Adding context to an event is no longer possible

[lttng-tools.git] / src / bin / lttng-sessiond / ust-app.c

/*
 * 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, 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.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#define _GNU_SOURCE
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <urcu/compiler.h>
#include <lttng/ust-error.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"

/*
 * Delete ust context safely. RCU read lock must be held before calling
 * this function.
 */
static
void delete_ust_app_ctx(int sock, struct ust_app_ctx *ua_ctx)
{
        if (ua_ctx->obj) {
                ustctl_release_object(sock, ua_ctx->obj);
                free(ua_ctx->obj);
        }
        free(ua_ctx);
}

/*
 * Delete ust app event safely. RCU read lock must be held before calling
 * this function.
 */
static
void delete_ust_app_event(int sock, struct ust_app_event *ua_event)
{
        free(ua_event->filter);

        if (ua_event->obj != NULL) {
                ustctl_release_object(sock, ua_event->obj);
                free(ua_event->obj);
        }
        free(ua_event);
}

/*
 * Delete ust app stream safely. RCU read lock must be held before calling
 * this function.
 */
static
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);
}

/*
 * Delete ust app channel safely. RCU read lock must be held before calling
 * this function.
 */
static
void delete_ust_app_channel(int sock, struct ust_app_channel *ua_chan)
{
        int ret;
        struct lttng_ht_iter iter;
        struct ust_app_event *ua_event;
        struct ust_app_ctx *ua_ctx;
        struct ltt_ust_stream *stream, *stmp;

        /* Wipe stream */
        cds_list_for_each_entry_safe(stream, stmp, &ua_chan->streams.head, list) {
                cds_list_del(&stream->list);
                delete_ust_app_stream(sock, stream);
        }

        /* Wipe context */
        cds_lfht_for_each_entry(ua_chan->ctx->ht, &iter.iter, ua_ctx, node.node) {
                ret = lttng_ht_del(ua_chan->ctx, &iter);
                assert(!ret);
                delete_ust_app_ctx(sock, ua_ctx);
        }
        lttng_ht_destroy(ua_chan->ctx);

        /* Wipe events */
        cds_lfht_for_each_entry(ua_chan->events->ht, &iter.iter, ua_event,
                        node.node) {
                ret = lttng_ht_del(ua_chan->events, &iter);
                assert(!ret);
                delete_ust_app_event(sock, ua_event);
        }
        lttng_ht_destroy(ua_chan->events);

        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);
}

/*
 * Delete ust app session safely. RCU read lock must be held before calling
 * this function.
 */
static
void delete_ust_app_session(int sock, struct ust_app_session *ua_sess)
{
        int ret;
        struct lttng_ht_iter iter;
        struct ust_app_channel *ua_chan;

        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,
                        node.node) {
                ret = lttng_ht_del(ua_sess->channels, &iter);
                assert(!ret);
                delete_ust_app_channel(sock, ua_chan);
        }
        lttng_ht_destroy(ua_sess->channels);

        if (ua_sess->handle != -1) {
                ustctl_release_handle(sock, ua_sess->handle);
        }
        free(ua_sess);
}

/*
 * Delete a traceable application structure from the global list. Never call
 * this function outside of a call_rcu call.
 */
static
void delete_ust_app(struct ust_app *app)
{
        int ret, sock;
        struct lttng_ht_iter iter;
        struct ust_app_session *ua_sess;

        rcu_read_lock();

        /* Delete ust app sessions info */
        sock = app->sock;
        app->sock = -1;

        /* 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->sock, ua_sess);
        }
        lttng_ht_destroy(app->sessions);

        /*
         * 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.
         */
        ret = close(sock);
        if (ret) {
                PERROR("close");
        }
        lttng_fd_put(LTTNG_FD_APPS, 1);

        DBG2("UST app pid %d deleted", app->pid);
        free(app);

        rcu_read_unlock();
}

/*
 * URCU intermediate call to delete an UST app.
 */
static
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, pid_n);

        DBG3("Call RCU deleting app PID %d", app->pid);
        delete_ust_app(app);
}

/*
 * Alloc new UST app session.
 */
static
struct ust_app_session *alloc_ust_app_session(void)
{
        struct ust_app_session *ua_sess;

        /* Init most of the default value by allocating and zeroing */
        ua_sess = zmalloc(sizeof(struct ust_app_session));
        if (ua_sess == NULL) {
                PERROR("malloc");
                goto error;
        }

        ua_sess->handle = -1;
        ua_sess->channels = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);

        return ua_sess;

error:
        return NULL;
}

/*
 * Alloc new UST app channel.
 */
static
struct ust_app_channel *alloc_ust_app_channel(char *name,
                struct lttng_ust_channel *attr)
{
        struct ust_app_channel *ua_chan;

        /* Init most of the default value by allocating and zeroing */
        ua_chan = zmalloc(sizeof(struct ust_app_channel));
        if (ua_chan == NULL) {
                PERROR("malloc");
                goto error;
        }

        /* Setup channel name */
        strncpy(ua_chan->name, name, sizeof(ua_chan->name));
        ua_chan->name[sizeof(ua_chan->name) - 1] = '\0';

        ua_chan->enabled = 1;
        ua_chan->handle = -1;
        ua_chan->ctx = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        ua_chan->events = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
        lttng_ht_node_init_str(&ua_chan->node, ua_chan->name);

        CDS_INIT_LIST_HEAD(&ua_chan->streams.head);

        /* Copy attributes */
        if (attr) {
                memcpy(&ua_chan->attr, attr, sizeof(ua_chan->attr));
        }

        DBG3("UST app channel %s allocated", ua_chan->name);

        return ua_chan;

error:
        return NULL;
}

/*
 * Alloc new UST app event.
 */
static
struct ust_app_event *alloc_ust_app_event(char *name,
                struct lttng_ust_event *attr)
{
        struct ust_app_event *ua_event;

        /* Init most of the default value by allocating and zeroing */
        ua_event = zmalloc(sizeof(struct ust_app_event));
        if (ua_event == NULL) {
                PERROR("malloc");
                goto error;
        }

        ua_event->enabled = 1;
        strncpy(ua_event->name, name, sizeof(ua_event->name));
        ua_event->name[sizeof(ua_event->name) - 1] = '\0';
        lttng_ht_node_init_str(&ua_event->node, ua_event->name);

        /* Copy attributes */
        if (attr) {
                memcpy(&ua_event->attr, attr, sizeof(ua_event->attr));
        }

