlock;
                        }
                }
-       }
-
-       pthread_mutex_unlock(&ua_sess->lock);
 
-       if (usess->active) {
-               ret = ust_app_start_trace(usess, app);
-               if (ret < 0) {
-                       goto error;
+               if (ua_chan->enabled != uchan->enabled) {
+                       ret = uchan->enabled ?
+                               enable_ust_app_channel(ua_sess, uchan, app) :
+                               disable_ust_app_channel(ua_sess, ua_chan, app);
+                       if (ret) {
+                               goto error_unlock;
+                       }
                }
-
-               DBG2("UST trace started for app pid %d", app->pid);
        }
+       rcu_read_unlock();
+
 end:
+       pthread_mutex_unlock(&ua_sess->lock);
        /* Everything went well at this point. */
        return;
 
 error_unlock:
+       rcu_read_unlock();
        pthread_mutex_unlock(&ua_sess->lock);
 error:
        if (ua_sess) {
@@ -5201,6 +5118,7 @@ void ust_app_global_destroy(struct ltt_ust_session *usess, struct ust_app *app)
 void ust_app_global_update(struct ltt_ust_session *usess, struct ust_app *app)
 {
        assert(usess);
+       assert(usess->active);
 
        DBG2("UST app global update for app sock %d for session id %" PRIu64,
                        app->sock, usess->id);
@@ -5208,9 +5126,17 @@ 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)) {
-               ust_app_global_create(usess, app);
+       if (trace_ust_id_tracker_lookup(LTTNG_TRACKER_VPID, usess, app->pid) &&
+                       trace_ust_id_tracker_lookup(
+                                       LTTNG_TRACKER_VUID, usess, app->uid) &&
+                       trace_ust_id_tracker_lookup(
+                                       LTTNG_TRACKER_VGID, usess, app->gid)) {
+               /*
+                * Synchronize the application's internal tracing configuration
+                * and start tracing.
+                */
+               ust_app_synchronize(usess, app);
+               ust_app_start_trace(usess, app);
        } else {
                ust_app_global_destroy(usess, app);
        }
@@ -5244,8 +5170,9 @@ int ust_app_add_ctx_channel_glb(struct ltt_ust_session *usess,
        struct ust_app_session *ua_sess;
        struct ust_app *app;
 
-       rcu_read_lock();
+       assert(usess->active);
 
+       rcu_read_lock();
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                if (!app->compatible) {
                        /*
@@ -5286,79 +5213,6 @@ int ust_app_add_ctx_channel_glb(struct ltt_ust_session *usess,
        return ret;
 }
 
-/*
- * Enable event for a channel from a UST session for a specific PID.
- */
-int ust_app_enable_event_pid(struct ltt_ust_session *usess,
-               struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent, pid_t pid)
-{
-       int ret = 0;
-       struct lttng_ht_iter iter;
-       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;
-
-       DBG("UST app enabling event %s for PID %d", uevent->attr.name, pid);
-
-       rcu_read_lock();
-
-       app = ust_app_find_by_pid(pid);
-       if (app == NULL) {
-               ERR("UST app enable event per PID %d not found", pid);
-               ret = -1;
-               goto end;
-       }
-
-       if (!app->compatible) {
-               ret = 0;
-               goto end;
-       }
-
-       ua_sess = lookup_session_by_app(usess, app);
-       if (!ua_sess) {
-               /* The application has problem or is probably dead. */
-               ret = 0;
-               goto end;
-       }
-
-       pthread_mutex_lock(&ua_sess->lock);
-
-       if (ua_sess->deleted) {
-               ret = 0;
-               goto end_unlock;
-       }
-
-       /* Lookup channel in the ust app session */
-       lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
-       ua_chan_node = lttng_ht_iter_get_node_str(&iter);
-       /* If the channel is not found, there is a code flow error */
-       assert(ua_chan_node);
-
-       ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
-
-       ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
-                       uevent->filter, uevent->attr.loglevel, uevent->exclusion);
-       if (ua_event == NULL) {
-               ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
-               if (ret < 0) {
-                       goto end_unlock;
-               }
-       } else {
-               ret = enable_ust_app_event(ua_sess, ua_event, app);
-               if (ret < 0) {
-                       goto end_unlock;
-               }
-       }
-
-end_unlock:
-       pthread_mutex_unlock(&ua_sess->lock);
-end:
-       rcu_read_unlock();
-       return ret;
-}
-
 /*
  * Receive registration and populate the given msg structure.
  *
@@ -5988,29 +5842,22 @@ void ust_app_destroy(struct ust_app *app)
  *
  * Returns LTTNG_OK on success or a LTTNG_ERR error code.
  */
-enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
-               struct snapshot_output *output, int wait,
+enum lttng_error_code ust_app_snapshot_record(
+               const struct ltt_ust_session *usess,
+               const struct consumer_output *output, int wait,
                uint64_t nb_packets_per_stream)
 {
        int ret = 0;
        enum lttng_error_code status = LTTNG_OK;
        struct lttng_ht_iter iter;
        struct ust_app *app;
-       char pathname[PATH_MAX];
-       struct ltt_session *session = NULL;
-       uint64_t trace_archive_id;
+       char *trace_path = NULL;
 
