Move stream name creation to fct create_ust_stream
[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c
index bd91b3c39decb8102b8c1b856fcc505ef0519cb9..374360e48c365937a20952e6623e356e21fae41c 100644 (file)
@@ -1,19 +1,18 @@
 /*
  * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
  *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; only version 2
- * of the License.
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2 only,
+ * as published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
 #define _GNU_SOURCE
 #include <sys/types.h>
 #include <unistd.h>
 #include <urcu/compiler.h>
+#include <lttng/ust-error.h>
 
-#include <common/lttngerr.h>
 #include <common/common.h>
+#include <common/sessiond-comm/sessiond-comm.h>
 
+#include "fd-limit.h"
+#include "health.h"
 #include "ust-app.h"
 #include "ust-consumer.h"
 #include "ust-ctl.h"
 
+/*
+ * Match function for the hash table lookup.
+ *
+ * It matches an ust app event based on three attributes which are the event
+ * name, the filter bytecode and the loglevel.
+ */
+static int ht_match_ust_app_event(struct cds_lfht_node *node, const void *_key)
+{
+       struct ust_app_event *event;
+       const struct ust_app_ht_key *key;
+
+       assert(node);
+       assert(_key);
+
+       event = caa_container_of(node, struct ust_app_event, node.node);
+       key = _key;
+
+       /* Match the 3 elements of the key: name, filter and loglevel. */
+
+       /* Event name */
+       if (strncmp(event->attr.name, key->name, sizeof(event->attr.name)) != 0) {
+               goto no_match;
+       }
+
+       /* Event loglevel. */
+       if (event->attr.loglevel != key->loglevel) {
+               if (event->attr.loglevel_type == LTTNG_UST_LOGLEVEL_ALL
+                               && key->loglevel == 0 && event->attr.loglevel == -1) {
+                       /*
+                        * Match is accepted. This is because on event creation, the
+                        * loglevel is set to -1 if the event loglevel type is ALL so 0 and
+                        * -1 are accepted for this loglevel type since 0 is the one set by
+                        * the API when receiving an enable event.
+                        */
+               } else {
+                       goto no_match;
+               }
+       }
+
+       /* One of the filters is NULL, fail. */
+       if ((key->filter && !event->filter) || (!key->filter && event->filter)) {
+               goto no_match;
+       }
+
+       if (key->filter && event->filter) {
+               /* Both filters exists, check length followed by the bytecode. */
+               if (event->filter->len != key->filter->len ||
+                               memcmp(event->filter->data, key->filter->data,
+                                       event->filter->len) != 0) {
+                       goto no_match;
+               }
+       }
+
+       /* Match. */
+       return 1;
+
+no_match:
+       return 0;
+}
+
+/*
+ * 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,
+               struct ust_app_event *event)
+{
+       struct cds_lfht_node *node_ptr;
+       struct ust_app_ht_key key;
+
+       assert(ht);
+       assert(ht->ht);
+       assert(event);
+
+       key.name = event->attr.name;
+       key.filter = event->filter;
+       key.loglevel = event->attr.loglevel;
+
+       node_ptr = cds_lfht_add_unique(ht->ht,
+                       ht->hash_fct(event->node.key, lttng_ht_seed),
+                       ht_match_ust_app_event, &key, &event->node.node);
+       assert(node_ptr == &event->node.node);
+}
+
 /*
  * Delete ust context safely. RCU read lock must be held before calling
  * this function.
@@ -55,18 +141,7 @@ 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;
-       struct lttng_ht_iter iter;
-       struct ust_app_ctx *ua_ctx;
-
-       /* Destroy each context of event */
-       cds_lfht_for_each_entry(ua_event->ctx->ht, &iter.iter, ua_ctx,
-                       node.node) {
-               ret = lttng_ht_del(ua_event->ctx, &iter);
-               assert(!ret);
-               delete_ust_app_ctx(sock, ua_ctx);
-       }
-       lttng_ht_destroy(ua_event->ctx);
+       free(ua_event->filter);
 
        if (ua_event->obj != NULL) {
                ustctl_release_object(sock, ua_event->obj);
@@ -84,6 +159,7 @@ void delete_ust_app_stream(int sock, struct ltt_ust_stream *stream)
 {
        if (stream->obj) {
                ustctl_release_object(sock, stream->obj);
+               lttng_fd_put(LTTNG_FD_APPS, 2);
                free(stream->obj);
        }
        free(stream);
@@ -127,6 +203,7 @@ void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan)
 
        if (ua_chan->obj != NULL) {
                ustctl_release_object(sock, ua_chan->obj);
+               lttng_fd_put(LTTNG_FD_APPS, 2);
                free(ua_chan->obj);
        }
        free(ua_chan);
@@ -146,12 +223,15 @@ void delete_ust_app_session(int sock, struct ust_app_session *ua_sess)
        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);
        }
 
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
@@ -176,32 +256,43 @@ static
 void delete_ust_app(struct ust_app *app)
 {
        int ret, sock;
-       struct lttng_ht_iter iter;
-       struct ust_app_session *ua_sess;
+       struct ust_app_session *ua_sess, *tmp_ua_sess;
 
        rcu_read_lock();
 
        /* Delete ust app sessions info */
-       sock = app->key.sock;
-       app->key.sock = -1;
+       sock = app->sock;
+       app->sock = -1;
+
+       lttng_ht_destroy(app->sessions);
 
        /* Wipe sessions */
-       cds_lfht_for_each_entry(app->sessions->ht, &iter.iter, ua_sess,
-                       node.node) {
-               ret = lttng_ht_del(app->sessions, &iter);
-               assert(!ret);
-               delete_ust_app_session(app->key.sock, ua_sess);
+       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);
        }
-       lttng_ht_destroy(app->sessions);
 
        /*
-        * Wait until we have removed the key from the sock hash table before
-        * closing this socket, otherwise an application could re-use the socket ID
-        * and race with the teardown, using the same hash table entry.
+        * Wait until we have deleted the application from the sock hash table
+        * before closing this socket, otherwise an application could re-use the
+        * socket ID and race with the teardown, using the same hash table entry.
+        *
+        * It's OK to leave the close in call_rcu. We want it to stay unique for
+        * all RCU readers that could run concurrently with unregister app,
+        * therefore we _need_ to only close that socket after a grace period. So
+        * it should stay in this RCU callback.
+        *
+        * This close() is a very important step of the synchronization model so
+        * every modification to this function must be carefully reviewed.
         */
-       close(sock);
+       ret = close(sock);
+       if (ret) {
+               PERROR("close");
+       }
+       lttng_fd_put(LTTNG_FD_APPS, 1);
 
-       DBG2("UST app pid %d deleted", app->key.pid);
+       DBG2("UST app pid %d deleted", app->pid);
        free(app);
 
        rcu_read_unlock();
@@ -216,9 +307,9 @@ void delete_ust_app_rcu(struct rcu_head *head)
        struct lttng_ht_node_ulong *node =
                caa_container_of(head, struct lttng_ht_node_ulong, head);
        struct ust_app *app =
-               caa_container_of(node, struct ust_app, node);
+               caa_container_of(node, struct ust_app, pid_n);
 
-       DBG3("Call RCU deleting app PID %d", app->key.pid);
+       DBG3("Call RCU deleting app PID %d", app->pid);
        delete_ust_app(app);
 }
 
@@ -306,7 +397,6 @@ struct ust_app_event *alloc_ust_app_event(char *name,
        ua_event->enabled = 1;
        strncpy(ua_event->name, name, sizeof(ua_event->name));
        ua_event->name[sizeof(ua_event->name) - 1] = '\0';
-       ua_event->ctx = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        lttng_ht_node_init_str(&ua_event->node, ua_event->name);
 
        /* Copy attributes */
@@ -345,6 +435,29 @@ error:
        return ua_ctx;
 }
 
+/*
+ * Allocate a filter and copy the given original filter.
+ *
+ * Return allocated filter or NULL on error.
+ */
+static struct lttng_ust_filter_bytecode *alloc_copy_ust_app_filter(
+               struct lttng_ust_filter_bytecode *orig_f)
+{
+       struct lttng_ust_filter_bytecode *filter = NULL;
+
+       /* Copy filter bytecode */
+       filter = zmalloc(sizeof(*filter) + orig_f->len);
+       if (!filter) {
+               PERROR("zmalloc alloc ust app filter");
+               goto error;
+       }
+
+       memcpy(filter, orig_f, sizeof(*filter) + orig_f->len);
+
+error:
+       return filter;
+}
+
 /*
  * Find an ust_app using the sock and return it. RCU read side lock must be
  * held before calling this helper function.
@@ -353,30 +466,57 @@ static
 struct ust_app *find_app_by_sock(int sock)
 {
        struct lttng_ht_node_ulong *node;
-       struct ust_app_key *key;
        struct lttng_ht_iter iter;
 
