docs: Add supported versions and fix-backport policy

[lttng-tools.git] / src / bin / lttng-sessiond / session.cpp

/*
 * Copyright (C) 2011 EfficiOS Inc.
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 */

#define _LGPL_SOURCE
#include "cmd.hpp"
#include "kernel.hpp"
#include "lttng-sessiond.hpp"
#include "session.hpp"
#include "timer.hpp"
#include "trace-ust.hpp"
#include "utils.hpp"

#include <common/common.hpp>
#include <common/sessiond-comm/sessiond-comm.hpp>
#include <common/trace-chunk.hpp>
#include <common/urcu.hpp>
#include <common/utils.hpp>

#include <lttng/location-internal.hpp>

#include <dirent.h>
#include <inttypes.h>
#include <limits.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <urcu.h>

namespace {
struct ltt_session_destroy_notifier_element {
        ltt_session_destroy_notifier notifier;
        void *user_data;
};

struct ltt_session_clear_notifier_element {
        ltt_session_clear_notifier notifier;
        void *user_data;
};

namespace ls = lttng::sessiond;

/*
 * NOTES:
 *
 * No ltt_session.lock is taken here because those data structure are widely
 * spread across the lttng-tools code base so before calling functions below
 * that can read/write a session, the caller MUST acquire the session lock
 * using session_lock() and session_unlock().
 */

/* These characters are forbidden in a session name. Used by validate_name. */
const char *forbidden_name_chars = "/";

/* Global hash table to keep the sessions, indexed by id. */
struct lttng_ht *ltt_sessions_ht_by_id = nullptr;
/* Global hash table to keep the sessions, indexed by name. */
struct lttng_ht *ltt_sessions_ht_by_name = nullptr;

/*
 * Init tracing session list.
 *
 * Please see session.h for more explanation and correct usage of the list.
 */
struct ltt_session_list the_session_list = {
        .lock = PTHREAD_MUTEX_INITIALIZER,
        .removal_cond = PTHREAD_COND_INITIALIZER,
        .next_uuid = 0,
        .head = CDS_LIST_HEAD_INIT(the_session_list.head),
};
} /* namespace */

/*
 * Validate the session name for forbidden characters.
 *
 * Return 0 on success else -1 meaning a forbidden char. has been found.
 */
static int validate_name(const char *name)
{
        int ret;
        char *tok, *tmp_name;

        LTTNG_ASSERT(name);

        tmp_name = strdup(name);
        if (!tmp_name) {
                /* ENOMEM here. */
                ret = -1;
                goto error;
        }

        tok = strpbrk(tmp_name, forbidden_name_chars);
        if (tok) {
                DBG("Session name %s contains a forbidden character", name);
                /* Forbidden character has been found. */
                ret = -1;
                goto error;
        }
        ret = 0;

error:
        free(tmp_name);
        return ret;
}

/*
 * Add a ltt_session structure to the global list.
 *
 * The caller MUST acquire the session list lock before.
 * Returns the unique identifier for the session.
 */
static uint64_t add_session_list(struct ltt_session *ls)
{
        LTTNG_ASSERT(ls);

        cds_list_add(&ls->list, &the_session_list.head);
        return the_session_list.next_uuid++;
}

/*
 * Delete a ltt_session structure to the global list.
 *
 * The caller MUST acquire the session list lock before.
 */
static void del_session_list(struct ltt_session *ls)
{
        LTTNG_ASSERT(ls);

        cds_list_del(&ls->list);
}

/*
 * Return a pointer to the session list.
 */
struct ltt_session_list *session_get_list()
{
        return &the_session_list;
}

/*
 * Returns once the session list is empty.
 */
void session_list_wait_empty()
{
        pthread_mutex_lock(&the_session_list.lock);
        while (!cds_list_empty(&the_session_list.head)) {
                pthread_cond_wait(&the_session_list.removal_cond, &the_session_list.lock);
        }
        pthread_mutex_unlock(&the_session_list.lock);
}

/*
 * Acquire session list lock
 */
void session_lock_list() noexcept
{
        pthread_mutex_lock(&the_session_list.lock);
}

/*
 * Try to acquire session list lock
 */
int session_trylock_list() noexcept
{
        return pthread_mutex_trylock(&the_session_list.lock);
}

/*
 * Release session list lock
 */
void session_unlock_list() noexcept
{
        pthread_mutex_unlock(&the_session_list.lock);
}

/*
 * Get the session's consumer destination type.
 *
 * The caller must hold the session lock.
 */
enum consumer_dst_type session_get_consumer_destination_type(const struct ltt_session *session)
{
        /*
         * The output information is duplicated in both of those session types.
         * Hence, it doesn't matter from which it is retrieved. However, it is
         * possible for only one of them to be set.
         */
        return session->kernel_session ? session->kernel_session->consumer->type :
                                         session->ust_session->consumer->type;
}

/*
 * Get the session's consumer network hostname.
 * The caller must ensure that the destination is of type "net".
 *
 * The caller must hold the session lock.
 */
const char *session_get_net_consumer_hostname(const struct ltt_session *session)
{
        const char *hostname = nullptr;
        const struct consumer_output *output;

        output = session->kernel_session ? session->kernel_session->consumer :
                                           session->ust_session->consumer;

        /*
         * hostname is assumed to be the same for both control and data
         * connections.
         */
        switch (output->dst.net.control.dtype) {
        case LTTNG_DST_IPV4:
                hostname = output->dst.net.control.dst.ipv4;
                break;
        case LTTNG_DST_IPV6:
                hostname = output->dst.net.control.dst.ipv6;
                break;
        default:
                abort();
        }
        return hostname;
}

