liblttng-ust/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 <lttng/ust-events.h>
  43 #include <lttng/usterr-signal-safe.h>
  44 #include <lttng/ust-abi.h>
  45 #include <lttng/tracepoint.h>
  46 #include <lttng/tracepoint-internal.h>
  47 #include <lttng/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         case LTTNG_UST_TRACEPOINT_LIST_GET:
 308                 memcpy(lur.u.tracepoint_list_entry,
 309                         lum->u.tracepoint_list_entry,
 310                         LTTNG_UST_SYM_NAME_LEN);
 311                 break;
 312         }
 313         ret = send_reply(sock, &lur);
 314         if (ret < 0) {
 315                 perror("error sending reply");
 316                 goto error;
 317         }
 318
 319         if ((lum->cmd == LTTNG_UST_STREAM
 320              || lum->cmd == LTTNG_UST_CHANNEL
 321              || lum->cmd == LTTNG_UST_METADATA)
 322                         && lur.ret_code == USTCOMM_OK) {
 323                 /* we also need to send the file descriptors. */
 324                 ret = ustcomm_send_fds_unix_sock(sock,
 325                         &shm_fd, &shm_fd,
 326                         1, sizeof(int));
 327                 if (ret < 0) {
 328                         perror("send shm_fd");
 329                         goto error;
 330                 }
 331                 ret = ustcomm_send_fds_unix_sock(sock,
 332                         &wait_fd, &wait_fd,
 333                         1, sizeof(int));
 334                 if (ret < 0) {
 335                         perror("send wait_fd");
 336                         goto error;
 337                 }
 338         }
 339 error:
 340         ust_unlock();
 341         return ret;
 342 }
 343
 344 static
 345 void cleanup_sock_info(struct sock_info *sock_info)
 346 {
 347         int ret;
 348
 349         if (sock_info->socket != -1) {
 350                 ret = close(sock_info->socket);
 351                 if (ret) {
 352                         ERR("Error closing apps socket");
 353                 }
 354                 sock_info->socket = -1;
 355         }
 356         if (sock_info->root_handle != -1) {
 357                 ret = lttng_ust_objd_unref(sock_info->root_handle);
 358                 if (ret) {
 359                         ERR("Error unref root handle");
 360                 }
 361                 sock_info->root_handle = -1;
 362         }
 363         sock_info->constructor_sem_posted = 0;
 364         if (sock_info->wait_shm_mmap) {
 365                 ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
 366                 if (ret) {
 367                         ERR("Error unmapping wait shm");
 368                 }
 369                 sock_info->wait_shm_mmap = NULL;
 370         }
 371 }
 372
 373 /*
 374  * Using fork to set umask in the child process (not multi-thread safe).
 375  * We deal with the shm_open vs ftruncate race (happening when the
 376  * sessiond owns the shm and does not let everybody modify it, to ensure
 377  * safety against shm_unlink) by simply letting the mmap fail and
 378  * retrying after a few seconds.
 379  * For global shm, everybody has rw access to it until the sessiond
 380  * starts.
 381  */
 382 static
 383 int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
 384 {
 385         int wait_shm_fd, ret;
 386         pid_t pid;
 387
 388         /*
 389          * Try to open read-only.
 390          */
 391         wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 392         if (wait_shm_fd >= 0) {
 393                 goto end;
 394         } else if (wait_shm_fd < 0 && errno != ENOENT) {
 395                 /*
 396                  * Real-only open did not work, and it's not because the
 397                  * entry was not present. It's a failure that prohibits
 398                  * using shm.
 399                  */
 400                 ERR("Error opening shm %s", sock_info->wait_shm_path);
 401                 goto end;
 402         }
 403         /*
 404          * If the open failed because the file did not exist, try
 405          * creating it ourself.
 406          */
 407         pid = fork();
 408         if (pid > 0) {
 409                 int status;
 410
 411                 /*
 412                  * Parent: wait for child to return, in which case the
 413                  * shared memory map will have been created.
 414                  */
 415                 pid = wait(&status);
 416                 if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 417                         wait_shm_fd = -1;
 418                         goto end;
 419                 }
 420                 /*
 421                  * Try to open read-only again after creation.
 422                  */
 423                 wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 424                 if (wait_shm_fd < 0) {
 425                         /*
 426                          * Real-only open did not work. It's a failure
 427                          * that prohibits using shm.
