src/bin/lttng/commands/create.c

   1 /*
   2  * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License, version 2 only,
   6  * as published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  16  */
  17
  18 #define _LGPL_SOURCE
  19 #include <assert.h>
  20 #include <ctype.h>
  21 #include <popt.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26 #include <sys/types.h>
  27 #include <common/compat/time.h>
  28 #include <unistd.h>
  29 #include <signal.h>
  30 #include <sys/wait.h>
  31
  32 #include <common/mi-lttng.h>
  33
  34 #include "../command.h"
  35 #include "../utils.h"
  36
  37 #include <common/defaults.h>
  38 #include <common/sessiond-comm/sessiond-comm.h>
  39 #include <common/uri.h>
  40 #include <common/utils.h>
  41 #include <lttng/snapshot.h>
  42
  43 static char *opt_output_path;
  44 static char *opt_session_name;
  45 static char *opt_url;
  46 static char *opt_ctrl_url;
  47 static char *opt_data_url;
  48 static char *opt_shm_path;
  49 static int opt_no_consumer;
  50 static int opt_no_output;
  51 static int opt_snapshot;
  52 static uint32_t opt_live_timer;
  53
  54 #ifdef LTTNG_EMBED_HELP
  55 static const char help_msg[] =
  56 #include <lttng-create.1.h>
  57 ;
  58 #endif
  59
  60 enum {
  61         OPT_HELP = 1,
  62         OPT_LIST_OPTIONS,
  63         OPT_LIVE_TIMER,
  64 };
  65
  66 static struct mi_writer *writer;
  67
  68 static struct poptOption long_options[] = {
  69         /* longName, shortName, argInfo, argPtr, value, descrip, argDesc */
  70         {"help", 'h', POPT_ARG_NONE, NULL, OPT_HELP, NULL, NULL},
  71         {"output", 'o', POPT_ARG_STRING, &opt_output_path, 0, NULL, NULL},
  72         {"list-options", 0, POPT_ARG_NONE, NULL, OPT_LIST_OPTIONS, NULL, NULL},
  73         {"set-url",        'U', POPT_ARG_STRING, &opt_url, 0, 0, 0},
  74         {"ctrl-url",       'C', POPT_ARG_STRING, &opt_ctrl_url, 0, 0, 0},
  75         {"data-url",       'D', POPT_ARG_STRING, &opt_data_url, 0, 0, 0},
  76         {"no-output",       0, POPT_ARG_VAL, &opt_no_output, 1, 0, 0},
  77         {"no-consumer",     0, POPT_ARG_VAL, &opt_no_consumer, 1, 0, 0},
  78         {"snapshot",        0, POPT_ARG_VAL, &opt_snapshot, 1, 0, 0},
  79         {"live",            0, POPT_ARG_INT | POPT_ARGFLAG_OPTIONAL, 0, OPT_LIVE_TIMER, 0, 0},
  80         {"shm-path",        0, POPT_ARG_STRING, &opt_shm_path, 0, 0, 0},
  81         {0, 0, 0, 0, 0, 0, 0}
  82 };
  83
  84 /*
  85  * Please have a look at src/lib/lttng-ctl/lttng-ctl.c for more information on
  86  * why this declaration exists and used ONLY in for this command.
  87  */
  88 extern int _lttng_create_session_ext(const char *name, const char *url,
  89                 const char *datetime);
  90
  91 /*
  92  * Retrieve the created session and mi output it based on provided argument
  93  * This is currently a summary of what was pretty printed and is subject to
  94  * enhancements.
  95  */
  96 static int mi_created_session(const char *session_name)
  97 {
  98         int ret, i, count, found;
  99         struct lttng_session *sessions;
 100
 101         /* session_name should not be null */
 102         assert(session_name);
 103         assert(writer);
 104
 105         count = lttng_list_sessions(&sessions);
 106         if (count < 0) {
 107                 ret = count;
 108                 ERR("%s", lttng_strerror(ret));
 109                 goto error;
 110         }
 111
 112         if (count == 0) {
 113                 ERR("Error session creation failed: session %s not found", session_name);
 114                 ret = -LTTNG_ERR_SESS_NOT_FOUND;
 115                 goto end;
 116         }
 117
 118         found = 0;
 119         for (i = 0; i < count; i++) {
 120                 if (strncmp(sessions[i].name, session_name, NAME_MAX) == 0) {
 121                         found = 1;
 122                         ret = mi_lttng_session(writer, &sessions[i], 0);
 123                         if (ret) {
 124                                 goto error;
 125                         }
 126                         break;
 127                 }
 128         }
 129
 130         if (!found) {
 131                 ret = -LTTNG_ERR_SESS_NOT_FOUND;
 132         } else {
 133                 ret = CMD_SUCCESS;
 134         }
 135
 136 error:
 137         free(sessions);
 138 end:
 139         return ret;
 140 }
 141
 142 /*
 143  * For a session name, set the consumer URLs.