/*
 * Get the session's consumer network control and data ports.
 * The caller must ensure that the destination is of type "net".
 *
 * The caller must hold the session lock.
 */
void session_get_net_consumer_ports(const struct ltt_session *session,
                                    uint16_t *control_port,
                                    uint16_t *data_port)
{
        const struct consumer_output *output;

        output = session->kernel_session ? session->kernel_session->consumer :
                                           session->ust_session->consumer;
        *control_port = output->dst.net.control.port;
        *data_port = output->dst.net.data.port;
}

/*
 * Get the location of the latest trace archive produced by a rotation.
 *
 * The caller must hold the session lock.
 */
struct lttng_trace_archive_location *
session_get_trace_archive_location(const struct ltt_session *session)
{
        int ret;
        struct lttng_trace_archive_location *location = nullptr;
        char *chunk_path = nullptr;

        if (session->rotation_state != LTTNG_ROTATION_STATE_COMPLETED ||
            !session->last_archived_chunk_name) {
                goto end;
        }

        switch (session_get_consumer_destination_type(session)) {
        case CONSUMER_DST_LOCAL:
                ret = asprintf(&chunk_path,
                               "%s/" DEFAULT_ARCHIVED_TRACE_CHUNKS_DIRECTORY "/%s",
                               session_get_base_path(session),
                               session->last_archived_chunk_name);
                if (ret == -1) {
                        goto end;
                }
                location = lttng_trace_archive_location_local_create(chunk_path);
                break;
        case CONSUMER_DST_NET:
        {
                const char *hostname;
                uint16_t control_port, data_port;

                hostname = session_get_net_consumer_hostname(session);
                session_get_net_consumer_ports(session, &control_port, &data_port);
                location = lttng_trace_archive_location_relay_create(
                        hostname,
                        LTTNG_TRACE_ARCHIVE_LOCATION_RELAY_PROTOCOL_TYPE_TCP,
                        control_port,
                        data_port,
                        session->last_chunk_path);
                break;
        }
        default:
                abort();
        }
end:
        free(chunk_path);
        return location;
}

/*
 * Allocate the ltt_sessions_ht_by_id and ltt_sessions_ht_by_name HT.
 *
 * The session list lock must be held.
 */
static int ltt_sessions_ht_alloc()
{
        int ret = 0;

        DBG("Allocating ltt_sessions_ht_by_id");
        ltt_sessions_ht_by_id = lttng_ht_new(0, LTTNG_HT_TYPE_U64);
        if (!ltt_sessions_ht_by_id) {
                ret = -1;
                ERR("Failed to allocate ltt_sessions_ht_by_id");
                goto end;
        }

        DBG("Allocating ltt_sessions_ht_by_name");
        ltt_sessions_ht_by_name = lttng_ht_new(0, LTTNG_HT_TYPE_STRING);
        if (!ltt_sessions_ht_by_name) {
                ret = -1;
                ERR("Failed to allocate ltt_sessions_ht_by_name");
                goto end;
        }

end:
        return ret;
}

/*
 * Destroy the ltt_sessions_ht_by_id HT.
 *
 * The session list lock must be held.
 */
static void ltt_sessions_ht_destroy()
{
        if (ltt_sessions_ht_by_id) {
                lttng_ht_destroy(ltt_sessions_ht_by_id);
                ltt_sessions_ht_by_id = nullptr;
        }

        if (ltt_sessions_ht_by_name) {
                lttng_ht_destroy(ltt_sessions_ht_by_name);
                ltt_sessions_ht_by_name = nullptr;
        }

        return;
}

/*
 * Add a ltt_session to the ltt_sessions_ht_by_id and ltt_sessions_ht_by_name.
 * If unallocated, the ltt_sessions_ht_by_id and ltt_sessions_ht_by_name. HTs
 * are allocated. The session list lock must be held.
 */
static void add_session_ht(struct ltt_session *ls)
{
        int ret;

        LTTNG_ASSERT(ls);

        if (!ltt_sessions_ht_by_id) {
                ret = ltt_sessions_ht_alloc();
                if (ret) {
                        ERR("Error allocating the sessions HT");
                        goto end;
                }
        }

        /* Should always be present with ltt_sessions_ht_by_id. */
        LTTNG_ASSERT(ltt_sessions_ht_by_name);

        lttng_ht_node_init_u64(&ls->node, ls->id);
        lttng_ht_add_unique_u64(ltt_sessions_ht_by_id, &ls->node);

        lttng_ht_node_init_str(&ls->node_by_name, ls->name);
        lttng_ht_add_unique_str(ltt_sessions_ht_by_name, &ls->node_by_name);

end:
        return;
}

/*
 * Test if ltt_sessions_ht_by_id/name are empty.
 * Return `false` if hash table objects are null.
 * The session list lock must be held.
 */
static bool ltt_sessions_ht_empty()
{
        bool empty = false;

        if (!ltt_sessions_ht_by_id) {
                /* The hash tables do not exist yet. */
                goto end;
        }

        LTTNG_ASSERT(ltt_sessions_ht_by_name);

        if (lttng_ht_get_count(ltt_sessions_ht_by_id) != 0) {
                /* Not empty.*/
                goto end;
        }

        /*
         * At this point it is expected that the `ltt_sessions_ht_by_name` ht is
         * empty.
         *
         * The removal from both hash tables is done in two different
         * places:
         *   - removal from `ltt_sessions_ht_by_name` is done during
         *     `session_destroy()`
         *   - removal from `ltt_sessions_ht_by_id` is done later
         *     in `session_release()` on the last reference put.
         *
         * This means that it is possible for `ltt_sessions_ht_by_name` to be
         * empty but for `ltt_sessions_ht_by_id` to still contain objects when
         * multiple sessions exists. The reverse is false, hence this sanity
         * check.
         */
        LTTNG_ASSERT(lttng_ht_get_count(ltt_sessions_ht_by_name) == 0);
        empty = true;
end:
        return empty;
}

