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

/*
 * Copyright (C) 2013 - David Goulet <dgoulet@efficios.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License, version 2 only, as
 * published by the Free Software Foundation.
 *
 * 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
#define _LGPL_SOURCE
#include <assert.h>
#include <urcu/uatomic.h>

#include <common/common.h>
#include <common/sessiond-comm/agent.h>

#include <common/compat/endian.h>

#include "agent.h"
#include "ust-app.h"
#include "utils.h"

/*
 * Match function for the events hash table lookup by name.
 */
static int ht_match_event_by_name(struct cds_lfht_node *node,
                const void *_key)
{
        struct agent_event *event;
        const struct agent_ht_key *key;

        assert(node);
        assert(_key);

        event = caa_container_of(node, struct agent_event, node.node);
        key = _key;

        /* Match 1 elements of the key: name. */

        /* Event name */
        if (strncmp(event->name, key->name, sizeof(event->name)) != 0) {
                goto no_match;
        }
        /* Match. */
        return 1;

no_match:
        return 0;
}

/*
 * Match function for the events hash table lookup by name and loglevel.
 */
static int ht_match_event(struct cds_lfht_node *node,
                const void *_key)
{
        struct agent_event *event;
        const struct agent_ht_key *key;
        int ll_match;

        assert(node);
        assert(_key);

        event = caa_container_of(node, struct agent_event, node.node);
        key = _key;

        /* Match 2 elements of the key: name and loglevel. */

        /* Event name */
        if (strncmp(event->name, key->name, sizeof(event->name)) != 0) {
                goto no_match;
        }

        /* Event loglevel value and type. */
        ll_match = loglevels_match(event->loglevel_type,
                event->loglevel_value, key->loglevel_type,
                key->loglevel_value, LTTNG_EVENT_LOGLEVEL_ALL);

        if (!ll_match) {
                goto no_match;
        }

        /* Filter expression */
        if (strncmp(event->filter_expression, key->filter_expression,
                        strlen(event->filter_expression)) != 0) {
                goto no_match;
        }

        return 1;

no_match:
        return 0;
}

/*
 * Add unique agent event based on the event name and loglevel.
 */
static void add_unique_agent_event(struct lttng_ht *ht,
                struct agent_event *event)
{
        struct cds_lfht_node *node_ptr;
        struct agent_ht_key key;

        assert(ht);
        assert(ht->ht);
        assert(event);

        key.name = event->name;
        key.loglevel_value = event->loglevel_value;
        key.loglevel_type = event->loglevel_type;
        key.filter_expression = event->filter_expression;

        node_ptr = cds_lfht_add_unique(ht->ht,
                        ht->hash_fct(event->node.key, lttng_ht_seed),
                        ht_match_event, &key, &event->node.node);
        assert(node_ptr == &event->node.node);
}

/*
 * URCU delayed agent event reclaim.
 */
static void destroy_event_agent_rcu(struct rcu_head *head)
{
        struct lttng_ht_node_str *node =
                caa_container_of(head, struct lttng_ht_node_str, head);
        struct agent_event *event =
                caa_container_of(node, struct agent_event, node);

        agent_destroy_event(event);
}

/*
 * URCU delayed agent app reclaim.
 */
static void destroy_app_agent_rcu(struct rcu_head *head)
{
        struct lttng_ht_node_ulong *node =
                caa_container_of(head, struct lttng_ht_node_ulong, head);
        struct agent_app *app =
                caa_container_of(node, struct agent_app, node);

        free(app);
}

/*
 * Communication with the agent. Send the message header to the given socket in
 * big endian.
 *
 * Return 0 on success or else a negative errno message of sendmsg() op.
 */
static int send_header(struct lttcomm_sock *sock, uint64_t data_size,
                uint32_t cmd, uint32_t cmd_version)
{
        int ret;
        ssize_t size;
        struct lttcomm_agent_hdr msg;

        assert(sock);

        memset(&msg, 0, sizeof(msg));
        msg.data_size = htobe64(data_size);
        msg.cmd = htobe32(cmd);
        msg.cmd_version = htobe32(cmd_version);