-       lttng_ht_lookup(ust_app_sock_key_map, (void *)((unsigned long) sock),
-                       &iter);
-       node = lttng_ht_iter_get_node_ulong(&iter);
-       if (node == NULL) {
-               DBG2("UST app find by sock %d key not found", sock);
-               goto error;
-       }
-       key = caa_container_of(node, struct ust_app_key, node);
-
-       lttng_ht_lookup(ust_app_ht, (void *)((unsigned long) key->pid), &iter);
+       lttng_ht_lookup(ust_app_ht_by_sock, (void *)((unsigned long) sock), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
                DBG2("UST app find by sock %d not found", sock);
                goto error;
        }
-       return caa_container_of(node, struct ust_app, node);
+
+       return caa_container_of(node, struct ust_app, sock_n);
 
 error:
        return NULL;
 }
 
+/*
+ * Lookup for an ust app event based on event name, filter bytecode and the
+ * event loglevel.
+ *
+ * Return an ust_app_event object or NULL on error.
+ */
+static struct ust_app_event *find_ust_app_event(struct lttng_ht *ht,
+               char *name, struct lttng_ust_filter_bytecode *filter, int loglevel)
+{
+       struct lttng_ht_iter iter;
+       struct lttng_ht_node_str *node;
+       struct ust_app_event *event = NULL;
+       struct ust_app_ht_key key;
+
+       assert(name);
+       assert(ht);
+
+       /* Setup key for event lookup. */
+       key.name = name;
+       key.filter = filter;
+       key.loglevel = loglevel;
+
+       /* Lookup using the event name as hash and a custom match fct. */
+       cds_lfht_lookup(ht->ht, ht->hash_fct((void *) name, lttng_ht_seed),
+                       ht_match_ust_app_event, &key, &iter.iter);
+       node = lttng_ht_iter_get_node_str(&iter);
+       if (node == NULL) {
+               goto end;
+       }
+
+       event = caa_container_of(node, struct ust_app_event, node);
+
+end:
+       return event;
+}
+
 /*
  * Create the channel context on the tracer.
  */
@@ -386,7 +526,9 @@ int create_ust_channel_context(struct ust_app_channel *ua_chan,
 {
        int ret;
 
-       ret = ustctl_add_context(app->key.sock, &ua_ctx->ctx,
+       health_code_update(&health_thread_cmd);
+
+       ret = ustctl_add_context(app->sock, &ua_ctx->ctx,
                        ua_chan->obj, &ua_ctx->obj);
        if (ret < 0) {
                goto error;
@@ -394,32 +536,39 @@ int create_ust_channel_context(struct ust_app_channel *ua_chan,
 
        ua_ctx->handle = ua_ctx->obj->handle;
 
-       DBG2("UST app context added to channel %s successfully", ua_chan->name);
+       DBG2("UST app context created successfully for channel %s", ua_chan->name);
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
 /*
- * Create the event context on the tracer.
+ * Set the filter on the tracer.
  */
 static
-int create_ust_event_context(struct ust_app_event *ua_event,
-               struct ust_app_ctx *ua_ctx, struct ust_app *app)
+int set_ust_event_filter(struct ust_app_event *ua_event,
+               struct ust_app *app)
 {
        int ret;
 
-       ret = ustctl_add_context(app->key.sock, &ua_ctx->ctx,
-                       ua_event->obj, &ua_ctx->obj);
-       if (ret < 0) {
+       health_code_update(&health_thread_cmd);
+
+       if (!ua_event->filter) {
+               ret = 0;
                goto error;
        }
 
-       ua_ctx->handle = ua_ctx->obj->handle;
+       ret = ustctl_set_filter(app->sock, ua_event->filter,
+                       ua_event->obj);
+       if (ret < 0) {
+               goto error;
+       }
 
-       DBG2("UST app context added to event %s successfully", ua_event->name);
+       DBG2("UST filter set successfully for event %s", ua_event->name);
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -431,18 +580,21 @@ static int disable_ust_event(struct ust_app *app,
 {
        int ret;
 
-       ret = ustctl_disable(app->key.sock, ua_event->obj);
+       health_code_update(&health_thread_cmd);
+
+       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->key.pid, ua_sess->handle, ret);
+                               ua_event->attr.name, app->pid, ua_sess->handle, ret);
                goto error;
        }
 
        DBG2("UST app event %s disabled successfully for app (pid: %d)",
-                       ua_event->attr.name, app->key.pid);
+                       ua_event->attr.name, app->pid);
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -454,18 +606,21 @@ static int disable_ust_channel(struct ust_app *app,
 {
        int ret;
 
-       ret = ustctl_disable(app->key.sock, ua_chan->obj);
+       health_code_update(&health_thread_cmd);
+
+       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->key.pid, ua_sess->handle, ret);
+                               ua_chan->name, app->pid, ua_sess->handle, ret);
                goto error;
        }
 
        DBG2("UST app channel %s disabled successfully for app (pid: %d)",
-                       ua_chan->name, app->key.pid);
+                       ua_chan->name, app->pid);
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -477,20 +632,23 @@ static int enable_ust_channel(struct ust_app *app,
 {
        int ret;
 
-       ret = ustctl_enable(app->key.sock, ua_chan->obj);
+       health_code_update(&health_thread_cmd);
+
+       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->key.pid, ua_sess->handle, ret);
+                               ua_chan->name, app->pid, ua_sess->handle, ret);
                goto error;
        }
 
        ua_chan->enabled = 1;
 
        DBG2("UST app channel %s enabled successfully for app (pid: %d)",
-                       ua_chan->name, app->key.pid);
+                       ua_chan->name, app->pid);
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -502,18 +660,21 @@ static int enable_ust_event(struct ust_app *app,
 {
        int ret;
 
-       ret = ustctl_enable(app->key.sock, ua_event->obj);
+       health_code_update(&health_thread_cmd);
+
+       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->key.pid, ua_sess->handle, ret);
+                               ua_event->attr.name, app->pid, ua_sess->handle, ret);
                goto error;
        }
 
        DBG2("UST app event %s enabled successfully for app (pid: %d)",
-                       ua_event->attr.name, app->key.pid);
+                       ua_event->attr.name, app->pid);
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -526,6 +687,8 @@ static int open_ust_metadata(struct ust_app *app,
        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;
@@ -535,37 +698,114 @@ static int open_ust_metadata(struct ust_app *app,
                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->key.sock, ua_sess->handle, &uattr,
+       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->key.pid, ret);
+                               app->pid, ret);
                goto error;
        }
 
        ua_sess->metadata->handle = ua_sess->metadata->obj->handle;
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
 /*
- * Create stream onto the UST tracer for a UST session.
+ * Create metadata stream onto the UST tracer for a given session.
  */
-static int create_ust_stream(struct ust_app *app,
+static int create_ust_metadata_stream(struct ust_app *app,
                struct ust_app_session *ua_sess)
 {
        int ret;
 
-       ret = ustctl_create_stream(app->key.sock, ua_sess->metadata->obj,
+       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);
+       return ret;
+}
+
+/*
+ * Create stream onto the UST tracer for a given channel.
+ *
+ * Return -ENOENT if no more stream is available for this channel.
+ * On success, return 0.
+ * On error, return a negative value.
+ */
+static int create_ust_stream(struct ust_app *app,
+               struct ust_app_channel *ua_chan, struct ltt_ust_stream *stream)
+{
+       int ret;
+
+       assert(app);
+       assert(ua_chan);
+       assert(ua_chan->obj);
+       assert(stream);
+
+       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 on stream creation");
+               /* Just to make sure we never return -ENOENT. */
+               ret = -1;
+               goto error;
+       }
+
+       /*
+        * Set the stream name before creating it. On error, we don't have to
+        * delete it on the tracer side.
+        */
+       ret = snprintf(stream->name, sizeof(stream->name), "%s_%u",
+                       ua_chan->name, ua_chan->streams.count);
+       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);
+       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;
+       }
+
+       /* Set stream handle with the returned value. */
+       stream->handle = stream->obj->handle;
+
+error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -577,21 +817,36 @@ static int create_ust_channel(struct ust_app *app,
 {
        int ret;
 
