libust/lttng-ust-comm.c

   1 /*
   2  * lttng-ust-comm.c
   3  *
   4  * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
   5  * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; only
  10  * version 2.1 of the License.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 #define _LGPL_SOURCE
  23 #include <sys/types.h>
  24 #include <sys/socket.h>
  25 #include <sys/prctl.h>
  26 #include <sys/mman.h>
  27 #include <sys/stat.h>
  28 #include <sys/types.h>
  29 #include <sys/wait.h>
  30 #include <fcntl.h>
  31 #include <unistd.h>
  32 #include <errno.h>
  33 #include <pthread.h>
  34 #include <semaphore.h>
  35 #include <time.h>
  36 #include <assert.h>
  37 #include <signal.h>
  38 #include <urcu/uatomic.h>
  39 #include <urcu/futex.h>
  40
  41 #include <lttng-ust-comm.h>
  42 #include <ust/lttng-events.h>
  43 #include <ust/usterr-signal-safe.h>
  44 #include <ust/lttng-ust-abi.h>
  45 #include <ust/tracepoint.h>
  46 #include <ust/tracepoint-internal.h>
  47 #include <ust/ust.h>
  48 #include "ltt-tracer-core.h"
  49
  50 /*
  51  * Has lttng ust comm constructor been called ?
  52  */
  53 static int initialized;
  54
  55 /*
  56  * The ust_lock/ust_unlock lock is used as a communication thread mutex.
  57  * Held when handling a command, also held by fork() to deal with
  58  * removal of threads, and by exit path.
  59  */
  60
  61 /* Should the ust comm thread quit ? */
  62 static int lttng_ust_comm_should_quit;
  63
  64 /*
  65  * Wait for either of these before continuing to the main
  66  * program:
  67  * - the register_done message from sessiond daemon
  68  *   (will let the sessiond daemon enable sessions before main
  69  *   starts.)
  70  * - sessiond daemon is not reachable.
  71  * - timeout (ensuring applications are resilient to session
  72  *   daemon problems).
  73  */
  74 static sem_t constructor_wait;
  75 /*
  76  * Doing this for both the global and local sessiond.
  77  */
  78 static int sem_count = { 2 };
  79
  80 /*
  81  * Info about socket and associated listener thread.
  82  */
  83 struct sock_info {
  84         const char *name;
  85         pthread_t ust_listener; /* listener thread */
  86         int root_handle;
  87         int constructor_sem_posted;
  88         int allowed;
  89         int global;
  90
  91         char sock_path[PATH_MAX];
  92         int socket;
  93
  94         char wait_shm_path[PATH_MAX];
  95         char *wait_shm_mmap;
  96 };
  97
  98 /* Socket from app (connect) to session daemon (listen) for communication */
  99 struct sock_info global_apps = {
 100         .name = "global",
 101         .global = 1,
 102
 103         .root_handle = -1,
 104         .allowed = 1,
 105
 106         .sock_path = DEFAULT_GLOBAL_APPS_UNIX_SOCK,
 107         .socket = -1,
 108
 109         .wait_shm_path = DEFAULT_GLOBAL_APPS_WAIT_SHM_PATH,
 110 };
 111
 112 /* TODO: allow global_apps_sock_path override */
 113
 114 struct sock_info local_apps = {
 115         .name = "local",
 116         .global = 0,
 117         .root_handle = -1,
 118         .allowed = 0,   /* Check setuid bit first */
 119
 120         .socket = -1,
 121 };
 122
 123 static int wait_poll_fallback;
 124
 125 extern void ltt_ring_buffer_client_overwrite_init(void);
 126 extern void ltt_ring_buffer_client_discard_init(void);
 127 extern void ltt_ring_buffer_metadata_client_init(void);
 128 extern void ltt_ring_buffer_client_overwrite_exit(void);
 129 extern void ltt_ring_buffer_client_discard_exit(void);
 130 extern void ltt_ring_buffer_metadata_client_exit(void);
 131
 132 static
 133 int setup_local_apps(void)
 134 {
 135         const char *home_dir;
 136         uid_t uid;
 137
 138         uid = getuid();
 139         /*
 140          * Disallow per-user tracing for setuid binaries.