        size = sock->ops->sendmsg(sock, &msg, sizeof(msg), 0);
        if (size < sizeof(msg)) {
                ret = -errno;
                goto error;
        }
        ret = 0;

error:
        return ret;
}

/*
 * Communication call with the agent. Send the payload to the given socket. The
 * header MUST be sent prior to this call.
 *
 * Return 0 on success or else a negative errno value of sendmsg() op.
 */
static int send_payload(struct lttcomm_sock *sock, void *data,
                size_t size)
{
        int ret;
        ssize_t len;

        assert(sock);
        assert(data);

        len = sock->ops->sendmsg(sock, data, size, 0);
        if (len < size) {
                ret = -errno;
                goto error;
        }
        ret = 0;

error:
        return ret;
}

/*
 * Communication call with the agent. Receive reply from the agent using the
 * given socket.
 *
 * Return 0 on success or else a negative errno value from recvmsg() op.
 */
static int recv_reply(struct lttcomm_sock *sock, void *buf, size_t size)
{
        int ret;
        ssize_t len;

        assert(sock);
        assert(buf);

        len = sock->ops->recvmsg(sock, buf, size, 0);
        if (len < size) {
                ret = -errno;
                goto error;
        }
        ret = 0;

error:
        return ret;
}

/*
 * Internal event listing for a given app. Populate events.
 *
 * Return number of element in the list or else a negative LTTNG_ERR* code.
 * On success, the caller is responsible for freeing the memory
 * allocated for "events".
 */
static ssize_t list_events(struct agent_app *app, struct lttng_event **events)
{
        int ret, i, len = 0, offset = 0;
        uint32_t nb_event;
        size_t data_size;
        struct lttng_event *tmp_events = NULL;
        struct lttcomm_agent_list_reply *reply = NULL;
        struct lttcomm_agent_list_reply_hdr reply_hdr;

        assert(app);
        assert(app->sock);
        assert(events);

        DBG2("Agent listing events for app pid: %d and socket %d", app->pid,
                        app->sock->fd);

        ret = send_header(app->sock, 0, AGENT_CMD_LIST, 0);
        if (ret < 0) {
                goto error_io;
        }

        /* Get list header so we know how much we'll receive. */
        ret = recv_reply(app->sock, &reply_hdr, sizeof(reply_hdr));
        if (ret < 0) {
                goto error_io;
        }

        switch (be32toh(reply_hdr.ret_code)) {
        case AGENT_RET_CODE_SUCCESS:
                data_size = be32toh(reply_hdr.data_size) + sizeof(*reply);
                break;
        default:
                ERR("Agent returned an unknown code: %" PRIu32,
                                be32toh(reply_hdr.ret_code));
                ret = LTTNG_ERR_FATAL;
                goto error;
        }

        reply = zmalloc(data_size);
        if (!reply) {
                ret = LTTNG_ERR_NOMEM;
                goto error;
        }

        /* Get the list with the appropriate data size. */
        ret = recv_reply(app->sock, reply, data_size);
        if (ret < 0) {
                goto error_io;
        }

        nb_event = be32toh(reply->nb_event);
        tmp_events = zmalloc(sizeof(*tmp_events) * nb_event);
        if (!tmp_events) {
                ret = LTTNG_ERR_NOMEM;
                goto error;
        }

        for (i = 0; i < nb_event; i++) {
                offset += len;
                if (lttng_strncpy(tmp_events[i].name, reply->payload + offset,
                                sizeof(tmp_events[i].name))) {
                        ret = LTTNG_ERR_INVALID;
                        goto error;
                }
                tmp_events[i].pid = app->pid;
                tmp_events[i].enabled = -1;
                len = strlen(reply->payload + offset) + 1;
        }

        *events = tmp_events;

        free(reply);
        return nb_event;

error_io:
        ret = LTTNG_ERR_UST_LIST_FAIL;
error:
        free(reply);
        free(tmp_events);
        return -ret;

