Fix: trigger: erroneous check for success of trigger creation

[lttng-tools.git] / src / lib / lttng-ctl / lttng-ctl.c

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

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

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

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

#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.
 */
int lttng_opt_quiet;
int lttng_opt_verbose;
int lttng_opt_mi;

/*
 * Copy string from src to dst and enforce null terminated byte.
 */
LTTNG_HIDDEN
void lttng_ctl_copy_string(char *dst, const char *src, size_t len)
{
        if (src && dst) {
                strncpy(dst, src, len);
                /* Enforce the NULL terminated byte */
                dst[len - 1] = '\0';
        } else if (dst) {
                dst[0] = '\0';
        }
}

/*
 * Copy domain to lttcomm_session_msg domain.
 *
 * If domain is unknown, default domain will be the kernel.
 */
LTTNG_HIDDEN
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 : %d", 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;

        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;
        }

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.
 */
LTTNG_HIDDEN
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 = zmalloc(grp_list_size * sizeof(gid_t));
        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 int check_enough_available_memory(size_t num_bytes_requested_per_cpu)
{
        int ret;
        long num_cpu;
        size_t best_mem_info;
        size_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) {
                goto error;
        }

        num_bytes_requested_total = num_bytes_requested_per_cpu * 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;
        }

error:
        return -1;
success:
        return best_mem_info >= num_bytes_requested_total;
}

/*
 * 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) {
                lttng_ctl_copy_string(sessiond_sock_path,
                                DEFAULT_GLOBAL_CLIENT_UNIX_SOCK, sizeof(sessiond_sock_path));
        }

        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.
 */
LTTNG_HIDDEN 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;
        void *buf = NULL;

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

                buf = zmalloc(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.
 */
LTTNG_HIDDEN
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;
}

LTTNG_HIDDEN
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);

        assert(reply->buffer.size == 0);
        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) {
                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)
{
        struct lttng_handle *handle = NULL;

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

        /* Copy session name */
        lttng_ctl_copy_string(handle->session_name, session_name,
                        sizeof(handle->session_name));

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

end:
        return handle;
}

/*
 * 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)
{
        struct lttcomm_session_msg lsm;

        if (handle == NULL || socket_path == NULL) {
                return -LTTNG_ERR_INVALID;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_REGISTER_CONSUMER;
        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        lttng_ctl_copy_string(lsm.u.reg.path, socket_path,
                        sizeof(lsm.u.reg.path));

        return lttng_ctl_ask_sessiond(&lsm, NULL);
}

/*
 * 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)
{
        struct lttcomm_session_msg lsm;

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

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

        lttng_ctl_copy_string(lsm.session.name, session_name,
                        sizeof(lsm.session.name));

        return lttng_ctl_ask_sessiond(&lsm, NULL);
}

/*
 * 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) {
                return -LTTNG_ERR_INVALID;
        }

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

        lttng_ctl_copy_string(lsm.session.name, session_name,
                        sizeof(lsm.session.name));

        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,
                const char *channel_name)
{
        int ret;
        size_t len = 0;
        char *buf = NULL;
        struct lttcomm_session_msg lsm;

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

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

        /* If no channel name, send empty string. */
        if (channel_name == NULL) {
                lttng_ctl_copy_string(lsm.u.context.channel_name, "",
                                sizeof(lsm.u.context.channel_name));
        } else {
                lttng_ctl_copy_string(lsm.u.context.channel_name, channel_name,
                                sizeof(lsm.u.context.channel_name));
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);
        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));

        if (ctx->ctx == LTTNG_EVENT_CONTEXT_APP_CONTEXT) {
                size_t provider_len, ctx_len;
                const char *provider_name = ctx->u.app_ctx.provider_name;
                const char *ctx_name = ctx->u.app_ctx.ctx_name;

                if (!provider_name || !ctx_name) {
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }

                provider_len = strlen(provider_name);
                if (provider_len == 0) {
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }
                lsm.u.context.provider_name_len = provider_len;

                ctx_len = strlen(ctx_name);
                if (ctx_len == 0) {
                        ret = -LTTNG_ERR_INVALID;
                        goto end;
                }
                lsm.u.context.context_name_len = ctx_len;

                len = provider_len + ctx_len;
                buf = zmalloc(len);
                if (!buf) {
                        ret = -LTTNG_ERR_NOMEM;
                        goto end;
                }