        DBG3("UST app event %s allocated", ua_event->name);

        return ua_event;

error:
        return NULL;
}

/*
 * Alloc new UST app context.
 */
static
struct ust_app_ctx *alloc_ust_app_ctx(struct lttng_ust_context *uctx)
{
        struct ust_app_ctx *ua_ctx;

        ua_ctx = zmalloc(sizeof(struct ust_app_ctx));
        if (ua_ctx == NULL) {
                goto error;
        }

        if (uctx) {
                memcpy(&ua_ctx->ctx, uctx, sizeof(ua_ctx->ctx));
        }

        DBG3("UST app context %d allocated", ua_ctx->ctx.ctx);

error:
        return ua_ctx;
}

/*
 * Find an ust_app using the sock and return it. RCU read side lock must be
 * held before calling this helper function.
 */
static
struct ust_app *find_app_by_sock(int sock)
{
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter 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, sock_n);

error:
        return NULL;
}

/*
 * Create the channel context on the tracer.
 */
static
int create_ust_channel_context(struct ust_app_channel *ua_chan,
                struct ust_app_ctx *ua_ctx, struct ust_app *app)
{
        int ret;

        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;
        }

        ua_ctx->handle = ua_ctx->obj->handle;

        DBG2("UST app context created successfully for channel %s", ua_chan->name);

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Set the filter on the tracer.
 */
static
int set_ust_event_filter(struct ust_app_event *ua_event,
                struct ust_app *app)
{
        int ret;

        health_code_update(&health_thread_cmd);

        if (!ua_event->filter) {
                ret = 0;
                goto error;
        }

        ret = ustctl_set_filter(app->sock, ua_event->filter,
                        ua_event->obj);
        if (ret < 0) {
                goto error;
        }

        DBG2("UST filter set successfully for event %s", ua_event->name);

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Disable the specified event on to UST tracer for the UST session.
 */
static int disable_ust_event(struct ust_app *app,
                struct ust_app_session *ua_sess, struct ust_app_event *ua_event)
{
        int ret;

        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->pid, ua_sess->handle, ret);
                goto error;
        }

        DBG2("UST app event %s disabled successfully for app (pid: %d)",
                        ua_event->attr.name, app->pid);

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Disable the specified channel on to UST tracer for the UST session.
 */
static int disable_ust_channel(struct ust_app *app,
                struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan)
{
        int ret;

        health_code_update(&health_thread_cmd);

        ret = ustctl_disable(app->sock, ua_chan->obj);
        if (ret < 0) {
                ERR("UST app channel %s disable failed for app (pid: %d) "
                                "and session handle %d with ret %d",
                                ua_chan->name, app->pid, ua_sess->handle, ret);
                goto error;
        }

        DBG2("UST app channel %s disabled successfully for app (pid: %d)",
                        ua_chan->name, app->pid);

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Enable the specified channel on to UST tracer for the UST session.
 */
static int enable_ust_channel(struct ust_app *app,
                struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan)
{
        int ret;

        health_code_update(&health_thread_cmd);

        ret = ustctl_enable(app->sock, ua_chan->obj);
        if (ret < 0) {
                ERR("UST app channel %s enable failed for app (pid: %d) "
                                "and session handle %d with ret %d",
                                ua_chan->name, app->pid, ua_sess->handle, ret);
                goto error;
        }

        ua_chan->enabled = 1;

        DBG2("UST app channel %s enabled successfully for app (pid: %d)",
                        ua_chan->name, app->pid);

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Enable the specified event on to UST tracer for the UST session.
 */
static int enable_ust_event(struct ust_app *app,
                struct ust_app_session *ua_sess, struct ust_app_event *ua_event)
{
        int ret;

        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->pid, ua_sess->handle, ret);
                goto error;
        }

        DBG2("UST app event %s enabled successfully for app (pid: %d)",
                        ua_event->attr.name, app->pid);

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Open metadata onto the UST tracer for a UST session.
 */
static int open_ust_metadata(struct ust_app *app,
                struct ust_app_session *ua_sess)
{
        int ret;
        struct lttng_ust_channel_attr uattr;

        health_code_update(&health_thread_cmd);

        uattr.overwrite = ua_sess->metadata->attr.overwrite;
        uattr.subbuf_size = ua_sess->metadata->attr.subbuf_size;
        uattr.num_subbuf = ua_sess->metadata->attr.num_subbuf;
        uattr.switch_timer_interval =
                ua_sess->metadata->attr.switch_timer_interval;
        uattr.read_timer_interval =
                ua_sess->metadata->attr.read_timer_interval;
        uattr.output = ua_sess->metadata->attr.output;

        /* We are going to receive 2 fds, we need to reserve them. */
        ret = lttng_fd_get(LTTNG_FD_APPS, 2);
        if (ret < 0) {
                ERR("Exhausted number of available FD upon metadata open");
                goto error;
        }
        /* UST tracer metadata creation */
        ret = ustctl_open_metadata(app->sock, ua_sess->handle, &uattr,
                        &ua_sess->metadata->obj);
        if (ret < 0) {
                ERR("UST app open metadata failed for app pid:%d with ret %d",
                                app->pid, ret);
                goto error;
        }

        ua_sess->metadata->handle = ua_sess->metadata->obj->handle;

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Create stream onto the UST tracer for a UST session.
 */
static int create_ust_stream(struct ust_app *app,
                struct ust_app_session *ua_sess)
{
        int ret;

        health_code_update(&health_thread_cmd);

        /* We are going to receive 2 fds, we need to reserve them. */
        ret = lttng_fd_get(LTTNG_FD_APPS, 2);
        if (ret < 0) {
                ERR("Exhausted number of available FD upon metadata stream create");
                goto error;
        }
        ret = ustctl_create_stream(app->sock, ua_sess->metadata->obj,
                        &ua_sess->metadata->stream_obj);
        if (ret < 0) {
                ERR("UST create metadata stream failed");
                goto error;
        }

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Create the specified channel onto the UST tracer for a UST session.
 */
static int create_ust_channel(struct ust_app *app,
                struct ust_app_session *ua_sess, struct ust_app_channel *ua_chan)
{
        int ret;

        health_code_update(&health_thread_cmd);

        /* TODO: remove cast and use lttng-ust-abi.h */

        /* We are going to receive 2 fds, we need to reserve them. */
        ret = lttng_fd_get(LTTNG_FD_APPS, 2);
        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->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->pid, app->sock);

        health_code_update(&health_thread_cmd);

        /* If channel is not enabled, disable it on the tracer */
        if (!ua_chan->enabled) {
                ret = disable_ust_channel(app, ua_sess, ua_chan);
                if (ret < 0) {
                        goto error;
                }
        }

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Create the specified event onto the UST tracer for a UST session.
 */
static
int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
                struct ust_app_channel *ua_chan, struct ust_app_event *ua_event)
{
        int ret = 0;

        health_code_update(&health_thread_cmd);