}

/*
 * Internal enable agent event on a agent application. This function
 * communicates with the agent to enable a given event.
 *
 * Return LTTNG_OK on success or else a LTTNG_ERR* code.
 */
static int enable_event(struct agent_app *app, struct agent_event *event)
{
        int ret;
        uint64_t data_size;
        struct lttcomm_agent_enable msg;
        struct lttcomm_agent_generic_reply reply;

        assert(app);
        assert(app->sock);
        assert(event);

        DBG2("Agent enabling event %s for app pid: %d and socket %d", event->name,
                        app->pid, app->sock->fd);

        data_size = sizeof(msg);

        ret = send_header(app->sock, data_size, AGENT_CMD_ENABLE, 0);
        if (ret < 0) {
                goto error_io;
        }

        memset(&msg, 0, sizeof(msg));
        msg.loglevel_value = event->loglevel_value;
        msg.loglevel_type = event->loglevel_type;
        strncpy(msg.name, event->name, sizeof(msg.name));
        ret = send_payload(app->sock, &msg, sizeof(msg));
        if (ret < 0) {
                goto error_io;
        }

        ret = recv_reply(app->sock, &reply, sizeof(reply));
        if (ret < 0) {
                goto error_io;
        }

        switch (be32toh(reply.ret_code)) {
        case AGENT_RET_CODE_SUCCESS:
                break;
        case AGENT_RET_CODE_UNKNOWN_NAME:
                ret = LTTNG_ERR_UST_EVENT_NOT_FOUND;
                goto error;
        default:
                ERR("Agent returned an unknown code: %" PRIu32,
                                be32toh(reply.ret_code));
                ret = LTTNG_ERR_FATAL;
                goto error;
        }

        return LTTNG_OK;

error_io:
        ret = LTTNG_ERR_UST_ENABLE_FAIL;
error:
        return ret;
}

/*
 * Internal disable agent event call on a agent application. This function
 * communicates with the agent to disable a given event.
 *
 * Return LTTNG_OK on success or else a LTTNG_ERR* code.
 */
static int disable_event(struct agent_app *app, struct agent_event *event)
{
        int ret;
        uint64_t data_size;
        struct lttcomm_agent_disable msg;
        struct lttcomm_agent_generic_reply reply;

        assert(app);
        assert(app->sock);
        assert(event);

        DBG2("Agent disabling event %s for app pid: %d and socket %d", event->name,
                        app->pid, app->sock->fd);

        data_size = sizeof(msg);
        memset(&msg, 0, sizeof(msg));
        if (lttng_strncpy(msg.name, event->name, sizeof(msg.name))) {
                ret = LTTNG_ERR_INVALID;
                goto error;
        }

        ret = send_header(app->sock, data_size, AGENT_CMD_DISABLE, 0);
        if (ret < 0) {
                goto error_io;
        }

        ret = send_payload(app->sock, &msg, sizeof(msg));
        if (ret < 0) {
                goto error_io;
        }

        ret = recv_reply(app->sock, &reply, sizeof(reply));
        if (ret < 0) {
                goto error_io;
        }

        switch (be32toh(reply.ret_code)) {
        case AGENT_RET_CODE_SUCCESS:
                break;
        case AGENT_RET_CODE_UNKNOWN_NAME:
                ret = LTTNG_ERR_UST_EVENT_NOT_FOUND;
                goto error;
        default:
                ERR("Agent returned an unknown code: %" PRIu32,
                                be32toh(reply.ret_code));
                ret = LTTNG_ERR_FATAL;
                goto error;
        }

        return LTTNG_OK;

error_io:
        ret = LTTNG_ERR_UST_DISABLE_FAIL;
error:
        return ret;
}

/*
 * Send back the registration DONE command to a given agent application.
 *
 * Return 0 on success or else a negative value.
 */
int agent_send_registration_done(struct agent_app *app)
{
        assert(app);
        assert(app->sock);