                memcpy(buf, provider_name, provider_len);
                memcpy(buf + provider_len, ctx_name, ctx_len);
        }
        memcpy(&lsm.u.context.ctx, ctx, sizeof(struct lttng_event_context));

        if (ctx->ctx == LTTNG_EVENT_CONTEXT_APP_CONTEXT) {
                /*
                 * Don't leak application addresses to the sessiond.
                 * This is only necessary when ctx is for an app ctx otherwise
                 * the values inside the union (type & config) are overwritten.
                 */
                lsm.u.context.ctx.u.app_ctx.provider_name = NULL;
                lsm.u.context.ctx.u.app_ctx.ctx_name = NULL;
        }

        ret = lttng_ctl_ask_sessiond_varlen_no_cmd_header(&lsm, buf, len, NULL);
end:
        free(buf);
        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;

        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;
        struct lttng_payload payload;
        int ret = 0, i;
        unsigned int free_filter_expression = 0;
        struct filter_parser_ctx *ctx = NULL;

        /*
         * 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;
        }

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

        /* If no channel name, send empty string. */
        if (channel_name == NULL) {
                lttng_ctl_copy_string(lsm.u.enable.channel_name, "",
                                sizeof(lsm.u.enable.channel_name));
        } else {
                lttng_ctl_copy_string(lsm.u.enable.channel_name, channel_name,
                                sizeof(lsm.u.enable.channel_name));
        }

        lsm.cmd_type = LTTNG_ENABLE_EVENT;
        if (ev->name[0] == '\0') {
                /* Enable all events */
                lttng_ctl_copy_string(ev->name, "*", sizeof(ev->name));
        }

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);
        memcpy(&lsm.u.enable.event, ev, sizeof(lsm.u.enable.event));

        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        lsm.u.enable.exclusion_count = exclusion_count;
        lsm.u.enable.bytecode_len = 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 JUL 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 ask_sessiond;
                                }
                        } 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;
                        }
                }

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

                lsm.u.enable.bytecode_len = sizeof(ctx->bytecode->b)
                        + bytecode_get_len(&ctx->bytecode->b);
                lsm.u.enable.expression_len = strlen(filter_expression) + 1;
        }

        ret = lttng_dynamic_buffer_set_capacity(&payload.buffer,
                        lsm.u.enable.bytecode_len +
                                        lsm.u.enable.expression_len +
                                        LTTNG_SYMBOL_NAME_LEN *
                                                        exclusion_count);
        if (ret) {
                ret = -LTTNG_ERR_EXCLUSION_NOMEM;
                goto mem_error;
        }

        /* Put exclusion names first in the data. */
        for (i = 0; i < exclusion_count; i++) {
                size_t exclusion_len;

                exclusion_len = lttng_strnlen(*(exclusion_list + i),
                                LTTNG_SYMBOL_NAME_LEN);
                if (exclusion_len == LTTNG_SYMBOL_NAME_LEN) {
                        /* Exclusion is not NULL-terminated. */
                        ret = -LTTNG_ERR_INVALID;
                        goto mem_error;
                }

                ret = lttng_dynamic_buffer_append(&payload.buffer,
                                *(exclusion_list + i), LTTNG_SYMBOL_NAME_LEN);
                if (ret) {
                        goto mem_error;
                }
        }

        /* Add filter expression next. */
        if (filter_expression) {
                ret = lttng_dynamic_buffer_append(&payload.buffer,
                                filter_expression, lsm.u.enable.expression_len);
                if (ret) {
                        goto mem_error;
                }
        }
        /* Add filter bytecode next. */
        if (ctx && lsm.u.enable.bytecode_len != 0) {
                ret = lttng_dynamic_buffer_append(&payload.buffer,
                                &ctx->bytecode->b, lsm.u.enable.bytecode_len);
                if (ret) {
                        goto mem_error;
                }
        }
        if (ev->extended.ptr) {
                struct lttng_event_extended *ev_ext =
                        (struct lttng_event_extended *) ev->extended.ptr;

                if (ev_ext->probe_location) {
                        /*
                         * lttng_userspace_probe_location_serialize returns the
                         * number of bytes that was appended to the buffer.
                         */
                        ret = lttng_userspace_probe_location_serialize(
                                        ev_ext->probe_location, &payload);
                        if (ret < 0) {
                                goto mem_error;
                        }

                        /*
                         * Set the size of the userspace probe location element
                         * of the buffer so that the receiving side knows where
                         * to split it.
                         */
                        lsm.u.enable.userspace_probe_location_len = ret;
                }
        }