 144  */
 145 static int set_consumer_url(const char *session_name, const char *ctrl_url,
 146                 const char *data_url)
 147 {
 148         int ret;
 149         struct lttng_handle *handle;
 150
 151         assert(session_name);
 152
 153         /*
 154          * Set handle with the session_name, but no domain. This implies that
 155          * the actions taken with this handle apply on the tracing session
 156          * rather then the domain-specific session.
 157          */
 158         handle = lttng_create_handle(session_name, NULL);
 159         if (handle == NULL) {
 160                 ret = CMD_FATAL;
 161                 goto error;
 162         }
 163
 164         ret = lttng_set_consumer_url(handle, ctrl_url, data_url);
 165         if (ret < 0) {
 166                 goto error;
 167         }
 168
 169         if (ctrl_url) {
 170                 MSG("Control URL %s set for session %s", ctrl_url, session_name);
 171         }
 172
 173         if (data_url) {
 174                 MSG("Data URL %s set for session %s", data_url, session_name);
 175         }
 176
 177 error:
 178         lttng_destroy_handle(handle);
 179         return ret;
 180 }
 181
 182 static int add_snapshot_output(const char *session_name, const char *ctrl_url,
 183                 const char *data_url)
 184 {
 185         int ret;
 186         struct lttng_snapshot_output *output = NULL;
 187
 188         assert(session_name);
 189
 190         output = lttng_snapshot_output_create();
 191         if (!output) {
 192                 ret = CMD_FATAL;
 193                 goto error_create;
 194         }
 195
 196         if (ctrl_url) {
 197                 ret = lttng_snapshot_output_set_ctrl_url(ctrl_url, output);
 198                 if (ret < 0) {
 199                         goto error;
 200                 }
 201         }
 202
 203         if (data_url) {
 204                 ret = lttng_snapshot_output_set_data_url(data_url, output);
 205                 if (ret < 0) {
 206                         goto error;
 207                 }
 208         }
 209
 210         /* This call, if successful, populates the id of the output object. */
 211         ret = lttng_snapshot_add_output(session_name, output);
 212         if (ret < 0) {
 213                 goto error;
 214         }
 215
 216 error:
 217         lttng_snapshot_output_destroy(output);
 218 error_create:
 219         return ret;
 220 }
 221
 222 /*
 223  *  Create a tracing session.
 224  *  If no name is specified, a default name is generated.
 225  *
 226  *  Returns one of the CMD_* result constants.
 227  */
 228 static int create_session(void)
 229 {
 230         int ret;
 231         char *session_name = NULL, *traces_path = NULL, *alloc_path = NULL;
 232         char *alloc_url = NULL, *url = NULL, datetime[16];
 233         char session_name_date[NAME_MAX + 17], *print_str_url = NULL;
 234         time_t rawtime;
 235         struct tm *timeinfo;
 236         char shm_path[PATH_MAX] = "";
 237
 238         /* Get date and time for automatic session name/path */
 239         time(&rawtime);
 240         timeinfo = localtime(&rawtime);
 241         strftime(datetime, sizeof(datetime), "%Y%m%d-%H%M%S", timeinfo);
 242
 243         /* Auto session name creation */
 244         if (opt_session_name == NULL) {
 245                 ret = snprintf(session_name_date, sizeof(session_name_date),
 246                                 DEFAULT_SESSION_NAME "-%s", datetime);
 247                 if (ret < 0) {
 248                         PERROR("snprintf session name");
 249                         goto error;
 250                 }
 251                 session_name = session_name_date;
 252                 DBG("Auto session name set to %s", session_name_date);
 253         } else {
 254                 if (strlen(opt_session_name) > NAME_MAX) {
 255                         ERR("Session name too long. Length must be lower or equal to %d",
 256                                         NAME_MAX);
 257                         ret = LTTNG_ERR_SESSION_FAIL;
 258                         goto error;
 259                 }
 260                 /*
 261                  * Check if the session name begins with "auto-" or is exactly "auto".