+       health_code_update(&health_thread_cmd);
+
        /* TODO: remove cast and use lttng-ust-abi.h */
-       ret = ustctl_create_channel(app->key.sock, ua_sess->handle,
+
+       /* 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 create channel");
+               goto error;
+       }
+
+       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);
        if (ret < 0) {
                ERR("Creating channel %s for app (pid: %d, sock: %d) "
                                "and session handle %d with ret %d",
-                               ua_chan->name, app->key.pid, app->key.sock,
+                               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;
 
        DBG2("UST app channel %s created successfully for pid:%d and sock:%d",
-                       ua_chan->name, app->key.pid, app->key.sock);
+                       ua_chan->name, app->pid, app->sock);
+
+       health_code_update(&health_thread_cmd);
 
        /* If channel is not enabled, disable it on the tracer */
        if (!ua_chan->enabled) {
@@ -602,6 +857,7 @@ static int create_ust_channel(struct ust_app *app,
        }
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -614,23 +870,31 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
 {
        int ret = 0;
 
+       health_code_update(&health_thread_cmd);
+
        /* Create UST event on tracer */
-       ret = ustctl_create_event(app->key.sock, &ua_event->attr, ua_chan->obj,
+       ret = ustctl_create_event(app->sock, &ua_event->attr, ua_chan->obj,
                        &ua_event->obj);
        if (ret < 0) {
-               if (ret == -EEXIST) {
-                       ret = 0;
-                       goto error;
-               }
                ERR("Error ustctl create event %s for app pid: %d with ret %d",
-                               ua_event->attr.name, app->key.pid, ret);
+                               ua_event->attr.name, app->pid, ret);
                goto error;
        }
 
        ua_event->handle = ua_event->obj->handle;
 
        DBG2("UST app event %s created successfully for pid:%d",
-                       ua_event->attr.name, app->key.pid);
+                       ua_event->attr.name, app->pid);
+
+       health_code_update(&health_thread_cmd);
+
+       /* Set filter if one is present. */
+       if (ua_event->filter) {
+               ret = set_ust_event_filter(ua_event, app);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
 
        /* If event not enabled, disable it on the tracer */
        if (ua_event->enabled == 0) {
@@ -642,10 +906,10 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
                         * just created it.
                         */
                        switch (ret) {
-                       case -EPERM:
+                       case -LTTNG_UST_ERR_PERM:
                                /* Code flow problem */
                                assert(0);
-                       case -EEXIST:
+                       case -LTTNG_UST_ERR_EXIST:
                                /* It's OK for our use case. */
                                ret = 0;
                                break;
@@ -657,6 +921,7 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
        }
 
 error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -666,10 +931,6 @@ error:
 static void shadow_copy_event(struct ust_app_event *ua_event,
                struct ltt_ust_event *uevent)
 {
-       struct lttng_ht_iter iter;
-       struct ltt_ust_context *uctx;
-       struct ust_app_ctx *ua_ctx;
-
        strncpy(ua_event->name, uevent->attr.name, sizeof(ua_event->name));
        ua_event->name[sizeof(ua_event->name) - 1] = '\0';
 
@@ -678,16 +939,10 @@ static void shadow_copy_event(struct ust_app_event *ua_event,
        /* Copy event attributes */
        memcpy(&ua_event->attr, &uevent->attr, sizeof(ua_event->attr));
 
-       cds_lfht_for_each_entry(uevent->ctx->ht, &iter.iter, uctx, node.node) {
-               ua_ctx = alloc_ust_app_ctx(&uctx->ctx);
-               if (ua_ctx == NULL) {
-                       /* malloc() failed. We should simply stop */
-                       return;
-               }
-
-               lttng_ht_node_init_ulong(&ua_ctx->node,
-                               (unsigned long) ua_ctx->ctx.ctx);
-               lttng_ht_add_unique_ulong(ua_event->ctx, &ua_ctx->node);
+       /* Copy filter bytecode */
+       if (uevent->filter) {
+               ua_event->filter = alloc_copy_ust_app_filter(uevent->filter);
+               /* Filter might be NULL here in case of ENONEM. */
        }
 }
 
@@ -698,7 +953,6 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
                struct ltt_ust_channel *uchan)
 {
        struct lttng_ht_iter iter;
-       struct lttng_ht_node_str *ua_event_node;
        struct ltt_ust_event *uevent;
        struct ltt_ust_context *uctx;
        struct ust_app_event *ua_event;
@@ -725,11 +979,9 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
 
        /* Copy all events from ltt ust channel to ust app channel */
        cds_lfht_for_each_entry(uchan->events->ht, &iter.iter, uevent, node.node) {
-               struct lttng_ht_iter uiter;
-
-               lttng_ht_lookup(ua_chan->events, (void *) uevent->attr.name, &uiter);
-               ua_event_node = lttng_ht_iter_get_node_str(&uiter);
-               if (ua_event_node == NULL) {
+               ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
+                               uevent->filter, uevent->attr.loglevel);
+               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);
@@ -737,7 +989,7 @@ static void shadow_copy_channel(struct ust_app_channel *ua_chan,
                                continue;
                        }
                        shadow_copy_event(ua_event, uevent);
-                       lttng_ht_add_unique_str(ua_chan->events, &ua_event->node);
+                       add_unique_ust_app_event(ua_chan->events, ua_event);
                }
        }
 
@@ -770,8 +1022,8 @@ static void shadow_copy_session(struct ust_app_session *ua_sess,
        ua_sess->uid = usess->uid;
        ua_sess->gid = usess->gid;
 
-       ret = snprintf(ua_sess->path, PATH_MAX, "%s/%s-%d-%s", usess->pathname,
-                       app->name, app->key.pid, datetime);
+       ret = snprintf(ua_sess->path, PATH_MAX, "%s-%d-%s/", app->name, app->pid,
+                       datetime);
        if (ret < 0) {
                PERROR("asprintf UST shadow copy session");
                /* TODO: We cannot return an error from here.. */
@@ -839,33 +1091,57 @@ error:
 }
 
 /*
- * Create a UST session onto the tracer of app and add it the session
- * hashtable.
+ * Create a session on the tracer side for the given app.
+ *
+ * On success, ua_sess_ptr is populated with the session pointer or else left
+ * untouched. If the session was created, is_created is set to 1. On error,
+ * it's left untouched. Note that ua_sess_ptr is mandatory but is_created can
+ * be NULL.
  *
- * Return ust app session or NULL on error.
+ * Returns 0 on success or else a negative code which is either -ENOMEM or
+ * -ENOTCONN which is the default code if the ustctl_create_session fails.
  */
-static struct ust_app_session *create_ust_app_session(
-               struct ltt_ust_session *usess, struct ust_app *app)
+static int create_ust_app_session(struct ltt_ust_session *usess,
+               struct ust_app *app, struct ust_app_session **ua_sess_ptr,
+               int *is_created)
 {
-       int ret;
+       int ret, created = 0;
        struct ust_app_session *ua_sess;
 
+       assert(usess);
+       assert(app);
+       assert(ua_sess_ptr);
+
+       health_code_update(&health_thread_cmd);
+
        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->key.pid, usess->id);
+                               app->pid, usess->id);
                ua_sess = alloc_ust_app_session();
                if (ua_sess == NULL) {
                        /* Only malloc can failed so something is really wrong */
-                       goto end;
+                       ret = -ENOMEM;
+                       goto error;
                }
                shadow_copy_session(ua_sess, usess, app);
+               created = 1;
        }
 
+       health_code_update(&health_thread_cmd);
+
        if (ua_sess->handle == -1) {
-               ret = ustctl_create_session(app->key.sock);
+               ret = ustctl_create_session(app->sock);
                if (ret < 0) {
-                       ERR("Creating session for app pid %d", app->key.pid);
+                       ERR("Creating session for app pid %d", app->pid);
+                       delete_ust_app_session(-1, ua_sess);
+                       if (ret != -ENOMEM) {
+                               /*
+                                * Tracer is probably gone or got an internal error so let's
+                                * behave like it will soon unregister or not usable.
+                                */
+                               ret = -ENOTCONN;
+                       }
                        goto error;
                }
 
@@ -878,12 +1154,16 @@ static struct ust_app_session *create_ust_app_session(
                DBG2("UST app session created successfully with handle %d", ret);
        }
 