        /* Create UST event on tracer */
        ret = ustctl_create_event(app->sock, &ua_event->attr, ua_chan->obj,
                        &ua_event->obj);
        if (ret < 0) {
                ERR("Error ustctl create event %s for app pid: %d with ret %d",
                                ua_event->attr.name, app->pid, ret);
                goto error;
        }

        ua_event->handle = ua_event->obj->handle;

        DBG2("UST app event %s created successfully for pid:%d",
                        ua_event->attr.name, app->pid);

        health_code_update(&health_thread_cmd);

        /* If event not enabled, disable it on the tracer */
        if (ua_event->enabled == 0) {
                ret = disable_ust_event(app, ua_sess, ua_event);
                if (ret < 0) {
                        /*
                         * If we hit an EPERM, something is wrong with our disable call. If
                         * we get an EEXIST, there is a problem on the tracer side since we
                         * just created it.
                         */
                        switch (ret) {
                        case -LTTNG_UST_ERR_PERM:
                                /* Code flow problem */
                                assert(0);
                        case -LTTNG_UST_ERR_EXIST:
                                /* It's OK for our use case. */
                                ret = 0;
                                break;
                        default:
                                break;
                        }
                        goto error;
                }
        }

error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Copy data between an UST app event and a LTT event.
 */
static void shadow_copy_event(struct ust_app_event *ua_event,
                struct ltt_ust_event *uevent)
{
        strncpy(ua_event->name, uevent->attr.name, sizeof(ua_event->name));
        ua_event->name[sizeof(ua_event->name) - 1] = '\0';

        ua_event->enabled = uevent->enabled;

        /* Copy event attributes */
        memcpy(&ua_event->attr, &uevent->attr, sizeof(ua_event->attr));

        /* Copy filter bytecode */
        if (uevent->filter) {
                ua_event->filter = zmalloc(sizeof(*ua_event->filter) +
                        uevent->filter->len);
                if (!ua_event->filter) {
                        return;
                }
                memcpy(ua_event->filter, uevent->filter,
                        sizeof(*ua_event->filter) + uevent->filter->len);
        }
}

/*
 * Copy data between an UST app channel and a LTT channel.
 */
static void shadow_copy_channel(struct ust_app_channel *ua_chan,
                struct ltt_ust_channel *uchan)
{
        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;
        struct ust_app_ctx *ua_ctx;

        DBG2("UST app shadow copy of channel %s started", ua_chan->name);

        strncpy(ua_chan->name, uchan->name, sizeof(ua_chan->name));
        ua_chan->name[sizeof(ua_chan->name) - 1] = '\0';
        /* Copy event attributes */
        memcpy(&ua_chan->attr, &uchan->attr, sizeof(ua_chan->attr));

        ua_chan->enabled = uchan->enabled;

        cds_lfht_for_each_entry(uchan->ctx->ht, &iter.iter, uctx, node.node) {
                ua_ctx = alloc_ust_app_ctx(&uctx->ctx);
                if (ua_ctx == NULL) {
                        continue;
                }
                lttng_ht_node_init_ulong(&ua_ctx->node,
                                (unsigned long) ua_ctx->ctx.ctx);
                lttng_ht_add_unique_ulong(ua_chan->ctx, &ua_ctx->node);
        }

        /* 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) {
                        DBG2("UST event %s not found on shadow copy channel",
                                        uevent->attr.name);
                        ua_event = alloc_ust_app_event(uevent->attr.name, &uevent->attr);
                        if (ua_event == NULL) {
                                continue;
                        }
                        shadow_copy_event(ua_event, uevent);
                        lttng_ht_add_unique_str(ua_chan->events, &ua_event->node);
                }
        }

        DBG3("UST app shadow copy of channel %s done", ua_chan->name);
}

/*
 * Copy data between a UST app session and a regular LTT session.
 */
static void shadow_copy_session(struct ust_app_session *ua_sess,
                struct ltt_ust_session *usess, struct ust_app *app)
{
        struct lttng_ht_node_str *ua_chan_node;
        struct lttng_ht_iter iter;
        struct ltt_ust_channel *uchan;
        struct ust_app_channel *ua_chan;
        time_t rawtime;
        struct tm *timeinfo;
        char datetime[16];
        int ret;

        /* Get date and time for unique app path */
        time(&rawtime);
        timeinfo = localtime(&rawtime);
        strftime(datetime, sizeof(datetime), "%Y%m%d-%H%M%S", timeinfo);

        DBG2("Shadow copy of session handle %d", ua_sess->handle);

        ua_sess->id = usess->id;
        ua_sess->uid = usess->uid;
        ua_sess->gid = usess->gid;

        ret = snprintf(ua_sess->path, PATH_MAX, "%s-%d-%s/", app->name, app->pid,
                        datetime);
        if (ret < 0) {
                PERROR("asprintf UST shadow copy session");
                /* TODO: We cannot return an error from here.. */
                assert(0);
        }

        /* TODO: support all UST domain */

        /* Iterate over all channels in global domain. */
        cds_lfht_for_each_entry(usess->domain_global.channels->ht, &iter.iter,
                        uchan, node.node) {
                struct lttng_ht_iter uiter;

                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
                ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
                if (ua_chan_node != NULL) {
                        /* Session exist. Contiuing. */
                        continue;
                }

                DBG2("Channel %s not found on shadow session copy, creating it",
                                uchan->name);
                ua_chan = alloc_ust_app_channel(uchan->name, &uchan->attr);
                if (ua_chan == NULL) {
                        /* malloc failed FIXME: Might want to do handle ENOMEM .. */
                        continue;
                }

                shadow_copy_channel(ua_chan, uchan);
                lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
        }
}

/*
 * Lookup sesison wrapper.
 */
static
void __lookup_session_by_app(struct ltt_ust_session *usess,
                        struct ust_app *app, struct lttng_ht_iter *iter)
{
        /* Get right UST app session from app */
        lttng_ht_lookup(app->sessions, (void *)((unsigned long) usess->id), iter);
}

/*
 * Return ust app session from the app session hashtable using the UST session
 * id.
 */
static struct ust_app_session *lookup_session_by_app(
                struct ltt_ust_session *usess, struct ust_app *app)
{
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;

        __lookup_session_by_app(usess, app, &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
                goto error;
        }

        return caa_container_of(node, struct ust_app_session, node);

error:
        return NULL;
}

/*
 * Create a UST session onto the tracer of app and add it the session
 * hashtable.
 *
 * Return ust app session or NULL on error.
 */
static struct ust_app_session *create_ust_app_session(
                struct ltt_ust_session *usess, struct ust_app *app)
{
        int ret;
        struct ust_app_session *ua_sess;