/*
 * Remove a ltt_session from the ltt_sessions_ht_by_id.
 * If empty, the ltt_sessions_ht_by_id/name HTs are freed.
 * The session list lock must be held.
 */
static void del_session_ht(struct ltt_session *ls)
{
        struct lttng_ht_iter iter;
        int ret;

        LTTNG_ASSERT(ls);
        LTTNG_ASSERT(ltt_sessions_ht_by_id);
        LTTNG_ASSERT(ltt_sessions_ht_by_name);

        iter.iter.node = &ls->node.node;
        ret = lttng_ht_del(ltt_sessions_ht_by_id, &iter);
        LTTNG_ASSERT(!ret);

        if (ltt_sessions_ht_empty()) {
                DBG("Empty ltt_sessions_ht_by_id/name, destroying hast tables");
                ltt_sessions_ht_destroy();
        }
}

/*
 * Acquire session lock
 */
void session_lock(struct ltt_session *session)
{
        LTTNG_ASSERT(session);

        pthread_mutex_lock(&session->lock);
}

/*
 * Release session lock
 */
void session_unlock(struct ltt_session *session)
{
        LTTNG_ASSERT(session);

        pthread_mutex_unlock(&session->lock);
}

static int _session_set_trace_chunk_no_lock_check(struct ltt_session *session,
                                                  struct lttng_trace_chunk *new_trace_chunk,
                                                  struct lttng_trace_chunk **_current_trace_chunk)
{
        int ret = 0;
        unsigned int i, refs_to_acquire = 0, refs_acquired = 0, refs_to_release = 0;
        struct cds_lfht_iter iter;
        struct consumer_socket *socket;
        struct lttng_trace_chunk *current_trace_chunk;
        uint64_t chunk_id;
        enum lttng_trace_chunk_status chunk_status;

        lttng::urcu::read_lock_guard read_lock;
        /*
         * Ownership of current trace chunk is transferred to
         * `current_trace_chunk`.
         */
        current_trace_chunk = session->current_trace_chunk;
        session->current_trace_chunk = nullptr;
        if (session->ust_session) {
                lttng_trace_chunk_put(session->ust_session->current_trace_chunk);
                session->ust_session->current_trace_chunk = nullptr;
        }
        if (session->kernel_session) {
                lttng_trace_chunk_put(session->kernel_session->current_trace_chunk);
                session->kernel_session->current_trace_chunk = nullptr;
        }
        if (!new_trace_chunk) {
                ret = 0;
                goto end;
        }
        chunk_status = lttng_trace_chunk_get_id(new_trace_chunk, &chunk_id);
        LTTNG_ASSERT(chunk_status == LTTNG_TRACE_CHUNK_STATUS_OK);

        refs_to_acquire = 1;
        refs_to_acquire += !!session->ust_session;
        refs_to_acquire += !!session->kernel_session;

        for (refs_acquired = 0; refs_acquired < refs_to_acquire; refs_acquired++) {
                if (!lttng_trace_chunk_get(new_trace_chunk)) {
                        ERR("Failed to acquire reference to new trace chunk of session \"%s\"",
                            session->name);
                        goto error;
                }
        }

        if (session->ust_session) {
                const uint64_t relayd_id = session->ust_session->consumer->net_seq_index;
                const bool is_local_trace = session->ust_session->consumer->type ==
                        CONSUMER_DST_LOCAL;

                session->ust_session->current_trace_chunk = new_trace_chunk;
                if (is_local_trace) {
                        enum lttng_error_code ret_error_code;

                        ret_error_code =
                                ust_app_create_channel_subdirectories(session->ust_session);
                        if (ret_error_code != LTTNG_OK) {
                                goto error;
                        }
                }
                cds_lfht_for_each_entry (
                        session->ust_session->consumer->socks->ht, &iter, socket, node.node) {
                        pthread_mutex_lock(socket->lock);
                        ret = consumer_create_trace_chunk(socket,
                                                          relayd_id,
                                                          session->id,
                                                          new_trace_chunk,
                                                          DEFAULT_UST_TRACE_DIR);
                        pthread_mutex_unlock(socket->lock);
                        if (ret) {
                                goto error;
                        }
                }
        }
        if (session->kernel_session) {
                const uint64_t relayd_id = session->kernel_session->consumer->net_seq_index;
                const bool is_local_trace = session->kernel_session->consumer->type ==
                        CONSUMER_DST_LOCAL;

                session->kernel_session->current_trace_chunk = new_trace_chunk;
                if (is_local_trace) {
                        enum lttng_error_code ret_error_code;

                        ret_error_code =
                                kernel_create_channel_subdirectories(session->kernel_session);
                        if (ret_error_code != LTTNG_OK) {
                                goto error;
                        }
                }
                cds_lfht_for_each_entry (
                        session->kernel_session->consumer->socks->ht, &iter, socket, node.node) {
                        pthread_mutex_lock(socket->lock);
                        ret = consumer_create_trace_chunk(socket,
                                                          relayd_id,
                                                          session->id,
                                                          new_trace_chunk,
                                                          DEFAULT_KERNEL_TRACE_DIR);
                        pthread_mutex_unlock(socket->lock);
                        if (ret) {
                                goto error;
                        }
                }
        }