 428                          */
 429                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 430                         goto end;
 431                 }
 432                 goto end;
 433         } else if (pid == 0) {
 434                 int create_mode;
 435
 436                 /* Child */
 437                 create_mode = S_IRUSR | S_IWUSR | S_IRGRP;
 438                 if (sock_info->global)
 439                         create_mode |= S_IROTH | S_IWGRP | S_IWOTH;
 440                 /*
 441                  * We're alone in a child process, so we can modify the
 442                  * process-wide umask.
 443                  */
 444                 umask(~create_mode);
 445                 /*
 446                  * Try creating shm (or get rw access).
 447                  * We don't do an exclusive open, because we allow other
 448                  * processes to create+ftruncate it concurrently.
 449                  */
 450                 wait_shm_fd = shm_open(sock_info->wait_shm_path,
 451                                 O_RDWR | O_CREAT, create_mode);
 452                 if (wait_shm_fd >= 0) {
 453                         ret = ftruncate(wait_shm_fd, mmap_size);
 454                         if (ret) {
 455                                 PERROR("ftruncate");
 456                                 exit(EXIT_FAILURE);
 457                         }
 458                         exit(EXIT_SUCCESS);
 459                 }
 460                 /*
 461                  * For local shm, we need to have rw access to accept
 462                  * opening it: this means the local sessiond will be
 463                  * able to wake us up. For global shm, we open it even
 464                  * if rw access is not granted, because the root.root
 465                  * sessiond will be able to override all rights and wake
 466                  * us up.
 467                  */
 468                 if (!sock_info->global && errno != EACCES) {
 469                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 470                         exit(EXIT_FAILURE);
 471                 }
 472                 /*
 473                  * The shm exists, but we cannot open it RW. Report
 474                  * success.
 475                  */
 476                 exit(EXIT_SUCCESS);
 477         } else {
 478                 return -1;
 479         }
 480 end:
 481         if (wait_shm_fd >= 0 && !sock_info->global) {
 482                 struct stat statbuf;
 483
 484                 /*
 485                  * Ensure that our user is the owner of the shm file for
 486                  * local shm. If we do not own the file, it means our
 487                  * sessiond will not have access to wake us up (there is
 488                  * probably a rogue process trying to fake our
 489                  * sessiond). Fallback to polling method in this case.
 490                  */
 491                 ret = fstat(wait_shm_fd, &statbuf);
 492                 if (ret) {
 493                         PERROR("fstat");
 494                         goto error_close;
 495                 }
 496                 if (statbuf.st_uid != getuid())
 497                         goto error_close;
 498         }
 499         return wait_shm_fd;
 500
 501 error_close:
 502         ret = close(wait_shm_fd);
 503         if (ret) {
 504                 PERROR("Error closing fd");
 505         }
 506         return -1;
 507 }
 508
 509 static
 510 char *get_map_shm(struct sock_info *sock_info)
 511 {
 512         size_t mmap_size = sysconf(_SC_PAGE_SIZE);
 513         int wait_shm_fd, ret;
 514         char *wait_shm_mmap;
 515
 516         wait_shm_fd = get_wait_shm(sock_info, mmap_size);
 517         if (wait_shm_fd < 0) {
 518                 goto error;
 519         }
 520         wait_shm_mmap = mmap(NULL, mmap_size, PROT_READ,
 521                   MAP_SHARED, wait_shm_fd, 0);
 522         /* close shm fd immediately after taking the mmap reference */
 523         ret = close(wait_shm_fd);
 524         if (ret) {
 525                 PERROR("Error closing fd");
 526         }
 527         if (wait_shm_mmap == MAP_FAILED) {
 528                 DBG("mmap error (can be caused by race with sessiond). Fallback to poll mode.");
 529                 goto error;
 530         }
 531         return wait_shm_mmap;
 532
 533 error:
 534         return NULL;
 535 }
 536
 537 static
 538 void wait_for_sessiond(struct sock_info *sock_info)
 539 {
 540         int ret;
 541
 542         ust_lock();
 543         if (lttng_ust_comm_should_quit) {
 544                 goto quit;
 545         }
 546         if (wait_poll_fallback) {
 547                 goto error;
 548         }
 549         if (!sock_info->wait_shm_mmap) {
 550                 sock_info->wait_shm_mmap = get_map_shm(sock_info);
 551                 if (!sock_info->wait_shm_mmap)
 552                         goto error;
 553         }
 554         ust_unlock();
 555
 556         DBG("Waiting for %s apps sessiond", sock_info->name);
 557         /* Wait for futex wakeup */
 558         if (uatomic_read((int32_t *) sock_info->wait_shm_mmap) == 0) {
 559                 ret = futex_async((int32_t *) sock_info->wait_shm_mmap,
 560                         FUTEX_WAIT, 0, NULL, NULL, 0);
 561                 if (ret < 0) {
 562                         if (errno == EFAULT) {
 563                                 wait_poll_fallback = 1;
 564                                 WARN(
 565 "Linux kernels 2.6.33 to 3.0 (with the exception of stable versions) "
 566 "do not support FUTEX_WAKE on read-only memory mappings correctly. "
 567 "Please upgrade your kernel "
 568 "(fix is commit 9ea71503a8ed9184d2d0b8ccc4d269d05f7940ae in Linux kernel "
 569 "mainline). LTTng-UST will use polling mode fallback.");
 570                         }
 571                         PERROR("futex");
 572                 }
 573         }
 574         return;
 575
 576 quit:
 577         ust_unlock();
 578         return;
 579
 580 error:
 581         ust_unlock();
 582         return;
 583 }
 584
 585 /*
 586  * This thread does not allocate any resource, except within
 587  * handle_message, within mutex protection. This mutex protects against
 588  * fork and exit.