        {
                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 mem_error;
                }

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

                        if (!handle) {
                                goto mem_error;
                        }

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

                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);
        }

mem_error:
        if (filter_expression && ctx) {
                filter_bytecode_free(ctx);
                filter_ir_free(ctx);
                filter_parser_ctx_free(ctx);
        }
filter_error:
        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);
        }
error:
        /*
         * 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;

ask_sessiond:
        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
        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;
        char *varlen_data;
        int ret = 0;
        unsigned int free_filter_expression = 0;
        struct filter_parser_ctx *ctx = NULL;
        /*
         * 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;
        }

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

        /* If no channel name, send empty string. */
        if (channel_name == NULL) {
                lttng_ctl_copy_string(lsm.u.disable.channel_name, "",
                                sizeof(lsm.u.disable.channel_name));
        } else {
                lttng_ctl_copy_string(lsm.u.disable.channel_name, channel_name,
                                sizeof(lsm.u.disable.channel_name));
        }

        lsm.cmd_type = LTTNG_DISABLE_EVENT;

        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);
        memcpy(&lsm.u.disable.event, ev, sizeof(lsm.u.disable.event));

        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        lsm.u.disable.bytecode_len = 0;

        /*
         * For the JUL domain, a filter is enforced except for the
         * disable all event. This is done to avoid having the event in
         * all sessions thus filtering by logger name.
         */
        if (filter_expression == NULL &&
                        (handle->domain.type != LTTNG_DOMAIN_JUL &&
                                handle->domain.type != LTTNG_DOMAIN_LOG4J &&
                                handle->domain.type != LTTNG_DOMAIN_PYTHON)) {
                goto ask_sessiond;
        }

        /*
         * We have a filter, so we need to set up a variable-length
         * memory block from where to send the data.
         */

        /* 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 JUL 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 ask_sessiond;
                                }
                        } else {
                                /*
                                 * With a JUL filter, the original filter has
                                 * been added to it thus replace the filter
                                 * expression.
                                 */
                                filter_expression = agent_filter;
                                free_filter_expression = 1;
                        }
                }

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

                lsm.u.enable.bytecode_len = sizeof(ctx->bytecode->b)
                        + bytecode_get_len(&ctx->bytecode->b);
                lsm.u.enable.expression_len = strlen(filter_expression) + 1;
        }

        varlen_data = zmalloc(lsm.u.disable.bytecode_len
                        + lsm.u.disable.expression_len);
        if (!varlen_data) {
                ret = -LTTNG_ERR_EXCLUSION_NOMEM;
                goto mem_error;
        }

        /* Add filter expression. */
        if (lsm.u.disable.expression_len != 0) {
                memcpy(varlen_data,
                        filter_expression,
                        lsm.u.disable.expression_len);
        }
        /* Add filter bytecode next. */
        if (ctx && lsm.u.disable.bytecode_len != 0) {
                memcpy(varlen_data
                        + lsm.u.disable.expression_len,
                        &ctx->bytecode->b,
                        lsm.u.disable.bytecode_len);
        }

        ret = lttng_ctl_ask_sessiond_varlen_no_cmd_header(&lsm, varlen_data,
                        lsm.u.disable.bytecode_len + lsm.u.disable.expression_len, NULL);
        free(varlen_data);

mem_error:
        if (filter_expression && ctx) {
                filter_bytecode_free(ctx);
                filter_ir_free(ctx);
                filter_parser_ctx_free(ctx);
        }
filter_error:
        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);
        }
error:
        /*
         * Return directly to the caller and don't ask the sessiond since
         * something went wrong in the parsing of data above.
         */
        return ret;

ask_sessiond:
        ret = lttng_ctl_ask_sessiond(&lsm, NULL);
        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)
{
        struct lttng_event ev;

        memset(&ev, 0, sizeof(ev));
        ev.loglevel = -1;
        ev.type = LTTNG_EVENT_ALL;
        lttng_ctl_copy_string(ev.name, name, sizeof(ev.name));
        return lttng_disable_event_ext(handle, &ev, channel_name, NULL);
}

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

        if (!domain) {
                goto error;
        }

        /* 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 error;
                }
                break;
        case LTTNG_DOMAIN_KERNEL:
                if (domain->buf_type != LTTNG_BUFFER_GLOBAL) {
                        goto error;
                }
                break;
        default:
                goto error;
        }