        DBG("Agent sending registration done to app socket %d", app->sock->fd);

        return send_header(app->sock, 0, AGENT_CMD_REG_DONE, 0);
}

/*
 * Enable agent event on every agent applications registered with the session
 * daemon.
 *
 * Return LTTNG_OK on success or else a LTTNG_ERR* code.
 */
int agent_enable_event(struct agent_event *event,
                enum lttng_domain_type domain)
{
        int ret;
        struct agent_app *app;
        struct lttng_ht_iter iter;

        assert(event);

        rcu_read_lock();

        cds_lfht_for_each_entry(agent_apps_ht_by_sock->ht, &iter.iter, app,
                        node.node) {
                if (app->domain != domain) {
                        continue;
                }

                /* Enable event on agent application through TCP socket. */
                ret = enable_event(app, event);
                if (ret != LTTNG_OK) {
                        goto error;
                }
        }

        event->enabled = 1;
        ret = LTTNG_OK;

error:
        rcu_read_unlock();
        return ret;
}

/*
 * Disable agent event on every agent applications registered with the session
 * daemon.
 *
 * Return LTTNG_OK on success or else a LTTNG_ERR* code.
 */
int agent_disable_event(struct agent_event *event,
                enum lttng_domain_type domain)
{
        int ret = LTTNG_OK;
        struct agent_app *app;
        struct lttng_ht_iter iter;

        assert(event);
        if (!event->enabled) {
                goto end;
        }

        rcu_read_lock();

        cds_lfht_for_each_entry(agent_apps_ht_by_sock->ht, &iter.iter, app,
                        node.node) {
                if (app->domain != domain) {
                        continue;
                }

                /* Enable event on agent application through TCP socket. */
                ret = disable_event(app, event);
                if (ret != LTTNG_OK) {
                        goto error;
                }
        }

        event->enabled = 0;

error:
        rcu_read_unlock();
end:
        return ret;
}

/*
 * Ask every agent for the list of possible event. Events is allocated with the
 * events of every agent application.
 *
 * Return the number of events or else a negative value.
 */
int agent_list_events(struct lttng_event **events,
                enum lttng_domain_type domain)
{
        int ret;
        size_t nbmem, count = 0;
        struct agent_app *app;
        struct lttng_event *tmp_events = NULL;
        struct lttng_ht_iter iter;

        assert(events);

        DBG2("Agent listing events for domain %d", domain);

        nbmem = UST_APP_EVENT_LIST_SIZE;
        tmp_events = zmalloc(nbmem * sizeof(*tmp_events));
        if (!tmp_events) {
                PERROR("zmalloc agent list events");
                ret = -ENOMEM;
                goto error;
        }

        rcu_read_lock();
        cds_lfht_for_each_entry(agent_apps_ht_by_sock->ht, &iter.iter, app,
                        node.node) {
                ssize_t nb_ev;
                struct lttng_event *agent_events;

                /* Skip domain not asked by the list. */
                if (app->domain != domain) {
                        continue;
                }

                nb_ev = list_events(app, &agent_events);
                if (nb_ev < 0) {
                        ret = nb_ev;
                        goto error_unlock;
                }

                if (count + nb_ev > nbmem) {
                        /* In case the realloc fails, we free the memory */
                        struct lttng_event *new_tmp_events;
                        size_t new_nbmem;

                        new_nbmem = max_t(size_t, count + nb_ev, nbmem << 1);
                        DBG2("Reallocating agent event list from %zu to %zu entries",
                                        nbmem, new_nbmem);
                        new_tmp_events = realloc(tmp_events,
                                new_nbmem * sizeof(*new_tmp_events));
                        if (!new_tmp_events) {
                                PERROR("realloc agent events");
                                ret = -ENOMEM;
                                free(agent_events);
                                goto error_unlock;
                        }
                        /* Zero the new memory */
                        memset(new_tmp_events + nbmem, 0,
                                (new_nbmem - nbmem) * sizeof(*new_tmp_events));
                        nbmem = new_nbmem;
                        tmp_events = new_tmp_events;
                }
                memcpy(tmp_events + count, agent_events,
                        nb_ev * sizeof(*tmp_events));
                free(agent_events);
                count += nb_ev;
        }
        rcu_read_unlock();

        ret = count;
        *events = tmp_events;
        return ret;

error_unlock:
        rcu_read_unlock();
error:
        free(tmp_events);
        return ret;
}

