Save/load: support session trace format

[deliverable/lttng-tools.git] / src / lib / lttng-ctl / lttng-ctl.cpp

/*
 * lttng-ctl.c
 *
 * Linux Trace Toolkit Control Library
 *
 * Copyright (C) 2011 EfficiOS Inc.
 * Copyright (C) 2016 Jérémie Galarneau <jeremie.galarneau@efficios.com>
 *
 * SPDX-License-Identifier: LGPL-2.1-only
 *
 */

#define _LGPL_SOURCE
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>

#include <common/bytecode/bytecode.hpp>
#include <common/align.hpp>
#include <common/common.hpp>
#include <common/compat/errno.hpp>
#include <common/compat/string.hpp>
#include <common/defaults.hpp>
#include <common/dynamic-array.hpp>
#include <common/dynamic-buffer.hpp>
#include <common/payload-view.hpp>
#include <common/payload.hpp>
#include <common/sessiond-comm/sessiond-comm.hpp>
#include <common/tracker.hpp>
#include <common/unix.hpp>
#include <common/uri.hpp>
#include <common/utils.hpp>
#include <lttng/channel-internal.hpp>
#include <lttng/destruction-handle.h>
#include <lttng/endpoint.h>
#include <lttng/error-query-internal.hpp>
#include <lttng/event-internal.hpp>
#include <lttng/health-internal.hpp>
#include <lttng/lttng-error.h>
#include <lttng/lttng.h>
#include <lttng/session-descriptor-internal.hpp>
#include <lttng/session-internal.hpp>
#include <lttng/trigger/trigger-internal.hpp>
#include <lttng/userspace-probe-internal.hpp>

#include "lttng-ctl-helper.hpp"
#include <common/filter/filter-ast.hpp>
#include <common/filter/filter-parser.hpp>
#include <common/filter/memstream.hpp>

#define COPY_DOMAIN_PACKED(dst, src)                            \
do {                                                            \
        struct lttng_domain _tmp_domain;                        \
                                                                \
        lttng_ctl_copy_lttng_domain(&_tmp_domain, &src);        \
        dst = _tmp_domain;                                      \
} while (0)

/* Socket to session daemon for communication */
static int sessiond_socket = -1;
static char sessiond_sock_path[PATH_MAX];

/* Variables */
static char *tracing_group;
static int connected;

/* Global */

/*
 * Those two variables are used by error.h to silent or control the verbosity of
 * error message. They are global to the library so application linking with it
 * are able to compile correctly and also control verbosity of the library.
 */
LTTNG_EXPORT int lttng_opt_quiet;
LTTNG_EXPORT int lttng_opt_verbose;
LTTNG_EXPORT int lttng_opt_mi;

/*
 * Copy domain to lttcomm_session_msg domain.
 *
 * If domain is unknown, default domain will be the kernel.
 */
void lttng_ctl_copy_lttng_domain(struct lttng_domain *dst,
                struct lttng_domain *src)
{
        if (src && dst) {
                switch (src->type) {
                case LTTNG_DOMAIN_KERNEL:
                case LTTNG_DOMAIN_UST:
                case LTTNG_DOMAIN_JUL:
                case LTTNG_DOMAIN_LOG4J:
                case LTTNG_DOMAIN_PYTHON:
                        memcpy(dst, src, sizeof(struct lttng_domain));
                        break;
                default:
                        memset(dst, 0, sizeof(struct lttng_domain));
                        break;
                }
        }
}

/*
 * Send lttcomm_session_msg to the session daemon.
 *
 * On success, returns the number of bytes sent (>=0)
 * On error, returns -1
 */
static int send_session_msg(struct lttcomm_session_msg *lsm)
{
        int ret;

        if (!connected) {
                ret = -LTTNG_ERR_NO_SESSIOND;
                goto end;
        }

        DBG("LSM cmd type: '%s' (%d)", lttcomm_sessiond_command_str((lttcomm_sessiond_command) lsm->cmd_type),
                        lsm->cmd_type);

        ret = lttcomm_send_creds_unix_sock(sessiond_socket, lsm,
                        sizeof(struct lttcomm_session_msg));
        if (ret < 0) {
                ret = -LTTNG_ERR_FATAL;
        }

end:
        return ret;
}

/*
 * Send var len data to the session daemon.
 *
 * On success, returns the number of bytes sent (>=0)
 * On error, returns -1
 */
static int send_session_varlen(const void *data, size_t len)
{
        int ret;

        if (!connected) {
                ret = -LTTNG_ERR_NO_SESSIOND;
                goto end;
        }

        if (!data || !len) {
                ret = 0;
                goto end;
        }

        ret = lttcomm_send_unix_sock(sessiond_socket, data, len);
        if (ret < 0) {
                ret = -LTTNG_ERR_FATAL;
        }

end:
        return ret;
}

/*
 * Send file descriptors to the session daemon.
 *
 * On success, returns the number of bytes sent (>=0)
 * On error, returns -1
 */
static int send_session_fds(const int *fds, size_t nb_fd)
{
        int ret;

        if (!connected) {
                ret = -LTTNG_ERR_NO_SESSIOND;
                goto end;
        }

        if (!fds || !nb_fd) {
                ret = 0;
                goto end;
        }

        ret = lttcomm_send_fds_unix_sock(sessiond_socket, fds, nb_fd);
        if (ret < 0) {
                ret = -LTTNG_ERR_FATAL;
        }

end:
        return ret;
}

/*
 * Receive data from the sessiond socket.
 *
 * On success, returns the number of bytes received (>=0)
 * On error, returns a negative lttng_error_code.
 */
static int recv_data_sessiond(void *buf, size_t len)
{
        int ret;

        LTTNG_ASSERT(len > 0);

        if (!connected) {
                ret = -LTTNG_ERR_NO_SESSIOND;
                goto end;
        }

        ret = lttcomm_recv_unix_sock(sessiond_socket, buf, len);
        if (ret < 0) {
                ret = -LTTNG_ERR_FATAL;
        } else if (ret == 0) {
                ret = -LTTNG_ERR_NO_SESSIOND;
        }

end:
        return ret;
}

/*
 * Receive a payload from the session daemon by appending to an existing
 * payload.
 * On success, returns the number of bytes received (>=0)
 * On error, returns a negative lttng_error_code.
 */
static int recv_payload_sessiond(struct lttng_payload *payload, size_t len)
{
        int ret;
        const size_t original_payload_size = payload->buffer.size;

        ret = lttng_dynamic_buffer_set_size(
                        &payload->buffer, payload->buffer.size + len);
        if (ret) {
                ret = -LTTNG_ERR_NOMEM;
                goto end;
        }

        ret = recv_data_sessiond(
                        payload->buffer.data + original_payload_size, len);
end:
        return ret;
}

/*
 * Check if we are in the specified group.
 *
 * If yes return 1, else return -1.
 */
int lttng_check_tracing_group(void)
{
        gid_t *grp_list, tracing_gid;
        int grp_list_size, grp_id, i;
        int ret = -1;
        const char *grp_name = tracing_group;

        /* Get GID of group 'tracing' */
        if (utils_get_group_id(grp_name, false, &tracing_gid)) {
                /* If grp_tracing is NULL, the group does not exist. */
                goto end;
        }

        /* Get number of supplementary group IDs */
        grp_list_size = getgroups(0, NULL);
        if (grp_list_size < 0) {
                PERROR("getgroups");
                goto end;
        }

        /* Alloc group list of the right size */
        grp_list = calloc<gid_t>(grp_list_size);
        if (!grp_list) {
                PERROR("malloc");
                goto end;
        }
        grp_id = getgroups(grp_list_size, grp_list);
        if (grp_id < 0) {
                PERROR("getgroups");
                goto free_list;
        }

        for (i = 0; i < grp_list_size; i++) {
                if (grp_list[i] == tracing_gid) {
                        ret = 1;
                        break;
                }
        }

free_list:
        free(grp_list);

end:
        return ret;
}

static enum lttng_error_code check_enough_available_memory(
                uint64_t num_bytes_requested_per_cpu)
{
        int ret;
        enum lttng_error_code ret_code;
        long num_cpu;
        uint64_t best_mem_info;
        uint64_t num_bytes_requested_total;

        /*
         * Get the number of CPU currently online to compute the amount of
         * memory needed to create a buffer for every CPU.
         */
        num_cpu = sysconf(_SC_NPROCESSORS_ONLN);
        if (num_cpu == -1) {
                ret_code = LTTNG_ERR_FATAL;
                goto end;
        }

        if (num_bytes_requested_per_cpu > UINT64_MAX / (uint64_t) num_cpu) {
                /* Overflow */
                ret_code = LTTNG_ERR_OVERFLOW;
                goto end;
        }

        num_bytes_requested_total =
                        num_bytes_requested_per_cpu * (uint64_t) num_cpu;

        /*
         * Try to get the `MemAvail` field of `/proc/meminfo`. This is the most
         * reliable estimate we can get but it is only exposed by the kernel
         * since 3.14. (See Linux kernel commit:
         * 34e431b0ae398fc54ea69ff85ec700722c9da773)
         */
        ret = utils_get_memory_available(&best_mem_info);
        if (ret >= 0) {
                goto success;
        }

        /*
         * As a backup plan, use `MemTotal` field of `/proc/meminfo`. This
         * is a sanity check for obvious user error.
         */
        ret = utils_get_memory_total(&best_mem_info);
        if (ret >= 0) {
                goto success;
        }

        /* No valid source of information. */
        ret_code = LTTNG_ERR_NOMEM;
        goto end;

success:
        if (best_mem_info >= num_bytes_requested_total) {
                ret_code = LTTNG_OK;
        } else {
                ret_code = LTTNG_ERR_NOMEM;
        }
end:
        return ret_code;
}

/*
 * Try connect to session daemon with sock_path.
 *
 * Return 0 on success, else -1
 */
static int try_connect_sessiond(const char *sock_path)
{
        int ret;

        /* If socket exist, we check if the daemon listens for connect. */
        ret = access(sock_path, F_OK);
        if (ret < 0) {
                /* Not alive */
                goto error;
        }

        ret = lttcomm_connect_unix_sock(sock_path);
        if (ret < 0) {
                /* Not alive. */
                goto error;
        }

        ret = lttcomm_close_unix_sock(ret);
        if (ret < 0) {
                PERROR("lttcomm_close_unix_sock");
        }

        return 0;

error:
        return -1;
}

/*
 * Set sessiond socket path by putting it in the global sessiond_sock_path
 * variable.
 *
 * Returns 0 on success, negative value on failure (the sessiond socket path
 * is somehow too long or ENOMEM).
 */
static int set_session_daemon_path(void)
{
        int in_tgroup = 0;      /* In tracing group. */
        uid_t uid;

        uid = getuid();

        if (uid != 0) {
                /* Are we in the tracing group ? */
                in_tgroup = lttng_check_tracing_group();
        }

        if ((uid == 0) || in_tgroup == 1) {
                const int ret = lttng_strncpy(sessiond_sock_path,
                                DEFAULT_GLOBAL_CLIENT_UNIX_SOCK,
                                sizeof(sessiond_sock_path));

                if (ret) {
                        goto error;
                }
        }

        if (uid != 0) {
                int ret;

                if (in_tgroup) {
                        /* Tracing group. */
                        ret = try_connect_sessiond(sessiond_sock_path);
                        if (ret >= 0) {
                                goto end;
                        }
                        /* Global session daemon not available... */
                }
                /* ...or not in tracing group (and not root), default */