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

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

        channel->attr.extended.ptr = extended;

        lttng_channel_set_default_attr(domain, &channel->attr);
        return channel;
error:
        free(channel);
        free(extended);
        return NULL;
}

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)
{
        struct lttcomm_session_msg lsm;
        size_t total_buffer_size_needed_per_cpu = 0;

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

        memset(&lsm, 0, sizeof(lsm));
        memcpy(&lsm.u.channel.chan, in_chan, sizeof(lsm.u.channel.chan));
        lsm.u.channel.chan.attr.extended.ptr = NULL;

        if (!in_chan->attr.extended.ptr) {
                struct lttng_channel *channel;
                struct lttng_channel_extended *extended;

                channel = lttng_channel_create(&handle->domain);
                if (!channel) {
                        return -LTTNG_ERR_NOMEM;
                }

                /*
                 * Create a new channel in order to use default extended
                 * attribute values.
                 */
                extended = (struct lttng_channel_extended *)
                                channel->attr.extended.ptr;
                memcpy(&lsm.u.channel.extended, extended, sizeof(*extended));
                lttng_channel_destroy(channel);
        } else {
                struct lttng_channel_extended *extended;

                extended = (struct lttng_channel_extended *)
                                in_chan->attr.extended.ptr;
                memcpy(&lsm.u.channel.extended, extended, sizeof(*extended));
        }

        /*
         * Verify that the amount of memory required to create the requested
         * buffer is available on the system at the moment.
         */
        total_buffer_size_needed_per_cpu = lsm.u.channel.chan.attr.num_subbuf *
                lsm.u.channel.chan.attr.subbuf_size;
        if (!check_enough_available_memory(total_buffer_size_needed_per_cpu)) {
                return -LTTNG_ERR_NOMEM;
        }

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

        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));

        return lttng_ctl_ask_sessiond(&lsm, NULL);
}

/*
 * 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)
{
        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;

        lttng_ctl_copy_string(lsm.u.disable.channel_name, name,
                        sizeof(lsm.u.disable.channel_name));

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

        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));

        return lttng_ctl_ask_sessiond(&lsm, NULL);
}

/*
 * 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)
{
        int ret;
        struct lttcomm_session_msg lsm;

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

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

        ret = lttng_ctl_ask_sessiond(&lsm, (void **) events);
        if (ret < 0) {
                return ret;
        }

        return ret / sizeof(struct lttng_event);
}

/*
 * 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)
{
        int ret;
        struct lttcomm_session_msg lsm;

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

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

        ret = lttng_ctl_ask_sessiond(&lsm, (void **) fields);
        if (ret < 0) {
                return ret;
        }

        return ret / sizeof(struct lttng_event_field);
}

/*
 * 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)
{
        int ret;
        struct lttcomm_session_msg lsm;

        if (!events) {
                return -LTTNG_ERR_INVALID;
        }

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_LIST_SYSCALLS;
        /* Force kernel domain for system calls. */
        lsm.domain.type = LTTNG_DOMAIN_KERNEL;

        ret = lttng_ctl_ask_sessiond(&lsm, (void **) events);
        if (ret < 0) {
                return ret;
        }

        return ret / sizeof(struct lttng_event);
}

/*
 * Returns a human readable string describing
 * the error code (a negative value).
 */
const char *lttng_strerror(int 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,
        };
        void *reply = NULL;
        struct lttng_buffer_view reply_view;
        int reply_ret;
        bool sessiond_must_generate_ouput;
        struct lttng_dynamic_buffer payload;
        int ret;
        size_t descriptor_size;
        struct lttng_session_descriptor *descriptor_reply = NULL;

        lttng_dynamic_buffer_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, home_dir,
                                home_dir_len);
                if (ret) {
                        ret_code = LTTNG_ERR_NOMEM;
                        goto end;
                }
        }

        descriptor_size = payload.size;
        ret = lttng_session_descriptor_serialize(session_descriptor,
                        &payload);
        if (ret) {
                ret_code = LTTNG_ERR_INVALID;
                goto end;
        }
        descriptor_size = payload.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.data,
                        payload.size, &reply);
        if (reply_ret < 0) {
                ret_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(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_dynamic_buffer_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;
        }
        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 ? ret_code : -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;
        const size_t session_size = sizeof(struct lttng_session) +
                        sizeof(struct lttng_session_extended);
        size_t session_count, i;
        struct lttng_session_extended *sessions_extended_begin;
        struct lttng_session *sessions = NULL;