        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->pid, usess->id);
                ua_sess = alloc_ust_app_session();
                if (ua_sess == NULL) {
                        /* Only malloc can failed so something is really wrong */
                        goto end;
                }
                shadow_copy_session(ua_sess, usess, app);
        }

        health_code_update(&health_thread_cmd);

        if (ua_sess->handle == -1) {
                ret = ustctl_create_session(app->sock);
                if (ret < 0) {
                        ERR("Creating session for app pid %d", app->pid);
                        delete_ust_app_session(-1, ua_sess);
                        /* This means that the tracer is gone... */
                        ua_sess = (void*) -1UL;
                        goto end;
                }

                ua_sess->handle = ret;

                /* Add ust app session to app's HT */
                lttng_ht_node_init_ulong(&ua_sess->node, (unsigned long) ua_sess->id);
                lttng_ht_add_unique_ulong(app->sessions, &ua_sess->node);

                DBG2("UST app session created successfully with handle %d", ret);
        }

end:
        health_code_update(&health_thread_cmd);
        return ua_sess;
}

/*
 * Create a context for the channel on the tracer.
 */
static
int create_ust_app_channel_context(struct ust_app_session *ua_sess,
                struct ust_app_channel *ua_chan, 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 channel %s", ua_chan->name);

        lttng_ht_lookup(ua_chan->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_chan->ctx, &ua_ctx->node);

        ret = create_ust_channel_context(ua_chan, ua_ctx, app);
        if (ret < 0) {
                goto error;
        }

error:
        return ret;
}

/*
 * Set UST filter for the event on the tracer.
 */
static
int set_ust_app_event_filter(struct ust_app_session *ua_sess,
                struct ust_app_event *ua_event,
                struct lttng_filter_bytecode *bytecode,
                struct ust_app *app)
{
        int ret = 0;

        DBG2("UST app adding context to event %s", ua_event->name);

        /* Copy filter bytecode */
        ua_event->filter = zmalloc(sizeof(*ua_event->filter) + bytecode->len);
        if (!ua_event->filter) {
                return -ENOMEM;
        }
        memcpy(ua_event->filter, bytecode,
                sizeof(*ua_event->filter) + bytecode->len);
        ret = set_ust_event_filter(ua_event, app);
        if (ret < 0) {
                goto error;
        }

error:
        return ret;
}

/*
 * Enable on the tracer side a ust app event for the session and channel.
 */
static
int enable_ust_app_event(struct ust_app_session *ua_sess,
                struct ust_app_event *ua_event, struct ust_app *app)
{
        int ret;

        ret = enable_ust_event(app, ua_sess, ua_event);
        if (ret < 0) {
                goto error;
        }

        ua_event->enabled = 1;

error:
        return ret;
}

/*
 * Disable on the tracer side a ust app event for the session and channel.
 */
static int disable_ust_app_event(struct ust_app_session *ua_sess,
                struct ust_app_event *ua_event, struct ust_app *app)
{
        int ret;

        ret = disable_ust_event(app, ua_sess, ua_event);
        if (ret < 0) {
                goto error;
        }

        ua_event->enabled = 0;

error:
        return ret;
}

/*
 * Lookup ust app channel for session and disable it on the tracer side.
 */
static
int disable_ust_app_channel(struct ust_app_session *ua_sess,
                struct ust_app_channel *ua_chan, struct ust_app *app)
{
        int ret;

        ret = disable_ust_channel(app, ua_sess, ua_chan);
        if (ret < 0) {
                goto error;
        }

        ua_chan->enabled = 0;

error:
        return ret;
}

/*
 * Lookup ust app channel for session and enable it on the tracer side.
 */
static int enable_ust_app_channel(struct ust_app_session *ua_sess,
                struct ltt_ust_channel *uchan, struct ust_app *app)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_str *ua_chan_node;
        struct ust_app_channel *ua_chan;

        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
        ua_chan_node = lttng_ht_iter_get_node_str(&iter);
        if (ua_chan_node == NULL) {
                DBG2("Unable to find channel %s in ust session id %u",
                                uchan->name, ua_sess->id);
                goto error;
        }

        ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);

        ret = enable_ust_channel(app, ua_sess, ua_chan);
        if (ret < 0) {
                goto error;
        }

error:
        return ret;
}

/*
 * Create UST app channel and create it on the tracer.
 */
static struct ust_app_channel *create_ust_app_channel(
                struct ust_app_session *ua_sess, struct ltt_ust_channel *uchan,
                struct ust_app *app)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_str *ua_chan_node;
        struct ust_app_channel *ua_chan;

        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
        ua_chan_node = lttng_ht_iter_get_node_str(&iter);
        if (ua_chan_node != NULL) {
                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
                goto end;
        }

        ua_chan = alloc_ust_app_channel(uchan->name, &uchan->attr);
        if (ua_chan == NULL) {
                /* Only malloc can fail here */
                goto error;
        }
        shadow_copy_channel(ua_chan, uchan);

        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 != -LTTNG_UST_ERR_EXIST);
                goto error;
        }

        lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);

        DBG2("UST app create channel %s for PID %d completed", ua_chan->name,
                        app->pid);

end:
        return ua_chan;

error:
        delete_ust_app_channel(-1, ua_chan);
        return NULL;
}

/*
 * Create UST app event and create it on the tracer side.
 */
static
int create_ust_app_event(struct ust_app_session *ua_sess,
                struct ust_app_channel *ua_chan, struct ltt_ust_event *uevent,
                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) {
                ret = -EEXIST;
                goto end;
        }

        /* Does not exist so create one */
        ua_event = alloc_ust_app_event(uevent->attr.name, &uevent->attr);
        if (ua_event == NULL) {
                /* Only malloc can failed so something is really wrong */
                ret = -ENOMEM;
                goto end;
        }
        shadow_copy_event(ua_event, uevent);

        /* Create it on the tracer side */
        ret = create_ust_event(app, ua_sess, ua_chan, ua_event);
        if (ret < 0) {
                /* Not found previously means that it does not exist on the tracer */
                assert(ret != -LTTNG_UST_ERR_EXIST);
                goto error;
        }

        lttng_ht_add_unique_str(ua_chan->events, &ua_event->node);

        DBG2("UST app create event %s for PID %d completed", ua_event->name,
                        app->pid);

end:
        return ret;

error:
        /* Valid. Calling here is already in a read side lock */
        delete_ust_app_event(-1, ua_event);
        return ret;
}

/*
 * Create UST metadata and open it on the tracer side.
 */
static int create_ust_app_metadata(struct ust_app_session *ua_sess,
                char *pathname, struct ust_app *app)
{
        int ret = 0;

        if (ua_sess->metadata == NULL) {
                /* Allocate UST metadata */
                ua_sess->metadata = trace_ust_create_metadata(pathname);
                if (ua_sess->metadata == NULL) {
                        /* malloc() failed */
                        goto error;
                }

                ret = open_ust_metadata(app, ua_sess);
                if (ret < 0) {
                        DBG3("Opening metadata failed. Cleaning up memory");