 141          */
 142         if (uid != geteuid()) {
 143                 local_apps.allowed = 0;
 144                 return 0;
 145         } else {
 146                 local_apps.allowed = 1;
 147         }
 148         home_dir = (const char *) getenv("HOME");
 149         if (!home_dir)
 150                 return -ENOENT;
 151         snprintf(local_apps.sock_path, PATH_MAX,
 152                  DEFAULT_HOME_APPS_UNIX_SOCK, home_dir);
 153         snprintf(local_apps.wait_shm_path, PATH_MAX,
 154                  DEFAULT_HOME_APPS_WAIT_SHM_PATH, uid);
 155         return 0;
 156 }
 157
 158 static
 159 int register_app_to_sessiond(int socket)
 160 {
 161         ssize_t ret;
 162         int prctl_ret;
 163         struct {
 164                 uint32_t major;
 165                 uint32_t minor;
 166                 pid_t pid;
 167                 pid_t ppid;
 168                 uid_t uid;
 169                 gid_t gid;
 170                 char name[16];  /* process name */
 171         } reg_msg;
 172
 173         reg_msg.major = LTTNG_UST_COMM_VERSION_MAJOR;
 174         reg_msg.minor = LTTNG_UST_COMM_VERSION_MINOR;
 175         reg_msg.pid = getpid();
 176         reg_msg.ppid = getppid();
 177         reg_msg.uid = getuid();
 178         reg_msg.gid = getgid();
 179         prctl_ret = prctl(PR_GET_NAME, (unsigned long) reg_msg.name, 0, 0, 0);
 180         if (prctl_ret) {
 181                 ERR("Error executing prctl");
 182                 return -errno;
 183         }
 184
 185         ret = ustcomm_send_unix_sock(socket, &reg_msg, sizeof(reg_msg));
 186         if (ret >= 0 && ret != sizeof(reg_msg))
 187                 return -EIO;
 188         return ret;
 189 }
 190
 191 static
 192 int send_reply(int sock, struct ustcomm_ust_reply *lur)
 193 {
 194         ssize_t len;
 195
 196         len = ustcomm_send_unix_sock(sock, lur, sizeof(*lur));
 197         switch (len) {
 198         case sizeof(*lur):
 199                 DBG("message successfully sent");
 200                 return 0;
 201         case -1:
 202                 if (errno == ECONNRESET) {
 203                         printf("remote end closed connection\n");
 204                         return 0;
 205                 }
 206                 return -1;
 207         default:
 208                 printf("incorrect message size: %zd\n", len);
 209                 return -1;
 210         }
 211 }
 212
 213 static
 214 int handle_register_done(struct sock_info *sock_info)
 215 {
 216         int ret;
 217
 218         if (sock_info->constructor_sem_posted)
 219                 return 0;
 220         sock_info->constructor_sem_posted = 1;
 221         if (uatomic_read(&sem_count) <= 0) {
 222                 return 0;
 223         }
 224         ret = uatomic_add_return(&sem_count, -1);
 225         if (ret == 0) {
 226                 ret = sem_post(&constructor_wait);
 227                 assert(!ret);
 228         }
 229         return 0;
 230 }
 231
 232 static
 233 int handle_message(struct sock_info *sock_info,
 234                 int sock, struct ustcomm_ust_msg *lum)
 235 {
 236         int ret = 0;
 237         const struct lttng_ust_objd_ops *ops;
 238         struct ustcomm_ust_reply lur;
 239         int shm_fd, wait_fd;
 240
 241         ust_lock();
 242
 243         memset(&lur, 0, sizeof(lur));
 244
 245         if (lttng_ust_comm_should_quit) {
 246                 ret = -EPERM;
 247                 goto end;
 248         }
 249
 250         ops = objd_ops(lum->handle);
 251         if (!ops) {
 252                 ret = -ENOENT;
 253                 goto end;
 254         }
 255
 256         switch (lum->cmd) {
 257         case LTTNG_UST_REGISTER_DONE:
 258                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 259                         ret = handle_register_done(sock_info);
 260                 else
 261                         ret = -EINVAL;
 262                 break;
 263         case LTTNG_UST_RELEASE:
 264                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 265                         ret = -EPERM;
 266                 else
 267                         ret = lttng_ust_objd_unref(lum->handle);
 268                 break;
 269         default:
 270                 if (ops->cmd)
 271                         ret = ops->cmd(lum->handle, lum->cmd,
 272                                         (unsigned long) &lum->u);
 273                 else
 274                         ret = -ENOSYS;
 275                 break;
 276         }
 277
 278 end:
 279         lur.handle = lum->handle;
 280         lur.cmd = lum->cmd;
 281         lur.ret_val = ret;
 282         if (ret >= 0) {
 283                 lur.ret_code = USTCOMM_OK;
 284         } else {
 285                 //lur.ret_code = USTCOMM_SESSION_FAIL;
 286                 lur.ret_code = ret;
 287         }
 288         switch (lum->cmd) {
 289         case LTTNG_UST_STREAM:
 290                 /*
 291                  * Special-case reply to send stream info.
 292                  * Use lum.u output.
 293                  */
 294                 lur.u.stream.memory_map_size = lum->u.stream.memory_map_size;
 295                 shm_fd = lum->u.stream.shm_fd;
 296                 wait_fd = lum->u.stream.wait_fd;
 297                 break;
 298         case LTTNG_UST_METADATA:
 299         case LTTNG_UST_CHANNEL:
 300                 lur.u.channel.memory_map_size = lum->u.channel.memory_map_size;
 301                 shm_fd = lum->u.channel.shm_fd;
 302                 wait_fd = lum->u.channel.wait_fd;
 303                 break;
 304         case LTTNG_UST_VERSION:
 305                 lur.u.version = lum->u.version;
 306                 break;
 307         }
 308         ret = send_reply(sock, &lur);
 309         if (ret < 0) {
 310                 perror("error sending reply");
 311                 goto error;
 312         }
 313
 314         if ((lum->cmd == LTTNG_UST_STREAM
 315              || lum->cmd == LTTNG_UST_CHANNEL
 316              || lum->cmd == LTTNG_UST_METADATA)
 317                         && lur.ret_code == USTCOMM_OK) {
 318                 /* we also need to send the file descriptors. */
 319                 ret = ustcomm_send_fds_unix_sock(sock,
 320                         &shm_fd, &shm_fd,
 321                         1, sizeof(int));
 322                 if (ret < 0) {
 323                         perror("send shm_fd");
 324                         goto error;
 325                 }
 326                 ret = ustcomm_send_fds_unix_sock(sock,
 327                         &wait_fd, &wait_fd,
 328                         1, sizeof(int));
 329                 if (ret < 0) {
 330                         perror("send wait_fd");
 331                         goto error;
 332                 }
 333         }
 334 error:
 335         ust_unlock();
 336         return ret;
 337 }
 338
 339 static
 340 void cleanup_sock_info(struct sock_info *sock_info)
 341 {
 342         int ret;
 343
 344         if (sock_info->socket != -1) {
 345                 ret = close(sock_info->socket);
 346                 if (ret) {
 347                         ERR("Error closing apps socket");
 348                 }
 349                 sock_info->socket = -1;
 350         }
 351         if (sock_info->root_handle != -1) {
 352                 ret = lttng_ust_objd_unref(sock_info->root_handle);
 353                 if (ret) {
 354                         ERR("Error unref root handle");
 355                 }
 356                 sock_info->root_handle = -1;
 357         }
 358         sock_info->constructor_sem_posted = 0;
 359         if (sock_info->wait_shm_mmap) {
 360                 ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
 361                 if (ret) {
 362                         ERR("Error unmapping wait shm");
 363                 }
 364                 sock_info->wait_shm_mmap = NULL;
 365         }
 366 }
 367
 368 /*
 369  * Using fork to set umask in the child process (not multi-thread safe).