                /*
                 * With GNU C <  2.1, snprintf returns -1 if the target buffer
                 * is too small;
                 * With GNU C >= 2.1, snprintf returns the required size
                 * (excluding closing null)
                 */
                ret = snprintf(sessiond_sock_path, sizeof(sessiond_sock_path),
                                DEFAULT_HOME_CLIENT_UNIX_SOCK, utils_get_home_dir());
                if ((ret < 0) || (ret >= sizeof(sessiond_sock_path))) {
                        goto error;
                }
        }
end:
        return 0;

error:
        return -1;
}

/*
 * Connect to the LTTng session daemon.
 *
 * On success, return the socket's file descriptor. On error, return -1.
 */
int connect_sessiond(void)
{
        int ret;

        ret = set_session_daemon_path();
        if (ret < 0) {
                goto error;
        }

        /* Connect to the sesssion daemon. */
        ret = lttcomm_connect_unix_sock(sessiond_sock_path);
        if (ret < 0) {
                goto error;
        }

        return ret;

error:
        return -1;
}

static void reset_global_sessiond_connection_state(void)
{
        sessiond_socket = -1;
        connected = 0;
}

/*
 *  Clean disconnect from the session daemon.
 *
 *  On success, return 0. On error, return -1.
 */
static int disconnect_sessiond(void)
{
        int ret = 0;

        if (connected) {
                ret = lttcomm_close_unix_sock(sessiond_socket);
                reset_global_sessiond_connection_state();
        }

        return ret;
}

static int recv_sessiond_optional_data(size_t len, void **user_buf,
        size_t *user_len)
{
        int ret = 0;
        char *buf = NULL;

        if (len) {
                if (!user_len) {
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }

                buf = zmalloc<char>(len);
                if (!buf) {
                        ret = -ENOMEM;
                        goto end;
                }

                ret = recv_data_sessiond(buf, len);
                if (ret < 0) {
                        goto end;
                }

                if (!user_buf) {
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }

                /* Move ownership of command header buffer to user. */
                *user_buf = buf;
                buf = NULL;
                *user_len = len;
        } else {
                /* No command header. */
                if (user_len) {
                        *user_len = 0;
                }

                if (user_buf) {
                        *user_buf = NULL;
                }
        }

end:
        free(buf);
        return ret;
}

/*
 * Ask the session daemon a specific command and put the data into buf.
 * Takes extra var. len. data and file descriptors as input to send to the
 * session daemon.
 *
 * Return size of data (only payload, not header) or a negative error code.
 */
int lttng_ctl_ask_sessiond_fds_varlen(struct lttcomm_session_msg *lsm,
                const int *fds, size_t nb_fd, const void *vardata,
                size_t vardata_len, void **user_payload_buf,
                void **user_cmd_header_buf, size_t *user_cmd_header_len)
{
        int ret;
        size_t payload_len;
        struct lttcomm_lttng_msg llm;

        ret = connect_sessiond();
        if (ret < 0) {
                ret = -LTTNG_ERR_NO_SESSIOND;
                goto end;
        } else {
                sessiond_socket = ret;
                connected = 1;
        }

        ret = send_session_msg(lsm);
        if (ret < 0) {
                /* Ret value is a valid lttng error code. */
                goto end;
        }
        /* Send var len data */
        ret = send_session_varlen(vardata, vardata_len);
        if (ret < 0) {
                /* Ret value is a valid lttng error code. */
                goto end;
        }

        /* Send fds */
        ret = send_session_fds(fds, nb_fd);
        if (ret < 0) {
                /* Ret value is a valid lttng error code. */
                goto end;
        }

        /* Get header from data transmission */
        ret = recv_data_sessiond(&llm, sizeof(llm));
        if (ret < 0) {
                /* Ret value is a valid lttng error code. */
                goto end;
        }

        /* Check error code if OK */
        if (llm.ret_code != LTTNG_OK) {
                ret = -llm.ret_code;
                goto end;
        }

        /* Get command header from data transmission */
        ret = recv_sessiond_optional_data(llm.cmd_header_size,
                user_cmd_header_buf, user_cmd_header_len);
        if (ret < 0) {
                goto end;
        }

        /* Get payload from data transmission */
        ret = recv_sessiond_optional_data(llm.data_size, user_payload_buf,
                &payload_len);
        if (ret < 0) {
                goto end;
        }

        ret = llm.data_size;

end:
        disconnect_sessiond();
        return ret;
}

int lttng_ctl_ask_sessiond_payload(struct lttng_payload_view *message,
        struct lttng_payload *reply)
{
        int ret;
        struct lttcomm_lttng_msg llm;
        const int fd_count = lttng_payload_view_get_fd_handle_count(message);

        LTTNG_ASSERT(reply->buffer.size == 0);
        LTTNG_ASSERT(lttng_dynamic_pointer_array_get_count(&reply->_fd_handles) == 0);

        ret = connect_sessiond();
        if (ret < 0) {
                ret = -LTTNG_ERR_NO_SESSIOND;
                goto end;
        } else {
                sessiond_socket = ret;
                connected = 1;
        }

        /* Send command to session daemon */
        ret = lttcomm_send_creds_unix_sock(sessiond_socket, message->buffer.data,
                        message->buffer.size);
        if (ret < 0) {
                ret = -LTTNG_ERR_FATAL;
                goto end;
        }

        if (fd_count > 0) {
                ret = lttcomm_send_payload_view_fds_unix_sock(sessiond_socket,
                                message);
                if (ret < 0) {
                        ret = -LTTNG_ERR_FATAL;
                        goto end;
                }
        }

        /* Get header from data transmission */
        ret = recv_payload_sessiond(reply, sizeof(llm));
        if (ret < 0) {
                /* Ret value is a valid lttng error code. */
                goto end;
        }

        llm = *((typeof(llm) *) reply->buffer.data);

        /* Check error code if OK */
        if (llm.ret_code != LTTNG_OK) {
                if (llm.ret_code < LTTNG_OK || llm.ret_code >= LTTNG_ERR_NR) {
                        /* Invalid error code received. */
                        ret = -LTTNG_ERR_UNK;
                } else {
                        ret = -llm.ret_code;
                }
                goto end;
        }

        if (llm.cmd_header_size > 0) {
                ret = recv_payload_sessiond(reply, llm.cmd_header_size);
                if (ret < 0) {
                        goto end;
                }
        }

        /* Get command header from data transmission */
        if (llm.data_size > 0) {
                ret = recv_payload_sessiond(reply, llm.data_size);
                if (ret < 0) {
                        goto end;
                }
        }

        if (llm.fd_count > 0) {
                ret = lttcomm_recv_payload_fds_unix_sock(
                                sessiond_socket, llm.fd_count, reply);
                if (ret < 0) {
                        goto end;
                }
        }

        /* Don't return the llm header to the caller. */
        memmove(reply->buffer.data, reply->buffer.data + sizeof(llm),
                        reply->buffer.size - sizeof(llm));
        ret = lttng_dynamic_buffer_set_size(
                        &reply->buffer, reply->buffer.size - sizeof(llm));
        if (ret) {
                /* Can't happen as size is reduced. */
                abort();
        }

        ret = reply->buffer.size;

end:
        disconnect_sessiond();
        return ret;
}

/*
 * Create lttng handle and return pointer.
 *
 * The returned pointer will be NULL in case of malloc() error.
 */
struct lttng_handle *lttng_create_handle(const char *session_name,
                struct lttng_domain *domain)
{
        int ret;
        struct lttng_handle *handle = NULL;

        handle = zmalloc<lttng_handle>();
        if (handle == NULL) {
                PERROR("malloc handle");
                goto end;
        }

        /* Copy session name */
        ret = lttng_strncpy(handle->session_name, session_name ? : "",
                            sizeof(handle->session_name));
        if (ret) {
                goto error;
        }

        /* Copy lttng domain or leave initialized to 0. */
        if (domain) {
                lttng_ctl_copy_lttng_domain(&handle->domain, domain);
        }

end:
        return handle;
error:
        free(handle);
        return NULL;
}

/*
 * Destroy handle by free(3) the pointer.
 */
void lttng_destroy_handle(struct lttng_handle *handle)
{
        free(handle);
}

/*
 * Register an outside consumer.
 *
 * Returns size of returned session payload data or a negative error code.
 */
int lttng_register_consumer(struct lttng_handle *handle,
                const char *socket_path)
{
        int ret;
        struct lttcomm_session_msg lsm;

        if (handle == NULL || socket_path == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_REGISTER_CONSUMER;
        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        ret = lttng_strncpy(lsm.u.reg.path, socket_path,
                            sizeof(lsm.u.reg.path));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
end:
        return ret;
}

/*
 * Start tracing for all traces of the session.
 *
 * Returns size of returned session payload data or a negative error code.
 */
int lttng_start_tracing(const char *session_name)
{
        int ret;
        struct lttcomm_session_msg lsm;

        if (session_name == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_START_TRACE;

        ret = lttng_strncpy(lsm.session.name, session_name,
                            sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
end:
        return ret;
}

/*
 * Stop tracing for all traces of the session.
 */
static int _lttng_stop_tracing(const char *session_name, int wait)
{
        int ret, data_ret;
        struct lttcomm_session_msg lsm;

        if (session_name == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_STOP_TRACE;

        ret = lttng_strncpy(lsm.session.name, session_name,
                            sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
        if (ret < 0 && ret != -LTTNG_ERR_TRACE_ALREADY_STOPPED) {
                goto error;
        }

        if (!wait) {
                goto end;
        }

        /* Check for data availability */
        do {
                data_ret = lttng_data_pending(session_name);
                if (data_ret < 0) {
                        /* Return the data available call error. */
                        ret = data_ret;
                        goto error;
                }

                /*
                 * Data sleep time before retrying (in usec). Don't sleep if the
                 * call returned value indicates availability.
                 */
                if (data_ret) {
                        usleep(DEFAULT_DATA_AVAILABILITY_WAIT_TIME_US);
                }
        } while (data_ret != 0);

end:
error:
        return ret;
}

/*
 * Stop tracing and wait for data availability.
 */
int lttng_stop_tracing(const char *session_name)
{
        return _lttng_stop_tracing(session_name, 1);
}

/*
 * Stop tracing but _don't_ wait for data availability.
 */
int lttng_stop_tracing_no_wait(const char *session_name)
{
        return _lttng_stop_tracing(session_name, 0);
}

/*
 * Add context to a channel.
 *
 * If the given channel is NULL, add the contexts to all channels.
 * The event_name param is ignored.
 *
 * Returns the size of the returned payload data or a negative error code.
 */
int lttng_add_context(struct lttng_handle *handle,
                struct lttng_event_context *ctx,
                const char *event_name __attribute__((unused)),
                const char *channel_name)
{
        int ret;
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_ADD_CONTEXT,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        struct lttng_payload payload;

        lttng_payload_init(&payload);

        /* Safety check. Both are mandatory. */
        if (handle == NULL || ctx == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_dynamic_buffer_set_size(&payload.buffer, sizeof(lsm));
        if (ret) {
                ret = -LTTNG_ERR_NOMEM;
                goto end;
        }

        /* If no channel name, send empty string. */
        ret = lttng_strncpy(lsm.u.context.channel_name, channel_name ?: "",
                        sizeof(lsm.u.context.channel_name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);
        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_event_context_serialize(ctx, &payload);
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        lsm.u.context.length = payload.buffer.size - sizeof(lsm);

        /* Update message header. */
        memcpy(payload.buffer.data, &lsm, sizeof(lsm));