                        /* Cleanup failed metadata struct */
                        free(ua_sess->metadata);
                        /*
                         * This is very important because delete_ust_app_session check if
                         * the pointer is null or not in order to delete the metadata.
                         */
                        ua_sess->metadata = NULL;
                        goto error;
                }

                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 = snprintf(ua_sess->metadata->pathname, PATH_MAX,
                                "%s/metadata", ua_sess->path);
                if (ret < 0) {
                        PERROR("asprintf UST create stream");
                        goto error;
                }

                DBG2("UST metadata stream object created for app pid %d",
                                app->pid);
        } else {
                ERR("Attempting to create stream without metadata opened");
                goto error;
        }

        return 0;

error:
        return -1;
}

/*
 * Return pointer to traceable apps list.
 */
struct lttng_ht *ust_app_get_ht(void)
{
        return ust_app_ht;
}

/*
 * Return ust app pointer or NULL if not found.
 */
struct ust_app *ust_app_find_by_pid(pid_t pid)
{
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;

        rcu_read_lock();
        lttng_ht_lookup(ust_app_ht, (void *)((unsigned long) pid), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
                DBG2("UST app no found with pid %d", pid);
                goto error;
        }
        rcu_read_unlock();

        DBG2("Found UST app by pid %d", pid);

        return caa_container_of(node, struct ust_app, pid_n);

error:
        rcu_read_unlock();
        return NULL;
}

/*
 * Using pid and uid (of the app), allocate a new ust_app struct and
 * add it to the global traceable app list.
 *
 * On success, return 0, else return malloc -ENOMEM, or -EINVAL if app
 * bitness is not supported.
 */
int ust_app_register(struct ust_register_msg *msg, int sock)
{
        struct ust_app *lta;
        int ret;

        if ((msg->bits_per_long == 64 &&
                                (uatomic_read(&ust_consumerd64_fd) == -EINVAL))
                        || (msg->bits_per_long == 32 &&
                                (uatomic_read(&ust_consumerd32_fd) == -EINVAL))) {
                ERR("Registration failed: application \"%s\" (pid: %d) has "
                        "%d-bit long, but no consumerd for this long size is available.\n",
                        msg->name, msg->pid, msg->bits_per_long);
                ret = close(sock);
                if (ret) {
                        PERROR("close");
                }
                lttng_fd_put(LTTNG_FD_APPS, 1);
                return -EINVAL;
        }
        if (msg->major != LTTNG_UST_COMM_MAJOR) {
                ERR("Registration failed: application \"%s\" (pid: %d) has "
                        "communication protocol version %u.%u, but sessiond supports 2.x.\n",
                        msg->name, msg->pid, msg->major, msg->minor);
                ret = close(sock);
                if (ret) {
                        PERROR("close");
                }
                lttng_fd_put(LTTNG_FD_APPS, 1);
                return -EINVAL;
        }
        lta = zmalloc(sizeof(struct ust_app));
        if (lta == NULL) {
                PERROR("malloc");
                return -ENOMEM;
        }

        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;
        strncpy(lta->name, msg->name, sizeof(lta->name));
        lta->name[16] = '\0';
        lta->sessions = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);

        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);

        rcu_read_lock();

        /*
         * On a re-registration, we want to kick out the previous registration of
         * that pid
         */
        lttng_ht_add_replace_ulong(ust_app_ht, &lta->pid_n);

        /*
         * 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->pid, lta->ppid, lta->uid, lta->gid,
                        lta->sock, lta->name, lta->v_major, lta->v_minor);

        return 0;
}

/*
 * Unregister app by removing it from the global traceable app list and freeing
 * the data struct.
 *
 * The socket is already closed at this point so no close to sock.
 */
void ust_app_unregister(int sock)
{
        struct ust_app *lta;
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;
        int ret;

        rcu_read_lock();

        /* Get the node reference for a call_rcu */
        lttng_ht_lookup(ust_app_ht_by_sock, (void *)((unsigned long) sock), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
                ERR("Unable to find app by sock %d", sock);
                goto error;
        }

        lta = caa_container_of(node, struct ust_app, sock_n);

        DBG("PID %d unregistering with sock %d", lta->pid, sock);

        /* Remove application from PID hash table */
        ret = lttng_ht_del(ust_app_ht_by_sock, &iter);
        assert(!ret);

        /* Assign second node for deletion */
        iter.iter.node = &lta->pid_n.node;

        /*
         * 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);
        }

        /* 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)
{
        unsigned long count;

        rcu_read_lock();
        count = lttng_ht_get_count(ust_app_ht);
        rcu_read_unlock();

        return count;
}

/*
 * Fill events array with all events name of all registered apps.
 */
int ust_app_list_events(struct lttng_event **events)
{
        int ret, handle;
        size_t nbmem, count = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;
        struct lttng_event *tmp;

        nbmem = UST_APP_EVENT_LIST_SIZE;
        tmp = zmalloc(nbmem * sizeof(struct lttng_event));
        if (tmp == NULL) {
                PERROR("zmalloc ust app events");
                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_tracepoint_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_list(app->sock);
                if (handle < 0) {
                        ERR("UST app list events getting handle failed for app pid %d",
                                        app->pid);
                        continue;
                }

                while ((ret = ustctl_tracepoint_list_get(app->sock, handle,
                                        &uiter)) != -LTTNG_UST_ERR_NOENT) {
                        health_code_update(&health_thread_cmd);
                        if (count >= nbmem) {
                                /* In case the realloc fails, we free the memory */
                                void *tmp_ptr = (void *) tmp;
                                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) {
                                        PERROR("realloc ust app events");
                                        free(tmp_ptr);
                                        ret = -ENOMEM;
                                        goto rcu_error;
                                }
                        }
                        memcpy(tmp[count].name, uiter.name, LTTNG_UST_SYM_NAME_LEN);
                        tmp[count].loglevel = uiter.loglevel;
                        tmp[count].type = (enum lttng_event_type) LTTNG_UST_TRACEPOINT;
                        tmp[count].pid = app->pid;
                        tmp[count].enabled = -1;
                        count++;
                }
        }

        ret = count;
        *events = tmp;

        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;

        nbmem = UST_APP_EVENT_LIST_SIZE;
        tmp = zmalloc(nbmem * sizeof(struct lttng_event_field));
        if (tmp == 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 *tmp_ptr = (void *) tmp;
                                DBG2("Reallocating event field list from %zu to %zu entries", nbmem,
                                                2 * nbmem);
                                nbmem *= 2;
                                tmp = realloc(tmp, nbmem * sizeof(struct lttng_event_field));
                                if (tmp == NULL) {
                                        PERROR("realloc ust app event fields");
                                        free(tmp_ptr);
                                        ret = -ENOMEM;
                                        goto rcu_error;
                                }
                        }