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_LIST_SESSIONS;
        ret = lttng_ctl_ask_sessiond(&lsm, (void**) &sessions);
        if (ret <= 0) {
                goto end;
        }
        if (!sessions) {
                ret = -LTTNG_ERR_FATAL;
                goto end;
        }

        if (ret % session_size) {
                ret = -LTTNG_ERR_UNK;
                free(sessions);
                *out_sessions = NULL;
                goto end;
        }
        session_count = (size_t) ret / session_size;
        sessions_extended_begin = (struct lttng_session_extended *)
                        (&sessions[session_count]);

        /* Set extended session info pointers. */
        for (i = 0; i < session_count; i++) {
                struct lttng_session *session = &sessions[i];
                struct lttng_session_extended *extended =
                                &(sessions_extended_begin[i]);

                session->extended.ptr = extended;
        }

        ret = (int) session_count;
        *out_sessions = sessions;
end:
        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 = 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)
{
        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;

        lttng_ctl_copy_string(lsm.session.name, session_name,
                        sizeof(lsm.session.name));
        lttng_ctl_copy_string(lsm.u.set_shm_path.shm_path, shm_path,
                        sizeof(lsm.u.set_shm_path.shm_path));

        return lttng_ctl_ask_sessiond(&lsm, NULL);
}

/*
 * 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) {
                return -LTTNG_ERR_INVALID;
        }

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

        lttng_ctl_copy_string(lsm.session.name, session_name,
                        sizeof(lsm.session.name));

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

        return ret / sizeof(struct lttng_domain);
}

/*
 * 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;
        size_t channel_count, i;
        const size_t channel_size = sizeof(struct lttng_channel) +
                        sizeof(struct lttng_channel_extended);
        struct lttcomm_session_msg lsm;
        void *extended_at;

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

        memset(&lsm, 0, sizeof(lsm));
        lsm.cmd_type = LTTNG_LIST_CHANNELS;
        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));

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

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

        if (ret % channel_size) {
                ret = -LTTNG_ERR_UNK;
                free(*channels);
                *channels = NULL;
                goto end;
        }
        channel_count = (size_t) ret / channel_size;

        /* Set extended info pointers */
        extended_at = ((void *) *channels) +
                        channel_count * sizeof(struct lttng_channel);
        for (i = 0; i < channel_count; i++) {
                struct lttng_channel *chan = &(*channels)[i];

                chan->attr.extended.ptr = extended_at;
                extended_at += sizeof(struct lttng_channel_extended);
        }

        ret = (int) channel_count;
end:
        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 = {};
        const struct lttcomm_event_command_header *cmd_header = NULL;
        uint32_t nb_events, i;
        const void *comm_ext_at;
        struct lttng_dynamic_buffer listing;
        size_t storage_req;
        struct lttng_payload payload;
        struct lttng_payload payload_copy;
        struct lttng_payload_view lsm_view =
                        lttng_payload_view_init_from_buffer(
                                (const char *) &lsm, 0, sizeof(lsm));
        struct lttng_buffer_view cmd_header_view;
        struct lttng_buffer_view cmd_payload_view;
        struct lttng_buffer_view flat_events_view;
        struct lttng_buffer_view ext_view;

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

        lttng_payload_init(&payload);
        lttng_payload_init(&payload_copy);

        lsm.cmd_type = LTTNG_LIST_EVENTS;
        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        lttng_ctl_copy_string(lsm.u.list.channel_name, channel_name,
                        sizeof(lsm.u.list.channel_name));
        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

        ret = lttng_ctl_ask_sessiond_payload(&lsm_view, &payload);
        if (ret < 0) {
                goto end;
        }

        /*
         * A copy of the payload is performed since it will be
         * consumed twice. Consuming the same payload twice is invalid since
         * it will cause any received file descriptor to become "shared"
         * between different instances of the resulting objects.
         */
        ret = lttng_payload_copy(&payload, &payload_copy);
        if (ret) {
                ret = -LTTNG_ERR_NOMEM;
                goto end;
        }

        cmd_header_view = lttng_buffer_view_from_dynamic_buffer(
                &payload.buffer, 0, sizeof(*cmd_header));
        if (!lttng_buffer_view_is_valid(&cmd_header_view)) {
                ret = -LTTNG_ERR_INVALID_PROTOCOL;
                goto end;
        }

        cmd_header = (typeof(cmd_header)) cmd_header_view.data;