 262                  * Both are reserved for the default session name. See bug #449 to
 263                  * understand why we need to check both here.
 264                  */
 265                 if ((strncmp(opt_session_name, DEFAULT_SESSION_NAME "-",
 266                                         strlen(DEFAULT_SESSION_NAME) + 1) == 0) ||
 267                                 (strncmp(opt_session_name, DEFAULT_SESSION_NAME,
 268                                         strlen(DEFAULT_SESSION_NAME)) == 0 &&
 269                                 strlen(opt_session_name) == strlen(DEFAULT_SESSION_NAME))) {
 270                         ERR("%s is a reserved keyword for default session(s)",
 271                                         DEFAULT_SESSION_NAME);
 272                         ret = CMD_ERROR;
 273                         goto error;
 274                 }
 275                 session_name = opt_session_name;
 276                 ret = snprintf(session_name_date, sizeof(session_name_date),
 277                                 "%s-%s", session_name, datetime);
 278                 if (ret < 0) {
 279                         PERROR("snprintf session name");
 280                         goto error;
 281                 }
 282         }
 283
 284         if ((!opt_ctrl_url && opt_data_url) || (opt_ctrl_url && !opt_data_url)) {
 285                 ERR("You need both control and data URL.");
 286                 ret = CMD_ERROR;
 287                 goto error;
 288         }
 289
 290         if (opt_output_path != NULL) {
 291                 traces_path = utils_expand_path(opt_output_path);
 292                 if (traces_path == NULL) {
 293                         ret = CMD_ERROR;
 294                         goto error;
 295                 }
 296
 297                 /* Create URL string from the local file system path */
 298                 ret = asprintf(&alloc_url, "file://%s", traces_path);
 299                 if (ret < 0) {
 300                         PERROR("asprintf url path");
 301                         ret = CMD_FATAL;
 302                         goto error;
 303                 }
 304                 /* URL to use in the lttng_create_session() call */
 305                 url = alloc_url;
 306                 print_str_url = traces_path;
 307         } else if (opt_url) { /* Handling URL (-U opt) */
 308                 url = opt_url;
 309                 print_str_url = url;
 310         } else if (opt_data_url && opt_ctrl_url) {
 311                 /*
 312                  * With both control and data, we'll be setting the consumer URL after
 313                  * session creation thus use no URL.
 314                  */
 315                 url = NULL;
 316         } else if (!opt_no_output) {
 317                 char *tmp_path;
 318
 319                 /* Auto output path */
 320                 tmp_path = utils_get_home_dir();
 321                 if (tmp_path == NULL) {
 322                         ERR("HOME path not found.\n \
 323                                         Please specify an output path using -o, --output PATH");
 324                         ret = CMD_FATAL;
 325                         goto error;
 326                 }
 327                 alloc_path = strdup(tmp_path);
 328                 if (!alloc_path) {
 329                         PERROR("allocating alloc_path");
 330                         ret = CMD_FATAL;
 331                         goto error;
 332                 }
 333                 ret = asprintf(&alloc_url,
 334                                 "file://%s/" DEFAULT_TRACE_DIR_NAME "/%s",
 335                                 alloc_path, session_name_date);
 336                 if (ret < 0) {
 337                         PERROR("asprintf trace dir name");
 338                         ret = CMD_FATAL;
 339                         goto error;
 340                 }
 341
 342                 url = alloc_url;
 343                 print_str_url = alloc_url + strlen("file://");
 344         } else {
 345                 /* No output means --no-output or --snapshot mode. */
 346                 url = NULL;
 347         }
 348
 349         /* Use default live URL if NO url is/are found. */
 350         if ((opt_live_timer && !opt_url) && (opt_live_timer && !opt_data_url)) {
 351                 /* Override the url */
 352                 free(url);
 353                 url = NULL;
 354
 355                 ret = asprintf(&alloc_url, "net://127.0.0.1");
 356                 if (ret < 0) {
 357                         PERROR("asprintf default live URL");
 358                         ret = CMD_FATAL;
 359                         goto error;
 360                 }
 361                 url = alloc_url;
 362                 print_str_url = url;
 363         }
 364
 365         if (opt_snapshot && opt_live_timer) {
 366                 ERR("Snapshot and live modes are mutually exclusive.");
 367                 ret = CMD_ERROR;
 368                 goto error;
 369         }
 370
 371         if (opt_snapshot) {
 372                 /* No output by default. */
