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/mman.h>
  26 #include <sys/stat.h>
  27 #include <sys/types.h>
  28 #include <sys/wait.h>
  29 #include <fcntl.h>
  30 #include <unistd.h>
  31 #include <errno.h>
  32 #include <pthread.h>
  33 #include <semaphore.h>
  34 #include <time.h>
  35 #include <assert.h>
  36 #include <signal.h>
  37 #include <urcu/uatomic.h>
  38 #include <urcu/futex.h>
  39 #include <urcu/compiler.h>
  40
  41 #include <lttng/ust-events.h>
  42 #include <lttng/ust-abi.h>
  43 #include <lttng/ust.h>
  44 #include <ust-comm.h>
  45 #include <usterr-signal-safe.h>
  46 #include "tracepoint-internal.h"
  47 #include "ltt-tracer-core.h"
  48 #include "compat.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         struct {
 163                 uint32_t major;
 164                 uint32_t minor;
 165                 pid_t pid;
 166                 pid_t ppid;
 167                 uid_t uid;
 168                 gid_t gid;
 169                 uint32_t bits_per_long;
 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         reg_msg.bits_per_long = CAA_BITS_PER_LONG;
 180         lttng_ust_getprocname(reg_msg.name);
 181
 182         ret = ustcomm_send_unix_sock(socket, &reg_msg, sizeof(reg_msg));
 183         if (ret >= 0 && ret != sizeof(reg_msg))
 184                 return -EIO;
 185         return ret;
 186 }
 187
 188 static
 189 int send_reply(int sock, struct ustcomm_ust_reply *lur)
 190 {
 191         ssize_t len;
 192
 193         len = ustcomm_send_unix_sock(sock, lur, sizeof(*lur));
 194         switch (len) {
 195         case sizeof(*lur):
 196                 DBG("message successfully sent");
 197                 return 0;
 198         case -1:
 199                 if (errno == ECONNRESET) {
 200                         printf("remote end closed connection\n");
 201                         return 0;
 202                 }
 203                 return -1;
 204         default:
 205                 printf("incorrect message size: %zd\n", len);
 206                 return -1;
 207         }
 208 }
 209
 210 static
 211 int handle_register_done(struct sock_info *sock_info)
 212 {
 213         int ret;
 214
 215         if (sock_info->constructor_sem_posted)
 216                 return 0;
 217         sock_info->constructor_sem_posted = 1;
 218         if (uatomic_read(&sem_count) <= 0) {
 219                 return 0;
 220         }
 221         ret = uatomic_add_return(&sem_count, -1);
 222         if (ret == 0) {
 223                 ret = sem_post(&constructor_wait);
 224                 assert(!ret);
 225         }
 226         return 0;
 227 }
 228
 229 static
 230 int handle_message(struct sock_info *sock_info,
 231                 int sock, struct ustcomm_ust_msg *lum)
 232 {
 233         int ret = 0;
 234         const struct lttng_ust_objd_ops *ops;
 235         struct ustcomm_ust_reply lur;
 236         int shm_fd, wait_fd;
 237         union ust_args args;
 238
 239         ust_lock();
 240
 241         memset(&lur, 0, sizeof(lur));
 242
 243         if (lttng_ust_comm_should_quit) {
 244                 ret = -EPERM;
 245                 goto end;
 246         }
 247
 248         ops = objd_ops(lum->handle);
 249         if (!ops) {
 250                 ret = -ENOENT;
 251                 goto end;
 252         }
 253
 254         switch (lum->cmd) {
 255         case LTTNG_UST_REGISTER_DONE:
 256                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 257                         ret = handle_register_done(sock_info);