-end:
-       return ua_sess;
+       *ua_sess_ptr = ua_sess;
+       if (is_created) {
+               *is_created = created;
+       }
+       /* Everything went well. */
+       ret = 0;
 
 error:
-       delete_ust_app_session(-1, ua_sess);
-       return NULL;
+       health_code_update(&health_thread_cmd);
+       return ret;
 }
 
 /*
@@ -927,47 +1207,6 @@ error:
        return ret;
 }
 
-/*
- * Create an UST context and enable it for the event on the tracer.
- */
-static
-int create_ust_app_event_context(struct ust_app_session *ua_sess,
-               struct ust_app_event *ua_event, struct lttng_ust_context *uctx,
-               struct ust_app *app)
-{
-       int ret = 0;
-       struct lttng_ht_iter iter;
-       struct lttng_ht_node_ulong *node;
-       struct ust_app_ctx *ua_ctx;
-
-       DBG2("UST app adding context to event %s", ua_event->name);
-
-       lttng_ht_lookup(ua_event->ctx, (void *)((unsigned long)uctx->ctx), &iter);
-       node = lttng_ht_iter_get_node_ulong(&iter);
-       if (node != NULL) {
-               ret = -EEXIST;
-               goto error;
-       }
-
-       ua_ctx = alloc_ust_app_ctx(uctx);
-       if (ua_ctx == NULL) {
-               /* malloc failed */
-               ret = -1;
-               goto error;
-       }
-
-       lttng_ht_node_init_ulong(&ua_ctx->node, (unsigned long) ua_ctx->ctx.ctx);
-       lttng_ht_add_unique_ulong(ua_event->ctx, &ua_ctx->node);
-
-       ret = create_ust_event_context(ua_event, ua_ctx, app);
-       if (ret < 0) {
-               goto error;
-       }
-
-error:
-       return ret;
-}
-
 /*
  * Enable on the tracer side a ust app event for the session and channel.
  */
@@ -1058,11 +1297,12 @@ error:
 }
 
 /*
- * Create UST app channel and create it on the tracer.
+ * Create UST app channel and create it on the tracer. Set ua_chanp of the
+ * newly created channel if not NULL.
  */
-static struct ust_app_channel *create_ust_app_channel(
-               struct ust_app_session *ua_sess, struct ltt_ust_channel *uchan,
-               struct ust_app *app)
+static int create_ust_app_channel(struct ust_app_session *ua_sess,
+               struct ltt_ust_channel *uchan, struct ust_app *app,
+               struct ust_app_channel **ua_chanp)
 {
        int ret = 0;
        struct lttng_ht_iter iter;
@@ -1080,6 +1320,7 @@ static struct ust_app_channel *create_ust_app_channel(
        ua_chan = alloc_ust_app_channel(uchan->name, &uchan->attr);
        if (ua_chan == NULL) {
                /* Only malloc can fail here */
+               ret = -ENOMEM;
                goto error;
        }
        shadow_copy_channel(ua_chan, uchan);
@@ -1087,21 +1328,27 @@ static struct ust_app_channel *create_ust_app_channel(
        ret = create_ust_channel(app, ua_sess, ua_chan);
        if (ret < 0) {
                /* Not found previously means that it does not exist on the tracer */
-               assert(ret != -EEXIST);
+               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->key.pid);
+                       app->pid);
 
 end:
-       return ua_chan;
+       if (ua_chanp) {
+               *ua_chanp = ua_chan;
+       }
+
+       /* Everything went well. */
+       return 0;
 
 error:
        delete_ust_app_channel(-1, ua_chan);
-       return NULL;
+       return ret;
 }
 
 /*
@@ -1113,14 +1360,12 @@ int create_ust_app_event(struct ust_app_session *ua_sess,
                struct ust_app *app)
 {
        int ret = 0;
-       struct lttng_ht_iter iter;
-       struct lttng_ht_node_str *ua_event_node;
        struct ust_app_event *ua_event;
 
        /* Get event node */
-       lttng_ht_lookup(ua_chan->events, (void *)uevent->attr.name, &iter);
-       ua_event_node = lttng_ht_iter_get_node_str(&iter);
-       if (ua_event_node != NULL) {
+       ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
+                       uevent->filter, uevent->attr.loglevel);
+       if (ua_event != NULL) {
                ret = -EEXIST;
                goto end;
        }
@@ -1138,14 +1383,14 @@ int create_ust_app_event(struct ust_app_session *ua_sess,
        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 != -EEXIST);
+               assert(ret != -LTTNG_UST_ERR_EXIST);
                goto error;
        }
 
-       lttng_ht_add_unique_str(ua_chan->events, &ua_event->node);
+       add_unique_ust_app_event(ua_chan->events, ua_event);
 
        DBG2("UST app create event %s for PID %d completed", ua_event->name,
-                       app->key.pid);
+                       app->pid);
 
 end:
        return ret;
@@ -1186,20 +1431,13 @@ static int create_ust_app_metadata(struct ust_app_session *ua_sess,
                        goto error;
                }
 
-               DBG2("UST metadata opened for app pid %d", app->key.pid);
+               DBG2("UST metadata opened for app pid %d", app->pid);
        }
 
        /* Open UST metadata stream */
        if (ua_sess->metadata->stream_obj == NULL) {
-               ret = create_ust_stream(app, ua_sess);
-               if (ret < 0) {
-                       goto error;
-               }
-
-               ret = run_as_mkdir(ua_sess->path, S_IRWXU | S_IRWXG,
-                               ua_sess->uid, ua_sess->gid);
+               ret = create_ust_metadata_stream(app, ua_sess);
                if (ret < 0) {
-                       PERROR("mkdir UST metadata");
                        goto error;
                }
 
@@ -1211,7 +1449,7 @@ static int create_ust_app_metadata(struct ust_app_session *ua_sess,
                }
 
                DBG2("UST metadata stream object created for app pid %d",
-                               app->key.pid);
+                               app->pid);
        } else {
                ERR("Attempting to create stream without metadata opened");
                goto error;
@@ -1250,7 +1488,7 @@ struct ust_app *ust_app_find_by_pid(pid_t pid)
 
        DBG2("Found UST app by pid %d", pid);
 
-       return caa_container_of(node, struct ust_app, node);
+       return caa_container_of(node, struct ust_app, pid_n);
 
 error:
        rcu_read_unlock();
@@ -1267,13 +1505,31 @@ error:
 int ust_app_register(struct ust_register_msg *msg, int sock)
 {
        struct ust_app *lta;
+       int ret;
 
-       if ((msg->bits_per_long == 64 && ust_consumerd64_fd == -EINVAL)
-                       || (msg->bits_per_long == 32 && ust_consumerd32_fd == -EINVAL)) {
+       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);
-               close(sock);
+               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;
        }
        lta = zmalloc(sizeof(struct ust_app));
@@ -1285,6 +1541,7 @@ int ust_app_register(struct ust_register_msg *msg, int sock)
        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->v_major = msg->major;
        lta->v_minor = msg->minor;
@@ -1292,20 +1549,33 @@ int ust_app_register(struct ust_register_msg *msg, int sock)
        lta->name[16] = '\0';
        lta->sessions = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
 
-       /* Set key map */
-       lta->key.pid = msg->pid;
-       lttng_ht_node_init_ulong(&lta->node, (unsigned long)lta->key.pid);
-       lta->key.sock = sock;
-       lttng_ht_node_init_ulong(&lta->key.node, (unsigned long)lta->key.sock);
+       lta->pid = msg->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);
+
+       CDS_INIT_LIST_HEAD(&lta->teardown_head);
 
        rcu_read_lock();
-       lttng_ht_add_unique_ulong(ust_app_sock_key_map, &lta->key.node);
-       lttng_ht_add_unique_ulong(ust_app_ht, &lta->node);
+
+       /*
+        * 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);
+
+       /*
+        * 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);
+
        rcu_read_unlock();
 
        DBG("App registered with pid:%d ppid:%d uid:%d gid:%d sock:%d name:%s"
-                       " (version %d.%d)", lta->key.pid, lta->ppid, lta->uid, lta->gid,
-                       lta->key.sock, lta->name, lta->v_major, lta->v_minor);
+                       " (version %d.%d)", lta->pid, lta->ppid, lta->uid, lta->gid,
+                       lta->sock, lta->name, lta->v_major, lta->v_minor);
 
        return 0;
 }
@@ -1321,41 +1591,67 @@ void ust_app_unregister(int sock)
        struct ust_app *lta;
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;
+       struct ust_app_session *ua_sess;
        int ret;
 
        rcu_read_lock();
-       lta = find_app_by_sock(sock);
-       if (lta == NULL) {
-               ERR("Unregister app sock %d not found!", sock);
-               goto error;
-       }
-
-       DBG("PID %d unregistering with sock %d", lta->key.pid, sock);
-
-       /* Remove application from socket hash table */
-       lttng_ht_lookup(ust_app_sock_key_map, (void *)((unsigned long) sock), &iter);
-       ret = lttng_ht_del(ust_app_sock_key_map, &iter);
-       assert(!ret);
 