        /*
         * Update local current trace chunk state last, only if all remote
         * creations succeeded.
         */
        session->current_trace_chunk = new_trace_chunk;
        LTTNG_OPTIONAL_SET(&session->most_recent_chunk_id, chunk_id);
end:
        if (_current_trace_chunk) {
                *_current_trace_chunk = current_trace_chunk;
                current_trace_chunk = nullptr;
        }
end_no_move:
        lttng_trace_chunk_put(current_trace_chunk);
        return ret;
error:
        if (session->ust_session) {
                session->ust_session->current_trace_chunk = nullptr;
        }
        if (session->kernel_session) {
                session->kernel_session->current_trace_chunk = nullptr;
        }
        /*
         * Release references taken in the case where all references could not
         * be acquired.
         */
        refs_to_release = refs_to_acquire - refs_acquired;
        for (i = 0; i < refs_to_release; i++) {
                lttng_trace_chunk_put(new_trace_chunk);
        }
        ret = -1;
        goto end_no_move;
}

struct lttng_trace_chunk *
session_create_new_trace_chunk(const struct ltt_session *session,
                               const struct consumer_output *consumer_output_override,
                               const char *session_base_path_override,
                               const char *chunk_name_override)
{
        int ret;
        struct lttng_trace_chunk *trace_chunk = nullptr;
        enum lttng_trace_chunk_status chunk_status;
        const time_t chunk_creation_ts = time(nullptr);
        bool is_local_trace;
        const char *base_path;
        struct lttng_directory_handle *session_output_directory = nullptr;
        const struct lttng_credentials session_credentials = {
                .uid = LTTNG_OPTIONAL_INIT_VALUE(session->uid),
                .gid = LTTNG_OPTIONAL_INIT_VALUE(session->gid),
        };
        uint64_t next_chunk_id;
        const struct consumer_output *output;
        const char *new_path;

        if (consumer_output_override) {
                output = consumer_output_override;
        } else {
                LTTNG_ASSERT(session->ust_session || session->kernel_session);
                output = session->ust_session ? session->ust_session->consumer :
                                                session->kernel_session->consumer;
        }

        is_local_trace = output->type == CONSUMER_DST_LOCAL;
        base_path = session_base_path_override ?: consumer_output_get_base_path(output);

        if (chunk_creation_ts == (time_t) -1) {
                PERROR("Failed to sample time while creation session \"%s\" trace chunk",
                       session->name);
                goto error;
        }

        next_chunk_id =
                session->most_recent_chunk_id.is_set ? session->most_recent_chunk_id.value + 1 : 0;

        if (session->current_trace_chunk &&
            !lttng_trace_chunk_get_name_overridden(session->current_trace_chunk)) {
                chunk_status = lttng_trace_chunk_rename_path(session->current_trace_chunk,
                                                             DEFAULT_CHUNK_TMP_OLD_DIRECTORY);
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        goto error;
                }
        }
        if (!session->current_trace_chunk) {
                if (!session->rotated) {
                        new_path = "";
                } else {
                        new_path = nullptr;
                }
        } else {
                new_path = DEFAULT_CHUNK_TMP_NEW_DIRECTORY;
        }

        trace_chunk = lttng_trace_chunk_create(next_chunk_id, chunk_creation_ts, new_path);
        if (!trace_chunk) {
                goto error;
        }

        if (chunk_name_override) {
                chunk_status = lttng_trace_chunk_override_name(trace_chunk, chunk_name_override);
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        goto error;
                }
        }

        if (!is_local_trace) {
                /*
                 * No need to set crendentials and output directory
                 * for remote trace chunks.
                 */
                goto end;
        }

        chunk_status = lttng_trace_chunk_set_credentials(trace_chunk, &session_credentials);
        if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                goto error;
        }

        DBG("Creating base output directory of session \"%s\" at %s", session->name, base_path);
        ret = utils_mkdir_recursive(base_path, S_IRWXU | S_IRWXG, session->uid, session->gid);
        if (ret) {
                goto error;
        }
        session_output_directory = lttng_directory_handle_create(base_path);
        if (!session_output_directory) {
                goto error;
        }
        chunk_status = lttng_trace_chunk_set_as_owner(trace_chunk, session_output_directory);
        lttng_directory_handle_put(session_output_directory);
        session_output_directory = nullptr;
        if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                goto error;
        }
end:
        return trace_chunk;
error:
        lttng_directory_handle_put(session_output_directory);
        lttng_trace_chunk_put(trace_chunk);
        trace_chunk = nullptr;
        goto end;
}

int session_close_trace_chunk(struct ltt_session *session,
                              struct lttng_trace_chunk *trace_chunk,
                              enum lttng_trace_chunk_command_type close_command,
                              char *closed_trace_chunk_path)
{
        int ret = 0;
        bool error_occurred = false;
        struct cds_lfht_iter iter;
        struct consumer_socket *socket;
        enum lttng_trace_chunk_status chunk_status;
        const time_t chunk_close_timestamp = time(nullptr);
        const char *new_path;

        chunk_status = lttng_trace_chunk_set_close_command(trace_chunk, close_command);
        if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                ret = -1;
                goto end;
        }

        if (chunk_close_timestamp == (time_t) -1) {
                ERR("Failed to sample the close timestamp of the current trace chunk of session \"%s\"",
                    session->name);
                ret = -1;
                goto end;
        }