        assert(usess);
        assert(output);
 
        rcu_read_lock();
 
-       session = session_find_by_id(usess->id);
-       assert(session);
-       assert(pthread_mutex_trylock(&session->lock));
-       assert(session_trylock_list());
-       trace_archive_id = session->current_archive_id;
-
        switch (usess->buffer_type) {
        case LTTNG_BUFFER_PER_UID:
        {
@@ -6019,6 +5866,8 @@ enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
                cds_list_for_each_entry(reg, &usess->buffer_reg_uid_list, lnode) {
                        struct buffer_reg_channel *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 */
@@ -6042,24 +5891,30 @@ enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
                                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) {
                                status = consumer_snapshot_channel(socket,
                                                reg_chan->consumer_key,
                                                output, 0, usess->uid,
-                                               usess->gid, pathname, wait,
-                                               nb_packets_per_stream,
-                                               trace_archive_id);
+                                               usess->gid, &trace_path[consumer_path_offset], wait,
+                                               nb_packets_per_stream);
                                if (status != LTTNG_OK) {
                                        goto error;
                                }
                        }
                        status = consumer_snapshot_channel(socket,
                                        reg->registry->reg.ust->metadata_key, output, 1,
-                                       usess->uid, usess->gid, pathname, wait, 0,
-                                       trace_archive_id);
+                                       usess->uid, usess->gid, &trace_path[consumer_path_offset],
+                                       wait, 0);
                        if (status != LTTNG_OK) {
                                goto error;
                        }
@@ -6074,6 +5929,8 @@ enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
                        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) {
@@ -6083,7 +5940,7 @@ enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
 
                        /* Get the right consumer socket for the application. */
                        socket = consumer_find_socket_by_bitness(app->bits_per_long,
-                                       output->consumer);
+                                       output);
                        if (!socket) {
                                status = LTTNG_ERR_INVALID;
                                goto error;
@@ -6098,15 +5955,24 @@ enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
                                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->euid, ua_sess->egid,
-                                               pathname, wait,
-                                               nb_packets_per_stream,
-                                               trace_archive_id);
+                                               ua_chan->key, output, 0,
+                                               ua_sess->effective_credentials
+                                                               .uid,
+                                               ua_sess->effective_credentials
+                                                               .gid,
+                                               &trace_path[consumer_path_offset], wait,
+                                               nb_packets_per_stream);
                                switch (status) {
                                case LTTNG_OK:
                                        break;
@@ -6123,10 +5989,10 @@ enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
                                continue;
                        }
                        status = consumer_snapshot_channel(socket,
-                                       registry->metadata_key, output,
-                                       1, ua_sess->euid, ua_sess->egid,
-                                       pathname, wait, 0,
-                                       trace_archive_id);
+                                       registry->metadata_key, output, 1,
+                                       ua_sess->effective_credentials.uid,
+                                       ua_sess->effective_credentials.gid,
+                                       &trace_path[consumer_path_offset], wait, 0);
                        switch (status) {
                        case LTTNG_OK:
                                break;
@@ -6144,18 +6010,16 @@ enum lttng_error_code ust_app_snapshot_record(struct ltt_ust_session *usess,
        }
 
 error:
+       free(trace_path);
        rcu_read_unlock();
-       if (session) {
-               session_put(session);
-       }
        return status;
 }
 