        /* Set number of events and free command header */
        nb_events = cmd_header->nb_events;
        if (nb_events > INT_MAX) {
                ret = -LTTNG_ERR_OVERFLOW;
                goto end;
        }

        cmd_payload_view = lttng_buffer_view_from_dynamic_buffer(
                        &payload.buffer, sizeof(*cmd_header), -1);

        /*
         * The buffer that is returned must contain a "flat" version of
         * the events that are returned. In other words, all pointers
         * within an lttng_event must point to a location within the returned
         * buffer so that the user may free everything by simply calling free()
         * on the returned buffer. This is needed in order to maintain API
         * compatibility.
         *
         * A first pass is performed to compute the size of the buffer that
         * must be allocated. A second pass is then performed to setup
         * the returned events so that their members always point within the
         * buffer.
         *
         * The layout of the returned buffer is as follows:
         *   - struct lttng_event[nb_events],
         *   - nb_events times the following:
         *     - struct lttng_event_extended,
         *     - flattened version of userspace_probe_location
         *     - filter_expression
         *     - exclusions
         *     - padding to align to 64-bits
         */
        ext_view = lttng_buffer_view_from_view(&cmd_payload_view,
                        nb_events * sizeof(struct lttng_event), -1);
        comm_ext_at = ext_view.data;
        storage_req = nb_events * sizeof(struct lttng_event);
        {
                struct lttng_payload_view payload_view =
                                lttng_payload_view_from_payload(&payload, 0, -1);

                for (i = 0; i < nb_events; i++) {
                        const struct lttcomm_event_extended_header *ext_comm =
                                        (struct lttcomm_event_extended_header *)
                                                        comm_ext_at;
                        int probe_storage_req = 0;

                        comm_ext_at += sizeof(*ext_comm);
                        comm_ext_at += ext_comm->filter_len;
                        comm_ext_at += ext_comm->nb_exclusions *
                                        LTTNG_SYMBOL_NAME_LEN;

                        if (ext_comm->userspace_probe_location_len) {
                                struct lttng_userspace_probe_location
                                                *probe_location = NULL;
                                struct lttng_payload_view probe_location_view = lttng_payload_view_from_view(
                                                &payload_view,
                                                (const char *) comm_ext_at -
                                                                payload_view.buffer.data,
                                                ext_comm->userspace_probe_location_len);

                                if (!lttng_payload_view_is_valid(&probe_location_view)) {
                                        ret = -LTTNG_ERR_PROBE_LOCATION_INVAL;
                                        goto end;
                                }

                                /*
                                 * Create a temporary userspace probe location
                                 * to determine the size needed by a "flattened"
                                 * version of that same probe location.
                                 */
                                ret = lttng_userspace_probe_location_create_from_payload(
                                                &probe_location_view,
                                                &probe_location);
                                if (ret < 0) {
                                        ret = -LTTNG_ERR_PROBE_LOCATION_INVAL;
                                        goto end;
                                }

                                ret = lttng_userspace_probe_location_flatten(
                                                probe_location, NULL);
                                lttng_userspace_probe_location_destroy(
                                                probe_location);
                                if (ret < 0) {
                                        ret = -LTTNG_ERR_PROBE_LOCATION_INVAL;
                                        goto end;
                                }

                                probe_storage_req = ret;
                                comm_ext_at += ext_comm->userspace_probe_location_len;
                        }

                        storage_req += sizeof(struct lttng_event_extended);
                        storage_req += ext_comm->filter_len;
                        storage_req += ext_comm->nb_exclusions *
                                        LTTNG_SYMBOL_NAME_LEN;
                        /* Padding to ensure the flat probe is aligned. */
                        storage_req = ALIGN_TO(storage_req, sizeof(uint64_t));
                        storage_req += probe_storage_req;
                }
        }

        lttng_dynamic_buffer_init(&listing);
        /*
         * We must ensure that "listing" is never resized so as to preserve
         * the validity of the flattened objects.
         */
        ret = lttng_dynamic_buffer_set_capacity(&listing, storage_req);
        if (ret) {
                ret = -LTTNG_ERR_NOMEM;
                goto end;
        }

        cmd_payload_view = lttng_buffer_view_from_dynamic_buffer(
                &payload_copy.buffer, sizeof(*cmd_header), -1);
        flat_events_view = lttng_buffer_view_from_view(&cmd_payload_view, 0,
                        nb_events * sizeof(struct lttng_event));
        ret = lttng_dynamic_buffer_append_view(&listing, &flat_events_view);
        if (ret) {
                ret = -LTTNG_ERR_NOMEM;
                goto free_dynamic_buffer;
        }

        ext_view = lttng_buffer_view_from_view(&cmd_payload_view,
                        nb_events * sizeof(struct lttng_event), -1);
        comm_ext_at = ext_view.data;