 373                 const char *snapshot_url = NULL;
 374
 375                 if (opt_url) {
 376                         snapshot_url = url;
 377                 } else if (!opt_data_url && !opt_ctrl_url) {
 378                         /* This is the session path that we need to use as output. */
 379                         snapshot_url = url;
 380                 }
 381                 ret = lttng_create_session_snapshot(session_name, snapshot_url);
 382         } else if (opt_live_timer) {
 383                 const char *pathname;
 384
 385                 if (opt_relayd_path) {
 386                         pathname = opt_relayd_path;
 387                 } else {
 388                         pathname = INSTALL_BIN_PATH "/lttng-relayd";
 389                 }
 390                 if (!opt_url && !opt_data_url && !check_relayd() &&
 391                                 spawn_relayd(pathname, 0) < 0) {
 392                         goto error;
 393                 }
 394                 ret = lttng_create_session_live(session_name, url, opt_live_timer);
 395         } else {
 396                 ret = _lttng_create_session_ext(session_name, url, datetime);
 397         }
 398         if (ret < 0) {
 399                 /* Don't set ret so lttng can interpret the sessiond error. */
 400                 switch (-ret) {
 401                 case LTTNG_ERR_EXIST_SESS:
 402                         WARN("Session %s already exists", session_name);
 403                         break;
 404                 default:
 405                         break;
 406                 }
 407                 goto error;
 408         }
 409
 410         if (opt_ctrl_url && opt_data_url) {
 411                 if (opt_snapshot) {
 412                         ret = add_snapshot_output(session_name, opt_ctrl_url,
 413                                         opt_data_url);
 414                 } else {
 415                         /* Setting up control URI (-C or/and -D opt) */
 416                         ret = set_consumer_url(session_name, opt_ctrl_url, opt_data_url);
 417                 }
 418                 if (ret < 0) {
 419                         /* Destroy created session because the URL are not valid. */
 420                         lttng_destroy_session(session_name);
 421                         goto error;
 422                 }
 423         }
 424
 425         if (opt_shm_path) {
 426                 ret = snprintf(shm_path, sizeof(shm_path),
 427                                 "%s/%s", opt_shm_path, session_name_date);
 428                 if (ret < 0) {
 429                         PERROR("snprintf shm_path");
 430                         goto error;
 431                 }
 432
 433                 ret = lttng_set_session_shm_path(session_name, shm_path);
 434                 if (ret < 0) {
 435                         lttng_destroy_session(session_name);
 436                         goto error;
 437                 }
 438         }
 439
 440         MSG("Session %s created.", session_name);
 441         if (print_str_url && !opt_snapshot) {
 442                 MSG("Traces will be written in %s", print_str_url);
 443
 444                 if (opt_live_timer) {
 445                         MSG("Live timer set to %u %s", opt_live_timer, USEC_UNIT);
 446                 }
 447         } else if (opt_snapshot) {
 448                 if (print_str_url) {
 449                         MSG("Default snapshot output set to: %s", print_str_url);
 450                 }
 451                 MSG("Snapshot mode set. Every channel enabled for that session will "
 452                                 "be set to mmap output, and default to overwrite mode.");
 453         }
 454         if (opt_shm_path) {
 455                 MSG("Session %s set to shm_path: %s.", session_name,
 456                         shm_path);
 457         }
 458
 459         /* Mi output */
 460         if (lttng_opt_mi) {
 461                 ret = mi_created_session(session_name);
 462                 if (ret) {
 463                         ret = CMD_ERROR;
 464                         goto error;
 465                 }
 466         }
 467
 468         /* Init lttng session config */
 469         ret = config_init(session_name);
 470         if (ret < 0) {
 471                 ret = CMD_ERROR;
 472                 goto error;
 473         }
 474
 475         ret = CMD_SUCCESS;
 476
 477 error:
 478         free(alloc_url);
 479         free(traces_path);
 480         free(alloc_path);
 481
 482         if (ret < 0) {
 483                 ERR("%s", lttng_strerror(ret));
 484         }
 485         return ret;
 486 }
 487
 488 /*
 489  *  spawn_sessiond
 490  *
 491  *  Spawn a session daemon by forking and execv.
 492  */
 493 static int spawn_sessiond(char *pathname)
 494 {
 495         int ret = 0;
 496         pid_t pid;
 497
 498         MSG("Spawning a session daemon");
 499         pid = fork();
 500         if (pid == 0) {
 501                 /*
 502                  * Spawn session daemon in daemon mode.