 258                 else
 259                         ret = -EINVAL;
 260                 break;
 261         case LTTNG_UST_RELEASE:
 262                 if (lum->handle == LTTNG_UST_ROOT_HANDLE)
 263                         ret = -EPERM;
 264                 else
 265                         ret = lttng_ust_objd_unref(lum->handle);
 266                 break;
 267         default:
 268                 if (ops->cmd)
 269                         ret = ops->cmd(lum->handle, lum->cmd,
 270                                         (unsigned long) &lum->u,
 271                                         &args);
 272                 else
 273                         ret = -ENOSYS;
 274                 break;
 275         }
 276
 277 end:
 278         lur.handle = lum->handle;
 279         lur.cmd = lum->cmd;
 280         lur.ret_val = ret;
 281         if (ret >= 0) {
 282                 lur.ret_code = USTCOMM_OK;
 283         } else {
 284                 //lur.ret_code = USTCOMM_SESSION_FAIL;
 285                 lur.ret_code = ret;
 286         }
 287         if (ret >= 0) {
 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 = *args.stream.memory_map_size;
 295                         shm_fd = *args.stream.shm_fd;
 296                         wait_fd = *args.stream.wait_fd;
 297                         break;
 298                 case LTTNG_UST_METADATA:
 299                 case LTTNG_UST_CHANNEL:
 300                         lur.u.channel.memory_map_size = *args.channel.memory_map_size;
 301                         shm_fd = *args.channel.shm_fd;
 302                         wait_fd = *args.channel.wait_fd;
 303                         break;
 304                 case LTTNG_UST_TRACER_VERSION:
 305                         lur.u.version = lum->u.version;
 306                         break;
 307                 case LTTNG_UST_TRACEPOINT_LIST_GET:
 308                         memcpy(&lur.u.tracepoint, &lum->u.tracepoint, sizeof(lur.u.tracepoint));
 309                         break;
 310                 }
 311         }
 312         ret = send_reply(sock, &lur);
 313         if (ret < 0) {
 314                 perror("error sending reply");
 315                 goto error;
 316         }
 317
 318         if ((lum->cmd == LTTNG_UST_STREAM
 319              || lum->cmd == LTTNG_UST_CHANNEL
 320              || lum->cmd == LTTNG_UST_METADATA)
 321                         && lur.ret_code == USTCOMM_OK) {
 322                 /* we also need to send the file descriptors. */
 323                 ret = ustcomm_send_fds_unix_sock(sock,
 324                         &shm_fd, &shm_fd,
 325                         1, sizeof(int));
 326                 if (ret < 0) {
 327                         perror("send shm_fd");
 328                         goto error;
 329                 }
 330                 ret = ustcomm_send_fds_unix_sock(sock,
 331                         &wait_fd, &wait_fd,
 332                         1, sizeof(int));
 333                 if (ret < 0) {
 334                         perror("send wait_fd");
 335                         goto error;
 336                 }
 337         }
 338         /*
 339          * We still have the memory map reference, and the fds have been
 340          * sent to the sessiond. We can therefore close those fds. Note
 341          * that we keep the write side of the wait_fd open, but close
 342          * the read side.