        {
                struct lttng_payload_view payload_copy_view =
                                lttng_payload_view_from_payload(
                                                &payload_copy, 0, -1);

                for (i = 0; i < nb_events; i++) {
                        struct lttng_event *event = (typeof(event))(
                                        listing.data +
                                        (sizeof(struct lttng_event) * i));
                        const struct lttcomm_event_extended_header *ext_comm =
                                        (typeof(ext_comm)) comm_ext_at;
                        struct lttng_event_extended *event_extended =
                                        (typeof(event_extended))(listing.data +
                                                        listing.size);

                        /* Insert struct lttng_event_extended. */
                        ret = lttng_dynamic_buffer_set_size(&listing,
                                        listing.size + sizeof(*event_extended));
                        if (ret) {
                                ret = -LTTNG_ERR_NOMEM;
                                goto free_dynamic_buffer;
                        }
                        event->extended.ptr = event_extended;

                        comm_ext_at += sizeof(*ext_comm);

                        /* Insert filter expression. */
                        if (ext_comm->filter_len) {
                                event_extended->filter_expression =
                                                listing.data + listing.size;
                                ret = lttng_dynamic_buffer_append(&listing,
                                                comm_ext_at,
                                                ext_comm->filter_len);
                                if (ret) {
                                        ret = -LTTNG_ERR_NOMEM;
                                        goto free_dynamic_buffer;
                                }
                                comm_ext_at += ext_comm->filter_len;
                        }

                        /* Insert exclusions. */
                        if (ext_comm->nb_exclusions) {
                                event_extended->exclusions.count =
                                                ext_comm->nb_exclusions;
                                event_extended->exclusions.strings =
                                                listing.data + listing.size;

                                ret = lttng_dynamic_buffer_append(&listing,
                                                comm_ext_at,
                                                ext_comm->nb_exclusions *
                                                                LTTNG_SYMBOL_NAME_LEN);
                                if (ret) {
                                        ret = -LTTNG_ERR_NOMEM;
                                        goto free_dynamic_buffer;
                                }
                                comm_ext_at += ext_comm->nb_exclusions *
                                                LTTNG_SYMBOL_NAME_LEN;
                        }

                        /* Insert padding to align to 64-bits. */
                        ret = lttng_dynamic_buffer_set_size(&listing,
                                        ALIGN_TO(listing.size,
                                                        sizeof(uint64_t)));
                        if (ret) {
                                ret = -LTTNG_ERR_NOMEM;
                                goto free_dynamic_buffer;
                        }

                        /* Insert flattened userspace probe location. */
                        if (ext_comm->userspace_probe_location_len) {
                                struct lttng_userspace_probe_location
                                                *probe_location = NULL;
                                struct lttng_payload_view probe_location_view = lttng_payload_view_from_view(
                                                &payload_copy_view,
                                                (const char *) comm_ext_at -
                                                                payload_copy_view.buffer.data,
                                                ext_comm->userspace_probe_location_len);

                                if (!lttng_payload_view_is_valid(&probe_location_view)) {
                                        ret = -LTTNG_ERR_PROBE_LOCATION_INVAL;
                                        goto free_dynamic_buffer;
                                }

                                ret = lttng_userspace_probe_location_create_from_payload(
                                                &probe_location_view,
                                                &probe_location);
                                if (ret < 0) {
                                        ret = -LTTNG_ERR_PROBE_LOCATION_INVAL;
                                        goto free_dynamic_buffer;
                                }

                                event_extended->probe_location = (struct lttng_userspace_probe_location
                                                                *) (listing.data +
                                                listing.size);
                                ret = lttng_userspace_probe_location_flatten(
                                                probe_location, &listing);
                                lttng_userspace_probe_location_destroy(
                                                probe_location);
                                if (ret < 0) {
                                        ret = -LTTNG_ERR_PROBE_LOCATION_INVAL;
                                        goto free_dynamic_buffer;
                                }