 503                  */
 504                 execlp(pathname, "lttng-sessiond",
 505                                 "--daemonize", NULL);
 506                 /* execlp only returns if error happened */
 507                 if (errno == ENOENT) {
 508                         ERR("No session daemon found. Use --sessiond-path.");
 509                 } else {
 510                         PERROR("execlp");
 511                 }
 512                 kill(getppid(), SIGTERM);       /* wake parent */
 513                 exit(EXIT_FAILURE);
 514         } else if (pid > 0) {
 515                 /*
 516                  * In daemon mode (--daemonize), sessiond only exits when
 517                  * it's ready to accept commands.
 518                  */
 519                 for (;;) {
 520                         int status;
 521                         pid_t wait_pid_ret = waitpid(pid, &status, 0);
 522
 523                         if (wait_pid_ret < 0) {
 524                                 if (errno == EINTR) {
 525                                         continue;
 526                                 }
 527                                 PERROR("waitpid");
 528                                 ret = -errno;
 529                                 goto end;
 530                         }
 531
 532                         if (WIFSIGNALED(status)) {
 533                                 ERR("Session daemon was killed by signal %d",
 534                                                 WTERMSIG(status));
 535                                 ret = -1;
 536                                 goto end;
 537                         } else if (WIFEXITED(status)) {
 538                                 DBG("Session daemon terminated normally (exit status: %d)",
 539                                                 WEXITSTATUS(status));
 540
 541                                 if (WEXITSTATUS(status) != 0) {
 542                                         ERR("Session daemon terminated with an error (exit status: %d)",
 543                                                         WEXITSTATUS(status));
 544                                         ret = -1;
 545                                         goto end;
 546                                 }
 547                                 break;
 548                         }
 549                 }
 550
 551                 goto end;
 552         } else {
 553                 PERROR("fork");
 554                 ret = -1;
 555                 goto end;
 556         }
 557
 558 end:
 559         return ret;
 560 }
 561
 562 /*
 563  *  launch_sessiond
 564  *
 565  *  Check if the session daemon is available using
 566  *  the liblttngctl API for the check. If not, try to
 567  *  spawn a daemon.
 568  */
 569 static int launch_sessiond(void)
 570 {
 571         int ret;
 572         char *pathname = NULL;
 573
 574         ret = lttng_session_daemon_alive();
 575         if (ret) {
 576                 /* Sessiond is alive, not an error */
 577                 ret = 0;
 578                 goto end;
 579         }
 580
 581         /* Try command line option path */
 582         pathname = opt_sessiond_path;
 583
 584         /* Try LTTNG_SESSIOND_PATH env variable */
 585         if (pathname == NULL) {
 586                 pathname = getenv(DEFAULT_SESSIOND_PATH_ENV);
 587         }
 588
 589         /* Try with configured path */
 590         if (pathname == NULL) {
 591                 if (CONFIG_SESSIOND_BIN[0] != '\0') {
 592                         pathname = CONFIG_SESSIOND_BIN;
 593                 }
 594         }
 595
 596         /* Try the default path */
 597         if (pathname == NULL) {
 598                 pathname = INSTALL_BIN_PATH "/lttng-sessiond";
 599         }
 600
 601         DBG("Session daemon binary path: %s", pathname);
 602
 603         /* Check existence and permissions */
 604         ret = access(pathname, F_OK | X_OK);
 605         if (ret < 0) {
 606                 ERR("No such file or access denied: %s", pathname);
 607                 goto end;
 608         }
 609
 610         ret = spawn_sessiond(pathname);
 611 end:
 612         if (ret) {
 613                 ERR("Problem occurred while launching session daemon (%s)",
 614                                 pathname);
 615         }
 616         return ret;
 617 }
 618
 619 /*
 620  *  The 'create <options>' first level command
 621  *
 622  *  Returns one of the CMD_* result constants.