        {
                struct lttng_payload reply;
                struct lttng_payload_view payload_view =
                                lttng_payload_view_from_payload(&payload, 0,
                                -1);

                lttng_payload_init(&reply);
                ret = lttng_ctl_ask_sessiond_payload(&payload_view, &reply);
                lttng_payload_reset(&reply);
                if (ret) {
                        goto end;
                }
        }

end:
        lttng_payload_reset(&payload);
        return ret;
}

/*
 * Enable event(s) for a channel.
 *
 * If no event name is specified, all events are enabled.
 * If no channel name is specified, the default 'channel0' is used.
 *
 * Returns size of returned session payload data or a negative error code.
 */
int lttng_enable_event(struct lttng_handle *handle,
                struct lttng_event *ev, const char *channel_name)
{
        return lttng_enable_event_with_exclusions(handle, ev, channel_name,
                        NULL, 0, NULL);
}

/*
 * Create or enable an event with a filter expression.
 *
 * Return negative error value on error.
 * Return size of returned session payload data if OK.
 */
int lttng_enable_event_with_filter(struct lttng_handle *handle,
                struct lttng_event *event, const char *channel_name,
                const char *filter_expression)
{
        return lttng_enable_event_with_exclusions(handle, event, channel_name,
                        filter_expression, 0, NULL);
}

/*
 * Depending on the event, return a newly allocated agent filter expression or
 * NULL if not applicable.
 *
 * An event with NO loglevel and the name is * will return NULL.
 */
static char *set_agent_filter(const char *filter, struct lttng_event *ev)
{
        int err;
        char *agent_filter = NULL;

        LTTNG_ASSERT(ev);

        /* Don't add filter for the '*' event. */
        if (strcmp(ev->name, "*") != 0) {
                if (filter) {
                        err = asprintf(&agent_filter, "(%s) && (logger_name == \"%s\")", filter,
                                        ev->name);
                } else {
                        err = asprintf(&agent_filter, "logger_name == \"%s\"", ev->name);
                }
                if (err < 0) {
                        PERROR("asprintf");
                        goto error;
                }
        }

        /* Add loglevel filtering if any for the JUL domain. */
        if (ev->loglevel_type != LTTNG_EVENT_LOGLEVEL_ALL) {
                const char *op;

                if (ev->loglevel_type == LTTNG_EVENT_LOGLEVEL_RANGE) {
                        op = ">=";
                } else {
                        op = "==";
                }

                if (filter || agent_filter) {
                        char *new_filter;

                        err = asprintf(&new_filter, "(%s) && (int_loglevel %s %d)",
                                        agent_filter ? agent_filter : filter, op,
                                        ev->loglevel);
                        if (agent_filter) {
                                free(agent_filter);
                        }
                        agent_filter = new_filter;
                } else {
                        err = asprintf(&agent_filter, "int_loglevel %s %d", op,
                                        ev->loglevel);
                }
                if (err < 0) {
                        PERROR("asprintf");
                        goto error;
                }
        }

        return agent_filter;
error:
        free(agent_filter);
        return NULL;
}

/*
 * Enable event(s) for a channel, possibly with exclusions and a filter.
 * If no event name is specified, all events are enabled.
 * If no channel name is specified, the default name is used.
 * If filter expression is not NULL, the filter is set for the event.
 * If exclusion count is not zero, the exclusions are set for the event.
 * Returns size of returned session payload data or a negative error code.
 */
int lttng_enable_event_with_exclusions(struct lttng_handle *handle,
                struct lttng_event *ev, const char *channel_name,
                const char *original_filter_expression,
                int exclusion_count, char **exclusion_list)
{
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_ENABLE_EVENT,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        struct lttng_payload payload;
        int ret = 0;
        unsigned int free_filter_expression = 0;
        struct filter_parser_ctx *ctx = NULL;
        size_t bytecode_len = 0;

        /*
         * We have either a filter or some exclusions, so we need to set up
         * a variable-length payload from where to send the data.
         */
        lttng_payload_init(&payload);

        /*
         * Cast as non-const since we may replace the filter expression
         * by a dynamically allocated string. Otherwise, the original
         * string is not modified.
         */
        char *filter_expression = (char *) original_filter_expression;

        if (handle == NULL || ev == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /*
         * Empty filter string will always be rejected by the parser
         * anyway, so treat this corner-case early to eliminate
         * lttng_fmemopen error for 0-byte allocation.
         */
        if (filter_expression && filter_expression[0] == '\0') {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        if (ev->name[0] == '\0') {
                /* Enable all events. */
                ret = lttng_strncpy(ev->name, "*", sizeof(ev->name));
                LTTNG_ASSERT(ret == 0);
        }

        /* Parse filter expression. */
        if (filter_expression != NULL || handle->domain.type == LTTNG_DOMAIN_JUL
                        || handle->domain.type == LTTNG_DOMAIN_LOG4J
                        || handle->domain.type == LTTNG_DOMAIN_PYTHON) {
                if (handle->domain.type == LTTNG_DOMAIN_JUL ||
                                handle->domain.type == LTTNG_DOMAIN_LOG4J ||
                                handle->domain.type == LTTNG_DOMAIN_PYTHON) {
                        char *agent_filter;

                        /* Setup agent filter if needed. */
                        agent_filter = set_agent_filter(filter_expression, ev);
                        if (!agent_filter) {
                                if (!filter_expression) {
                                        /*
                                         * No JUL and no filter, just skip
                                         * everything below.
                                         */
                                        goto serialize;
                                }
                        } else {
                                /*
                                 * With an agent filter, the original filter has
                                 * been added to it thus replace the filter
                                 * expression.
                                 */
                                filter_expression = agent_filter;
                                free_filter_expression = 1;
                        }
                }

                if (strnlen(filter_expression, LTTNG_FILTER_MAX_LEN) ==
                                LTTNG_FILTER_MAX_LEN) {
                        ret = -LTTNG_ERR_FILTER_INVAL;
                        goto error;
                }

                ret = filter_parser_ctx_create_from_filter_expression(filter_expression, &ctx);
                if (ret) {
                        goto error;
                }

                bytecode_len = bytecode_get_len(&ctx->bytecode->b) +
                                sizeof(ctx->bytecode->b);
                if (bytecode_len > LTTNG_FILTER_MAX_LEN) {
                        ret = -LTTNG_ERR_FILTER_INVAL;
                        goto error;
                }
        }

serialize:
        ret = lttng_event_serialize(ev, exclusion_count, exclusion_list,
                        filter_expression, bytecode_len,
                        (ctx && bytecode_len) ? &ctx->bytecode->b : NULL,
                        &payload);
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /* If no channel name, send empty string. */
        ret = lttng_strncpy(lsm.u.enable.channel_name, channel_name ?: "",
                        sizeof(lsm.u.enable.channel_name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /* Domain */
        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        /* Session name */
        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /* Length of the serialized event. */
        lsm.u.enable.length = (uint32_t) payload.buffer.size;

        {
                struct lttng_payload_view view = lttng_payload_view_from_payload(
                        &payload, 0, -1);
                int fd_count = lttng_payload_view_get_fd_handle_count(&view);
                int fd_to_send;

                if (fd_count < 0) {
                        goto error;
                }

                LTTNG_ASSERT(fd_count == 0 || fd_count == 1);
                if (fd_count == 1) {
                        struct fd_handle *h =
                                        lttng_payload_view_pop_fd_handle(&view);

                        if (!h) {
                                goto error;
                        }

                        fd_to_send = fd_handle_get_fd(h);
                        fd_handle_put(h);
                }

                lsm.fd_count = fd_count;

                ret = lttng_ctl_ask_sessiond_fds_varlen(&lsm,
                                fd_count ? &fd_to_send : NULL, fd_count,
                                view.buffer.size ? view.buffer.data : NULL,
                                view.buffer.size, NULL, NULL, 0);
        }

error:
        if (filter_expression && ctx) {
                filter_bytecode_free(ctx);
                filter_ir_free(ctx);
                filter_parser_ctx_free(ctx);
        }
        if (free_filter_expression) {
                /*
                 * The filter expression has been replaced and must be freed as
                 * it is not the original filter expression received as a
                 * parameter.
                 */
                free(filter_expression);
        }
        /*
         * Return directly to the caller and don't ask the sessiond since
         * something went wrong in the parsing of data above.
         */
        lttng_payload_reset(&payload);
        return ret;
}

int lttng_disable_event_ext(struct lttng_handle *handle,
                struct lttng_event *ev, const char *channel_name,
                const char *original_filter_expression)
{
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_DISABLE_EVENT,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        struct lttng_payload payload;
        int ret = 0;
        unsigned int free_filter_expression = 0;
        struct filter_parser_ctx *ctx = NULL;
        size_t bytecode_len = 0;

        /*
         * We have either a filter or some exclusions, so we need to set up
         * a variable-length payload from where to send the data.
         */
        lttng_payload_init(&payload);

        /*
         * Cast as non-const since we may replace the filter expression
         * by a dynamically allocated string. Otherwise, the original
         * string is not modified.
         */
        char *filter_expression = (char *) original_filter_expression;

        if (handle == NULL || ev == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /*
         * Empty filter string will always be rejected by the parser
         * anyway, so treat this corner-case early to eliminate
         * lttng_fmemopen error for 0-byte allocation.
         */
        if (filter_expression && filter_expression[0] == '\0') {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /* Parse filter expression. */
        if (filter_expression != NULL || handle->domain.type == LTTNG_DOMAIN_JUL
                        || handle->domain.type == LTTNG_DOMAIN_LOG4J
                        || handle->domain.type == LTTNG_DOMAIN_PYTHON) {
                if (handle->domain.type == LTTNG_DOMAIN_JUL ||
                                handle->domain.type == LTTNG_DOMAIN_LOG4J ||
                                handle->domain.type == LTTNG_DOMAIN_PYTHON) {
                        char *agent_filter;

                        /* Setup agent filter if needed. */
                        agent_filter = set_agent_filter(filter_expression, ev);
                        if (!agent_filter) {
                                if (!filter_expression) {
                                        /*
                                         * No JUL and no filter, just skip
                                         * everything below.
                                         */
                                        goto serialize;
                                }
                        } else {
                                /*
                                 * With an agent filter, the original filter has
                                 * been added to it thus replace the filter
                                 * expression.
                                 */
                                filter_expression = agent_filter;
                                free_filter_expression = 1;
                        }
                }

                if (strnlen(filter_expression, LTTNG_FILTER_MAX_LEN) ==
                                LTTNG_FILTER_MAX_LEN) {
                        ret = -LTTNG_ERR_FILTER_INVAL;
                        goto error;
                }

                ret = filter_parser_ctx_create_from_filter_expression(filter_expression, &ctx);
                if (ret) {
                        goto error;
                }

                bytecode_len = bytecode_get_len(&ctx->bytecode->b) +
                                sizeof(ctx->bytecode->b);
                if (bytecode_len > LTTNG_FILTER_MAX_LEN) {
                        ret = -LTTNG_ERR_FILTER_INVAL;
                        goto error;
                }
        }

serialize:
        ret = lttng_event_serialize(ev, 0, NULL,
                        filter_expression, bytecode_len,
                        (ctx && bytecode_len) ? &ctx->bytecode->b : NULL,
                        &payload);
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /* If no channel name, send empty string. */
        ret = lttng_strncpy(lsm.u.disable.channel_name, channel_name ?: "",
                        sizeof(lsm.u.disable.channel_name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /* Domain */
        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        /* Session name */
        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        /* Length of the serialized event. */
        lsm.u.disable.length = (uint32_t) payload.buffer.size;

        {
                struct lttng_payload_view view = lttng_payload_view_from_payload(
                        &payload, 0, -1);
                int fd_count = lttng_payload_view_get_fd_handle_count(&view);
                int fd_to_send;

                if (fd_count < 0) {
                        goto error;
                }

                LTTNG_ASSERT(fd_count == 0 || fd_count == 1);
                if (fd_count == 1) {
                        struct fd_handle *h =
                                        lttng_payload_view_pop_fd_handle(&view);