 343          */
 344         if (lur.ret_code == USTCOMM_OK) {
 345                 switch (lum->cmd) {
 346                 case LTTNG_UST_STREAM:
 347                         if (shm_fd >= 0) {
 348                                 ret = close(shm_fd);
 349                                 if (ret) {
 350                                         PERROR("Error closing stream shm_fd");
 351                                 }
 352                                 *args.stream.shm_fd = -1;
 353                         }
 354                         if (wait_fd >= 0) {
 355                                 ret = close(wait_fd);
 356                                 if (ret) {
 357                                         PERROR("Error closing stream wait_fd");
 358                                 }
 359                                 *args.stream.wait_fd = -1;
 360                         }
 361                         break;
 362                 case LTTNG_UST_METADATA:
 363                 case LTTNG_UST_CHANNEL:
 364                         if (shm_fd >= 0) {
 365                                 ret = close(shm_fd);
 366                                 if (ret) {
 367                                         PERROR("Error closing channel shm_fd");
 368                                 }
 369                                 *args.channel.shm_fd = -1;
 370                         }
 371                         if (wait_fd >= 0) {
 372                                 ret = close(wait_fd);
 373                                 if (ret) {
 374                                         PERROR("Error closing channel wait_fd");
 375                                 }
 376                                 *args.channel.wait_fd = -1;
 377                         }
 378                         break;
 379                 }
 380         }
 381
 382 error:
 383         ust_unlock();
 384         return ret;
 385 }
 386
 387 static
 388 void cleanup_sock_info(struct sock_info *sock_info, int exiting)
 389 {
 390         int ret;
 391
 392         if (sock_info->socket != -1) {
 393                 ret = close(sock_info->socket);
 394                 if (ret) {
 395                         ERR("Error closing apps socket");
 396                 }
 397                 sock_info->socket = -1;
 398         }
 399         if (sock_info->root_handle != -1) {
 400                 ret = lttng_ust_objd_unref(sock_info->root_handle);
 401                 if (ret) {
 402                         ERR("Error unref root handle");
 403                 }
 404                 sock_info->root_handle = -1;
 405         }
 406         sock_info->constructor_sem_posted = 0;
 407         /*
 408          * wait_shm_mmap is used by listener threads outside of the
 409          * ust lock, so we cannot tear it down ourselves, because we
 410          * cannot join on these threads. Leave this task to the OS
 411          * process exit.
 412          */
 413         if (!exiting && sock_info->wait_shm_mmap) {
 414                 ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
 415                 if (ret) {
 416                         ERR("Error unmapping wait shm");
 417                 }
 418                 sock_info->wait_shm_mmap = NULL;
 419         }
 420 }
 421
 422 /*
 423  * Using fork to set umask in the child process (not multi-thread safe).
 424  * We deal with the shm_open vs ftruncate race (happening when the
 425  * sessiond owns the shm and does not let everybody modify it, to ensure
 426  * safety against shm_unlink) by simply letting the mmap fail and
 427  * retrying after a few seconds.
 428  * For global shm, everybody has rw access to it until the sessiond
 429  * starts.
 430  */
 431 static
 432 int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
 433 {
 434         int wait_shm_fd, ret;
 435         pid_t pid;
 436
 437         /*
 438          * Try to open read-only.
 439          */
 440         wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 441         if (wait_shm_fd >= 0) {
 442                 goto end;
 443         } else if (wait_shm_fd < 0 && errno != ENOENT) {
 444                 /*
 445                  * Real-only open did not work, and it's not because the
 446                  * entry was not present. It's a failure that prohibits
 447                  * using shm.
 448                  */
 449                 ERR("Error opening shm %s", sock_info->wait_shm_path);
 450                 goto end;
 451         }
 452         /*
 453          * If the open failed because the file did not exist, try
 454          * creating it ourself.
 455          */
 456         pid = fork();
 457         if (pid > 0) {
 458                 int status;
 459
 460                 /*
 461                  * Parent: wait for child to return, in which case the
 462                  * shared memory map will have been created.
 463                  */
 464                 pid = wait(&status);
 465                 if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 466                         wait_shm_fd = -1;
 467                         goto end;
 468                 }
 469                 /*
 470                  * Try to open read-only again after creation.
 471                  */
 472                 wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
 473                 if (wait_shm_fd < 0) {
 474                         /*
 475                          * Real-only open did not work. It's a failure
 476                          * that prohibits using shm.
 477                          */
 478                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 479                         goto end;
 480                 }
 481                 goto end;
 482         } else if (pid == 0) {
 483                 int create_mode;
 484
 485                 /* Child */
 486                 create_mode = S_IRUSR | S_IWUSR | S_IRGRP;
 487                 if (sock_info->global)
 488                         create_mode |= S_IROTH | S_IWGRP | S_IWOTH;
 489                 /*
 490                  * We're alone in a child process, so we can modify the
 491                  * process-wide umask.