 623  */
 624 int cmd_create(int argc, const char **argv)
 625 {
 626         int opt, ret = CMD_SUCCESS, command_ret = CMD_SUCCESS, success = 1;
 627         char *opt_arg = NULL;
 628         const char *leftover = NULL;
 629         static poptContext pc;
 630
 631         pc = poptGetContext(NULL, argc, argv, long_options, 0);
 632         poptReadDefaultConfig(pc, 0);
 633
 634         while ((opt = poptGetNextOpt(pc)) != -1) {
 635                 switch (opt) {
 636                 case OPT_HELP:
 637                         SHOW_HELP();
 638                         goto end;
 639                 case OPT_LIST_OPTIONS:
 640                         list_cmd_options(stdout, long_options);
 641                         goto end;
 642                 case OPT_LIVE_TIMER:
 643                 {
 644                         uint64_t v;
 645
 646                         errno = 0;
 647                         opt_arg = poptGetOptArg(pc);
 648                         if (!opt_arg) {
 649                                 /* Set up default values. */
 650                                 opt_live_timer = (uint32_t) DEFAULT_LTTNG_LIVE_TIMER;
 651                                 DBG("Session live timer interval set to default value %d",
 652                                                 opt_live_timer);
 653                                 break;
 654                         }
 655
 656                         if (utils_parse_time_suffix(opt_arg, &v) < 0) {
 657                                 ERR("Wrong value for --live parameter: %s", opt_arg);
 658                                 ret = CMD_ERROR;
 659                                 goto end;
 660                         }
 661
 662                         if (v != (uint32_t) v) {
 663                                 ERR("32-bit overflow in --live parameter: %s", opt_arg);
 664                                 ret = CMD_ERROR;
 665                                 goto end;
 666                         }
 667
 668                         if (v == 0) {
 669                                 ERR("Live timer interval must be greater than zero");
 670                                 ret = CMD_ERROR;
 671                                 goto end;
 672                         }
 673
 674                         opt_live_timer = (uint32_t) v;
 675                         DBG("Session live timer interval set to %d", opt_live_timer);
 676                         break;
 677                 }
 678                 default:
 679                         ret = CMD_UNDEFINED;
 680                         goto end;
 681                 }
 682         }
 683
 684         if (opt_no_consumer) {
 685                 MSG("The option --no-consumer is obsolete. Use --no-output now.");
 686                 ret = CMD_WARNING;
 687                 goto end;
 688         }
 689
 690         /* Spawn a session daemon if needed */
 691         if (!opt_no_sessiond) {
 692                 ret = launch_sessiond();
 693                 if (ret) {
 694                         ret = CMD_ERROR;
 695                         goto end;
 696                 }
 697         }
 698
 699         /* MI initialization */
 700         if (lttng_opt_mi) {
 701                 writer = mi_lttng_writer_create(fileno(stdout), lttng_opt_mi);
 702                 if (!writer) {
 703                         ret = -LTTNG_ERR_NOMEM;
 704                         goto end;
 705                 }
 706
 707                 /* Open command element */
 708                 ret = mi_lttng_writer_command_open(writer,
 709                                 mi_lttng_element_command_create);
 710                 if (ret) {
 711                         ret = CMD_ERROR;
 712                         goto end;
 713                 }
 714
 715                 /* Open output element */
 716                 ret = mi_lttng_writer_open_element(writer,
 717                                 mi_lttng_element_command_output);
 718                 if (ret) {
 719                         ret = CMD_ERROR;
 720                         goto end;
 721                 }
 722         }
 723         opt_session_name = (char*) poptGetArg(pc);
 724
 725         leftover = poptGetArg(pc);
 726         if (leftover) {
 727                 ERR("Unknown argument: %s", leftover);
 728                 ret = CMD_ERROR;
 729                 goto end;
 730         }
 731
 732         command_ret = create_session();
 733         if (command_ret) {
 734                 success = 0;
 735         }
 736
 737         if (lttng_opt_mi) {
 738                 /* Close  output element */
 739                 ret = mi_lttng_writer_close_element(writer);
 740                 if (ret) {
 741                         ret = CMD_ERROR;
 742                         goto end;
 743                 }
 744
 745                 /* Success ? */
 746                 ret = mi_lttng_writer_write_element_bool(writer,
 747                                 mi_lttng_element_command_success, success);
 748                 if (ret) {
 749                         ret = CMD_ERROR;
 750                         goto end;
 751                 }
 752
 753                 /* Command element close */
 754                 ret = mi_lttng_writer_command_close(writer);
 755                 if (ret) {
 756                         ret = CMD_ERROR;
 757                         goto end;
 758                 }
 759         }
 760
 761 end:
 762         /* Mi clean-up */
 763         if (writer && mi_lttng_writer_destroy(writer)) {
 764                 /* Preserve original error code */
 765                 ret = ret ? ret : -LTTNG_ERR_MI_IO_FAIL;
 766         }
 767
 768         /* Overwrite ret if an error occurred in create_session() */
 769         ret = command_ret ? command_ret : ret;
 770
 771         poptFreeContext(pc);
 772         return ret;
 773 }