                        memcpy(tmp[count].field_name, uiter.field_name, LTTNG_UST_SYM_NAME_LEN);
                        tmp[count].type = uiter.type;
                        tmp[count].nowrite = uiter.nowrite;

                        memcpy(tmp[count].event.name, uiter.event_name, LTTNG_UST_SYM_NAME_LEN);
                        tmp[count].event.loglevel = uiter.loglevel;
                        tmp[count].event.type = LTTNG_UST_TRACEPOINT;
                        tmp[count].event.pid = app->pid;
                        tmp[count].event.enabled = -1;
                        count++;
                }
        }

        ret = count;
        *fields = tmp;

        DBG2("UST app list event fields done (%zu events)", count);

rcu_error:
        rcu_read_unlock();
error:
        health_code_update(&health_thread_cmd);
        return ret;
}

/*
 * Free and clean all traceable apps of the global list.
 */
void ust_app_clean_list(void)
{
        int ret;
        struct ust_app *app;
        struct lttng_ht_iter iter;

        DBG2("UST app cleaning registered apps hash table");

        rcu_read_lock();

        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(&app->pid_n.head, delete_ust_app_rcu);
        }

        /* 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_ht);
        lttng_ht_destroy(ust_app_ht_by_sock);

        rcu_read_unlock();
}

/*
 * Init UST app hash table.
 */
void ust_app_ht_alloc(void)
{
        ust_app_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        ust_app_ht_by_sock = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
}

/*
 * For a specific UST session, disable the channel for all registered apps.
 */
int ust_app_disable_channel_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_str *ua_chan_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;

        if (usess == NULL || uchan == NULL) {
                ERR("Disabling UST global channel with NULL values");
                ret = -1;
                goto error;
        }

        DBG2("UST app disabling channel %s from global domain for session id %d",
                        uchan->name, usess->id);

        rcu_read_lock();

        /* For every registered applications */
        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;
                }

                /* Get channel */
                lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &uiter);
                ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
                /* If the session if found for the app, the channel must be there */
                assert(ua_chan_node);

                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);
                /* The channel must not be already disabled */
                assert(ua_chan->enabled == 1);

                /* Disable channel onto application */
                ret = disable_ust_app_channel(ua_sess, ua_chan, app);
                if (ret < 0) {
                        /* XXX: We might want to report this error at some point... */
                        continue;
                }
        }

        rcu_read_unlock();

error:
        return ret;
}

/*
 * For a specific UST session, enable the channel for all registered apps.
 */
int ust_app_enable_channel_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;
        struct ust_app_session *ua_sess;

        if (usess == NULL || uchan == NULL) {
                ERR("Adding UST global channel to NULL values");
                ret = -1;
                goto error;
        }

        DBG2("UST app enabling channel %s to global domain for session id %d",
                        uchan->name, usess->id);

        rcu_read_lock();

        /* For every registered applications */
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                if (!app->compatible) {
                        /*
                         * TODO: In time, we should notice the caller of this error by
                         * telling him that this is a version error.
                         */
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
                if (ua_sess == NULL) {
                        continue;
                }

                /* Enable channel onto application */
                ret = enable_ust_app_channel(ua_sess, uchan, app);
                if (ret < 0) {
                        /* XXX: We might want to report this error at some point... */
                        continue;
                }
        }

        rcu_read_unlock();

error:
        return ret;
}

/*
 * Disable an event in a channel and for a specific session.
 */
int ust_app_disable_event_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent)
{
        int ret = 0;
        struct lttng_ht_iter iter, uiter;
        struct lttng_ht_node_str *ua_chan_node, *ua_event_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;

        DBG("UST app disabling event %s for all apps in channel "
                        "%s for session id %d", uevent->attr.name, uchan->name, usess->id);

        rcu_read_lock();

        /* For all registered applications */
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                if (!app->compatible) {
                        /*
                         * TODO: In time, we should notice the caller of this error by
                         * telling him that this is a version error.
                         */
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
                if (ua_sess == NULL) {
                        /* Next app */
                        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) {
                        DBG2("Channel %s not found in session id %d for app pid %d."
                                        "Skipping", uchan->name, usess->id, app->pid);
                        continue;
                }
                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) {
                        DBG2("Event %s not found in channel %s for app pid %d."
                                        "Skipping", uevent->attr.name, uchan->name, app->pid);
                        continue;
                }
                ua_event = caa_container_of(ua_event_node, struct ust_app_event, node);

                ret = disable_ust_app_event(ua_sess, ua_event, app);
                if (ret < 0) {
                        /* XXX: Report error someday... */
                        continue;
                }
        }

        rcu_read_unlock();

        return ret;
}

/*
 * For a specific UST session and UST channel, the event for all
 * registered apps.
 */
int ust_app_disable_all_event_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan)
{
        int ret = 0;
        struct lttng_ht_iter iter, uiter;
        struct lttng_ht_node_str *ua_chan_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;

        DBG("UST app disabling all event for all apps in channel "
                        "%s for session id %d", uchan->name, usess->id);

        rcu_read_lock();

        /* For all registered applications */
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                if (!app->compatible) {
                        /*
                         * TODO: In time, we should notice the caller of this error by
                         * telling him that this is a version error.
                         */
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
                /* If ua_sess is NULL, there is a code flow error */
                assert(ua_sess);

                /* 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 the channel is not found, there is a code flow error */
                assert(ua_chan_node);

                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);

                /* Disable each events of channel */
                cds_lfht_for_each_entry(ua_chan->events->ht, &uiter.iter, ua_event,
                                node.node) {
                        ret = disable_ust_app_event(ua_sess, ua_event, app);
                        if (ret < 0) {
                                /* XXX: Report error someday... */
                                continue;
                        }
                }
        }

        rcu_read_unlock();

        return ret;
}

/*
 * For a specific UST session, create the channel for all registered apps.
 */
int ust_app_create_channel_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;

        /* Very wrong code flow */
        assert(usess);
        assert(uchan);

        DBG2("UST app adding channel %s to global domain for session id %d",
                        uchan->name, usess->id);

        rcu_read_lock();

        /* For every registered applications */
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                if (!app->compatible) {
                        /*
                         * TODO: In time, we should notice the caller of this error by
                         * telling him that this is a version error.
                         */
                        continue;
                }
                /*
                 * 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) {
                        /* The malloc() failed. */
                        ret = -1;
                        goto error;
                } else if (ua_sess == (void *) -1UL) {
                        /* The application's socket is not valid. Contiuing */
                        ret = -1;
                        continue;
                }