                                comm_ext_at += ext_comm->userspace_probe_location_len;
                        }
                }
        }

        /* Don't reset listing buffer as we return its content. */
        *events = (struct lttng_event *) listing.data;
        lttng_dynamic_buffer_init(&listing);
        ret = (int) nb_events;
free_dynamic_buffer:
        lttng_dynamic_buffer_reset(&listing);
end:
        lttng_payload_reset(&payload);
        lttng_payload_reset(&payload_copy);
        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)
{
        if (name == NULL) {
                return -LTTNG_ERR_INVALID;
        }

        if (asprintf(&tracing_group, "%s", name) < 0) {
                return -LTTNG_ERR_FATAL;
        }

        return 0;
}

int lttng_calibrate(struct lttng_handle *handle,
                struct lttng_calibrate *calibrate)
{
        /*
         * 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;
        }

        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;
                if (extended) {
                        extended->monitor_timer_interval =
                                        DEFAULT_KERNEL_CHANNEL_MONITOR_TIMER;
                        extended->blocking_timeout =
                                        DEFAULT_KERNEL_CHANNEL_BLOCKING_TIMEOUT;
                }
                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;
                        if (extended) {
                                extended->monitor_timer_interval =
                                                DEFAULT_UST_UID_CHANNEL_MONITOR_TIMER;
                                extended->blocking_timeout =
                                                DEFAULT_UST_UID_CHANNEL_BLOCKING_TIMEOUT;
                        }
                        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;
                        if (extended) {
                                extended->monitor_timer_interval =
                                                DEFAULT_UST_PID_CHANNEL_MONITOR_TIMER;
                                extended->blocking_timeout =
                                                DEFAULT_UST_PID_CHANNEL_BLOCKING_TIMEOUT;
                        }
                        break;
                }
        default:
                /* Default behavior: leave set to 0. */
                break;
        }

        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 = 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 = 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.
                 */
                assert(0);
        }

        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)) {
                return -LTTNG_ERR_INVALID;
        }

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

        lsm.cmd_type = LTTNG_SET_CONSUMER_URI;

        lttng_ctl_copy_string(lsm.session.name, handle->session_name,
                        sizeof(lsm.session.name));
        COPY_DOMAIN_PACKED(lsm.domain, handle->domain);

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

        lsm.u.uri.size = size;

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

        free(uris);
        return ret;
}

/*
 * [OBSOLETE]
 */
int lttng_enable_consumer(struct lttng_handle *handle);
int lttng_enable_consumer(struct lttng_handle *handle)
{
        return -ENOSYS;
}

/*
 * [OBSOLETE]
 */
int lttng_disable_consumer(struct lttng_handle *handle);
int lttng_disable_consumer(struct lttng_handle *handle)
{
        return -ENOSYS;
}

/*
 * [OBSOLETE]
 */
int _lttng_create_session_ext(const char *name, const char *url,
                const char *datetime);
int _lttng_create_session_ext(const char *name, const char *url,
                const char *datetime)
{
        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;

        lttng_ctl_copy_string(lsm.session.name, session_name,
                        sizeof(lsm.session.name));

        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;

        lttng_ctl_copy_string(lsm.session.name, session_name,
                        sizeof(lsm.session.name));

        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;

        lttng_ctl_copy_string(lsm.session.name, session_name,
                        sizeof(lsm.session.name));

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

        ret = 0;
end:
        return ret;
}

int lttng_register_trigger(struct lttng_trigger *trigger)
{
        int ret;
        struct lttcomm_session_msg lsm = {
                .cmd_type = LTTNG_REGISTER_TRIGGER,
        };
        struct lttcomm_session_msg *message_lsm;
        struct lttng_payload message;
        struct lttng_payload reply;
        struct lttng_trigger *reply_trigger = 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;
        }

        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;
                        }
                }
        }

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

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

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

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

        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;
                }
        }

        {
                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_FATAL;
                        goto end;
                }
        }

        ret = lttng_trigger_assign_name(trigger, reply_trigger);
        if (ret < 0) {
                ret = -LTTNG_ERR_FATAL;
                goto end;
        }

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

int lttng_unregister_trigger(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;
        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;
        }

        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;
                        }
                }
        }

        if (!lttng_trigger_validate(trigger)) {
                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;
        }

        /*
         * 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;

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

        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_payload_reset(&message);
        lttng_payload_reset(&reply);
        return ret;
}

/*
 * 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);
}