 492                  */
 493                 umask(~create_mode);
 494                 /*
 495                  * Try creating shm (or get rw access).
 496                  * We don't do an exclusive open, because we allow other
 497                  * processes to create+ftruncate it concurrently.
 498                  */
 499                 wait_shm_fd = shm_open(sock_info->wait_shm_path,
 500                                 O_RDWR | O_CREAT, create_mode);
 501                 if (wait_shm_fd >= 0) {
 502                         ret = ftruncate(wait_shm_fd, mmap_size);
 503                         if (ret) {
 504                                 PERROR("ftruncate");
 505                                 exit(EXIT_FAILURE);
 506                         }
 507                         exit(EXIT_SUCCESS);
 508                 }
 509                 /*
 510                  * For local shm, we need to have rw access to accept
 511                  * opening it: this means the local sessiond will be
 512                  * able to wake us up. For global shm, we open it even
 513                  * if rw access is not granted, because the root.root
 514                  * sessiond will be able to override all rights and wake
 515                  * us up.
 516                  */
 517                 if (!sock_info->global && errno != EACCES) {
 518                         ERR("Error opening shm %s", sock_info->wait_shm_path);
 519                         exit(EXIT_FAILURE);
 520                 }
 521                 /*
 522                  * The shm exists, but we cannot open it RW. Report
 523                  * success.
 524                  */
 525                 exit(EXIT_SUCCESS);
 526         } else {
 527                 return -1;
 528         }
 529 end:
 530         if (wait_shm_fd >= 0 && !sock_info->global) {
 531                 struct stat statbuf;
 532
 533                 /*
 534                  * Ensure that our user is the owner of the shm file for
 535                  * local shm. If we do not own the file, it means our
 536                  * sessiond will not have access to wake us up (there is
 537                  * probably a rogue process trying to fake our
 538                  * sessiond). Fallback to polling method in this case.
 539                  */
 540                 ret = fstat(wait_shm_fd, &statbuf);
 541                 if (ret) {
 542                         PERROR("fstat");
 543                         goto error_close;
 544                 }
 545                 if (statbuf.st_uid != getuid())
 546                         goto error_close;
 547         }
 548         return wait_shm_fd;
 549
 550 error_close:
 551         ret = close(wait_shm_fd);
 552         if (ret) {
 553                 PERROR("Error closing fd");
 554         }
 555         return -1;
 556 }
 557
 558 static
 559 char *get_map_shm(struct sock_info *sock_info)
 560 {
 561         size_t mmap_size = sysconf(_SC_PAGE_SIZE);
 562         int wait_shm_fd, ret;
 563         char *wait_shm_mmap;
 564
 565         wait_shm_fd = get_wait_shm(sock_info, mmap_size);
 566         if (wait_shm_fd < 0) {
 567                 goto error;
 568         }
 569         wait_shm_mmap = mmap(NULL, mmap_size, PROT_READ,
 570                   MAP_SHARED, wait_shm_fd, 0);
 571         /* close shm fd immediately after taking the mmap reference */
 572         ret = close(wait_shm_fd);
 573         if (ret) {
 574                 PERROR("Error closing fd");
 575         }
 576         if (wait_shm_mmap == MAP_FAILED) {
 577                 DBG("mmap error (can be caused by race with sessiond). Fallback to poll mode.");
 578                 goto error;
 579         }
 580         return wait_shm_mmap;
 581
 582 error:
 583         return NULL;
 584 }
 585
 586 static
 587 void wait_for_sessiond(struct sock_info *sock_info)
 588 {
 589         int ret;
 590
 591         ust_lock();
 592         if (lttng_ust_comm_should_quit) {
 593                 goto quit;
 594         }
 595         if (wait_poll_fallback) {
 596                 goto error;
 597         }
 598         if (!sock_info->wait_shm_mmap) {
 599                 sock_info->wait_shm_mmap = get_map_shm(sock_info);
 600                 if (!sock_info->wait_shm_mmap)