/*
 * Create a agent app object using the given PID.
 *
 * Return newly allocated object or else NULL on error.
 */
struct agent_app *agent_create_app(pid_t pid, enum lttng_domain_type domain,
                struct lttcomm_sock *sock)
{
        struct agent_app *app;

        assert(sock);

        app = zmalloc(sizeof(*app));
        if (!app) {
                PERROR("zmalloc agent create");
                goto error;
        }

        app->pid = pid;
        app->domain = domain;
        app->sock = sock;
        lttng_ht_node_init_ulong(&app->node, (unsigned long) app->sock->fd);

error:
        return app;
}

/*
 * Lookup agent app by socket in the global hash table.
 *
 * RCU read side lock MUST be acquired.
 *
 * Return object if found else NULL.
 */
struct agent_app *agent_find_app_by_sock(int sock)
{
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;
        struct agent_app *app;

        assert(sock >= 0);

        lttng_ht_lookup(agent_apps_ht_by_sock, (void *)((unsigned long) sock), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node == NULL) {
                goto error;
        }
        app = caa_container_of(node, struct agent_app, node);

        DBG3("Agent app pid %d found by sock %d.", app->pid, sock);
        return app;

error:
        DBG3("Agent app NOT found by sock %d.", sock);
        return NULL;
}

/*
 * Add agent application object to the global hash table.
 */
void agent_add_app(struct agent_app *app)
{
        assert(app);

        DBG3("Agent adding app sock: %d and pid: %d to ht", app->sock->fd, app->pid);

        rcu_read_lock();
        lttng_ht_add_unique_ulong(agent_apps_ht_by_sock, &app->node);
        rcu_read_unlock();
}

/*
 * Delete agent application from the global hash table.
 *
 * rcu_read_lock() must be held by the caller.
 */
void agent_delete_app(struct agent_app *app)
{
        int ret;
        struct lttng_ht_iter iter;

        assert(app);

        DBG3("Agent deleting app pid: %d and sock: %d", app->pid, app->sock->fd);

        iter.iter.node = &app->node.node;
        ret = lttng_ht_del(agent_apps_ht_by_sock, &iter);
        assert(!ret);
}

/*
 * Destroy a agent application object by detaching it from its corresponding
 * UST app if one is connected by closing the socket. Finally, perform a
 * delayed memory reclaim.
 */
void agent_destroy_app(struct agent_app *app)
{
        assert(app);

        if (app->sock) {
                app->sock->ops->close(app->sock);
                lttcomm_destroy_sock(app->sock);
        }

        call_rcu(&app->node.head, destroy_app_agent_rcu);
}

/*
 * Initialize an already allocated agent object.
 *
 * Return 0 on success or else a negative errno value.
 */
int agent_init(struct agent *agt)
{
        int ret;

        assert(agt);

        agt->events = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
        if (!agt->events) {
                ret = -ENOMEM;
                goto error;
        }
        lttng_ht_node_init_u64(&agt->node, agt->domain);

        return 0;

error:
        return ret;
}

/*
 * Add agent object to the given hash table.
 */
void agent_add(struct agent *agt, struct lttng_ht *ht)
{
        assert(agt);
        assert(ht);

        DBG3("Agent adding from domain %d", agt->domain);

        rcu_read_lock();
        lttng_ht_add_unique_u64(ht, &agt->node);
        rcu_read_unlock();
}