 589  * The other moment it allocates resources is at socket connexion, which
 590  * is also protected by the mutex.
 591  */
 592 static
 593 void *ust_listener_thread(void *arg)
 594 {
 595         struct sock_info *sock_info = arg;
 596         int sock, ret, prev_connect_failed = 0, has_waited = 0;
 597
 598         /* Restart trying to connect to the session daemon */
 599 restart:
 600         if (prev_connect_failed) {
 601                 /* Wait for sessiond availability with pipe */
 602                 wait_for_sessiond(sock_info);
 603                 if (has_waited) {
 604                         has_waited = 0;
 605                         /*
 606                          * Sleep for 5 seconds before retrying after a
 607                          * sequence of failure / wait / failure. This
 608                          * deals with a killed or broken session daemon.
 609                          */
 610                         sleep(5);
 611                 }
 612                 has_waited = 1;
 613                 prev_connect_failed = 0;
 614         }
 615         ust_lock();
 616
 617         if (lttng_ust_comm_should_quit) {
 618                 ust_unlock();
 619                 goto quit;
 620         }
 621
 622         if (sock_info->socket != -1) {
 623                 ret = close(sock_info->socket);
 624                 if (ret) {
 625                         ERR("Error closing %s apps socket", sock_info->name);
 626                 }
 627                 sock_info->socket = -1;
 628         }
 629
 630         /* Register */
 631         ret = ustcomm_connect_unix_sock(sock_info->sock_path);
 632         if (ret < 0) {
 633                 DBG("Info: sessiond not accepting connections to %s apps socket", sock_info->name);
 634                 prev_connect_failed = 1;
 635                 /*
 636                  * If we cannot find the sessiond daemon, don't delay
 637                  * constructor execution.
 638                  */
 639                 ret = handle_register_done(sock_info);
 640                 assert(!ret);
 641                 ust_unlock();
 642                 goto restart;
 643         }
 644
 645         sock_info->socket = sock = ret;
 646
 647         /*
 648          * Create only one root handle per listener thread for the whole
 649          * process lifetime.
 650          */
 651         if (sock_info->root_handle == -1) {
 652                 ret = lttng_abi_create_root_handle();
 653                 if (ret < 0) {
 654                         ERR("Error creating root handle");
 655                         ust_unlock();
 656                         goto quit;
 657                 }
 658                 sock_info->root_handle = ret;
 659         }
 660
 661         ret = register_app_to_sessiond(sock);
 662         if (ret < 0) {
 663                 ERR("Error registering to %s apps socket", sock_info->name);
 664                 prev_connect_failed = 1;
 665                 /*
 666                  * If we cannot register to the sessiond daemon, don't
 667                  * delay constructor execution.