 370  * We deal with the shm_open vs ftruncate race (happening when the
 371  * sessiond owns the shm and does not let everybody modify it, to ensure
 372  * safety against shm_unlink) by simply letting the mmap fail and
 373  * retrying after a few seconds.
 374  * For global shm, everybody has rw access to it until the sessiond
 375  * starts.
 376  */
 377 static
 378 int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
 379 {
 380         int wait_shm_fd, ret;
 381         pid_t pid;
 382
 383         /*
 384          * Try to open read-only.
 385          */
 386         wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 387         if (wait_shm_fd >= 0) {
 388                 goto end;
 389         } else if (wait_shm_fd < 0 && errno != ENOENT) {
 390                 /*
 391                  * Real-only open did not work, and it's not because the
 392                  * entry was not present. It's a failure that prohibits
 393                  * using shm.
 394                  */
 395                 ERR("Error opening shm %s", sock_info->wait_shm_path);
 396                 goto end;
 397         }
 398         /*
 399          * If the open failed because the file did not exist, try
 400          * creating it ourself.
 401          */
 402         pid = fork();
 403         if (pid > 0) {
 404                 int status;
 405
 406                 /*
 407                  * Parent: wait for child to return, in which case the
 408                  * shared memory map will have been created.
 409                  */
 410                 pid = wait(&status);
 411                 if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 412                         wait_shm_fd = -1;
 413                         goto end;
 414                 }
 415                 /*
 416                  * Try to open read-only again after creation.
 417                  */
 418                 wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 419                 if (wait_shm_fd < 0) {
 420                         /*
 421                          * Real-only open did not work. It's a failure
 422                          * that prohibits using shm.
 423                          */
 424                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 425                         goto end;
 426                 }
 427                 goto end;
 428         } else if (pid == 0) {
 429                 int create_mode;
 430
 431                 /* Child */
 432                 create_mode = S_IRUSR | S_IWUSR | S_IRGRP;
 433                 if (sock_info->global)
 434                         create_mode |= S_IROTH | S_IWGRP | S_IWOTH;
 435                 /*
 436                  * We're alone in a child process, so we can modify the
 437                  * process-wide umask.
 438                  */
 439                 umask(~create_mode);
 440                 /*
 441                  * Try creating shm (or get rw access).
 442                  * We don't do an exclusive open, because we allow other
 443                  * processes to create+ftruncate it concurrently.
 444                  */
 445                 wait_shm_fd = shm_open(sock_info->wait_shm_path,
 446                                 O_RDWR | O_CREAT, create_mode);
 447                 if (wait_shm_fd >= 0) {
 448                         ret = ftruncate(wait_shm_fd, mmap_size);
 449                         if (ret) {
 450                                 PERROR("ftruncate");
 451                                 exit(EXIT_FAILURE);
 452                         }
 453                         exit(EXIT_SUCCESS);
 454                 }
 455                 /*
 456                  * For local shm, we need to have rw access to accept
 457                  * opening it: this means the local sessiond will be
 458                  * able to wake us up. For global shm, we open it even
 459                  * if rw access is not granted, because the root.root
 460                  * sessiond will be able to override all rights and wake
 461                  * us up.
 462                  */
 463                 if (!sock_info->global && errno != EACCES) {
 464                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 465                         exit(EXIT_FAILURE);
 466                 }
 467                 /*
 468                  * The shm exists, but we cannot open it RW. Report
 469                  * success.
 470                  */
 471                 exit(EXIT_SUCCESS);
 472         } else {
 473                 return -1;
 474         }
 475 end:
 476         if (wait_shm_fd >= 0 && !sock_info->global) {
 477                 struct stat statbuf;
 478
 479                 /*
 480                  * Ensure that our user is the owner of the shm file for
 481                  * local shm. If we do not own the file, it means our
 482                  * sessiond will not have access to wake us up (there is
 483                  * probably a rogue process trying to fake our
 484                  * sessiond). Fallback to polling method in this case.