                        if (!h) {
                                goto error;
                        }

                        fd_to_send = fd_handle_get_fd(h);
                        fd_handle_put(h);
                }

                ret = lttng_ctl_ask_sessiond_fds_varlen(&lsm,
                                fd_count ? &fd_to_send : NULL, fd_count,
                                view.buffer.size ? view.buffer.data : NULL,
                                view.buffer.size, NULL, NULL, 0);
        }

error:
        if (filter_expression && ctx) {
                filter_bytecode_free(ctx);
                filter_ir_free(ctx);
                filter_parser_ctx_free(ctx);
        }
        if (free_filter_expression) {
                /*
                 * The filter expression has been replaced and must be freed as
                 * it is not the original filter expression received as a
                 * parameter.
                 */
                free(filter_expression);
        }
        /*
         * Return directly to the caller and don't ask the sessiond since
         * something went wrong in the parsing of data above.
         */
        lttng_payload_reset(&payload);
        return ret;
}

/*
 * Disable event(s) of a channel and domain.
 * If no event name is specified, all events are disabled.
 * If no channel name is specified, the default 'channel0' is used.
 * Returns size of returned session payload data or a negative error code.
 */
int lttng_disable_event(struct lttng_handle *handle, const char *name,
                const char *channel_name)
{
        int ret;
        struct lttng_event ev;

        memset(&ev, 0, sizeof(ev));
        ev.loglevel = -1;
        ev.type = LTTNG_EVENT_ALL;
        ret = lttng_strncpy(ev.name, name ?: "", sizeof(ev.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_disable_event_ext(handle, &ev, channel_name, NULL);
end:
        return ret;
}

struct lttng_channel *lttng_channel_create(struct lttng_domain *domain)
{
        struct lttng_channel *channel = NULL;

        if (!domain) {
                goto end;
        }

        /* Validate domain. */
        switch (domain->type) {
        case LTTNG_DOMAIN_UST:
                switch (domain->buf_type) {
                case LTTNG_BUFFER_PER_UID:
                case LTTNG_BUFFER_PER_PID:
                        break;
                default:
                        goto end;
                }
                break;
        case LTTNG_DOMAIN_KERNEL:
                if (domain->buf_type != LTTNG_BUFFER_GLOBAL) {
                        goto end;
                }
                break;
        default:
                goto end;
        }

        channel = lttng_channel_create_internal();
        if (!channel) {
                goto end;
        }

        lttng_channel_set_default_attr(domain, &channel->attr);
end:
        return channel;
}

void lttng_channel_destroy(struct lttng_channel *channel)
{
        if (!channel) {
                return;
        }

        if (channel->attr.extended.ptr) {
                free(channel->attr.extended.ptr);
        }
        free(channel);
}

/*
 * Enable channel per domain
 * Returns size of returned session payload data or a negative error code.
 */
int lttng_enable_channel(struct lttng_handle *handle,
                struct lttng_channel *in_chan)
{
        enum lttng_error_code ret_code;
        int ret;
        struct lttng_dynamic_buffer buffer;
        struct lttcomm_session_msg lsm;
        uint64_t total_buffer_size_needed_per_cpu = 0;
        struct lttng_channel *channel = NULL;

        lttng_dynamic_buffer_init(&buffer);

        /* NULL arguments are forbidden. No default values. */
        if (handle == NULL || in_chan == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        /*
         * Verify that the amount of memory required to create the requested
         * buffer is available on the system at the moment.
         */
        if (in_chan->attr.num_subbuf >
                        UINT64_MAX / in_chan->attr.subbuf_size) {
                /* Overflow */
                ret = -LTTNG_ERR_OVERFLOW;
                goto end;
        }

        total_buffer_size_needed_per_cpu =
                        in_chan->attr.num_subbuf * in_chan->attr.subbuf_size;
        ret_code = check_enough_available_memory(
                        total_buffer_size_needed_per_cpu);
        if (ret_code != LTTNG_OK) {
                ret = -ret_code;
                goto end;
        }

        /* Copy the channel for easier manipulation. */
        channel = lttng_channel_copy(in_chan);
        if (!channel) {
                ret = -LTTNG_ERR_NOMEM;
                goto end;
        }

        /* Populate the channel extended attribute if necessary. */
        if (!channel->attr.extended.ptr) {
                struct lttng_channel_extended *extended =
                                zmalloc<lttng_channel_extended>();

                if (!extended) {
                        ret = -LTTNG_ERR_NOMEM;
                        goto end;
                }

                lttng_channel_set_default_extended_attr(
                                &handle->domain, extended);
                channel->attr.extended.ptr = extended;
        }

        /* Prepare the payload */
        memset(&lsm, 0, sizeof(lsm));

        lsm.cmd_type = LTTNG_ENABLE_CHANNEL;
        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                                    sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_channel_serialize(channel, &buffer);
        if (ret) {
                ret = -LTTNG_ERR_FATAL;
                goto end;
        }

        lsm.u.channel.length = buffer.size;

        ret = lttng_ctl_ask_sessiond_varlen_no_cmd_header(
                        &lsm, buffer.data, buffer.size, NULL);
end:
        lttng_channel_destroy(channel);
        lttng_dynamic_buffer_reset(&buffer);
        return ret;
}

/*
 * All tracing will be stopped for registered events of the channel.
 * Returns size of returned session payload data or a negative error code.
 */
int lttng_disable_channel(struct lttng_handle *handle, const char *name)
{
        int ret;
        struct lttcomm_session_msg lsm;

        /* Safety check. Both are mandatory. */
        if (handle == NULL || name == NULL) {
                return -LTTNG_ERR_INVALID;
        }

        memset(&lsm, 0, sizeof(lsm));

        lsm.cmd_type = LTTNG_DISABLE_CHANNEL;

        ret = lttng_strncpy(lsm.u.disable.channel_name, name,
                        sizeof(lsm.u.disable.channel_name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                            sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
end:
        return ret;
}

/*
 * Lists all available tracepoints of domain.
 * Sets the contents of the events array.
 * Returns the number of lttng_event entries in events;
 * on error, returns a negative value.
 */
int lttng_list_tracepoints(struct lttng_handle *handle,
                struct lttng_event **events)
{
        enum lttng_error_code ret_code;
        int ret, total_payload_received;
        char *reception_buffer = NULL;
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_LIST_TRACEPOINTS,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        struct lttcomm_list_command_header *cmd_header = NULL;
        size_t cmd_header_len;
        unsigned int nb_events = 0;

        if (handle == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        ret = lttng_ctl_ask_sessiond_fds_varlen(&lsm, NULL, 0, NULL, 0,
                        (void **) &reception_buffer, (void **) &cmd_header,
                        &cmd_header_len);
        if (ret < 0) {
                goto end;
        }

        total_payload_received = ret;

        if (!cmd_header) {
                ret = -LTTNG_ERR_UNK;
                goto end;
        }

        if (cmd_header->count > INT_MAX) {
                ret = -LTTNG_ERR_OVERFLOW;
                goto end;
        }

        nb_events = (unsigned int) cmd_header->count;

        {
                struct lttng_buffer_view events_view =
                                lttng_buffer_view_init(reception_buffer, 0,
                                                total_payload_received);
                struct lttng_payload_view events_payload_view =
                                lttng_payload_view_from_buffer_view(
                                                &events_view, 0, -1);

                ret_code = lttng_events_create_and_flatten_from_payload(
                                &events_payload_view, nb_events, events);
                if (ret_code != LTTNG_OK) {
                        ret = -ret_code;
                        goto end;
                }
        }

        ret = (int) nb_events;

end:
        free(cmd_header);
        free(reception_buffer);
        return ret;
}

/*
 * Lists all available tracepoint fields of domain.
 * Sets the contents of the event field array.
 * Returns the number of lttng_event_field entries in events;
 * on error, returns a negative value.
 */
int lttng_list_tracepoint_fields(struct lttng_handle *handle,
                struct lttng_event_field **fields)
{
        enum lttng_error_code ret_code;
        int ret;
        struct lttcomm_session_msg lsm;
        const struct lttcomm_list_command_header *cmd_header = NULL;
        unsigned int nb_event_fields = 0;
        struct lttng_payload reply;

        lttng_payload_init(&reply);

        if (handle == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_LIST_TRACEPOINT_FIELDS;
        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        {
                lttng_payload_view message_view =
                                lttng_payload_view_init_from_buffer(
                                        (const char *) &lsm, 0,
                                        sizeof(lsm));

                ret = lttng_ctl_ask_sessiond_payload(&message_view, &reply);
                if (ret < 0) {
                        goto end;
                }
        }

        {
                const lttng_buffer_view cmd_header_view =
                                lttng_buffer_view_from_dynamic_buffer(
                                        &reply.buffer, 0, sizeof(*cmd_header));

                if (!lttng_buffer_view_is_valid(&cmd_header_view)) {
                        ret = -LTTNG_ERR_INVALID_PROTOCOL;
                        goto end;
                }

                cmd_header = (struct lttcomm_list_command_header *)
                                cmd_header_view.data;
        }

        if (cmd_header->count > INT_MAX) {
                ret = -LTTNG_ERR_OVERFLOW;
                goto end;
        }

        nb_event_fields = cmd_header->count;

        {
                lttng_payload_view reply_view =
                                lttng_payload_view_from_payload(&reply,
                                sizeof(*cmd_header), -1);

                ret_code = lttng_event_fields_create_and_flatten_from_payload(
                                &reply_view, nb_event_fields, fields);
                if (ret_code != LTTNG_OK) {
                        ret = -ret_code;
                        goto end;
                }
        }

        ret = nb_event_fields;

end:
        lttng_payload_reset(&reply);
        return ret;
}

/*
 * Lists all available kernel system calls. Allocates and sets the contents of
 * the events array.
 *
 * Returns the number of lttng_event entries in events; on error, returns a
 * negative value.
 */
int lttng_list_syscalls(struct lttng_event **events)
{
        enum lttng_error_code ret_code;
        int ret, total_payload_received;
        char *reception_buffer = NULL;
        struct lttcomm_session_msg lsm = {};
        struct lttcomm_list_command_header *cmd_header = NULL;
        size_t cmd_header_len;
        uint32_t nb_events = 0;

        if (!events) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        lsm.cmd_type = LTTNG_LIST_SYSCALLS;
        /* Force kernel domain for system calls. */
        lsm.domain.type = LTTNG_DOMAIN_KERNEL;

        ret = lttng_ctl_ask_sessiond_fds_varlen(&lsm, NULL, 0, NULL, 0,
                        (void **) &reception_buffer, (void **) &cmd_header,
                        &cmd_header_len);
        if (ret < 0) {
                goto end;
        }
        total_payload_received = ret;

        if (!cmd_header) {
                ret = -LTTNG_ERR_UNK;
                goto end;
        }

        if (cmd_header->count > INT_MAX) {
                ret = -LTTNG_ERR_OVERFLOW;
                goto end;
        }

        nb_events = (unsigned int) cmd_header->count;

        {
                const struct lttng_buffer_view events_view =
                                lttng_buffer_view_init(reception_buffer, 0,
                                                total_payload_received);
                struct lttng_payload_view events_payload_view =
                                lttng_payload_view_from_buffer_view(
                                                &events_view, 0, -1);

                ret_code = lttng_events_create_and_flatten_from_payload(
                                &events_payload_view, nb_events, events);
                if (ret_code != LTTNG_OK) {
                        ret = -ret_code;
                        goto end;
                }
        }

        ret = (int) nb_events;

end:
        free(reception_buffer);
        free(cmd_header);
        return ret;
}