 668                  */
 669                 ret = handle_register_done(sock_info);
 670                 assert(!ret);
 671                 ust_unlock();
 672                 goto restart;
 673         }
 674         ust_unlock();
 675
 676         for (;;) {
 677                 ssize_t len;
 678                 struct ustcomm_ust_msg lum;
 679
 680                 len = ustcomm_recv_unix_sock(sock, &lum, sizeof(lum));
 681                 switch (len) {
 682                 case 0: /* orderly shutdown */
 683                         DBG("%s ltt-sessiond has performed an orderly shutdown\n", sock_info->name);
 684                         goto end;
 685                 case sizeof(lum):
 686                         DBG("message received\n");
 687                         ret = handle_message(sock_info, sock, &lum);
 688                         if (ret < 0) {
 689                                 ERR("Error handling message for %s socket", sock_info->name);
 690                         }
 691                         continue;
 692                 case -1:
 693                         if (errno == ECONNRESET) {
 694                                 ERR("%s remote end closed connection\n", sock_info->name);
 695                                 goto end;
 696                         }
 697                         goto end;
 698                 default:
 699                         ERR("incorrect message size (%s socket): %zd\n", sock_info->name, len);
 700                         continue;
 701                 }
 702
 703         }
 704 end:
 705         goto restart;   /* try to reconnect */
 706 quit:
 707         return NULL;
 708 }
 709
 710 /*
 711  * Return values: -1: don't wait. 0: wait forever. 1: timeout wait.
 712  */
 713 static
 714 int get_timeout(struct timespec *constructor_timeout)
 715 {
 716         long constructor_delay_ms = LTTNG_UST_DEFAULT_CONSTRUCTOR_TIMEOUT_MS;
 717         char *str_delay;
 718         int ret;
 719
 720         str_delay = getenv("LTTNG_UST_REGISTER_TIMEOUT");
 721         if (str_delay) {
 722                 constructor_delay_ms = strtol(str_delay, NULL, 10);
 723         }
 724
 725         switch (constructor_delay_ms) {
 726         case -1:/* fall-through */
 727         case 0:
 728                 return constructor_delay_ms;
 729         default:
 730                 break;
 731         }
 732
 733         /*
 734          * If we are unable to find the current time, don't wait.
 735          */
 736         ret = clock_gettime(CLOCK_REALTIME, constructor_timeout);
 737         if (ret) {
 738                 return -1;
 739         }
 740         constructor_timeout->tv_sec += constructor_delay_ms / 1000UL;
 741         constructor_timeout->tv_nsec +=
 742                 (constructor_delay_ms % 1000UL) * 1000000UL;
 743         if (constructor_timeout->tv_nsec >= 1000000000UL) {
 744                 constructor_timeout->tv_sec++;
 745                 constructor_timeout->tv_nsec -= 1000000000UL;
 746         }
 747         return 1;
 748 }
 749
 750 /*
 751  * sessiond monitoring thread: monitor presence of global and per-user
 752  * sessiond by polling the application common named pipe.
 753  */
 754 /* TODO */
 755
 756 void __attribute__((constructor)) lttng_ust_init(void)
 757 {
 758         struct timespec constructor_timeout;
 759         int timeout_mode;
 760         int ret;
 761
 762         if (uatomic_xchg(&initialized, 1) == 1)
 763                 return;
 764
 765         /*
 766          * We want precise control over the order in which we construct
 767          * our sub-libraries vs starting to receive commands from
 768          * sessiond (otherwise leading to errors when trying to create
 769          * sessiond before the init functions are completed).
 770          */
 771         init_usterr();
 772         init_tracepoint();
 773         ltt_ring_buffer_metadata_client_init();
 774         ltt_ring_buffer_client_overwrite_init();
 775         ltt_ring_buffer_client_discard_init();
 776
 777         timeout_mode = get_timeout(&constructor_timeout);
 778
 779         ret = sem_init(&constructor_wait, 0, 0);
 780         assert(!ret);
 781
 782         ret = setup_local_apps();
 783         if (ret) {
 784                 ERR("Error setting up to local apps");
 785         }
 786         ret = pthread_create(&local_apps.ust_listener, NULL,
 787                         ust_listener_thread, &local_apps);
 788
 789         if (local_apps.allowed) {
 790                 ret = pthread_create(&global_apps.ust_listener, NULL,
 791                                 ust_listener_thread, &global_apps);
 792         } else {
 793                 handle_register_done(&local_apps);
 794         }
 795
 796         switch (timeout_mode) {
 797         case 1: /* timeout wait */
 798                 do {
 799                         ret = sem_timedwait(&constructor_wait,
 800                                         &constructor_timeout);
 801                 } while (ret < 0 && errno == EINTR);
 802                 if (ret < 0 && errno == ETIMEDOUT) {
 803                         ERR("Timed out waiting for ltt-sessiond");
 804                 } else {
 805                         assert(!ret);
 806                 }
 807                 break;
 808         case -1:/* wait forever */
 809                 do {
 810                         ret = sem_wait(&constructor_wait);
 811                 } while (ret < 0 && errno == EINTR);
 812                 assert(!ret);
 813                 break;
 814         case 0: /* no timeout */
 815                 break;
 816         }
 817 }
 818
 819 static
 820 void lttng_ust_cleanup(int exiting)
 821 {
 822         cleanup_sock_info(&global_apps);
 823         if (local_apps.allowed) {
 824                 cleanup_sock_info(&local_apps);
 825         }
 826         lttng_ust_abi_exit();
 827         lttng_ust_events_exit();
 828         ltt_ring_buffer_client_discard_exit();
 829         ltt_ring_buffer_client_overwrite_exit();
 830         ltt_ring_buffer_metadata_client_exit();
 831         exit_tracepoint();
 832         if (!exiting) {
 833                 /* Reinitialize values for fork */
 834                 sem_count = 2;
 835                 lttng_ust_comm_should_quit = 0;
 836                 initialized = 0;
 837         }
 838 }
 839
 840 void __attribute__((destructor)) lttng_ust_exit(void)
 841 {
 842         int ret;
 843
 844         /*
 845          * Using pthread_cancel here because:
 846          * A) we don't want to hang application teardown.