        if (close_command == LTTNG_TRACE_CHUNK_COMMAND_TYPE_DELETE && !session->rotated) {
                /* New chunk stays in session output directory. */
                new_path = "";
        } else {
                /* Use chunk name for new chunk. */
                new_path = nullptr;
        }
        if (session->current_trace_chunk &&
            !lttng_trace_chunk_get_name_overridden(session->current_trace_chunk)) {
                /* Rename new chunk path. */
                chunk_status =
                        lttng_trace_chunk_rename_path(session->current_trace_chunk, new_path);
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        ret = -1;
                        goto end;
                }
        }
        if (!lttng_trace_chunk_get_name_overridden(trace_chunk) &&
            close_command == LTTNG_TRACE_CHUNK_COMMAND_TYPE_NO_OPERATION) {
                const char *old_path;

                if (!session->rotated) {
                        old_path = "";
                } else {
                        old_path = nullptr;
                }
                /* We need to move back the .tmp_old_chunk to its rightful place. */
                chunk_status = lttng_trace_chunk_rename_path(trace_chunk, old_path);
                if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                        ret = -1;
                        goto end;
                }
        }
        if (close_command == LTTNG_TRACE_CHUNK_COMMAND_TYPE_MOVE_TO_COMPLETED) {
                session->rotated = true;
        }
        chunk_status = lttng_trace_chunk_set_close_timestamp(trace_chunk, chunk_close_timestamp);
        if (chunk_status != LTTNG_TRACE_CHUNK_STATUS_OK) {
                ERR("Failed to set the close timestamp of the current trace chunk of session \"%s\"",
                    session->name);
                ret = -1;
                goto end;
        }

        if (session->ust_session) {
                const uint64_t relayd_id = session->ust_session->consumer->net_seq_index;

                cds_lfht_for_each_entry (
                        session->ust_session->consumer->socks->ht, &iter, socket, node.node) {
                        pthread_mutex_lock(socket->lock);
                        ret = consumer_close_trace_chunk(socket,
                                                         relayd_id,
                                                         session->id,
                                                         trace_chunk,
                                                         closed_trace_chunk_path);
                        pthread_mutex_unlock(socket->lock);
                        if (ret) {
                                ERR("Failed to close trace chunk on user space consumer");
                                error_occurred = true;
                        }
                }
        }
        if (session->kernel_session) {
                const uint64_t relayd_id = session->kernel_session->consumer->net_seq_index;

                cds_lfht_for_each_entry (
                        session->kernel_session->consumer->socks->ht, &iter, socket, node.node) {
                        pthread_mutex_lock(socket->lock);
                        ret = consumer_close_trace_chunk(socket,
                                                         relayd_id,
                                                         session->id,
                                                         trace_chunk,
                                                         closed_trace_chunk_path);
                        pthread_mutex_unlock(socket->lock);
                        if (ret) {
                                ERR("Failed to close trace chunk on kernel consumer");
                                error_occurred = true;
                        }
                }
        }
        ret = error_occurred ? -1 : 0;
end:
        return ret;
}

/*
 * This function skips the metadata channel as the begin/end timestamps of a
 * metadata packet are useless.
 *
 * Moreover, opening a packet after a "clear" will cause problems for live
 * sessions as it will introduce padding that was not part of the first trace
 * chunk. The relay daemon expects the content of the metadata stream of
 * successive metadata trace chunks to be strict supersets of one another.
 *
 * For example, flushing a packet at the beginning of the metadata stream of
 * a trace chunk resulting from a "clear" session command will cause the
 * size of the metadata stream of the new trace chunk to not match the size of
 * the metadata stream of the original chunk. This will confuse the relay
 * daemon as the same "offset" in a metadata stream will no longer point
 * to the same content.
 */
static enum lttng_error_code session_kernel_open_packets(struct ltt_session *session)
{
        enum lttng_error_code ret = LTTNG_OK;
        struct consumer_socket *socket;
        struct lttng_ht_iter iter;
        struct cds_lfht_node *node;
        struct ltt_kernel_channel *chan;

        lttng::urcu::read_lock_guard read_lock;

        cds_lfht_first(session->kernel_session->consumer->socks->ht, &iter.iter);
        node = cds_lfht_iter_get_node(&iter.iter);
        socket = caa_container_of(node, typeof(*socket), node.node);

        cds_list_for_each_entry (chan, &session->kernel_session->channel_list.head, list) {
                int open_ret;

                DBG("Open packet of kernel channel: channel key = %" PRIu64
                    ", session name = %s, session_id = %" PRIu64,
                    chan->key,
                    session->name,
                    session->id);

                open_ret = consumer_open_channel_packets(socket, chan->key);
                if (open_ret < 0) {
                        /* General error (no known error expected). */
                        ret = LTTNG_ERR_UNK;
                        goto end;
                }
        }

end:
        return ret;
}

enum lttng_error_code session_open_packets(struct ltt_session *session)
{
        enum lttng_error_code ret = LTTNG_OK;

        DBG("Opening packets of session channels: session name = %s, session id = %" PRIu64,
            session->name,
            session->id);

        if (session->ust_session) {
                ret = ust_app_open_packets(session);
                if (ret != LTTNG_OK) {
                        goto end;
                }
        }

        if (session->kernel_session) {
                ret = session_kernel_open_packets(session);
                if (ret != LTTNG_OK) {
                        goto end;
                }
        }

end:
        return ret;
}

/*
 * Set a session's current trace chunk.
 *
 * Must be called with the session lock held.
 */
int session_set_trace_chunk(struct ltt_session *session,
                            struct lttng_trace_chunk *new_trace_chunk,
                            struct lttng_trace_chunk **current_trace_chunk)
{
        ASSERT_LOCKED(session->lock);
        return _session_set_trace_chunk_no_lock_check(
                session, new_trace_chunk, current_trace_chunk);
}