/*
 * Returns a human readable string describing
 * the error code (positive or negative value).
 */
const char *lttng_strerror(int code)
{
        if (code > 0) {
                code = -code;
        }

        return error_get_str(code);
}

enum lttng_error_code lttng_create_session_ext(
                struct lttng_session_descriptor *session_descriptor)
{
        enum lttng_error_code ret_code;
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_CREATE_SESSION_EXT,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        void *reply = NULL;
        struct lttng_buffer_view reply_view;
        int reply_ret;
        bool sessiond_must_generate_ouput;
        struct lttng_payload payload;
        int ret;
        size_t descriptor_size;
        struct lttng_session_descriptor *descriptor_reply = NULL;

        lttng_payload_init(&payload);
        if (!session_descriptor) {
                ret_code = LTTNG_ERR_INVALID;
                goto end;
        }

        sessiond_must_generate_ouput =
                        !lttng_session_descriptor_is_output_destination_initialized(
                                session_descriptor);
        if (sessiond_must_generate_ouput) {
                const char *home_dir = utils_get_home_dir();
                size_t home_dir_len = home_dir ? strlen(home_dir) + 1 : 0;

                if (!home_dir || home_dir_len > LTTNG_PATH_MAX) {
                        ret_code = LTTNG_ERR_FATAL;
                        goto end;
                }

                lsm.u.create_session.home_dir_size = (uint16_t) home_dir_len;
                ret = lttng_dynamic_buffer_append(&payload.buffer, home_dir, home_dir_len);
                if (ret) {
                        ret_code = LTTNG_ERR_NOMEM;
                        goto end;
                }
        }

        descriptor_size = payload.buffer.size;
        ret = lttng_session_descriptor_serialize(session_descriptor,
                        &payload);
        if (ret) {
                ret_code = LTTNG_ERR_INVALID;
                goto end;
        }
        descriptor_size = payload.buffer.size - descriptor_size;
        lsm.u.create_session.session_descriptor_size = descriptor_size;

        /* Command returns a session descriptor on success. */
        reply_ret = lttng_ctl_ask_sessiond_varlen_no_cmd_header(
                        &lsm, payload.buffer.data, payload.buffer.size, &reply);
        if (reply_ret < 0) {
                ret_code = (lttng_error_code) -reply_ret;
                goto end;
        } else if (reply_ret == 0) {
                /* Socket unexpectedly closed by the session daemon. */
                ret_code = LTTNG_ERR_FATAL;
                goto end;
        }

        reply_view = lttng_buffer_view_init((const char *) reply, 0, reply_ret);
        ret = lttng_session_descriptor_create_from_buffer(&reply_view,
                        &descriptor_reply);
        if (ret < 0) {
                ret_code = LTTNG_ERR_FATAL;
                goto end;
        }
        ret_code = LTTNG_OK;
        lttng_session_descriptor_assign(session_descriptor, descriptor_reply);
end:
        free(reply);
        lttng_payload_reset(&payload);
        lttng_session_descriptor_destroy(descriptor_reply);
        return ret_code;
}

/*
 * Create a new session using name and url for destination.
 *
 * Return 0 on success else a negative LTTng error code.
 */
int lttng_create_session(const char *name, const char *url)
{
        int ret;
        ssize_t size;
        struct lttng_uri *uris = NULL;
        struct lttng_session_descriptor *descriptor = NULL;
        enum lttng_error_code ret_code;

        if (!name) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        size = uri_parse_str_urls(url, NULL, &uris);
        if (size < 0) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }
        switch (size) {
        case 0:
                descriptor = lttng_session_descriptor_create(name);
                break;
        case 1:
                if (uris[0].dtype != LTTNG_DST_PATH) {
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }
                descriptor = lttng_session_descriptor_local_create(name,
                                uris[0].dst.path);
                break;
        case 2:
                descriptor = lttng_session_descriptor_network_create(name, url,
                                NULL);
                break;
        default:
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }
        if (!descriptor) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }
        ret_code = lttng_create_session_ext(descriptor);
        ret = ret_code == LTTNG_OK ? 0 : -ret_code;
end:
        lttng_session_descriptor_destroy(descriptor);
        free(uris);
        return ret;
}

/*
 * Create a session exclusively used for snapshot.
 *
 * Return 0 on success else a negative LTTng error code.
 */
int lttng_create_session_snapshot(const char *name, const char *snapshot_url)
{
        int ret;
        enum lttng_error_code ret_code;
        ssize_t size;
        struct lttng_uri *uris = NULL;
        struct lttng_session_descriptor *descriptor = NULL;

        if (!name) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        size = uri_parse_str_urls(snapshot_url, NULL, &uris);
        if (size < 0) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }
        /*
         * If the user does not specify a custom subdir, use the session name.
         */
        if (size > 0 && uris[0].dtype != LTTNG_DST_PATH &&
                        strlen(uris[0].subdir) == 0) {
                ret = snprintf(uris[0].subdir, sizeof(uris[0].subdir), "%s",
                                name);
                if (ret < 0) {
                        PERROR("Failed to set session name as network destination sub-directory");
                        ret = -LTTNG_ERR_FATAL;
                        goto end;
                } else if (ret >= sizeof(uris[0].subdir)) {
                        /* Truncated output. */
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }
        }

        switch (size) {
        case 0:
                descriptor = lttng_session_descriptor_snapshot_create(name);
                break;
        case 1:
                if (uris[0].dtype != LTTNG_DST_PATH) {
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }
                descriptor = lttng_session_descriptor_snapshot_local_create(
                                name,
                                uris[0].dst.path);
                break;
        case 2:
                descriptor = lttng_session_descriptor_snapshot_network_create(
                                name,
                                snapshot_url,
                                NULL);
                break;
        default:
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }
        if (!descriptor) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }
        ret_code = lttng_create_session_ext(descriptor);
        ret = ret_code == LTTNG_OK ? 0 : -ret_code;
end:
        lttng_session_descriptor_destroy(descriptor);
        free(uris);
        return ret;
}

/*
 * Create a session exclusively used for live.
 *
 * Return 0 on success else a negative LTTng error code.
 */
int lttng_create_session_live(const char *name, const char *url,
                unsigned int timer_interval)
{
        int ret;
        enum lttng_error_code ret_code;
        struct lttng_session_descriptor *descriptor = NULL;

        if (!name) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        if (url) {
                descriptor = lttng_session_descriptor_live_network_create(
                                name, url, NULL, timer_interval);
        } else {
                descriptor = lttng_session_descriptor_live_create(
                                name, timer_interval);
        }
        if (!descriptor) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }
        ret_code = lttng_create_session_ext(descriptor);
        ret = ret_code == LTTNG_OK ? 0 : -ret_code;
end:
        lttng_session_descriptor_destroy(descriptor);
        return ret;
}

/*
 * Stop the session and wait for the data before destroying it
 *
 * Return 0 on success else a negative LTTng error code.
 */
int lttng_destroy_session(const char *session_name)
{
        int ret;
        enum lttng_error_code ret_code;
        enum lttng_destruction_handle_status status;
        struct lttng_destruction_handle *handle = NULL;

        /*
         * Stop the tracing and wait for the data to be
         * consumed.
         */
        ret = _lttng_stop_tracing(session_name, 1);
        if (ret && ret != -LTTNG_ERR_TRACE_ALREADY_STOPPED) {
                goto end;
        }

        ret_code = lttng_destroy_session_ext(session_name, &handle);
        if (ret_code != LTTNG_OK) {
                ret = (int) -ret_code;
                goto end;
        }
        LTTNG_ASSERT(handle);

        /* Block until the completion of the destruction of the session. */
        status = lttng_destruction_handle_wait_for_completion(handle, -1);
        if (status != LTTNG_DESTRUCTION_HANDLE_STATUS_COMPLETED) {
                ret = -LTTNG_ERR_UNK;
                goto end;
        }

        status = lttng_destruction_handle_get_result(handle, &ret_code);
        if (status != LTTNG_DESTRUCTION_HANDLE_STATUS_OK) {
                ret = -LTTNG_ERR_UNK;
                goto end;
        }
        ret = ret_code == LTTNG_OK ? 0 : -ret_code;
end:
        lttng_destruction_handle_destroy(handle);
        return ret;
}

/*
 * Destroy the session without waiting for the data.
 */
int lttng_destroy_session_no_wait(const char *session_name)
{
        enum lttng_error_code ret_code;

        ret_code = lttng_destroy_session_ext(session_name, NULL);
        return ret_code == LTTNG_OK ? 0 : -ret_code;
}

/*
 * Ask the session daemon for all available sessions.
 * Sets the contents of the sessions array.
 * Returns the number of lttng_session entries in sessions;
 * on error, returns a negative value.
 */
int lttng_list_sessions(struct lttng_session **out_sessions)
{
        int ret;
        struct lttcomm_session_msg lsm = {};
        struct lttng_payload reply;
        struct lttng_payload_view lsm_view =
                        lttng_payload_view_init_from_buffer((const char *) &lsm, 0, sizeof(lsm));
        unsigned int nb_sessions = 0;

        lttng_payload_init(&reply);

        /* Initialize command parameters. */
        lsm.cmd_type = LTTNG_LIST_SESSIONS;

        /* Execute command against the session daemon. */
        ret = lttng_ctl_ask_sessiond_payload(&lsm_view, &reply);
        if (ret < 0) {
                goto end;
        }

        {
                const struct lttcomm_list_command_header *cmd_reply_header = NULL;
                const lttng_payload_view cmd_reply_header_view = lttng_payload_view_from_payload(
                                &reply, 0, sizeof(*cmd_reply_header));

                if (!lttng_payload_view_is_valid(&cmd_reply_header_view)) {
                        ret = -LTTNG_ERR_INVALID_PROTOCOL;
                        goto end;
                }

                cmd_reply_header = (const struct lttcomm_list_command_header *)
                                                   cmd_reply_header_view.buffer.data;
                if (cmd_reply_header->count > INT_MAX) {
                        ret = -LTTNG_ERR_OVERFLOW;
                        goto end;
                }

                nb_sessions = (unsigned int) cmd_reply_header->count;
        }

        {
                enum lttng_error_code ret_code;
                lttng_payload_view cmd_reply_payload = lttng_payload_view_from_payload(
                                &reply, sizeof(struct lttcomm_list_command_header), -1);

                ret_code = lttng_sessions_create_and_flatten_from_payload(
                                &cmd_reply_payload, nb_sessions, out_sessions);
                if (ret_code != LTTNG_OK) {
                        ret = -((int) ret_code);
                        goto end;
                }
        }

        ret = (int) nb_sessions;
end:
        lttng_payload_reset(&reply);
        return ret;
}

enum lttng_error_code lttng_session_get_creation_time(
                const struct lttng_session *session, uint64_t *creation_time)
{
        enum lttng_error_code ret = LTTNG_OK;
        struct lttng_session_extended *extended;

        if (!session || !creation_time || !session->extended.ptr) {
                ret = LTTNG_ERR_INVALID;
                goto end;
        }

        extended = (lttng_session_extended *) session->extended.ptr;
        if (!extended->creation_time.is_set) {
                /* Not created on the session daemon yet. */
                ret = LTTNG_ERR_SESSION_NOT_EXIST;
                goto end;
        }
        *creation_time = extended->creation_time.value;
end:
        return ret;
}

int lttng_set_session_shm_path(const char *session_name,
                const char *shm_path)
{
        int ret;
        struct lttcomm_session_msg lsm;

        if (session_name == NULL) {
                return -LTTNG_ERR_INVALID;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_SET_SESSION_SHM_PATH;

        ret = lttng_strncpy(lsm.session.name, session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_strncpy(lsm.u.set_shm_path.shm_path, shm_path ?: "",
                        sizeof(lsm.u.set_shm_path.shm_path));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
end:
        return ret;
}