                /* 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() */
                        ret = -1;
                        goto error;
                }
        }

        rcu_read_unlock();

error:
        return ret;
}

/*
 * Enable event for a specific session and channel on the tracer.
 */
int ust_app_enable_event_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent)
{
        int ret = 0;
        struct lttng_ht_iter iter, uiter;
        struct lttng_ht_node_str *ua_chan_node, *ua_event_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;

        DBG("UST app enabling event %s for all apps for session id %d",
                        uevent->attr.name, usess->id);

        /*
         * NOTE: At this point, this function is called only if the session and
         * channel passed are already created for all apps. and enabled on the
         * tracer also.
         */

        rcu_read_lock();

        /* For all registered applications */
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                if (!app->compatible) {
                        /*
                         * TODO: In time, we should notice the caller of this error by
                         * telling him that this is a version error.
                         */
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
                /* If ua_sess is NULL, there is a code flow error */
                assert(ua_sess);

                /* 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 the channel is not found, there is a code flow error */
                assert(ua_chan_node);

                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);

                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) {
                        DBG3("UST app enable event %s not found for app PID %d."
                                        "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) {
                        goto error;
                }
        }

error:
        rcu_read_unlock();
        return ret;
}

/*
 * For a specific existing UST session and UST channel, creates the event for
 * all registered apps.
 */
int ust_app_create_event_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent)
{
        int ret = 0;
        struct lttng_ht_iter iter, uiter;
        struct lttng_ht_node_str *ua_chan_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;

        DBG("UST app creating event %s for all apps for session id %d",
                        uevent->attr.name, usess->id);

        rcu_read_lock();

        /* For all registered applications */
        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                if (!app->compatible) {
                        /*
                         * TODO: In time, we should notice the caller of this error by
                         * telling him that this is a version error.
                         */
                        continue;
                }
                ua_sess = lookup_session_by_app(usess, app);
                /* If ua_sess is NULL, there is a code flow error */
                assert(ua_sess);

                /* 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 the channel is not found, there is a code flow error */
                assert(ua_chan_node);

                ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);

                ret = create_ust_app_event(ua_sess, ua_chan, uevent, app);
                if (ret < 0) {
                        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->pid);
                        continue;
                }
        }

        rcu_read_unlock();

        return ret;
}

/*
 * Start tracing for a specific UST session and app.
 */
int ust_app_start_trace(struct ltt_ust_session *usess, struct ust_app *app)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
        struct ltt_ust_stream *ustream;
        struct consumer_socket *socket;

        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;
        }

        /* Upon restart, we skip the setup, already done */
        if (ua_sess->started) {
                goto skip_setup;
        }

        /* Create directories if consumer is LOCAL and has a path defined. */
        if (usess->consumer->type == CONSUMER_DST_LOCAL &&
                        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;
                        }
                }
        }

        /* Indicate that the session has been started once */
        ua_sess->started = 1;

        ret = create_ust_app_metadata(ua_sess, usess->pathname, app);
        if (ret < 0) {
                ret = LTTNG_ERR_UST_META_FAIL;
                goto error_rcu_unlock;
        }

        /* For each channel */
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
                /* Create all streams */
                while (1) {
                        /* Create UST stream */
                        ustream = zmalloc(sizeof(*ustream));
                        if (ustream == NULL) {
                                PERROR("zmalloc ust stream");
                                goto error_rcu_unlock;
                        }

                        /* 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 stream create");
                                free(ustream);
                                goto error_rcu_unlock;
                        }

                        health_code_update(&health_thread_cmd);

                        ret = ustctl_create_stream(app->sock, ua_chan->obj,
                                        &ustream->obj);
                        if (ret < 0) {
                                /* Got all streams */
                                lttng_fd_put(LTTNG_FD_APPS, 2);
                                free(ustream);
                                ret = LTTNG_ERR_UST_STREAM_FAIL;
                                break;
                        }
                        ustream->handle = ustream->obj->handle;

                        health_code_update(&health_thread_cmd);

                        /* Order is important */
                        cds_list_add_tail(&ustream->list, &ua_chan->streams.head);
                        ret = snprintf(ustream->name, sizeof(ustream->name), "%s_%u",
                                        ua_chan->name, ua_chan->streams.count);
                        ua_chan->streams.count++;
                        if (ret < 0) {
                                PERROR("asprintf UST create stream");
                                /*
                                 * XXX what should we do here with the
                                 * stream ?
                                 */
                                continue;
                        }
                        DBG2("UST stream %d ready (handle: %d)", ua_chan->streams.count,
                                        ustream->handle);
                }

                health_code_update(&health_thread_cmd);
        }

        switch (app->bits_per_long) {
        case 64:
                socket = consumer_find_socket(uatomic_read(&ust_consumerd64_fd),
                                usess->consumer);
                if (socket == NULL) {
                        goto skip_setup;
                }
                break;
        case 32:
                socket = consumer_find_socket(uatomic_read(&ust_consumerd32_fd),
                                usess->consumer);
                if (socket == NULL) {
                        goto skip_setup;
                }
                break;
        default:
                ret = -EINVAL;
                goto error_rcu_unlock;
        }

        /* Setup UST consumer socket and send fds to it */
        ret = ust_consumer_send_session(ua_sess, usess->consumer, socket);
        if (ret < 0) {
                goto error_rcu_unlock;
        }

        health_code_update(&health_thread_cmd);

skip_setup:
        /* This start the UST tracing */
        ret = ustctl_start_session(app->sock, ua_sess->handle);
        if (ret < 0) {
                ERR("Error starting tracing for app pid: %d", app->pid);
                goto error_rcu_unlock;
        }

        health_code_update(&health_thread_cmd);

        /* Quiescent wait after starting trace */
        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;
}

/*
 * Stop tracing for a specific UST session and app.
 */
int ust_app_stop_trace(struct ltt_ust_session *usess, struct ust_app *app)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;

        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;
        }

        /*
         * If started = 0, it means that stop trace has been called for a session
         * that was never started. This is a code flow error and should never
         * happen.
         */
        assert(ua_sess->started == 1);

        health_code_update(&health_thread_cmd);

        /* This inhibits UST tracing */
        ret = ustctl_stop_session(app->sock, ua_sess->handle);
        if (ret < 0) {
                ERR("Error stopping tracing for app pid: %d", app->pid);
                goto error_rcu_unlock;
        }

        health_code_update(&health_thread_cmd);

        /* Quiescent wait after stopping trace */
        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) {
                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->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->sock, ua_sess->metadata->obj);
        if (ret < 0) {
                ERR("UST app PID %d metadata flush failed with ret %d", app->pid,
                                ret);
        }