static void session_notify_destruction(const struct ltt_session *session)
{
        size_t i;
        const size_t count = lttng_dynamic_array_get_count(&session->destroy_notifiers);

        for (i = 0; i < count; i++) {
                const struct ltt_session_destroy_notifier_element *element =
                        (ltt_session_destroy_notifier_element *) lttng_dynamic_array_get_element(
                                &session->destroy_notifiers, i);

                element->notifier(session, element->user_data);
        }
}

/*
 * Fire each clear notifier once, and remove them from the array.
 */
void session_notify_clear(ltt_session& session)
{
        size_t i;
        const size_t count = lttng_dynamic_array_get_count(&session.clear_notifiers);

        for (i = 0; i < count; i++) {
                const struct ltt_session_clear_notifier_element *element =
                        (ltt_session_clear_notifier_element *) lttng_dynamic_array_get_element(
                                &session.clear_notifiers, i);

                element->notifier(&session, element->user_data);
        }
        lttng_dynamic_array_clear(&session.clear_notifiers);
}

static void session_release(struct urcu_ref *ref)
{
        int ret;
        struct ltt_ust_session *usess;
        struct ltt_kernel_session *ksess;
        struct ltt_session *session = lttng::utils::container_of(ref, &ltt_session::ref);
        const bool session_published = session->published;

        LTTNG_ASSERT(!session->chunk_being_archived);

        usess = session->ust_session;
        ksess = session->kernel_session;

        /* Clean kernel session teardown, keeping data for destroy notifier. */
        kernel_destroy_session(ksess);

        /* UST session teardown, keeping data for destroy notifier. */
        if (usess) {
                /* Close any relayd session */
                consumer_output_send_destroy_relayd(usess->consumer);

                /* Destroy every UST application related to this session. */
                ret = ust_app_destroy_trace_all(usess);
                if (ret) {
                        ERR("Error in ust_app_destroy_trace_all");
                }

                /* Clean up the rest, keeping destroy notifier data. */
                trace_ust_destroy_session(usess);
        }

        /*
         * Must notify the kernel thread here to update it's poll set in order to
         * remove the channel(s)' fd just destroyed.
         */
        ret = notify_thread_pipe(the_kernel_poll_pipe[1]);
        if (ret < 0) {
                PERROR("write kernel poll pipe");
        }

        DBG("Destroying session %s (id %" PRIu64 ")", session->name, session->id);

        snapshot_destroy(&session->snapshot);

        pthread_mutex_destroy(&session->lock);

        if (session_published) {
                ASSERT_LOCKED(the_session_list.lock);
                del_session_list(session);
                del_session_ht(session);
        }
        session_notify_destruction(session);

        consumer_output_put(session->consumer);
        kernel_free_session(ksess);
        session->kernel_session = nullptr;
        if (usess) {
                trace_ust_free_session(usess);
                session->ust_session = nullptr;
        }
        lttng_dynamic_array_reset(&session->destroy_notifiers);
        lttng_dynamic_array_reset(&session->clear_notifiers);
        free(session->last_archived_chunk_name);
        free(session->base_path);
        lttng_trigger_put(session->rotate_trigger);
        free(session);
        if (session_published) {
                /*
                 * Broadcast after free-ing to ensure the memory is
                 * reclaimed before the main thread exits.
                 */
                ASSERT_LOCKED(the_session_list.lock);
                pthread_cond_broadcast(&the_session_list.removal_cond);
        }
}

/*
 * Acquire a reference to a session.
 * This function may fail (return false); its return value must be checked.
 */
bool session_get(struct ltt_session *session)
{
        return urcu_ref_get_unless_zero(&session->ref);
}

/*
 * Release a reference to a session.
 */
void session_put(struct ltt_session *session)
{
        if (!session) {
                return;
        }
        /*
         * The session list lock must be held as any session_put()
         * may cause the removal of the session from the session_list.
         */
        ASSERT_LOCKED(the_session_list.lock);
        LTTNG_ASSERT(session->ref.refcount);
        urcu_ref_put(&session->ref, session_release);
}

/*
 * Destroy a session.
 *
 * This method does not immediately release/free the session as other
 * components may still hold a reference to the session. However,
 * the session should no longer be presented to the user.
 *
 * Releases the session list's reference to the session
 * and marks it as destroyed. Iterations on the session list should be
 * mindful of the "destroyed" flag.
 */
void session_destroy(struct ltt_session *session)
{
        int ret;
        struct lttng_ht_iter iter;

        LTTNG_ASSERT(!session->destroyed);
        session->destroyed = true;

        /*
         * Remove immediately from the "session by name" hash table. Only one
         * session is expected to exist with a given name for at any given time.
         *
         * Even if a session still technically exists for a little while longer,
         * there is no point in performing action on a "destroyed" session.
         */
        iter.iter.node = &session->node_by_name.node;
        ret = lttng_ht_del(ltt_sessions_ht_by_name, &iter);
        LTTNG_ASSERT(!ret);

        session_put(session);
}

int session_add_destroy_notifier(struct ltt_session *session,
                                 ltt_session_destroy_notifier notifier,
                                 void *user_data)
{
        const struct ltt_session_destroy_notifier_element element = { .notifier = notifier,
                                                                      .user_data = user_data };

        return lttng_dynamic_array_add_element(&session->destroy_notifiers, &element);
}

int session_add_clear_notifier(struct ltt_session *session,
                               ltt_session_clear_notifier notifier,
                               void *user_data)
{
        const struct ltt_session_clear_notifier_element element = { .notifier = notifier,
                                                                    .user_data = user_data };

        return lttng_dynamic_array_add_element(&session->clear_notifiers, &element);
}

/*
 * Return a ltt_session structure ptr that matches name. If no session found,
 * NULL is returned. This must be called with the session list lock held using
 * session_lock_list and session_unlock_list.
 * A reference to the session is implicitly acquired by this function.
 */
struct ltt_session *session_find_by_name(const char *name)
{
        struct ltt_session *iter;