/*
 * Ask the session daemon for all available domains of a session.
 * Sets the contents of the domains array.
 * Returns the number of lttng_domain entries in domains;
 * on error, returns a negative value.
 */
int lttng_list_domains(const char *session_name,
                struct lttng_domain **domains)
{
        int ret;
        struct lttcomm_session_msg lsm;

        if (session_name == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_LIST_DOMAINS;

        ret = lttng_strncpy(lsm.session.name, session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, (void**) domains);
        if (ret < 0) {
                goto error;
        }

        return ret / sizeof(struct lttng_domain);
error:
        return ret;
}

/*
 * Ask the session daemon for all available channels of a session.
 * Sets the contents of the channels array.
 * Returns the number of lttng_channel entries in channels;
 * on error, returns a negative value.
 */
int lttng_list_channels(struct lttng_handle *handle,
                struct lttng_channel **channels)
{
        int ret, total_payload_received;
        struct lttcomm_session_msg lsm;
        char *reception_buffer = NULL;
        size_t cmd_header_len = 0;
        struct lttcomm_list_command_header *cmd_header = NULL;
        struct lttng_dynamic_buffer tmp_buffer;

        lttng_dynamic_buffer_init(&tmp_buffer);

        if (handle == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_LIST_CHANNELS;
        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        ret = lttng_ctl_ask_sessiond_fds_varlen(&lsm, NULL, 0, NULL, 0,
                        (void **) &reception_buffer, (void **) &cmd_header,
                        &cmd_header_len);
        if (ret < 0) {
                goto end;
        }

        total_payload_received = ret;

        if (cmd_header_len != sizeof(*cmd_header)) {
                ret = -LTTNG_ERR_FATAL;
                goto end;
        }

        if (!cmd_header) {
                ret = LTTNG_ERR_UNK;
                goto end;
        }

        if (cmd_header->count > INT_MAX) {
                ret = -LTTNG_ERR_OVERFLOW;
                goto end;
        }

        {
                enum lttng_error_code ret_code;
                const struct lttng_buffer_view events_view =
                                lttng_buffer_view_init(reception_buffer, 0,
                                                total_payload_received);

                ret_code = lttng_channels_create_and_flatten_from_buffer(
                                &events_view, cmd_header->count, channels);
                if (ret_code != LTTNG_OK) {
                        ret = -ret_code;
                        goto end;
                }
        }

        ret = (int) cmd_header->count;
end:
        free(cmd_header);
        free(reception_buffer);
        return ret;
}

/*
 * Ask the session daemon for all available events of a session channel.
 * Sets the contents of the events array.
 * Returns the number of lttng_event entries in events;
 * on error, returns a negative value.
 */
int lttng_list_events(struct lttng_handle *handle,
                const char *channel_name, struct lttng_event **events)
{
        int ret;
        struct lttcomm_session_msg lsm = {};
        struct lttng_payload reply;
        struct lttng_payload_view lsm_view =
                        lttng_payload_view_init_from_buffer(
                                (const char *) &lsm, 0, sizeof(lsm));
        unsigned int nb_events = 0;

        lttng_payload_init(&reply);

        /* Safety check. An handle and channel name are mandatory. */
        if (handle == NULL || channel_name == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        /* Initialize command parameters. */
        lsm.cmd_type = LTTNG_LIST_EVENTS;
        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_strncpy(lsm.u.list.channel_name, channel_name,
                        sizeof(lsm.u.list.channel_name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        /* Execute command against the session daemon. */
        ret = lttng_ctl_ask_sessiond_payload(&lsm_view, &reply);
        if (ret < 0) {
                goto end;
        }

        {
                const struct lttcomm_list_command_header *cmd_reply_header =
                                NULL;
                const lttng_payload_view cmd_reply_header_view =
                                lttng_payload_view_from_payload(&reply, 0,
                                                sizeof(*cmd_reply_header));

                if (!lttng_payload_view_is_valid(&cmd_reply_header_view)) {
                        ret = -LTTNG_ERR_INVALID_PROTOCOL;
                        goto end;
                }

                cmd_reply_header = (const struct lttcomm_list_command_header *)
                                                   cmd_reply_header_view.buffer
                                                                   .data;
                if (cmd_reply_header->count > INT_MAX) {
                        ret = -LTTNG_ERR_OVERFLOW;
                        goto end;
                }

                nb_events = (unsigned int) cmd_reply_header->count;
        }

        {
                enum lttng_error_code ret_code;
                lttng_payload_view cmd_reply_payload = lttng_payload_view_from_payload(
                                &reply,
                                sizeof(struct lttcomm_list_command_header), -1);

                ret_code = lttng_events_create_and_flatten_from_payload(
                                &cmd_reply_payload, nb_events, events);
                if (ret_code != LTTNG_OK) {
                        ret = -((int) ret_code);
                        goto end;
                }
        }

        ret = (int) nb_events;
end:
        lttng_payload_reset(&reply);
        return ret;
}

/*
 * Sets the tracing_group variable with name.
 * This function allocates memory pointed to by tracing_group.
 * On success, returns 0, on error, returns -1 (null name) or -ENOMEM.
 */
int lttng_set_tracing_group(const char *name)
{
        int ret = 0;
        char *new_group;

        if (name == NULL) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        new_group = strdup(name);
        if (!new_group) {
                ret = -LTTNG_ERR_FATAL;
                goto end;
        }

        free(tracing_group);
        tracing_group = new_group;
        new_group = NULL;

end:
        return ret;
}

int lttng_calibrate(struct lttng_handle *handle __attribute__((unused)),
                struct lttng_calibrate *calibrate __attribute__((unused)))
{
        /*
         * This command was removed in LTTng 2.9.
         */
        return -LTTNG_ERR_UND;
}

/*
 * Set default channel attributes.
 * If either or both of the arguments are null, attr content is zeroe'd.
 */
void lttng_channel_set_default_attr(struct lttng_domain *domain,
                struct lttng_channel_attr *attr)
{
        struct lttng_channel_extended *extended;

        /* Safety check */
        if (attr == NULL || domain == NULL) {
                return;
        }

        /* Save the pointer for later use */
        extended = (struct lttng_channel_extended *) attr->extended.ptr;
        memset(attr, 0, sizeof(struct lttng_channel_attr));

        /* Same for all domains. */
        attr->overwrite = DEFAULT_CHANNEL_OVERWRITE;
        attr->tracefile_size = DEFAULT_CHANNEL_TRACEFILE_SIZE;
        attr->tracefile_count = DEFAULT_CHANNEL_TRACEFILE_COUNT;

        switch (domain->type) {
        case LTTNG_DOMAIN_KERNEL:
                attr->switch_timer_interval =
                                DEFAULT_KERNEL_CHANNEL_SWITCH_TIMER;
                attr->read_timer_interval = DEFAULT_KERNEL_CHANNEL_READ_TIMER;
                attr->subbuf_size = default_get_kernel_channel_subbuf_size();
                attr->num_subbuf = DEFAULT_KERNEL_CHANNEL_SUBBUF_NUM;
                attr->output = DEFAULT_KERNEL_CHANNEL_OUTPUT;
                break;
        case LTTNG_DOMAIN_UST:
                switch (domain->buf_type) {
                case LTTNG_BUFFER_PER_UID:
                        attr->subbuf_size = default_get_ust_uid_channel_subbuf_size();
                        attr->num_subbuf = DEFAULT_UST_UID_CHANNEL_SUBBUF_NUM;
                        attr->output = DEFAULT_UST_UID_CHANNEL_OUTPUT;
                        attr->switch_timer_interval =
                                        DEFAULT_UST_UID_CHANNEL_SWITCH_TIMER;
                        attr->read_timer_interval =
                                        DEFAULT_UST_UID_CHANNEL_READ_TIMER;
                        break;
                case LTTNG_BUFFER_PER_PID:
                default:
                        attr->subbuf_size = default_get_ust_pid_channel_subbuf_size();
                        attr->num_subbuf = DEFAULT_UST_PID_CHANNEL_SUBBUF_NUM;
                        attr->output = DEFAULT_UST_PID_CHANNEL_OUTPUT;
                        attr->switch_timer_interval =
                                        DEFAULT_UST_PID_CHANNEL_SWITCH_TIMER;
                        attr->read_timer_interval =
                                        DEFAULT_UST_PID_CHANNEL_READ_TIMER;
                        break;
                }
        default:
                /* Default behavior: leave set to 0. */
                break;
        }

        if (extended) {
                lttng_channel_set_default_extended_attr(domain, extended);
        }

        /* Reassign the extended pointer. */
        attr->extended.ptr = extended;
}

int lttng_channel_get_discarded_event_count(struct lttng_channel *channel,
                uint64_t *discarded_events)
{
        int ret = 0;
        struct lttng_channel_extended *chan_ext;

        if (!channel || !discarded_events) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        chan_ext = (lttng_channel_extended *) channel->attr.extended.ptr;
        if (!chan_ext) {
                /*
                 * This can happen since the lttng_channel structure is
                 * used for other tasks where this pointer is never set.
                 */
                *discarded_events = 0;
                goto end;
        }

        *discarded_events = chan_ext->discarded_events;
end:
        return ret;
}

int lttng_channel_get_lost_packet_count(struct lttng_channel *channel,
                uint64_t *lost_packets)
{
        int ret = 0;
        struct lttng_channel_extended *chan_ext;

        if (!channel || !lost_packets) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        chan_ext = (lttng_channel_extended *) channel->attr.extended.ptr;
        if (!chan_ext) {
                /*
                 * This can happen since the lttng_channel structure is
                 * used for other tasks where this pointer is never set.
                 */
                *lost_packets = 0;
                goto end;
        }

        *lost_packets = chan_ext->lost_packets;
end:
        return ret;
}

int lttng_channel_get_monitor_timer_interval(struct lttng_channel *chan,
                uint64_t *monitor_timer_interval)
{
        int ret = 0;

        if (!chan || !monitor_timer_interval) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        if (!chan->attr.extended.ptr) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        *monitor_timer_interval = ((struct lttng_channel_extended *)
                        chan->attr.extended.ptr)->monitor_timer_interval;
end:
        return ret;
}

int lttng_channel_set_monitor_timer_interval(struct lttng_channel *chan,
                uint64_t monitor_timer_interval)
{
        int ret = 0;

        if (!chan || !chan->attr.extended.ptr) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ((struct lttng_channel_extended *)
                        chan->attr.extended.ptr)->monitor_timer_interval =
                        monitor_timer_interval;
end:
        return ret;
}

int lttng_channel_get_blocking_timeout(struct lttng_channel *chan,
                int64_t *blocking_timeout)
{
        int ret = 0;

        if (!chan || !blocking_timeout) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        if (!chan->attr.extended.ptr) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        *blocking_timeout = ((struct lttng_channel_extended *)
                        chan->attr.extended.ptr)->blocking_timeout;
end:
        return ret;
}

int lttng_channel_set_blocking_timeout(struct lttng_channel *chan,
                int64_t blocking_timeout)
{
        int ret = 0;
        int64_t msec_timeout;

        if (!chan || !chan->attr.extended.ptr) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        if (blocking_timeout < 0 && blocking_timeout != -1) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        /*
         * LTTng-ust's use of poll() to implement this timeout mechanism forces
         * us to accept a narrower range of values (msecs expressed as a signed
         * 32-bit integer).
         */
        msec_timeout = blocking_timeout / 1000;
        if (msec_timeout != (int32_t) msec_timeout) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ((struct lttng_channel_extended *)
                        chan->attr.extended.ptr)->blocking_timeout =
                        blocking_timeout;
end:
        return ret;
}