 /*
  * Return the size taken by one more packet per stream.
  */
-uint64_t ust_app_get_size_one_more_packet_per_stream(struct ltt_ust_session *usess,
-               uint64_t cur_nr_packets)
+uint64_t ust_app_get_size_one_more_packet_per_stream(
+               const struct ltt_ust_session *usess, uint64_t cur_nr_packets)
 {
        uint64_t tot_size = 0;
        struct ust_app *app;
@@ -6394,7 +6258,6 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
        struct lttng_ht_iter iter;
        struct ust_app *app;
        struct ltt_ust_session *usess = session->ust_session;
-       char pathname[LTTNG_PATH_MAX];
 
        assert(usess);
 
@@ -6409,6 +6272,11 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                        struct buffer_reg_channel *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);
@@ -6417,24 +6285,14 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                                goto error;
                        }
 
-                       ret = snprintf(pathname, sizeof(pathname),
-                                       DEFAULT_UST_TRACE_DIR "/" DEFAULT_UST_TRACE_UID_PATH,
-                                       reg->uid, reg->bits_per_long);
-                       if (ret < 0 || ret == sizeof(pathname)) {
-                               PERROR("Failed to format rotation path");
-                               cmd_ret = LTTNG_ERR_INVALID;
-                               goto error;
-                       }
-
                        /* Rotate the data channels. */
                        cds_lfht_for_each_entry(reg->registry->channels->ht, &iter.iter,
                                        reg_chan, node.node) {
                                ret = consumer_rotate_channel(socket,
                                                reg_chan->consumer_key,
                                                usess->uid, usess->gid,
-                                               usess->consumer, pathname,
-                                               /* is_metadata_channel */ false,
-                                               session->current_archive_id);
+                                               usess->consumer,
+                                               /* is_metadata_channel */ false);
                                if (ret < 0) {
                                        cmd_ret = LTTNG_ERR_ROTATION_FAIL_CONSUMER;
                                        goto error;
@@ -6446,9 +6304,8 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                        ret = consumer_rotate_channel(socket,
                                        reg->registry->reg.ust->metadata_key,
                                        usess->uid, usess->gid,
-                                       usess->consumer, pathname,
-                                       /* is_metadata_channel */ true,
-                                       session->current_archive_id);
+                                       usess->consumer,
+                                       /* is_metadata_channel */ true);
                        if (ret < 0) {
                                cmd_ret = LTTNG_ERR_ROTATION_FAIL_CONSUMER;
                                goto error;
@@ -6470,14 +6327,6 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                                /* Session not associated with this app. */
                                continue;
                        }
-                       ret = snprintf(pathname, sizeof(pathname),
-                                       DEFAULT_UST_TRACE_DIR "/%s",
-                                       ua_sess->path);
-                       if (ret < 0 || ret == sizeof(pathname)) {
-                               PERROR("Failed to format rotation path");
-                               cmd_ret = LTTNG_ERR_INVALID;
-                               goto error;
-                       }
 
                        /* Get the right consumer socket for the application. */
                        socket = consumer_find_socket_by_bitness(app->bits_per_long,
@@ -6493,15 +6342,17 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
                                continue;
                        }
 