        LTTNG_ASSERT(name);
        ASSERT_LOCKED(the_session_list.lock);

        DBG2("Trying to find session by name %s", name);

        cds_list_for_each_entry (iter, &the_session_list.head, list) {
                if (!strncmp(iter->name, name, NAME_MAX) && !iter->destroyed) {
                        goto found;
                }
        }

        return nullptr;
found:
        return session_get(iter) ? iter : nullptr;
}

/*
 * Return an ltt_session that matches the id. If no session is found,
 * NULL is returned. This must be called with rcu_read_lock and
 * session list lock held (to guarantee the lifetime of the session).
 */
struct ltt_session *session_find_by_id(uint64_t id)
{
        struct lttng_ht_node_u64 *node;
        struct lttng_ht_iter iter;
        struct ltt_session *ls;

        ASSERT_RCU_READ_LOCKED();
        ASSERT_LOCKED(the_session_list.lock);

        if (!ltt_sessions_ht_by_id) {
                goto end;
        }

        lttng_ht_lookup(ltt_sessions_ht_by_id, &id, &iter);
        node = lttng_ht_iter_get_node_u64(&iter);
        if (node == nullptr) {
                goto end;
        }
        ls = lttng::utils::container_of(node, &ltt_session::node);

        DBG3("Session %" PRIu64 " found by id.", id);
        return session_get(ls) ? ls : nullptr;

end:
        DBG3("Session %" PRIu64 " NOT found by id", id);
        return nullptr;
}

/*
 * Create a new session and add it to the session list.
 * Session list lock must be held by the caller.
 */
enum lttng_error_code
session_create(const char *name, uid_t uid, gid_t gid, struct ltt_session **out_session)
{
        int ret;
        enum lttng_error_code ret_code;
        struct ltt_session *new_session = nullptr;

        ASSERT_LOCKED(the_session_list.lock);
        if (name) {
                struct ltt_session *clashing_session;

                clashing_session = session_find_by_name(name);
                if (clashing_session) {
                        session_put(clashing_session);
                        ret_code = LTTNG_ERR_EXIST_SESS;
                        goto error;
                }
        }
        new_session = zmalloc<ltt_session>();
        if (!new_session) {
                PERROR("Failed to allocate an ltt_session structure");
                ret_code = LTTNG_ERR_NOMEM;
                goto error;
        }

        lttng_dynamic_array_init(&new_session->destroy_notifiers,
                                 sizeof(struct ltt_session_destroy_notifier_element),
                                 nullptr);
        lttng_dynamic_array_init(&new_session->clear_notifiers,
                                 sizeof(struct ltt_session_clear_notifier_element),
                                 nullptr);
        urcu_ref_init(&new_session->ref);
        pthread_mutex_init(&new_session->lock, nullptr);

        new_session->creation_time = time(nullptr);
        if (new_session->creation_time == (time_t) -1) {
                PERROR("Failed to sample session creation time");
                ret_code = LTTNG_ERR_SESSION_FAIL;
                goto error;
        }

        /* Create default consumer output. */
        new_session->consumer = consumer_create_output(CONSUMER_DST_LOCAL);
        if (new_session->consumer == nullptr) {
                ret_code = LTTNG_ERR_NOMEM;
                goto error;
        }

        if (name) {
                ret = lttng_strncpy(new_session->name, name, sizeof(new_session->name));
                if (ret) {
                        ret_code = LTTNG_ERR_SESSION_INVALID_CHAR;
                        goto error;
                }
                ret = validate_name(name);
                if (ret < 0) {
                        ret_code = LTTNG_ERR_SESSION_INVALID_CHAR;
                        goto error;
                }
        } else {
                int i = 0;
                bool found_name = false;
                char datetime[16];
                struct tm *timeinfo;

                timeinfo = localtime(&new_session->creation_time);
                if (!timeinfo) {
                        ret_code = LTTNG_ERR_SESSION_FAIL;
                        goto error;
                }
                strftime(datetime, sizeof(datetime), "%Y%m%d-%H%M%S", timeinfo);
                for (i = 0; i < INT_MAX; i++) {
                        struct ltt_session *clashing_session;

                        if (i == 0) {
                                ret = snprintf(new_session->name,
                                               sizeof(new_session->name),
                                               "%s-%s",
                                               DEFAULT_SESSION_NAME,
                                               datetime);
                        } else {
                                ret = snprintf(new_session->name,
                                               sizeof(new_session->name),
                                               "%s%d-%s",
                                               DEFAULT_SESSION_NAME,
                                               i,
                                               datetime);
                        }
                        new_session->name_contains_creation_time = true;
                        if (ret == -1 || ret >= sizeof(new_session->name)) {
                                /*
                                 * Null-terminate in case the name is used
                                 * in logging statements.
                                 */
                                new_session->name[sizeof(new_session->name) - 1] = '\0';
                                ret_code = LTTNG_ERR_SESSION_FAIL;
                                goto error;
                        }