/*
 * Check if session daemon is alive.
 *
 * Return 1 if alive or 0 if not.
 * On error returns a negative value.
 */
int lttng_session_daemon_alive(void)
{
        int ret;

        ret = set_session_daemon_path();
        if (ret < 0) {
                /* Error. */
                return ret;
        }

        if (*sessiond_sock_path == '\0') {
                /*
                 * No socket path set. Weird error which means the constructor
                 * was not called.
                 */
                abort();
        }

        ret = try_connect_sessiond(sessiond_sock_path);
        if (ret < 0) {
                /* Not alive. */
                return 0;
        }

        /* Is alive. */
        return 1;
}

/*
 * Set URL for a consumer for a session and domain.
 *
 * Return 0 on success, else a negative value.
 */
int lttng_set_consumer_url(struct lttng_handle *handle,
                const char *control_url, const char *data_url)
{
        int ret;
        ssize_t size;
        struct lttcomm_session_msg lsm;
        struct lttng_uri *uris = NULL;

        if (handle == NULL || (control_url == NULL && data_url == NULL)) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        memset(&lsm, 0, sizeof(lsm));

        lsm.cmd_type = LTTNG_SET_CONSUMER_URI;

        ret = lttng_strncpy(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        size = uri_parse_str_urls(control_url, data_url, &uris);
        if (size < 0) {
                ret = -LTTNG_ERR_INVALID;
                goto error;
        }

        lsm.u.uri.size = size;

        ret = lttng_ctl_ask_sessiond_varlen_no_cmd_header(&lsm, uris,
                        sizeof(struct lttng_uri) * size, NULL);

        free(uris);
error:
        return ret;
}

/*
 * [OBSOLETE]
 */
extern "C"
LTTNG_EXPORT int lttng_enable_consumer(struct lttng_handle *handle);
int lttng_enable_consumer(struct lttng_handle *handle __attribute__((unused)))
{
        return -ENOSYS;
}

/*
 * [OBSOLETE]
 */
extern "C"
LTTNG_EXPORT int lttng_disable_consumer(struct lttng_handle *handle);
int lttng_disable_consumer(struct lttng_handle *handle __attribute__((unused)))
{
        return -ENOSYS;
}

/*
 * [OBSOLETE]
 */
extern "C"
LTTNG_EXPORT int _lttng_create_session_ext(const char *name, const char *url,
                const char *datetime);
int _lttng_create_session_ext(const char *name __attribute__((unused)),
                const char *url __attribute__((unused)),
                const char *datetime __attribute__((unused)))
{
        return -ENOSYS;
}

/*
 * For a given session name, this call checks if the data is ready to be read
 * or is still being extracted by the consumer(s) hence not ready to be used by
 * any readers.
 */
int lttng_data_pending(const char *session_name)
{
        int ret;
        struct lttcomm_session_msg lsm;
        uint8_t *pending = NULL;

        if (session_name == NULL) {
                return -LTTNG_ERR_INVALID;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_DATA_PENDING;

        ret = lttng_strncpy(lsm.session.name, session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, (void **) &pending);
        if (ret < 0) {
                goto end;
        } else if (ret != 1) {
                /* Unexpected payload size */
                ret = -LTTNG_ERR_INVALID;
                goto end;
        } else if (!pending) {
                /* Internal error. */
                ret = -LTTNG_ERR_UNK;
                goto end;
        }

        ret = (int) *pending;
end:
        free(pending);
        return ret;
}

/*
 * Regenerate the metadata for a session.
 * Return 0 on success, a negative error code on error.
 */
int lttng_regenerate_metadata(const char *session_name)
{
        int ret;
        struct lttcomm_session_msg lsm;

        if (!session_name) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_REGENERATE_METADATA;

        ret = lttng_strncpy(lsm.session.name, session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
        if (ret < 0) {
                goto end;
        }

        ret = 0;
end:
        return ret;
}

/*
 * Deprecated, replaced by lttng_regenerate_metadata.
 */
int lttng_metadata_regenerate(const char *session_name)
{
        return lttng_regenerate_metadata(session_name);
}

/*
 * Regenerate the statedump of a session.
 * Return 0 on success, a negative error code on error.
 */
int lttng_regenerate_statedump(const char *session_name)
{
        int ret;
        struct lttcomm_session_msg lsm;

        if (!session_name) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_REGENERATE_STATEDUMP;

        ret = lttng_strncpy(lsm.session.name, session_name,
                        sizeof(lsm.session.name));
        if (ret) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
        if (ret < 0) {
                goto end;
        }

        ret = 0;
end:
        return ret;
}

static
int _lttng_register_trigger(struct lttng_trigger *trigger, const char *name,
                bool generate_name)
{
        int ret;
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_REGISTER_TRIGGER,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        lsm.u.trigger.is_trigger_anonymous = !name && !generate_name;
        struct lttcomm_session_msg *message_lsm;
        struct lttng_payload message;
        struct lttng_payload reply;
        struct lttng_trigger *reply_trigger = NULL;
        enum lttng_domain_type domain_type;
        const struct lttng_credentials user_creds = {
                .uid = LTTNG_OPTIONAL_INIT_VALUE(geteuid()),
                .gid = LTTNG_OPTIONAL_INIT_UNSET,
        };
        const char *unused_trigger_name = NULL;
        enum lttng_trigger_status trigger_status;

        lttng_payload_init(&message);
        lttng_payload_init(&reply);

        if (!trigger) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        trigger_status = lttng_trigger_get_name(trigger, &unused_trigger_name);
        if (trigger_status != LTTNG_TRIGGER_STATUS_UNSET) {
                /* Re-using already registered trigger. */
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        if (name) {
                trigger_status = lttng_trigger_set_name(trigger, name);
                if (trigger_status != LTTNG_TRIGGER_STATUS_OK) {
                        ret = -LTTNG_ERR_NOMEM;
                        goto end;
                }
        }

        if (!trigger->creds.uid.is_set) {
                /* Use the client's credentials as the trigger credentials. */
                lttng_trigger_set_credentials(trigger, &user_creds);
        } else {
                /*
                 * Validate that either the current trigger credentials and the
                 * client credentials are identical or that the current user is
                 * root. The root user can register, unregister triggers for
                 * himself and other users.
                 *
                 * This check is also present on the sessiond side, using the
                 * credentials passed on the socket. These check are all
                 * "safety" checks.
                 */
                const struct lttng_credentials *trigger_creds =
                                lttng_trigger_get_credentials(trigger);

                if (!lttng_credentials_is_equal_uid(trigger_creds, &user_creds)) {
                        if (lttng_credentials_get_uid(&user_creds) != 0) {
                                ret = -LTTNG_ERR_EPERM;
                                goto end_unset_name;
                        }
                }
        }

        if (!lttng_trigger_validate(trigger)) {
                ret = -LTTNG_ERR_INVALID_TRIGGER;
                goto end_unset_name;
        }

        domain_type = lttng_trigger_get_underlying_domain_type_restriction(
                        trigger);

        lsm.domain.type = domain_type;

        ret = lttng_dynamic_buffer_append(&message.buffer, &lsm, sizeof(lsm));
        if (ret) {
                ret = -LTTNG_ERR_NOMEM;
                goto end_unset_name;
        }

        ret = lttng_trigger_serialize(trigger, &message);
        if (ret < 0) {
                ret = -LTTNG_ERR_UNK;
                goto end_unset_name;
        }

        /*
         * This is needed to populate the trigger object size for the command
         * header.
         */
        message_lsm = (struct lttcomm_session_msg *) message.buffer.data;

        message_lsm->u.trigger.length = (uint32_t) message.buffer.size - sizeof(lsm);

        {
                struct lttng_payload_view message_view =
                                lttng_payload_view_from_payload(
                                                &message, 0, -1);

                message_lsm->fd_count = lttng_payload_view_get_fd_handle_count(
                                &message_view);
                ret = lttng_ctl_ask_sessiond_payload(&message_view, &reply);
                if (ret < 0) {
                        goto end_unset_name;
                }
        }

        {
                struct lttng_payload_view reply_view =
                                lttng_payload_view_from_payload(
                                                &reply, 0, reply.buffer.size);

                ret = lttng_trigger_create_from_payload(
                                &reply_view, &reply_trigger);
                if (ret < 0) {
                        ret = -LTTNG_ERR_INVALID_PROTOCOL;
                        goto end_unset_name;
                }
        }

        if (name || generate_name) {
                ret = lttng_trigger_assign_name(trigger, reply_trigger);
                if (ret < 0) {
                        ret = -LTTNG_ERR_NOMEM;
                        goto end;
                }
        }

        ret = 0;
        goto end;

end_unset_name:
        trigger_status = lttng_trigger_set_name(trigger, NULL);
        if (trigger_status != LTTNG_TRIGGER_STATUS_OK) {
                ret = -LTTNG_ERR_UNK;
        }
end:
        lttng_payload_reset(&message);
        lttng_payload_reset(&reply);
        lttng_trigger_destroy(reply_trigger);
        return ret;
}

int lttng_register_trigger(struct lttng_trigger *trigger)
{
        /* Register an anonymous trigger. */
        return _lttng_register_trigger(trigger, NULL, false);
}

enum lttng_error_code lttng_register_trigger_with_name(
                struct lttng_trigger *trigger, const char *name)
{
        const int ret = _lttng_register_trigger(trigger, name, false);

        return ret == 0 ? LTTNG_OK : (enum lttng_error_code) -ret;
}

enum lttng_error_code lttng_register_trigger_with_automatic_name(
                struct lttng_trigger *trigger)
{
        const int ret =  _lttng_register_trigger(trigger, nullptr, true);

        return ret == 0 ? LTTNG_OK : (enum lttng_error_code) -ret;
}

enum lttng_error_code lttng_error_query_execute(
                const struct lttng_error_query *query,
                const struct lttng_endpoint *endpoint,
                struct lttng_error_query_results **results)
{
        int ret;
        enum lttng_error_code ret_code;
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_EXECUTE_ERROR_QUERY,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        struct lttng_payload message;
        struct lttng_payload reply;
        struct lttcomm_session_msg *message_lsm;

        lttng_payload_init(&message);
        lttng_payload_init(&reply);

        if (!query || !results) {
                ret_code = LTTNG_ERR_INVALID;
                goto end;
        }

        if (endpoint != lttng_session_daemon_command_endpoint) {
                ret_code = LTTNG_ERR_INVALID_ERROR_QUERY_TARGET;
                goto end;
        }

        ret = lttng_dynamic_buffer_append(&message.buffer, &lsm, sizeof(lsm));
        if (ret) {
                ret_code = LTTNG_ERR_NOMEM;
                goto end;
        }

        ret = lttng_error_query_serialize(query, &message);
        if (ret) {
                ret_code = LTTNG_ERR_UNK;
                goto end;
        }

        message_lsm = (struct lttcomm_session_msg *) message.buffer.data;
        message_lsm->u.error_query.length =
                        (uint32_t) message.buffer.size - sizeof(lsm);

        {
                struct lttng_payload_view message_view =
                                lttng_payload_view_from_payload(
                                                &message, 0, -1);

                message_lsm->fd_count = lttng_payload_view_get_fd_handle_count(
                                &message_view);
                ret = lttng_ctl_ask_sessiond_payload(&message_view, &reply);
                if (ret < 0) {
                        ret_code =(lttng_error_code) -ret;
                        goto end;
                }
        }