 485                  */
 486                 ret = fstat(wait_shm_fd, &statbuf);
 487                 if (ret) {
 488                         PERROR("fstat");
 489                         goto error_close;
 490                 }
 491                 if (statbuf.st_uid != getuid())
 492                         goto error_close;
 493         }
 494         return wait_shm_fd;
 495
 496 error_close:
 497         ret = close(wait_shm_fd);
 498         if (ret) {
 499                 PERROR("Error closing fd");
 500         }
 501         return -1;
 502 }
 503
 504 static
 505 char *get_map_shm(struct sock_info *sock_info)
 506 {
 507         size_t mmap_size = sysconf(_SC_PAGE_SIZE);
 508         int wait_shm_fd, ret;
 509         char *wait_shm_mmap;
 510
 511         wait_shm_fd = get_wait_shm(sock_info, mmap_size);
 512         if (wait_shm_fd < 0) {
 513                 goto error;
 514         }
 515         wait_shm_mmap = mmap(NULL, mmap_size, PROT_READ,
 516                   MAP_SHARED, wait_shm_fd, 0);
 517         /* close shm fd immediately after taking the mmap reference */
 518         ret = close(wait_shm_fd);
 519         if (ret) {
 520                 PERROR("Error closing fd");
 521         }
 522         if (wait_shm_mmap == MAP_FAILED) {
 523                 DBG("mmap error (can be caused by race with sessiond). Fallback to poll mode.");
 524                 goto error;
 525         }
 526         return wait_shm_mmap;
 527
 528 error:
 529         return NULL;
 530 }
 531
 532 static
 533 void wait_for_sessiond(struct sock_info *sock_info)
 534 {
 535         int ret;
 536
 537         ust_lock();
 538         if (lttng_ust_comm_should_quit) {
 539                 goto quit;
 540         }
 541         if (wait_poll_fallback) {
 542                 goto error;
 543         }
 544         if (!sock_info->wait_shm_mmap) {
 545                 sock_info->wait_shm_mmap = get_map_shm(sock_info);
 546                 if (!sock_info->wait_shm_mmap)
 547                         goto error;
 548         }
 549         ust_unlock();
 550
 551         DBG("Waiting for %s apps sessiond", sock_info->name);
 552         /* Wait for futex wakeup */
 553         if (uatomic_read((int32_t *) sock_info->wait_shm_mmap) == 0) {
 554                 ret = futex_async((int32_t *) sock_info->wait_shm_mmap,
 555                         FUTEX_WAIT, 0, NULL, NULL, 0);
 556                 if (ret < 0) {
 557                         if (errno == EFAULT) {
 558                                 wait_poll_fallback = 1;
 559                                 WARN(
 560 "Linux kernels 2.6.33 to 3.0 (with the exception of stable versions) "
 561 "do not support FUTEX_WAKE on read-only memory mappings correctly. "
 562 "Please upgrade your kernel "
 563 "(fix is commit 9ea71503a8ed9184d2d0b8ccc4d269d05f7940ae in Linux kernel "
 564 "mainline). LTTng-UST will use polling mode fallback.");
 565                         }
 566                         PERROR("futex");
 567                 }
 568         }
 569         return;
 570
 571 quit:
 572         ust_unlock();
 573         return;
 574
 575 error:
 576         ust_unlock();
 577         return;
 578 }
 579
 580 /*
 581  * This thread does not allocate any resource, except within
 582  * handle_message, within mutex protection. This mutex protects against
 583  * fork and exit.
 584  * The other moment it allocates resources is at socket connexion, which
 585  * is also protected by the mutex.