 847          * B) the thread is not allocating any resource.
 848          */
 849
 850         /*
 851          * Require the communication thread to quit. Synchronize with
 852          * mutexes to ensure it is not in a mutex critical section when
 853          * pthread_cancel is later called.
 854          */
 855         ust_lock();
 856         lttng_ust_comm_should_quit = 1;
 857         ust_unlock();
 858
 859         ret = pthread_cancel(global_apps.ust_listener);
 860         if (ret) {
 861                 ERR("Error cancelling global ust listener thread");
 862         }
 863         if (local_apps.allowed) {
 864                 ret = pthread_cancel(local_apps.ust_listener);
 865                 if (ret) {
 866                         ERR("Error cancelling local ust listener thread");
 867                 }
 868         }
 869         lttng_ust_cleanup(1);
 870 }
 871
 872 /*
 873  * We exclude the worker threads across fork and clone (except
 874  * CLONE_VM), because these system calls only keep the forking thread
 875  * running in the child.  Therefore, we don't want to call fork or clone
 876  * in the middle of an tracepoint or ust tracing state modification.
 877  * Holding this mutex protects these structures across fork and clone.
 878  */
 879 void ust_before_fork(ust_fork_info_t *fork_info)
 880 {
 881         /*
 882          * Disable signals. This is to avoid that the child intervenes
 883          * before it is properly setup for tracing. It is safer to
 884          * disable all signals, because then we know we are not breaking
 885          * anything by restoring the original mask.
 886          */
 887         sigset_t all_sigs;
 888         int ret;
 889
 890         /* Disable signals */
 891         sigfillset(&all_sigs);
 892         ret = sigprocmask(SIG_BLOCK, &all_sigs, &fork_info->orig_sigs);
 893         if (ret == -1) {
 894                 PERROR("sigprocmask");
 895         }
 896         ust_lock();
 897         rcu_bp_before_fork();
 898 }
 899
 900 static void ust_after_fork_common(ust_fork_info_t *fork_info)
 901 {
 902         int ret;
 903
 904         DBG("process %d", getpid());
 905         ust_unlock();
 906         /* Restore signals */
 907         ret = sigprocmask(SIG_SETMASK, &fork_info->orig_sigs, NULL);
 908         if (ret == -1) {
 909                 PERROR("sigprocmask");
 910         }
 911 }
 912
 913 void ust_after_fork_parent(ust_fork_info_t *fork_info)
 914 {
 915         DBG("process %d", getpid());
 916         rcu_bp_after_fork_parent();
 917         /* Release mutexes and reenable signals */
 918         ust_after_fork_common(fork_info);
 919 }
 920
 921 /*
 922  * After fork, in the child, we need to cleanup all the leftover state,
 923  * except the worker thread which already magically disappeared thanks
 924  * to the weird Linux fork semantics. After tyding up, we call
 925  * lttng_ust_init() again to start over as a new PID.
 926  *
 927  * This is meant for forks() that have tracing in the child between the
 928  * fork and following exec call (if there is any).
 929  */
 930 void ust_after_fork_child(ust_fork_info_t *fork_info)
 931 {
 932         DBG("process %d", getpid());
 933         /* Release urcu mutexes */
 934         rcu_bp_after_fork_child();
 935         lttng_ust_cleanup(0);
 936         lttng_context_vtid_reset();
 937         /* Release mutexes and reenable signals */
 938         ust_after_fork_common(fork_info);
 939         lttng_ust_init();
 940 }