        /* Get the node reference for a call_rcu */
-       lttng_ht_lookup(ust_app_ht, (void *)((unsigned long) lta->key.pid), &iter);
+       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 sock %d by pid %d", sock, lta->key.pid);
+               ERR("Unable to find app by sock %d", sock);
                goto error;
        }
 
+       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, &iter);
+       ret = lttng_ht_del(ust_app_ht_by_sock, &iter);
        assert(!ret);
-       call_rcu(&node->head, delete_ust_app_rcu);
-error:
-       rcu_read_unlock();
-       return;
-}
 
-/*
- * Return traceable_app_count
+       /* Assign second node for deletion */
+       iter.iter.node = &lta->pid_n.node;
+
+       /*
+        * 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.
+        */
+       ret = lttng_ht_del(ust_app_ht, &iter);
+       if (ret) {
+               DBG3("Unregister app by PID %d failed. This can happen on pid reuse",
+                               lta->pid);
+       }
+
+       /* Remove sessions so they are not visible during deletion.*/
+       cds_lfht_for_each_entry(lta->sessions->ht, &iter.iter, ua_sess,
+                       node.node) {
+               ret = lttng_ht_del(lta->sessions, &iter);
+               if (ret) {
+                       /* The session was already removed so scheduled for teardown. */
+                       continue;
+               }
+
+               /*
+                * Add session to list for teardown. This is safe since at this point we
+                * are the only one using this list.
+                */
+               cds_list_add(&ua_sess->teardown_node, &lta->teardown_head);
+       }
+
+       /* Free memory */
+       call_rcu(&lta->pid_n.head, delete_ust_app_rcu);
+
+error:
+       rcu_read_unlock();
+       return;
+}
+
+/*
+ * Return traceable_app_count
  */
 unsigned long ust_app_list_count(void)
 {
@@ -1377,11 +1673,11 @@ int ust_app_list_events(struct lttng_event **events)
        size_t nbmem, count = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;
-       struct lttng_event *tmp;
+       struct lttng_event *tmp_event;
 
        nbmem = UST_APP_EVENT_LIST_SIZE;
-       tmp = zmalloc(nbmem * sizeof(struct lttng_event));
-       if (tmp == NULL) {
+       tmp_event = zmalloc(nbmem * sizeof(struct lttng_event));
+       if (tmp_event == NULL) {
                PERROR("zmalloc ust app events");
                ret = -ENOMEM;
                goto error;
@@ -1389,47 +1685,147 @@ int ust_app_list_events(struct lttng_event **events)
 
        rcu_read_lock();
 
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                struct lttng_ust_tracepoint_iter uiter;
 
-               handle = ustctl_tracepoint_list(app->key.sock);
+               health_code_update(&health_thread_cmd);
+
+               if (!app->compatible) {
+                       /*
+                        * TODO: In time, we should notice the caller of this error by
+                        * telling him that this is a version error.
+                        */
+                       continue;
+               }
+               handle = ustctl_tracepoint_list(app->sock);
                if (handle < 0) {
                        ERR("UST app list events getting handle failed for app pid %d",
-                                       app->key.pid);
+                                       app->pid);
                        continue;
                }
 
-               while ((ret = ustctl_tracepoint_list_get(app->key.sock, handle,
-                                               &uiter)) != -ENOENT) {
+               while ((ret = ustctl_tracepoint_list_get(app->sock, handle,
+                                       &uiter)) != -LTTNG_UST_ERR_NOENT) {
+                       health_code_update(&health_thread_cmd);
                        if (count >= nbmem) {
+                               /* In case the realloc fails, we free the memory */
+                               void *ptr;
+
                                DBG2("Reallocating event list from %zu to %zu entries", nbmem,
                                                2 * nbmem);
                                nbmem *= 2;
-                               tmp = realloc(tmp, nbmem * sizeof(struct lttng_event));
-                               if (tmp == NULL) {
+                               ptr = realloc(tmp_event, nbmem * sizeof(struct lttng_event));
+                               if (ptr == NULL) {
                                        PERROR("realloc ust app events");
+                                       free(tmp_event);
                                        ret = -ENOMEM;
                                        goto rcu_error;
                                }
+                               tmp_event = ptr;
                        }
-                       memcpy(tmp[count].name, uiter.name, LTTNG_UST_SYM_NAME_LEN);
-                       memcpy(tmp[count].loglevel, uiter.loglevel, LTTNG_UST_SYM_NAME_LEN);
-                       tmp[count].loglevel_value = uiter.loglevel_value;
-                       tmp[count].type = LTTNG_UST_TRACEPOINT;
-                       tmp[count].pid = app->key.pid;
-                       tmp[count].enabled = -1;
+                       memcpy(tmp_event[count].name, uiter.name, LTTNG_UST_SYM_NAME_LEN);
+                       tmp_event[count].loglevel = uiter.loglevel;
+                       tmp_event[count].type = (enum lttng_event_type) LTTNG_UST_TRACEPOINT;
+                       tmp_event[count].pid = app->pid;
+                       tmp_event[count].enabled = -1;
                        count++;
                }
        }
 
        ret = count;
-       *events = tmp;
+       *events = tmp_event;
 
        DBG2("UST app list events done (%zu events)", count);
 
 rcu_error:
        rcu_read_unlock();
 error:
+       health_code_update(&health_thread_cmd);
+       return ret;
+}
+
+/*
+ * Fill events array with all events name of all registered apps.
+ */
+int ust_app_list_event_fields(struct lttng_event_field **fields)
+{
+       int ret, handle;
+       size_t nbmem, count = 0;
+       struct lttng_ht_iter iter;
+       struct ust_app *app;
+       struct lttng_event_field *tmp_event;
+
+       nbmem = UST_APP_EVENT_LIST_SIZE;
+       tmp_event = zmalloc(nbmem * sizeof(struct lttng_event_field));
+       if (tmp_event == NULL) {
+               PERROR("zmalloc ust app event fields");
+               ret = -ENOMEM;
+               goto error;
+       }
+
+       rcu_read_lock();
+
+       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);
+
+               if (!app->compatible) {
+                       /*
+                        * TODO: In time, we should notice the caller of this error by
+                        * telling him that this is a version error.
+                        */
+                       continue;
+               }
+               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);
+                       continue;
+               }
+
+               while ((ret = ustctl_tracepoint_field_list_get(app->sock, handle,
+                                       &uiter)) != -LTTNG_UST_ERR_NOENT) {
+                       health_code_update(&health_thread_cmd);
+                       if (count >= nbmem) {
+                               /* In case the realloc fails, we free the memory */
+                               void *ptr;
+
+                               DBG2("Reallocating event field list from %zu to %zu entries", nbmem,
+                                               2 * nbmem);
+                               nbmem *= 2;
+                               ptr = realloc(tmp_event, nbmem * sizeof(struct lttng_event_field));
+                               if (ptr == NULL) {
+                                       PERROR("realloc ust app event fields");
+                                       free(tmp_event);
+                                       ret = -ENOMEM;
+                                       goto rcu_error;
+                               }
+                               tmp_event = ptr;
+                       }
+
+                       memcpy(tmp_event[count].field_name, uiter.field_name, LTTNG_UST_SYM_NAME_LEN);
+                       tmp_event[count].type = uiter.type;
+                       tmp_event[count].nowrite = uiter.nowrite;
+
+                       memcpy(tmp_event[count].event.name, uiter.event_name, LTTNG_UST_SYM_NAME_LEN);
+                       tmp_event[count].event.loglevel = uiter.loglevel;
+                       tmp_event[count].event.type = LTTNG_UST_TRACEPOINT;
+                       tmp_event[count].event.pid = app->pid;
+                       tmp_event[count].event.enabled = -1;
+                       count++;
+               }
+       }
+
+       ret = count;
+       *fields = tmp_event;
+
+       DBG2("UST app list event fields done (%zu events)", count);
+
+rcu_error:
+       rcu_read_unlock();
+error:
+       health_code_update(&health_thread_cmd);
        return ret;
 }
 