 586  */
 587 static
 588 void *ust_listener_thread(void *arg)
 589 {
 590         struct sock_info *sock_info = arg;
 591         int sock, ret, prev_connect_failed = 0, has_waited = 0;
 592
 593         /* Restart trying to connect to the session daemon */
 594 restart:
 595         if (prev_connect_failed) {
 596                 /* Wait for sessiond availability with pipe */
 597                 wait_for_sessiond(sock_info);
 598                 if (has_waited) {
 599                         has_waited = 0;
 600                         /*
 601                          * Sleep for 5 seconds before retrying after a
 602                          * sequence of failure / wait / failure. This
 603                          * deals with a killed or broken session daemon.
 604                          */
 605                         sleep(5);
 606                 }
 607                 has_waited = 1;
 608                 prev_connect_failed = 0;
 609         }
 610         ust_lock();
 611
 612         if (lttng_ust_comm_should_quit) {
 613                 ust_unlock();
 614                 goto quit;
 615         }
 616
 617         if (sock_info->socket != -1) {
 618                 ret = close(sock_info->socket);
 619                 if (ret) {
 620                         ERR("Error closing %s apps socket", sock_info->name);
 621                 }
 622                 sock_info->socket = -1;
 623         }
 624
 625         /* Register */
 626         ret = ustcomm_connect_unix_sock(sock_info->sock_path);
 627         if (ret < 0) {
 628                 ERR("Error connecting to %s apps socket", sock_info->name);
 629                 prev_connect_failed = 1;
 630                 /*
 631                  * If we cannot find the sessiond daemon, don't delay
 632                  * constructor execution.
 633                  */
 634                 ret = handle_register_done(sock_info);
 635                 assert(!ret);
 636                 ust_unlock();
 637                 goto restart;
 638         }
 639
 640         sock_info->socket = sock = ret;
 641
 642         /*
 643          * Create only one root handle per listener thread for the whole
 644          * process lifetime.
 645          */
 646         if (sock_info->root_handle == -1) {
 647                 ret = lttng_abi_create_root_handle();
 648                 if (ret < 0) {
 649                         ERR("Error creating root handle");
 650                         ust_unlock();
 651                         goto quit;
 652                 }
 653                 sock_info->root_handle = ret;
 654         }
 655
 656         ret = register_app_to_sessiond(sock);
 657         if (ret < 0) {
 658                 ERR("Error registering to %s apps socket", sock_info->name);
 659                 prev_connect_failed = 1;
 660                 /*
 661                  * If we cannot register to the sessiond daemon, don't
 662                  * delay constructor execution.
 663                  */
 664                 ret = handle_register_done(sock_info);
 665                 assert(!ret);
 666                 ust_unlock();
 667                 goto restart;
 668         }
 669         ust_unlock();
 670
 671         for (;;) {
 672                 ssize_t len;
 673                 struct ustcomm_ust_msg lum;
 674
 675                 len = ustcomm_recv_unix_sock(sock, &lum, sizeof(lum));
 676                 switch (len) {
 677                 case 0: /* orderly shutdown */
 678                         DBG("%s ltt-sessiond has performed an orderly shutdown\n", sock_info->name);
 679                         goto end;
 680                 case sizeof(lum):
 681                         DBG("message received\n");
 682                         ret = handle_message(sock_info, sock, &lum);
 683                         if (ret < 0) {
 684                                 ERR("Error handling message for %s socket", sock_info->name);
 685                         }
 686                         continue;
 687                 case -1:
 688                         if (errno == ECONNRESET) {
 689                                 ERR("%s remote end closed connection\n", sock_info->name);
 690                                 goto end;
 691                         }
 692                         goto end;
 693                 default:
 694                         ERR("incorrect message size (%s socket): %zd\n", sock_info->name, len);
 695                         continue;
 696                 }
 697
 698         }
 699 end:
 700         goto restart;   /* try to reconnect */
 701 quit:
 702         return NULL;
 703 }
 704
 705 /*
 706  * Return values: -1: don't wait. 0: wait forever. 1: timeout wait.