/*
 * Create an agent object for the given domain.
 *
 * Return the allocated agent or NULL on error.
 */
struct agent *agent_create(enum lttng_domain_type domain)
{
        int ret;
        struct agent *agt;

        agt = zmalloc(sizeof(*agt));
        if (!agt) {
                goto error;
        }
        agt->domain = domain;

        ret = agent_init(agt);
        if (ret < 0) {
                free(agt);
                agt = NULL;
                goto error;
        }

error:
        return agt;
}

/*
 * Create a newly allocated agent event data structure.
 * Ownership of filter_expression is taken.
 *
 * Return a new object else NULL on error.
 */
struct agent_event *agent_create_event(const char *name,
                enum lttng_loglevel_type loglevel_type, int loglevel_value,
                struct lttng_filter_bytecode *filter, char *filter_expression)
{
        struct agent_event *event = NULL;

        DBG3("Agent create new event with name %s, loglevel type %d, \
                        loglevel value %d and filter %s",
                        name, loglevel_type, loglevel_value,
                        filter_expression ? filter_expression : "NULL");

        if (!name) {
                ERR("Failed to create agent event; no name provided.");
                goto error;
        }

        event = zmalloc(sizeof(*event));
        if (!event) {
                goto error;
        }

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

        event->loglevel_value = loglevel_value;
        event->loglevel_type = loglevel_type;
        event->filter = filter;
        event->filter_expression = filter_expression;
error:
        return event;
}

/*
 * Unique add of a agent event to an agent object.
 */
void agent_add_event(struct agent_event *event, struct agent *agt)
{
        assert(event);
        assert(agt);
        assert(agt->events);

        DBG3("Agent adding event %s", event->name);

        rcu_read_lock();
        add_unique_agent_event(agt->events, event);
        rcu_read_unlock();
        agt->being_used = 1;
}

/*
 * Find multiple agent events sharing the given name.
 *
 * RCU read side lock MUST be acquired. It must be held for the
 * duration of the iteration.
 *
 * Sets the given iterator.
 */
void agent_find_events_by_name(const char *name, struct agent *agt,
                struct lttng_ht_iter* iter)
{
        struct lttng_ht *ht;
        struct agent_ht_key key;

        assert(name);
        assert(agt);
        assert(agt->events);
        assert(iter);

        ht = agt->events;
        key.name = name;

        cds_lfht_lookup(ht->ht, ht->hash_fct((void *) name, lttng_ht_seed),
                        ht_match_event_by_name, &key, &iter->iter);
}

/*
 * Get the next agent event duplicate by name. This should be called
 * after a call to agent_find_events_by_name() to iterate on events.
 *
 * The RCU read lock must be held during the iteration and for as long
 * as the object the iterator points to remains in use.
 */
void agent_event_next_duplicate(const char *name,
                struct agent *agt, struct lttng_ht_iter* iter)
{
        struct agent_ht_key key;

        key.name = name;

        cds_lfht_next_duplicate(agt->events->ht, ht_match_event_by_name,
                &key, &iter->iter);
}

/*
 * Find a agent event in the given agent using name, loglevel and filter.
 *
 * RCU read side lock MUST be acquired.
 *
 * Return object if found else NULL.
 */
struct agent_event *agent_find_event(const char *name,
                enum lttng_loglevel_type loglevel_type, int loglevel_value,
                char *filter_expression, struct agent *agt)
{
        struct lttng_ht_node_str *node;
        struct lttng_ht_iter iter;
        struct lttng_ht *ht;
        struct agent_ht_key key;

        assert(name);
        assert(agt);
        assert(agt->events);

        ht = agt->events;
        key.name = name;
        key.loglevel_value = loglevel_value;
        key.loglevel_type = loglevel_type;
        key.filter_expression = filter_expression;

        cds_lfht_lookup(ht->ht, ht->hash_fct((void *) name, lttng_ht_seed),
                        ht_match_event, &key, &iter.iter);
        node = lttng_ht_iter_get_node_str(&iter);
        if (node == NULL) {
                goto error;
        }

        DBG3("Agent event found %s.", name);
        return caa_container_of(node, struct agent_event, node);

error:
        DBG3("Agent event NOT found %s.", name);
        return NULL;
}

/*
 * Free given agent event. This event must not be globally visible at this
 * point (only expected to be used on failure just after event creation). After
 * this call, the pointer is not usable anymore.
 */
void agent_destroy_event(struct agent_event *event)
{
        assert(event);

        free(event->filter);
        free(event->filter_expression);
        free(event->exclusion);
        free(event);
}