@@ -1439,27 +1835,29 @@ error:
 void ust_app_clean_list(void)
 {
        int ret;
+       struct ust_app *app;
        struct lttng_ht_iter iter;
-       struct lttng_ht_node_ulong *node;
 
        DBG2("UST app cleaning registered apps hash table");
 
        rcu_read_lock();
 
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, node, node) {
+       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                ret = lttng_ht_del(ust_app_ht, &iter);
                assert(!ret);
-               call_rcu(&node->head, delete_ust_app_rcu);
+               call_rcu(&app->pid_n.head, delete_ust_app_rcu);
        }
-       /* Destroy is done only when the ht is empty */
-       lttng_ht_destroy(ust_app_ht);
 
-       cds_lfht_for_each_entry(ust_app_sock_key_map->ht, &iter.iter, node, node) {
-               ret = lttng_ht_del(ust_app_sock_key_map, &iter);
+       /* Cleanup socket hash table */
+       cds_lfht_for_each_entry(ust_app_ht_by_sock->ht, &iter.iter, app,
+                       sock_n.node) {
+               ret = lttng_ht_del(ust_app_ht_by_sock, &iter);
                assert(!ret);
        }
+
        /* Destroy is done only when the ht is empty */
-       lttng_ht_destroy(ust_app_sock_key_map);
+       lttng_ht_destroy(ust_app_ht);
+       lttng_ht_destroy(ust_app_ht_by_sock);
 
        rcu_read_unlock();
 }
@@ -1470,7 +1868,7 @@ void ust_app_clean_list(void)
 void ust_app_ht_alloc(void)
 {
        ust_app_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
-       ust_app_sock_key_map = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
+       ust_app_ht_by_sock = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
 }
 
 /*
@@ -1498,8 +1896,15 @@ int ust_app_disable_channel_glb(struct ltt_ust_session *usess,
        rcu_read_lock();
 
        /* For every registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                struct lttng_ht_iter uiter;
+               if (!app->compatible) {
+                       /*
+                        * TODO: In time, we should notice the caller of this error by
+                        * telling him that this is a version error.
+                        */
+                       continue;
+               }
                ua_sess = lookup_session_by_app(usess, app);
                if (ua_sess == NULL) {
                        continue;
@@ -1552,7 +1957,14 @@ int ust_app_enable_channel_glb(struct ltt_ust_session *usess,
        rcu_read_lock();
 
        /* For every registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       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;
+               }
                ua_sess = lookup_session_by_app(usess, app);
                if (ua_sess == NULL) {
                        continue;
@@ -1592,7 +2004,14 @@ int ust_app_disable_event_glb(struct ltt_ust_session *usess,
        rcu_read_lock();
 
        /* For all registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       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;
+               }
                ua_sess = lookup_session_by_app(usess, app);
                if (ua_sess == NULL) {
                        /* Next app */
@@ -1604,7 +2023,7 @@ int ust_app_disable_event_glb(struct ltt_ust_session *usess,
                ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
                if (ua_chan_node == NULL) {
                        DBG2("Channel %s not found in session id %d for app pid %d."
-                                       "Skipping", uchan->name, usess->id, app->key.pid);
+                                       "Skipping", uchan->name, usess->id, app->pid);
                        continue;
                }
                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
@@ -1613,7 +2032,7 @@ int ust_app_disable_event_glb(struct ltt_ust_session *usess,
                ua_event_node = lttng_ht_iter_get_node_str(&uiter);
                if (ua_event_node == NULL) {
                        DBG2("Event %s not found in channel %s for app pid %d."
-                                       "Skipping", uevent->attr.name, uchan->name, app->key.pid);
+                                       "Skipping", uevent->attr.name, uchan->name, app->pid);
                        continue;
                }
                ua_event = caa_container_of(ua_event_node, struct ust_app_event, node);
@@ -1651,10 +2070,19 @@ int ust_app_disable_all_event_glb(struct ltt_ust_session *usess,
        rcu_read_lock();
 
        /* For all registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       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;
+               }
                ua_sess = lookup_session_by_app(usess, app);
-               /* If ua_sess is NULL, there is a code flow error */
-               assert(ua_sess);
+               if (!ua_sess) {
+                       /* The application has problem or is probably dead. */
+                       continue;
+               }
 
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
@@ -1686,10 +2114,10 @@ int ust_app_disable_all_event_glb(struct ltt_ust_session *usess,
 int ust_app_create_channel_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan)
 {
+       int ret = 0, created;
        struct lttng_ht_iter iter;
        struct ust_app *app;
-       struct ust_app_session *ua_sess;
-       struct ust_app_channel *ua_chan;
+       struct ust_app_session *ua_sess = NULL;
 
        /* Very wrong code flow */
        assert(usess);
@@ -1701,32 +2129,53 @@ int ust_app_create_channel_glb(struct ltt_ust_session *usess,
        rcu_read_lock();
 
        /* For every registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       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;
+               }
                /*
                 * 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.
                 */
-               ua_sess = create_ust_app_session(usess, app);
-               if (ua_sess == NULL) {
-                       /* Major problem here and it's maybe the tracer or malloc() */
-                       goto error;
+               ret = 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.
+                                */
+                               continue;
+                       case -ENOMEM:
+                       default:
+                               goto error_rcu_unlock;
+                       }
                }
+               assert(ua_sess);
 
-               /* Create channel onto application */
-               ua_chan = create_ust_app_channel(ua_sess, uchan, app);
-               if (ua_chan == NULL) {
-                       /* Major problem here and it's maybe the tracer or malloc() */
-                       goto error;
+               /* Create channel onto application. We don't need the chan ref. */
+               ret = create_ust_app_channel(ua_sess, uchan, app, NULL);
+               if (ret < 0) {
+                       if (ret == -ENOMEM) {
+                               /* No more memory is a fatal error. Stop right now. */
+                               goto error_rcu_unlock;
+                       }
+                       /* Cleanup the created session if it's the case. */
+                       if (created) {
+                               delete_ust_app_session(app->sock, ua_sess);
+                       }
                }
        }
 
+error_rcu_unlock:
        rcu_read_unlock();
-
-       return 0;
-
-error:
-       return -1;
+       return ret;
 }
 
 /*
@@ -1737,7 +2186,7 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
 {
        int ret = 0;
        struct lttng_ht_iter iter, uiter;
-       struct lttng_ht_node_str *ua_chan_node, *ua_event_node;
+       struct lttng_ht_node_str *ua_chan_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
@@ -1755,10 +2204,19 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
        rcu_read_lock();
 
        /* For all registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       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;
+               }
                ua_sess = lookup_session_by_app(usess, app);
-               /* If ua_sess is NULL, there is a code flow error */
-               assert(ua_sess);
+               if (!ua_sess) {
+                       /* The application has problem or is probably dead. */
+                       continue;
+               }
 
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
@@ -1768,14 +2226,14 @@ int ust_app_enable_event_glb(struct ltt_ust_session *usess,
 
                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
 
-               lttng_ht_lookup(ua_chan->events, (void*)uevent->attr.name, &uiter);
-               ua_event_node = lttng_ht_iter_get_node_str(&uiter);
-               if (ua_event_node == NULL) {
+               /* Get event node */
+               ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
+                               uevent->filter, uevent->attr.loglevel);
+               if (ua_event == NULL) {
                        DBG3("UST app enable event %s not found for app PID %d."
-                                       "Skipping app", uevent->attr.name, app->key.pid);
+                                       "Skipping app", uevent->attr.name, app->pid);
                        continue;
                }
-               ua_event = caa_container_of(ua_event_node, struct ust_app_event, node);
 
                ret = enable_ust_app_event(ua_sess, ua_event, app);
                if (ret < 0) {
@@ -1808,10 +2266,19 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
        rcu_read_lock();
 
        /* For all registered applications */
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       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;
+               }
                ua_sess = lookup_session_by_app(usess, app);
-               /* If ua_sess is NULL, there is a code flow error */
-               assert(ua_sess);
+               if (!ua_sess) {
+                       /* The application has problem or is probably dead. */
+                       continue;
+               }
 
                /* Lookup channel in the ust app session */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
@@ -1823,12 +2290,12 @@ int ust_app_create_event_glb(struct ltt_ust_session *usess,
 
                ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
                if (ret < 0) {
-                       if (ret != -EEXIST) {
+                       if (ret != -LTTNG_UST_ERR_EXIST) {
                                /* Possible value at this point: -ENOMEM. If so, we stop! */
                                break;
                        }
                        DBG2("UST app event %s already exist on app PID %d",
-                                       uevent->attr.name, app->key.pid);
+                                       uevent->attr.name, app->pid);
                        continue;
                }
        }
@@ -1848,15 +2315,20 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
        struct ltt_ust_stream *ustream;
-       int consumerd_fd;
+       struct consumer_socket *socket;
 
-       DBG("Starting tracing for ust app pid %d", app->key.pid);
+       DBG("Starting tracing for ust app pid %d", app->pid);
 
        rcu_read_lock();
 
+       if (!app->compatible) {
+               goto end;
+       }
+
        ua_sess = lookup_session_by_app(usess, app);
        if (ua_sess == NULL) {
-               goto error_rcu_unlock;
+               /* The session is in teardown process. Ignore and continue. */
+               goto end;
        }
 
        /* Upon restart, we skip the setup, already done */
@@ -1864,8 +2336,23 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                goto skip_setup;
        }
 
+       /* Create directories if consumer is LOCAL and has a path defined. */
+       if (usess->consumer->type == CONSUMER_DST_LOCAL &&
+                       strlen(usess->consumer->dst.trace_path) > 0) {
+               ret = run_as_mkdir_recursive(usess->consumer->dst.trace_path,
+                               S_IRWXU | S_IRWXG, usess->uid, usess->gid);
+               if (ret < 0) {
+                       if (ret != -EEXIST) {
+                               ERR("Trace directory creation error");
+                               ret = -1;
+                               goto error_rcu_unlock;
+                       }
+               }
+       }
+
        ret = create_ust_app_metadata(ua_sess, usess->pathname, app);
        if (ret < 0) {
+               ret = LTTNG_ERR_UST_META_FAIL;
                goto error_rcu_unlock;
        }
 
@@ -1881,34 +2368,48 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
                                goto error_rcu_unlock;
                        }
 
-                       ret = ustctl_create_stream(app->key.sock, ua_chan->obj,
-                                       &ustream->obj);
+                       health_code_update(&health_thread_cmd);
+
+                       ret = create_ust_stream(app, ua_chan, ustream);
                        if (ret < 0) {
-                               /* Got all streams */
-                               break;
+                               /* 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;
                        }
-                       ustream->handle = ustream->obj->handle;
 
-                       /* Order is important */
+                       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);
-                       ret = snprintf(ustream->pathname, PATH_MAX, "%s/%s_%u",
-                                       ua_sess->path, ua_chan->name,
-                                       ua_chan->streams.count++);
-                       if (ret < 0) {
-                               PERROR("asprintf UST create stream");
-                               continue;
-                       }
-                       DBG2("UST stream %d ready at %s", ua_chan->streams.count,
-                                       ustream->pathname);
+                       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:
-               consumerd_fd = ust_consumerd64_fd;
+               socket = consumer_find_socket(uatomic_read(&ust_consumerd64_fd),
+                               usess->consumer);
+               if (socket == NULL) {
+                       goto skip_setup;
+               }
                break;
        case 32:
-               consumerd_fd = ust_consumerd32_fd;
+               socket = consumer_find_socket(uatomic_read(&ust_consumerd32_fd),
+                               usess->consumer);
+               if (socket == NULL) {
+                       goto skip_setup;
+               }
                break;
        default:
                ret = -EINVAL;
@@ -1916,29 +2417,37 @@ int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
        }
 
        /* Setup UST consumer socket and send fds to it */
-       ret = ust_consumer_send_session(consumerd_fd, ua_sess);
+       ret = ust_consumer_send_session(ua_sess, usess->consumer, socket);
        if (ret < 0) {
                goto error_rcu_unlock;
        }
-       ua_sess->started = 1;
+
+       health_code_update(&health_thread_cmd);
 
 skip_setup:
        /* This start the UST tracing */
-       ret = ustctl_start_session(app->key.sock, ua_sess->handle);
+       ret = ustctl_start_session(app->sock, ua_sess->handle);
        if (ret < 0) {
-               ERR("Error starting tracing for app pid: %d", app->key.pid);
+               ERR("Error starting tracing for app pid: %d (ret: %d)", app->pid, ret);
                goto error_rcu_unlock;
        }
 
-       rcu_read_unlock();
+       /* Indicate that the session has been started once */
+       ua_sess->started = 1;
+
+       health_code_update(&health_thread_cmd);
 
        /* Quiescent wait after starting trace */
-       ustctl_wait_quiescent(app->key.sock);
+       ustctl_wait_quiescent(app->sock);
 
+end:
+       rcu_read_unlock();
+       health_code_update(&health_thread_cmd);
        return 0;
 
 error_rcu_unlock:
        rcu_read_unlock();
+       health_code_update(&health_thread_cmd);
        return -1;
 }
 
@@ -1952,65 +2461,82 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
 
-       DBG("Stopping tracing for ust app pid %d", app->key.pid);
+       DBG("Stopping tracing for ust app pid %d", app->pid);
 
        rcu_read_lock();
 
+       if (!app->compatible) {
+               goto end;
+       }
+
        ua_sess = lookup_session_by_app(usess, app);
        if (ua_sess == NULL) {
-               /* Only malloc can failed so something is really wrong */
-               goto error_rcu_unlock;
+               goto end;
        }
 
-       /* Not started, continuing. */
-       if (ua_sess->started == 0) {
-               goto end;
+       /*
+        * If started = 0, it means that stop trace has been called for a session
+        * that was never started. It's possible since we can have a fail start
+        * from either the application manager thread or the command thread. Simply
+        * indicate that this is a stop error.
+        */
+       if (!ua_sess->started) {
+               goto error_rcu_unlock;
        }
 
+       health_code_update(&health_thread_cmd);
+
        /* This inhibits UST tracing */
-       ret = ustctl_stop_session(app->key.sock, ua_sess->handle);
+       ret = ustctl_stop_session(app->sock, ua_sess->handle);
        if (ret < 0) {
-               ERR("Error stopping tracing for app pid: %d", app->key.pid);
+               ERR("Error stopping tracing for app pid: %d (ret: %d)", app->pid, ret);
                goto error_rcu_unlock;
        }
 
+       health_code_update(&health_thread_cmd);
+
        /* Quiescent wait after stopping trace */
-       ustctl_wait_quiescent(app->key.sock);
+       ustctl_wait_quiescent(app->sock);
+
+       health_code_update(&health_thread_cmd);
 
        /* Flushing buffers */
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
-               ret = ustctl_sock_flush_buffer(app->key.sock, ua_chan->obj);
+               health_code_update(&health_thread_cmd);
+               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->key.pid, ua_chan->name, ret);
+                                       app->pid, ua_chan->name, ret);
                        /* Continuing flushing all buffers */
                        continue;
                }
        }
 
+       health_code_update(&health_thread_cmd);
+
        /* Flush all buffers before stopping */
-       ret = ustctl_sock_flush_buffer(app->key.sock, ua_sess->metadata->obj);
+       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->key.pid,
+               ERR("UST app PID %d metadata flush failed with ret %d", app->pid,
                                ret);
        }
 
-       ua_sess->started = 0;
-
 end:
        rcu_read_unlock();
+       health_code_update(&health_thread_cmd);
        return 0;
 
 error_rcu_unlock:
        rcu_read_unlock();
+       health_code_update(&health_thread_cmd);
        return -1;
 }
 
 /*
  * Destroy a specific UST session in apps.
  */
-int ust_app_destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
+static int destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
 {
        struct ust_app_session *ua_sess;
        struct lttng_ust_object_data obj;
@@ -2018,37 +2544,44 @@ int ust_app_destroy_trace(struct ltt_ust_session *usess, struct ust_app *app)
        struct lttng_ht_node_ulong *node;
        int ret;
 
-       DBG("Destroy tracing for ust app pid %d", app->key.pid);
+       DBG("Destroy tracing for ust app pid %d", app->pid);
 
        rcu_read_lock();
 
+       if (!app->compatible) {
+               goto end;
+       }
+
        __lookup_session_by_app(usess, app, &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
-               /* Only malloc can failed so something is really wrong */
-               goto error_rcu_unlock;
+               /* Session is being or is deleted. */
+               goto end;
        }
        ua_sess = caa_container_of(node, struct ust_app_session, node);
        ret = lttng_ht_del(app->sessions, &iter);
-       assert(!ret);
+       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;
-       ustctl_release_object(app->key.sock, &obj);
-
-       delete_ust_app_session(app->key.sock, ua_sess);
+       health_code_update(&health_thread_cmd);
+       ustctl_release_object(app->sock, &obj);
 