 707  */
 708 static
 709 int get_timeout(struct timespec *constructor_timeout)
 710 {
 711         long constructor_delay_ms = LTTNG_UST_DEFAULT_CONSTRUCTOR_TIMEOUT_MS;
 712         char *str_delay;
 713         int ret;
 714
 715         str_delay = getenv("UST_REGISTER_TIMEOUT");
 716         if (str_delay) {
 717                 constructor_delay_ms = strtol(str_delay, NULL, 10);
 718         }
 719
 720         switch (constructor_delay_ms) {
 721         case -1:/* fall-through */
 722         case 0:
 723                 return constructor_delay_ms;
 724         default:
 725                 break;
 726         }
 727
 728         /*
 729          * If we are unable to find the current time, don't wait.
 730          */
 731         ret = clock_gettime(CLOCK_REALTIME, constructor_timeout);
 732         if (ret) {
 733                 return -1;
 734         }
 735         constructor_timeout->tv_sec += constructor_delay_ms / 1000UL;
 736         constructor_timeout->tv_nsec +=
 737                 (constructor_delay_ms % 1000UL) * 1000000UL;
 738         if (constructor_timeout->tv_nsec >= 1000000000UL) {
 739                 constructor_timeout->tv_sec++;
 740                 constructor_timeout->tv_nsec -= 1000000000UL;
 741         }
 742         return 1;
 743 }
 744
 745 /*
 746  * sessiond monitoring thread: monitor presence of global and per-user
 747  * sessiond by polling the application common named pipe.
 748  */
 749 /* TODO */
 750
 751 void __attribute__((constructor)) lttng_ust_init(void)
 752 {
 753         struct timespec constructor_timeout;
 754         int timeout_mode;
 755         int ret;
 756
 757         if (uatomic_xchg(&initialized, 1) == 1)
 758                 return;
 759
 760         /*
 761          * We want precise control over the order in which we construct
 762          * our sub-libraries vs starting to receive commands from
 763          * sessiond (otherwise leading to errors when trying to create
 764          * sessiond before the init functions are completed).
 765          */
 766         init_usterr();
 767         init_tracepoint();
 768         ltt_ring_buffer_metadata_client_init();
 769         ltt_ring_buffer_client_overwrite_init();
 770         ltt_ring_buffer_client_discard_init();
 771
 772         timeout_mode = get_timeout(&constructor_timeout);
 773
 774         ret = sem_init(&constructor_wait, 0, 0);
 775         assert(!ret);
 776
 777         ret = setup_local_apps();
 778         if (ret) {
 779                 ERR("Error setting up to local apps");
 780         }
 781         ret = pthread_create(&local_apps.ust_listener, NULL,
 782                         ust_listener_thread, &local_apps);
 783
 784         if (local_apps.allowed) {
 785                 ret = pthread_create(&global_apps.ust_listener, NULL,
 786                                 ust_listener_thread, &global_apps);
 787         } else {
 788                 handle_register_done(&local_apps);
 789         }
 790
 791         switch (timeout_mode) {
 792         case 1: /* timeout wait */
 793                 do {
 794                         ret = sem_timedwait(&constructor_wait,
 795                                         &constructor_timeout);
 796                 } while (ret < 0 && errno == EINTR);
 797                 if (ret < 0 && errno == ETIMEDOUT) {
 798                         ERR("Timed out waiting for ltt-sessiond");
 799                 } else {
 800                         assert(!ret);
 801                 }
 802                 break;
 803         case -1:/* wait forever */
 804                 do {
 805                         ret = sem_wait(&constructor_wait);
 806                 } while (ret < 0 && errno == EINTR);
 807                 assert(!ret);
 808                 break;
 809         case 0: /* no timeout */
 810                 break;
 811         }
 812 }
 813
 814 static
 815 void lttng_ust_cleanup(int exiting)
 816 {
 817         cleanup_sock_info(&global_apps);
 818         if (local_apps.allowed) {
 819                 cleanup_sock_info(&local_apps);
 820         }
 821         lttng_ust_abi_exit();
 822         lttng_ust_events_exit();
 823         ltt_ring_buffer_client_discard_exit();
 824         ltt_ring_buffer_client_overwrite_exit();
 825         ltt_ring_buffer_metadata_client_exit();
 826         exit_tracepoint();
 827         if (!exiting) {
 828                 /* Reinitialize values for fork */
 829                 sem_count = 2;
 830                 lttng_ust_comm_should_quit = 0;
 831                 initialized = 0;
 832         }
 833 }
 834
 835 void __attribute__((destructor)) lttng_ust_exit(void)
 836 {
 837         int ret;
 838
 839         /*
 840          * Using pthread_cancel here because:
 841          * A) we don't want to hang application teardown.