        {
                ssize_t reply_create_ret;
                struct lttng_payload_view reply_view =
                                lttng_payload_view_from_payload(
                                                &reply, 0, reply.buffer.size);

                reply_create_ret = lttng_error_query_results_create_from_payload(
                                &reply_view, results);
                if (reply_create_ret < 0) {
                        ret_code = LTTNG_ERR_INVALID_PROTOCOL;
                        goto end;
                }
        }

        ret_code = LTTNG_OK;
end:
        lttng_payload_reset(&message);
        lttng_payload_reset(&reply);
        return ret_code;
}

int lttng_unregister_trigger(const struct lttng_trigger *trigger)
{
        int ret;
        struct lttcomm_session_msg lsm;
        struct lttcomm_session_msg *message_lsm;
        struct lttng_payload message;
        struct lttng_payload reply;
        struct lttng_trigger *copy = NULL;
        const struct lttng_credentials user_creds = {
                .uid = LTTNG_OPTIONAL_INIT_VALUE(geteuid()),
                .gid = LTTNG_OPTIONAL_INIT_UNSET,
        };

        lttng_payload_init(&message);
        lttng_payload_init(&reply);

        if (!trigger) {
                ret = -LTTNG_ERR_INVALID;
                goto end;
        }

        copy = lttng_trigger_copy(trigger);
        if (!copy) {
                ret = -LTTNG_ERR_UNK;
                goto end;
        }

        if (!copy->creds.uid.is_set) {
                /* Use the client credentials as the trigger credentials */
                lttng_trigger_set_credentials(copy, &user_creds);
        } else {
                /*
                 * Validate that either the current trigger credentials and the
                 * client credentials are identical or that the current user is
                 * root. The root user can register, unregister triggers for
                 * himself and other users.
                 *
                 * This check is also present on the sessiond side, using the
                 * credentials passed on the socket. These check are all
                 * "safety" checks.
                 */
                const struct lttng_credentials *trigger_creds =
                                lttng_trigger_get_credentials(copy);
                if (!lttng_credentials_is_equal_uid(trigger_creds, &user_creds)) {
                        if (lttng_credentials_get_uid(&user_creds) != 0) {
                                ret = -LTTNG_ERR_EPERM;
                                goto end;
                        }
                }
        }

        if (!lttng_trigger_validate(copy)) {
                ret = -LTTNG_ERR_INVALID_TRIGGER;
                goto end;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_UNREGISTER_TRIGGER;

        ret = lttng_dynamic_buffer_append(&message.buffer, &lsm, sizeof(lsm));
        if (ret) {
                ret = -LTTNG_ERR_NOMEM;
                goto end;
        }

        ret = lttng_trigger_serialize(copy, &message);
        if (ret < 0) {
                ret = -LTTNG_ERR_UNK;
                goto end;
        }

        /*
         * This is needed to populate the trigger object size for the command
         * header and number of fds sent.
        */
        message_lsm = (struct lttcomm_session_msg *) message.buffer.data;

        message_lsm->u.trigger.length = (uint32_t) message.buffer.size - sizeof(lsm);

        {
                struct lttng_payload_view message_view =
                                lttng_payload_view_from_payload(
                                                &message, 0, -1);

                /*
                 * Update the message header with the number of fd that will be
                 * sent.
                 */
                message_lsm->fd_count = lttng_payload_view_get_fd_handle_count(
                                &message_view);

                ret = lttng_ctl_ask_sessiond_payload(&message_view, &reply);
                if (ret < 0) {
                        goto end;
                }
        }

        ret = 0;
end:
        lttng_trigger_destroy(copy);
        lttng_payload_reset(&message);
        lttng_payload_reset(&reply);
        return ret;
}

/*
 * Ask the session daemon for all registered triggers for the current user.
 *
 * Allocates and return an lttng_triggers set.
 * On error, returns a suitable lttng_error_code.
 */
enum lttng_error_code lttng_list_triggers(struct lttng_triggers **triggers)
{
        int ret;
        enum lttng_error_code ret_code = LTTNG_OK;
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_LIST_TRIGGERS,
                .session = {},
                .domain = {},
                .u = {},
                .fd_count = 0,
        };
        struct lttng_triggers *local_triggers = NULL;
        struct lttng_payload reply;
        struct lttng_payload_view lsm_view =
                        lttng_payload_view_init_from_buffer(
                                (const char *) &lsm, 0, sizeof(lsm));

        lttng_payload_init(&reply);

        ret = lttng_ctl_ask_sessiond_payload(&lsm_view, &reply);
        if (ret < 0) {
                ret_code = (enum lttng_error_code) -ret;
                goto end;
        }

        {
                struct lttng_payload_view reply_view =
                                lttng_payload_view_from_payload(
                                                &reply, 0, reply.buffer.size);

                ret = lttng_triggers_create_from_payload(
                                &reply_view, &local_triggers);
                if (ret < 0) {
                        ret_code = LTTNG_ERR_FATAL;
                        goto end;
                }
        }

        *triggers = local_triggers;
        local_triggers = NULL;
end:
        lttng_payload_reset(&reply);
        lttng_triggers_destroy(local_triggers);
        return ret_code;
}

/*
 * lib constructor.
 */
static void __attribute__((constructor)) init(void)
{
        /* Set default session group */
        lttng_set_tracing_group(DEFAULT_TRACING_GROUP);
}

/*
 * lib destructor.
 */
static void __attribute__((destructor)) lttng_ctl_exit(void)
{
        free(tracing_group);
}

LTTNG_EXPORT enum lttng_error_code lttng_domain_supports_trace_format(
                const struct lttng_endpoint *session_daemon_endpoint,
                enum lttng_domain_type domain_type,
                const struct lttng_trace_format_descriptor *trace_format_descriptor)
{
        int ret;
        enum lttng_error_code ret_code;
        struct lttcomm_session_msg lsm = {
                        .cmd_type = LTTNG_EXECUTE_TRACE_FORMAT_SUPPORT_QUERY,
                        .session = {},
                        .domain = {},
                        .u = {},
                        .fd_count = 0,
        };
        struct lttng_payload message;
        struct lttng_payload reply;
        struct lttcomm_session_msg *message_lsm;

        lttng_payload_init(&message);
        lttng_payload_init(&reply);

        if (!session_daemon_endpoint || !trace_format_descriptor) {
                ret_code = LTTNG_ERR_INVALID;
                goto end;
        }

        lsm.domain.type = domain_type;
        lsm.u.trace_format_support_query.query_type = 0;
        lsm.u.trace_format_support_query.type_payload_length = 0;

        if (session_daemon_endpoint != lttng_session_daemon_command_endpoint) {
                ret_code = LTTNG_ERR_INVALID_ERROR_QUERY_TARGET;
                goto end;
        }

        ret = lttng_dynamic_buffer_append(&message.buffer, &lsm, sizeof(lsm));
        if (ret) {
                ret_code = LTTNG_ERR_NOMEM;
                goto end;
        }

        ret = reinterpret_cast<const lttng::trace_format_descriptor *>(trace_format_descriptor)
                              ->serialize(&message);
        if (ret) {
                ret_code = LTTNG_ERR_UNK;
                goto end;
        }

        message_lsm = (struct lttcomm_session_msg *) message.buffer.data;
        message_lsm->u.trace_format_support_query.trace_format_length =
                        (uint32_t) message.buffer.size - sizeof(lsm);

        {
                struct lttng_payload_view message_view =
                                lttng_payload_view_from_payload(&message, 0, -1);

                message_lsm->fd_count = lttng_payload_view_get_fd_handle_count(&message_view);
                ret = lttng_ctl_ask_sessiond_payload(&message_view, &reply);
                if (ret < 0) {
                        ret_code = (lttng_error_code) -ret;
                        goto end;
                }
                if (ret != 0) {
                        /* No payload expected */
                        ret = LTTNG_ERR_INVALID_PROTOCOL;
                }
        }

        ret_code = LTTNG_OK;
end:
        lttng_payload_reset(&message);
        lttng_payload_reset(&reply);
        return ret_code;
}

LTTNG_EXPORT extern enum lttng_error_code lttng_destination_supports_trace_format(
                const struct lttng_endpoint *session_daemon_endpoint,
                const char *destination_url,
                const struct lttng_trace_format_descriptor *trace_format_descriptor)
{
        int ret;
        ssize_t size;
        enum lttng_error_code ret_code;
        struct lttcomm_session_msg lsm = {
                        .cmd_type = LTTNG_EXECUTE_TRACE_FORMAT_SUPPORT_QUERY,
                        .session = {},
                        .domain = {},
                        .u = {},
                        .fd_count = 0,
        };
        struct lttng_payload message;
        struct lttng_payload reply;
        struct lttcomm_session_msg *message_lsm;
        struct lttng_uri *uris = NULL;
        size_t size_before_payload = 0;

        lttng_payload_init(&message);
        lttng_payload_init(&reply);

        if (!session_daemon_endpoint || !trace_format_descriptor) {
                ret_code = LTTNG_ERR_INVALID;
                goto end;
        }

        size = uri_parse_str_urls(destination_url, NULL, &uris);
        if (size < 1) {
                ret_code = LTTNG_ERR_INVALID;
                goto end;
        }

        if (uris[0].dtype == LTTNG_DST_PATH) {
                /* Local output */
                ret_code = LTTNG_OK;
                goto end;
        }

        lsm.u.trace_format_support_query.query_type = 1;

        if (session_daemon_endpoint != lttng_session_daemon_command_endpoint) {
                ret_code = LTTNG_ERR_INVALID_ERROR_QUERY_TARGET;
                goto end;
        }

        ret = lttng_dynamic_buffer_append(&message.buffer, &lsm, sizeof(lsm));
        if (ret) {
                ret_code = LTTNG_ERR_NOMEM;
                goto end;
        }

        size_before_payload = message.buffer.size;

        ret = reinterpret_cast<const lttng::trace_format_descriptor *>(trace_format_descriptor)
                              ->serialize(&message);
        if (ret) {
                ret_code = LTTNG_ERR_UNK;
                goto end;
        }

        message_lsm = (struct lttcomm_session_msg *) message.buffer.data;
        message_lsm->u.trace_format_support_query.trace_format_length =
                        (uint32_t) message.buffer.size - size_before_payload;

        /* FIXME replace all this with good old serialization of sub query type
         * object. (internal) */
        size_before_payload = message.buffer.size;
        ret = lttng_dynamic_buffer_append(&message.buffer, &uris[0], sizeof(*uris));
        if (ret) {
                ret_code = LTTNG_ERR_NOMEM;
                goto end;
        }

        message_lsm = (struct lttcomm_session_msg *) message.buffer.data;
        message_lsm->u.trace_format_support_query.type_payload_length =
                        (uint32_t) message.buffer.size - size_before_payload;

        {
                struct lttng_payload_view message_view =
                                lttng_payload_view_from_payload(&message, 0, -1);

                message_lsm->fd_count = lttng_payload_view_get_fd_handle_count(&message_view);
                ret = lttng_ctl_ask_sessiond_payload(&message_view, &reply);
                if (ret < 0) {
                        ret_code = (lttng_error_code) -ret;
                        goto end;
                }
                if (ret != 0) {
                        /* No payload expected */
                        ret_code = LTTNG_ERR_INVALID_PROTOCOL;
                        goto end;
                }
        }

        ret_code = LTTNG_OK;
end:
        lttng_payload_reset(&message);
        lttng_payload_reset(&reply);
        return ret_code;
}