-
                        /* Rotate the data channels. */
                        cds_lfht_for_each_entry(ua_sess->channels->ht, &chan_iter.iter,
                                        ua_chan, node.node) {
-                               ret = consumer_rotate_channel(socket, ua_chan->key,
-                                               ua_sess->euid, ua_sess->egid,
-                                               ua_sess->consumer, pathname,
-                                               /* is_metadata_channel */ false,
-                                               session->current_archive_id);
+                               ret = consumer_rotate_channel(socket,
+                                               ua_chan->key,
+                                               ua_sess->effective_credentials
+                                                               .uid,
+                                               ua_sess->effective_credentials
+                                                               .gid,
+                                               ua_sess->consumer,
+                                               /* is_metadata_channel */ false);
                                if (ret < 0) {
                                        /* Per-PID buffer and application going away. */
                                        if (ret == -LTTNG_ERR_CHAN_NOT_FOUND)
@@ -6513,11 +6364,12 @@ enum lttng_error_code ust_app_rotate_session(struct ltt_session *session)
 
                        /* Rotate the metadata channel. */
                        (void) push_metadata(registry, usess->consumer);
-                       ret = consumer_rotate_channel(socket, registry->metadata_key,
-                                       ua_sess->euid, ua_sess->egid,
-                                       ua_sess->consumer, pathname,
-                                       /* is_metadata_channel */ true,
-                                       session->current_archive_id);
+                       ret = consumer_rotate_channel(socket,
+                                       registry->metadata_key,
+                                       ua_sess->effective_credentials.uid,
+                                       ua_sess->effective_credentials.gid,
+                                       ua_sess->consumer,
+                                       /* is_metadata_channel */ true);
                        if (ret < 0) {
                                /* Per-PID buffer and application going away. */
                                if (ret == -LTTNG_ERR_CHAN_NOT_FOUND)
@@ -6539,3 +6391,258 @@ error:
        rcu_read_unlock();
        return cmd_ret;
 }
+
+enum lttng_error_code ust_app_create_channel_subdirectories(
+               const struct ltt_ust_session *usess)
+{
+       enum lttng_error_code ret = LTTNG_OK;
+       struct lttng_ht_iter iter;
+       enum lttng_trace_chunk_status chunk_status;
+       char *pathname_index;
+       int fmt_ret;
+
+       assert(usess->current_trace_chunk);
+       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) {
+                       fmt_ret = asprintf(&pathname_index,
+                                      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");
+                               ret = LTTNG_ERR_CREATE_DIR_FAIL;
+                               goto error;
+                       }
+
+                       /*
+                        * Create the index subdirectory which will take care
+                        * of implicitly creating the channel's path.
+                        */
+                       chunk_status = lttng_trace_chunk_create_subdirectory(
+                                       usess->current_trace_chunk,
+                                       pathname_index);
+                       free(pathname_index);
+                       if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
+                               ret = LTTNG_ERR_CREATE_DIR_FAIL;
+                               goto error;
+                       }
+               }
+               break;
+       }
+       case LTTNG_BUFFER_PER_PID:
+       {
+               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;
+                       struct ust_registry_session *registry;
+
+                       ua_sess = lookup_session_by_app(usess, app);
+                       if (!ua_sess) {
+                               /* Session not associated with this app. */
+                               continue;
+                       }
+
+                       registry = get_session_registry(ua_sess);
+                       if (!registry) {
+                               DBG("Application session is being torn down. Skip application.");
+                               continue;
+                       }
+
+                       fmt_ret = asprintf(&pathname_index,
+                                       DEFAULT_UST_TRACE_DIR "/%s/" DEFAULT_INDEX_DIR,
+                                       ua_sess->path);
+                       if (fmt_ret < 0) {
+                               ERR("Failed to format channel index directory");
+                               ret = LTTNG_ERR_CREATE_DIR_FAIL;
+                               goto error;
+                       }
+                       /*
+                        * Create the index subdirectory which will take care
+                        * of implicitly creating the channel's path.
+                        */
+                       chunk_status = lttng_trace_chunk_create_subdirectory(
+                                       usess->current_trace_chunk,
+                                       pathname_index);
+                       free(pathname_index);
+                       if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
+                               ret = LTTNG_ERR_CREATE_DIR_FAIL;
+                               goto error;
+                       }
+               }
+               break;
+       }
+       default:
+               abort();
+       }
+
+       ret = LTTNG_OK;
+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 *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,
+                                       reg_chan, node.node) {
+                               ret = consumer_clear_channel(socket,
+                                               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;
+}
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