 842          * B) the thread is not allocating any resource.
 843          */
 844
 845         /*
 846          * Require the communication thread to quit. Synchronize with
 847          * mutexes to ensure it is not in a mutex critical section when
 848          * pthread_cancel is later called.
 849          */
 850         ust_lock();
 851         lttng_ust_comm_should_quit = 1;
 852         ust_unlock();
 853
 854         ret = pthread_cancel(global_apps.ust_listener);
 855         if (ret) {
 856                 ERR("Error cancelling global ust listener thread");
 857         }
 858         if (local_apps.allowed) {
 859                 ret = pthread_cancel(local_apps.ust_listener);
 860                 if (ret) {
 861                         ERR("Error cancelling local ust listener thread");
 862                 }
 863         }
 864         lttng_ust_cleanup(1);
 865 }
 866
 867 /*
 868  * We exclude the worker threads across fork and clone (except
 869  * CLONE_VM), because these system calls only keep the forking thread
 870  * running in the child.  Therefore, we don't want to call fork or clone
 871  * in the middle of an tracepoint or ust tracing state modification.
 872  * Holding this mutex protects these structures across fork and clone.
 873  */
 874 void ust_before_fork(ust_fork_info_t *fork_info)
 875 {
 876         /*
 877          * Disable signals. This is to avoid that the child intervenes
 878          * before it is properly setup for tracing. It is safer to
 879          * disable all signals, because then we know we are not breaking
 880          * anything by restoring the original mask.
 881          */
 882         sigset_t all_sigs;
 883         int ret;
 884
 885         /* Disable signals */
 886         sigfillset(&all_sigs);
 887         ret = sigprocmask(SIG_BLOCK, &all_sigs, &fork_info->orig_sigs);
 888         if (ret == -1) {
 889                 PERROR("sigprocmask");
 890         }
 891         ust_lock();
 892         rcu_bp_before_fork();
 893 }
 894
 895 static void ust_after_fork_common(ust_fork_info_t *fork_info)
 896 {
 897         int ret;
 898
 899         DBG("process %d", getpid());
 900         ust_unlock();
 901         /* Restore signals */
 902         ret = sigprocmask(SIG_SETMASK, &fork_info->orig_sigs, NULL);
 903         if (ret == -1) {
 904                 PERROR("sigprocmask");
 905         }
 906 }
 907
 908 void ust_after_fork_parent(ust_fork_info_t *fork_info)
 909 {
 910         DBG("process %d", getpid());
 911         rcu_bp_after_fork_parent();
 912         /* Release mutexes and reenable signals */
 913         ust_after_fork_common(fork_info);
 914 }
 915
 916 /*
 917  * After fork, in the child, we need to cleanup all the leftover state,
 918  * except the worker thread which already magically disappeared thanks
 919  * to the weird Linux fork semantics. After tyding up, we call
 920  * lttng_ust_init() again to start over as a new PID.
 921  *
 922  * This is meant for forks() that have tracing in the child between the
 923  * fork and following exec call (if there is any).
 924  */
 925 void ust_after_fork_child(ust_fork_info_t *fork_info)
 926 {
 927         DBG("process %d", getpid());
 928         /* Release urcu mutexes */
 929         rcu_bp_after_fork_child();
 930         lttng_ust_cleanup(0);
 931         lttng_context_vtid_reset();
 932         /* Release mutexes and reenable signals */
 933         ust_after_fork_common(fork_info);
 934         lttng_ust_init();
 935 }