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)
{
        struct ust_app_session *ua_sess;
        struct lttng_ust_object_data obj;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_ulong *node;
        int ret;

        DBG("Destroy tracing for ust app pid %d", app->pid);

        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;
        }
        ua_sess = caa_container_of(node, struct ust_app_session, node);
        ret = lttng_ht_del(app->sessions, &iter);
        assert(!ret);
        obj.handle = ua_sess->handle;
        obj.shm_fd = -1;
        obj.wait_fd = -1;
        obj.memory_map_size = 0;
        health_code_update(&health_thread_cmd);
        ustctl_release_object(app->sock, &obj);

        health_code_update(&health_thread_cmd);
        delete_ust_app_session(app->sock, ua_sess);

        /* Quiescent wait after stopping trace */
        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;
}

/*
 * Start tracing for the UST session.
 */
int ust_app_start_trace_all(struct ltt_ust_session *usess)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;

        DBG("Starting all UST traces");

        rcu_read_lock();

        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                ret = ust_app_start_trace(usess, app);
                if (ret < 0) {
                        /* Continue to next apps even on error */
                        continue;
                }
        }

        rcu_read_unlock();

        return 0;
}

/*
 * Start tracing for the UST session.
 */
int ust_app_stop_trace_all(struct ltt_ust_session *usess)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;

        DBG("Stopping all UST traces");

        rcu_read_lock();

        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 */
                        continue;
                }
        }

        rcu_read_unlock();

        return 0;
}

/*
 * Destroy app UST session.
 */
int ust_app_destroy_trace_all(struct ltt_ust_session *usess)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct ust_app *app;

        DBG("Destroy all UST traces");

        rcu_read_lock();

        cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
                ret = ust_app_destroy_trace(usess, app);
                if (ret < 0) {
                        /* Continue to next apps even on error */
                        continue;
                }
        }

        rcu_read_unlock();

        return 0;
}

/*
 * Add channels/events from UST global domain to registered apps at sock.
 */
void ust_app_global_update(struct ltt_ust_session *usess, int sock)
{
        int ret = 0;
        struct lttng_ht_iter iter, uiter, iter_ctx;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        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;
        }

        DBG2("UST app global update for app sock %d for session id %d", sock,
                        usess->id);

        rcu_read_lock();

        app = find_app_by_sock(sock);
        if (app == NULL) {
                ERR("Failed to update app sock %d", sock);
                goto error;
        }

        if (!app->compatible) {
                goto error;
        }

        ua_sess = create_ust_app_session(usess, app);
        if (ua_sess == NULL || ua_sess == (void *) -1UL) {
                /* Tracer is gone for this session and has been freed */
                goto error;
        }

        /*
         * 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
         * ltt ust session.
         */
        cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
                        node.node) {
                ret = create_ust_channel(app, ua_sess, ua_chan);
                if (ret < 0) {
                        /* FIXME: Should we quit here or continue... */
                        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) {
                        ret = create_ust_event(app, ua_sess, ua_chan, ua_event);
                        if (ret < 0) {
                                /* FIXME: Should we quit here or continue... */
                                continue;
                        }

                        ret = set_ust_event_filter(ua_event, app);
                        if (ret < 0) {
                                /* FIXME: Should we quit here or continue... */
                                continue;
                        }
                }
        }

        if (usess->start_trace) {
                ret = ust_app_start_trace(usess, app);
                if (ret < 0) {
                        goto error;
                }

                DBG2("UST trace started for app pid %d", app->pid);
        }

error:
        rcu_read_unlock();
        return;
}

/*
 * Add context to a specific channel for global UST domain.
 */
int ust_app_add_ctx_channel_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan, struct ltt_ust_context *uctx)
{
        int ret = 0;
        struct lttng_ht_node_str *ua_chan_node;
        struct lttng_ht_iter iter, uiter;
        struct ust_app_channel *ua_chan = NULL;
        struct ust_app_session *ua_sess;
        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;
                }
                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) {
                        continue;
                }
        }

        rcu_read_unlock();
        return ret;
}

/*
 * Add context to a specific event in a channel for global UST domain.
 */
int ust_app_set_filter_event_glb(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent,
                struct lttng_filter_bytecode *bytecode)
{
        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, 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;
                }

                /* 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);

                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 = set_ust_app_event_filter(ua_sess, ua_event, bytecode, app);
                if (ret < 0) {
                        continue;
                }
        }

        rcu_read_unlock();
        return ret;
}

/*
 * Enable event for a channel from a UST session for a specific PID.
 */
int ust_app_enable_event_pid(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent, pid_t pid)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_str *ua_chan_node, *ua_event_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;

        DBG("UST app enabling event %s for PID %d", uevent->attr.name, pid);

        rcu_read_lock();

        app = ust_app_find_by_pid(pid);
        if (app == NULL) {
                ERR("UST app enable event per PID %d not found", pid);
                ret = -1;
                goto 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);

        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
        ua_chan_node = lttng_ht_iter_get_node_str(&iter);
        /* If the channel is not found, there is a code flow error */
        assert(ua_chan_node);

        ua_chan = caa_container_of(ua_chan_node, struct ust_app_channel, node);

        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) {
                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;
                }
        }

error:
        rcu_read_unlock();
        return ret;
}

/*
 * Disable event for a channel from a UST session for a specific PID.
 */
int ust_app_disable_event_pid(struct ltt_ust_session *usess,
                struct ltt_ust_channel *uchan, struct ltt_ust_event *uevent, pid_t pid)
{
        int ret = 0;
        struct lttng_ht_iter iter;
        struct lttng_ht_node_str *ua_chan_node, *ua_event_node;
        struct ust_app *app;
        struct ust_app_session *ua_sess;
        struct ust_app_channel *ua_chan;
        struct ust_app_event *ua_event;

        DBG("UST app disabling event %s for PID %d", uevent->attr.name, pid);

        rcu_read_lock();

        app = ust_app_find_by_pid(pid);
        if (app == NULL) {
                ERR("UST app disable event per PID %d not found", pid);
                ret = -1;
                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);

        /* Lookup channel in the ust app session */
        lttng_ht_lookup(ua_sess->channels, (void *)uchan->name, &iter);
        ua_chan_node = lttng_ht_iter_get_node_str(&iter);
        if (ua_chan_node == NULL) {
                /* Channel does not exist, skip disabling */
                goto error;
        }
        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) {
                /* Event does not exist, skip disabling */
                goto error;
        }
        ua_event = caa_container_of(ua_event_node, struct ust_app_event, node);

        ret = disable_ust_app_event(ua_sess, ua_event, app);
        if (ret < 0) {
                goto error;
        }

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;
}