-       rcu_read_unlock();
+       health_code_update(&health_thread_cmd);
+       delete_ust_app_session(app->sock, ua_sess);
 
        /* Quiescent wait after stopping trace */
-       ustctl_wait_quiescent(app->key.sock);
+       ustctl_wait_quiescent(app->sock);
 
-       return 0;
-
-error_rcu_unlock:
+end:
        rcu_read_unlock();
-       return -1;
+       health_code_update(&health_thread_cmd);
+       return 0;
 }
 
 /*
@@ -2064,7 +2597,7 @@ int ust_app_start_trace_all(struct ltt_ust_session *usess)
 
        rcu_read_lock();
 
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       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 */
@@ -2090,7 +2623,7 @@ int ust_app_stop_trace_all(struct ltt_ust_session *usess)
 
        rcu_read_lock();
 
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
+       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                ret = ust_app_stop_trace(usess, app);
                if (ret < 0) {
                        /* Continue to next apps even on error */
@@ -2116,8 +2649,8 @@ int ust_app_destroy_trace_all(struct ltt_ust_session *usess)
 
        rcu_read_lock();
 
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
-               ret = ust_app_destroy_trace(usess, app);
+       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+               ret = destroy_trace(usess, app);
                if (ret < 0) {
                        /* Continue to next apps even on error */
                        continue;
@@ -2135,16 +2668,14 @@ int ust_app_destroy_trace_all(struct ltt_ust_session *usess)
 void ust_app_global_update(struct ltt_ust_session *usess, int sock)
 {
        int ret = 0;
-       struct lttng_ht_iter iter, uiter;
+       struct lttng_ht_iter iter, uiter, iter_ctx;
        struct ust_app *app;
-       struct ust_app_session *ua_sess;
+       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;
 
-       if (usess == NULL) {
-               ERR("No UST session on global update. Returning");
-               goto error;
-       }
+       assert(usess);
 
        DBG2("UST app global update for app sock %d for session id %d", sock,
                        usess->id);
@@ -2157,11 +2688,17 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
                goto error;
        }
 
-       ua_sess = create_ust_app_session(usess, app);
-       if (ua_sess == NULL) {
+       if (!app->compatible) {
                goto error;
        }
 
+       ret = create_ust_app_session(usess, app, &ua_sess, NULL);
+       if (ret < 0) {
+               /* Tracer is probably gone or ENOMEM. */
+               goto error;
+       }
+       assert(ua_sess);
+
        /*
         * We can iterate safely here over all UST app session sicne the create ust
         * app session above made a shadow copy of the UST global domain from the
@@ -2175,6 +2712,16 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
                        continue;
                }
 
+               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;
+                       }
+               }
+
+
                /* For each events */
                cds_lfht_for_each_entry(ua_chan->events->ht, &uiter.iter, ua_event,
                                node.node) {
@@ -2192,7 +2739,7 @@ void ust_app_global_update(struct ltt_ust_session *usess, int sock)
                        goto error;
                }
 
-               DBG2("UST trace started for app pid %d", app->key.pid);
+               DBG2("UST trace started for app pid %d", app->pid);
        }
 
 error:
@@ -2215,49 +2762,14 @@ int ust_app_add_ctx_channel_glb(struct ltt_ust_session *usess,
 
        rcu_read_lock();
 
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
-               ua_sess = lookup_session_by_app(usess, app);
-               if (ua_sess == NULL) {
-                       continue;
-               }
-
-               /* 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;
-               }
-               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) {
+       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;
                }
-       }
-
-       rcu_read_unlock();
-       return ret;
-}
-
-/*
- * Add context to a specific event in a channel for global UST domain.
- */
-int ust_app_add_ctx_event_glb(struct ltt_ust_session *usess,
-               struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent,
-               struct ltt_ust_context *uctx)
-{
-       int ret = 0;
-       struct lttng_ht_node_str *ua_chan_node, *ua_event_node;
-       struct lttng_ht_iter iter, uiter;
-       struct ust_app_session *ua_sess;
-       struct ust_app_event *ua_event;
-       struct ust_app_channel *ua_chan = NULL;
-       struct ust_app *app;
-
-       rcu_read_lock();
-
-       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
                ua_sess = lookup_session_by_app(usess, app);
                if (ua_sess == NULL) {
                        continue;
@@ -2272,15 +2784,7 @@ int ust_app_add_ctx_event_glb(struct ltt_ust_session *usess,
                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel,
                                node);
 
-               lttng_ht_lookup(ua_chan->events, (void *)uevent->attr.name, &uiter);
-               ua_event_node = lttng_ht_iter_get_node_str(&uiter);
-               if (ua_event_node == NULL) {
-                       continue;
-               }
-               ua_event = caa_container_of(ua_event_node, struct ust_app_event,
-                               node);
-
-               ret = create_ust_app_event_context(ua_sess, ua_event, &uctx->ctx, app);
+               ret = create_ust_app_channel_context(ua_sess, ua_chan, &uctx->ctx, app);
                if (ret < 0) {
                        continue;
                }
@@ -2298,7 +2802,7 @@ int ust_app_enable_event_pid(struct ltt_ust_session *usess,
 {
        int ret = 0;
        struct lttng_ht_iter iter;
-       struct lttng_ht_node_str *ua_chan_node, *ua_event_node;
+       struct lttng_ht_node_str *ua_chan_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
@@ -2315,9 +2819,16 @@ int ust_app_enable_event_pid(struct ltt_ust_session *usess,
                goto error;
        }
 
+       if (!app->compatible) {
+               ret = 0;
+               goto error;
+       }
+
        ua_sess = lookup_session_by_app(usess, app);
-       /* If ua_sess is NULL, there is a code flow error */
-       assert(ua_sess);
+       if (!ua_sess) {
+               /* The application has problem or is probably dead. */
+               goto error;
+       }
 
        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
@@ -2327,16 +2838,14 @@ int ust_app_enable_event_pid(struct ltt_ust_session *usess,
 
        ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
 
-       lttng_ht_lookup(ua_chan->events, (void *)uevent->attr.name, &iter);
-       ua_event_node = lttng_ht_iter_get_node_str(&iter);
-       if (ua_event_node == NULL) {
+       ua_event = find_ust_app_event(ua_chan->events, uevent->attr.name,
+                       uevent->filter, uevent->attr.loglevel);
+       if (ua_event == NULL) {
                ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
                if (ret < 0) {
                        goto error;
                }
        } else {
-               ua_event = caa_container_of(ua_event_node, struct ust_app_event, node);
-
                ret = enable_ust_app_event(ua_sess, ua_event, app);
                if (ret < 0) {
                        goto error;
@@ -2373,9 +2882,16 @@ int ust_app_disable_event_pid(struct ltt_ust_session *usess,
                goto error;
        }
 
+       if (!app->compatible) {
+               ret = 0;
+               goto error;
+       }
+
        ua_sess = lookup_session_by_app(usess, app);
-       /* If ua_sess is NULL, there is a code flow error */
-       assert(ua_sess);
+       if (!ua_sess) {
+               /* The application has problem or is probably dead. */
+               goto error;
+       }
 
        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
@@ -2403,3 +2919,93 @@ error:
        rcu_read_unlock();
        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.
+ */
+int ust_app_calibrate_glb(struct lttng_ust_calibrate *calibrate)
+{
+       int ret = 0;
+       struct lttng_ht_iter iter;
+       struct ust_app *app;
+
+       rcu_read_lock();
+
+       cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
+               if (!app->compatible) {
+                       /*
+                        * TODO: In time, we should notice the caller of this error by
+                        * telling him that this is a version error.
+                        */
+                       continue;
+               }
+
+               health_code_update(&health_thread_cmd);
+
+               ret = ustctl_calibrate(app->sock, calibrate);
+               if (ret < 0) {
+                       switch (ret) {
+                       case -ENOSYS:
+                               /* Means that it's not implemented on the tracer side. */
+                               ret = 0;
+                               break;
+                       default:
+                               /* TODO: Report error to user */
+                               DBG2("Calibrate app PID %d returned with error %d",
+                                               app->pid, ret);
+                               break;
+                       }
+               }
+       }
+
+       DBG("UST app global domain calibration finished");
+
+       rcu_read_unlock();
+
+       health_code_update(&health_thread_cmd);
+
+       return ret;
+}
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