/*
 * Destroy an agent completely.
 */
void agent_destroy(struct agent *agt)
{
        struct lttng_ht_node_str *node;
        struct lttng_ht_iter iter;

        assert(agt);

        DBG3("Agent destroy");

        /*
         * Just ignore if no events hash table exists. This is possible if for
         * instance an agent object was allocated but not initialized.
         */
        if (!agt->events) {
                return;
        }

        rcu_read_lock();
        cds_lfht_for_each_entry(agt->events->ht, &iter.iter, node, node) {
                int ret;
                struct agent_event *event;

                /*
                 * When destroying an event, we have to try to disable it on the agent
                 * side so the event stops generating data. The return value is not
                 * important since we have to continue anyway destroying the object.
                 */
                event = caa_container_of(node, struct agent_event, node);
                (void) agent_disable_event(event, agt->domain);

                ret = lttng_ht_del(agt->events, &iter);
                assert(!ret);
                call_rcu(&node->head, destroy_event_agent_rcu);
        }
        rcu_read_unlock();

        ht_cleanup_push(agt->events);
        free(agt);
}

/*
 * Allocate agent_apps_ht_by_sock.
 */
int agent_app_ht_alloc(void)
{
        int ret = 0;

        agent_apps_ht_by_sock = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        if (!agent_apps_ht_by_sock) {
                ret = -1;
        }

        return ret;
}

/*
 * Destroy a agent application by socket.
 */
void agent_destroy_app_by_sock(int sock)
{
        struct agent_app *app;

        assert(sock >= 0);

        /*
         * Not finding an application is a very important error that should NEVER
         * happen. The hash table deletion is ONLY done through this call when the
         * main sessiond thread is torn down.
         */
        rcu_read_lock();
        app = agent_find_app_by_sock(sock);
        assert(app);

        /* RCU read side lock is assumed to be held by this function. */
        agent_delete_app(app);

        /* The application is freed in a RCU call but the socket is closed here. */
        agent_destroy_app(app);
        rcu_read_unlock();
}

/*
 * Clean-up the agent app hash table and destroy it.
 */
void agent_app_ht_clean(void)
{
        struct lttng_ht_node_ulong *node;
        struct lttng_ht_iter iter;

        if (!agent_apps_ht_by_sock) {
                return;
        }
        rcu_read_lock();
        cds_lfht_for_each_entry(agent_apps_ht_by_sock->ht, &iter.iter, node, node) {
                struct agent_app *app;

                app = caa_container_of(node, struct agent_app, node);
                agent_destroy_app_by_sock(app->sock->fd);
        }
        rcu_read_unlock();

        lttng_ht_destroy(agent_apps_ht_by_sock);
}

/*
 * Update a agent application (given socket) using the given agent.
 *
 * Note that this function is most likely to be used with a tracing session
 * thus the caller should make sure to hold the appropriate lock(s).
 */
void agent_update(struct agent *agt, int sock)
{
        int ret;
        struct agent_app *app;
        struct agent_event *event;
        struct lttng_ht_iter iter;

        assert(agt);
        assert(sock >= 0);

        DBG("Agent updating app socket %d", sock);

        rcu_read_lock();
        cds_lfht_for_each_entry(agt->events->ht, &iter.iter, event, node.node) {
                /* Skip event if disabled. */
                if (!event->enabled) {
                        continue;
                }

                app = agent_find_app_by_sock(sock);
                /*
                 * We are in the registration path thus if the application is gone,
                 * there is a serious code flow error.
                 */
                assert(app);

                ret = enable_event(app, event);
                if (ret != LTTNG_OK) {
                        DBG2("Agent update unable to enable event %s on app pid: %d sock %d",
                                        event->name, app->pid, app->sock->fd);
                        /* Let's try the others here and don't assume the app is dead. */
                        continue;
                }
        }
        rcu_read_unlock();
}