                        clashing_session = session_find_by_name(new_session->name);
                        session_put(clashing_session);
                        if (!clashing_session) {
                                found_name = true;
                                break;
                        }
                }
                if (found_name) {
                        DBG("Generated session name \"%s\"", new_session->name);
                        new_session->has_auto_generated_name = true;
                } else {
                        ERR("Failed to auto-generate a session name");
                        ret_code = LTTNG_ERR_SESSION_FAIL;
                        goto error;
                }
        }

        ret = gethostname(new_session->hostname, sizeof(new_session->hostname));
        if (ret < 0) {
                if (errno == ENAMETOOLONG) {
                        new_session->hostname[sizeof(new_session->hostname) - 1] = '\0';
                        ERR("Hostname exceeds the maximal permitted length and has been truncated to %s",
                            new_session->hostname);
                } else {
                        ret_code = LTTNG_ERR_SESSION_FAIL;
                        goto error;
                }
        }

        new_session->uid = uid;
        new_session->gid = gid;

        ret = snapshot_init(&new_session->snapshot);
        if (ret < 0) {
                ret_code = LTTNG_ERR_NOMEM;
                goto error;
        }

        new_session->rotation_state = LTTNG_ROTATION_STATE_NO_ROTATION;

        /* Add new session to the session list. */
        new_session->id = add_session_list(new_session);

        /*
         * Add the new session to the ltt_sessions_ht_by_id.
         * No ownership is taken by the hash table; it is merely
         * a wrapper around the session list used for faster access
         * by session id.
         */
        add_session_ht(new_session);
        new_session->published = true;

        /*
         * Consumer is left to NULL since the create_session_uri command will
         * set it up and, if valid, assign it to the session.
         */
        DBG("Tracing session %s created with ID %" PRIu64 " by uid = %d, gid = %d",
            new_session->name,
            new_session->id,
            new_session->uid,
            new_session->gid);
        ret_code = LTTNG_OK;
end:
        if (new_session) {
                (void) session_get(new_session);
                *out_session = new_session;
        }
        return ret_code;
error:
        session_put(new_session);
        new_session = nullptr;
        goto end;
}

/*
 * Check if the UID matches the session. Root user has access to all
 * sessions.
 */
bool session_access_ok(struct ltt_session *session, uid_t uid)
{
        LTTNG_ASSERT(session);
        return (uid == session->uid) || uid == 0;
}

/*
 * Set a session's rotation state and reset all associated state.
 *
 * This function resets the rotation state (check timers, pending
 * flags, etc.) and sets the result of the last rotation. The result
 * can be queries by a liblttng-ctl client.
 *
 * Be careful of the result passed to this function. For instance,
 * on failure to launch a rotation, a client will expect the rotation
 * state to be set to "NO_ROTATION". If an error occurred while the
 * rotation was "ONGOING", result should be set to "ERROR", which will
 * allow a client to report it.
 *
 * Must be called with the session and session_list locks held.
 */
int session_reset_rotation_state(ltt_session& session, enum lttng_rotation_state result)
{
        int ret = 0;

        ASSERT_LOCKED(the_session_list.lock);
        ASSERT_LOCKED(session.lock);

        session.rotation_state = result;
        if (session.rotation_pending_check_timer_enabled) {
                ret = timer_session_rotation_pending_check_stop(session);
        }
        if (session.chunk_being_archived) {
                uint64_t chunk_id;
                enum lttng_trace_chunk_status chunk_status;

                chunk_status = lttng_trace_chunk_get_id(session.chunk_being_archived, &chunk_id);
                LTTNG_ASSERT(chunk_status == LTTNG_TRACE_CHUNK_STATUS_OK);
                LTTNG_OPTIONAL_SET(&session.last_archived_chunk_id, chunk_id);
                lttng_trace_chunk_put(session.chunk_being_archived);
                session.chunk_being_archived = nullptr;
                /*
                 * Fire the clear reply notifiers if we are completing a clear
                 * rotation.
                 */
                session_notify_clear(session);
        }
        return ret;
}

/*
 * Sample the id of a session looked up via its name.
 * Here the term "sampling" hint the caller that this return the id at a given
 * point in time with no guarantee that the session for which the id was
 * sampled still exist at that point.
 *
 * Return 0 when the session is not found,
 * Return 1 when the session is found and set `id`.
 */
bool sample_session_id_by_name(const char *name, uint64_t *id)
{
        bool found = false;
        struct lttng_ht_node_str *node;
        struct lttng_ht_iter iter;
        struct ltt_session *ls;

        lttng::urcu::read_lock_guard read_lock;

        if (!ltt_sessions_ht_by_name) {
                found = false;
                goto end;
        }

        lttng_ht_lookup(ltt_sessions_ht_by_name, name, &iter);
        node = lttng_ht_iter_get_node_str(&iter);
        if (node == nullptr) {
                found = false;
                goto end;
        }

        ls = lttng::utils::container_of(node, &ltt_session::node_by_name);
        *id = ls->id;
        found = true;

        DBG3("Session id `%" PRIu64 "` sampled for session `%s", *id, name);
end:
        return found;
}

void ls::details::locked_session_release(ltt_session *session)
{
        if (!session) {
                return;
        }

        session_unlock(session);
        session_put(session);
}

ltt_session::locked_ptr ls::find_locked_session_by_id(ltt_session::id_t id)
{
        lttng::urcu::read_lock_guard rcu_lock;
        auto session = session_find_by_id(id);

        if (!session) {
                return nullptr;
        }

        /*
         * The pointer falling out of scope will unlock and release the reference to the
         * session.
         */
        session_lock(session);
        return ltt_session::locked_ptr(session);
}

ltt_session::sptr ls::find_session_by_id(ltt_session::id_t id)
{
        lttng::urcu::read_lock_guard rcu_lock;
        auto session = session_find_by_id(id);

        if (!session) {
                return nullptr;
        }

        return { session, session_put };
}