 601                         goto error;
 602         }
 603         ust_unlock();
 604
 605         DBG("Waiting for %s apps sessiond", sock_info->name);
 606         /* Wait for futex wakeup */
 607         if (uatomic_read((int32_t *) sock_info->wait_shm_mmap) == 0) {
 608                 ret = futex_async((int32_t *) sock_info->wait_shm_mmap,
 609                         FUTEX_WAIT, 0, NULL, NULL, 0);
 610                 if (ret < 0) {
 611                         if (errno == EFAULT) {
 612                                 wait_poll_fallback = 1;
 613                                 DBG(
 614 "Linux kernels 2.6.33 to 3.0 (with the exception of stable versions) "
 615 "do not support FUTEX_WAKE on read-only memory mappings correctly. "
 616 "Please upgrade your kernel "
 617 "(fix is commit 9ea71503a8ed9184d2d0b8ccc4d269d05f7940ae in Linux kernel "
 618 "mainline). LTTng-UST will use polling mode fallback.");
 619                                 if (ust_debug())
 620                                         PERROR("futex");
 621                         }
 622                 }
 623         }
 624         return;
 625
 626 quit:
 627         ust_unlock();
 628         return;
 629
 630 error:
 631         ust_unlock();
 632         return;
 633 }
 634
 635 /*
 636  * This thread does not allocate any resource, except within
 637  * handle_message, within mutex protection. This mutex protects against
 638  * fork and exit.
 639  * The other moment it allocates resources is at socket connexion, which
 640  * is also protected by the mutex.
 641  */
 642 static
 643 void *ust_listener_thread(void *arg)
 644 {
 645         struct sock_info *sock_info = arg;
 646         int sock, ret, prev_connect_failed = 0, has_waited = 0;
 647
 648         /* Restart trying to connect to the session daemon */
 649 restart:
 650         if (prev_connect_failed) {
 651                 /* Wait for sessiond availability with pipe */
 652                 wait_for_sessiond(sock_info);
 653                 if (has_waited) {
 654                         has_waited = 0;
 655                         /*
 656                          * Sleep for 5 seconds before retrying after a
 657                          * sequence of failure / wait / failure. This
 658                          * deals with a killed or broken session daemon.
 659                          */
 660                         sleep(5);
 661                 }
 662                 has_waited = 1;
 663                 prev_connect_failed = 0;
 664         }
 665         ust_lock();
 666
 667         if (lttng_ust_comm_should_quit) {
 668                 ust_unlock();
 669                 goto quit;
 670         }
 671
 672         if (sock_info->socket != -1) {
 673                 ret = close(sock_info->socket);
 674                 if (ret) {
 675                         ERR("Error closing %s apps socket", sock_info->name);
 676                 }
 677                 sock_info->socket = -1;
 678         }
 679
 680         /* Register */
 681         ret = ustcomm_connect_unix_sock(sock_info->sock_path);
 682         if (ret < 0) {
 683                 DBG("Info: sessiond not accepting connections to %s apps socket", sock_info->name);
 684                 prev_connect_failed = 1;
 685                 /*
 686                  * If we cannot find the sessiond daemon, don't delay
 687                  * constructor execution.
 688                  */
 689                 ret = handle_register_done(sock_info);
 690                 assert(!ret);
 691                 ust_unlock();
 692                 goto restart;
 693         }
 694
 695         sock_info->socket = sock = ret;
 696
 697         /*
 698          * Create only one root handle per listener thread for the whole
 699          * process lifetime.
 700          */
 701         if (sock_info->root_handle == -1) {
 702                 ret = lttng_abi_create_root_handle();
 703                 if (ret < 0) {
 704                         ERR("Error creating root handle");
 705                         ust_unlock();
 706                         goto quit;
 707                 }
 708                 sock_info->root_handle = ret;
 709         }
 710
 711         ret = register_app_to_sessiond(sock);
 712         if (ret < 0) {
 713                 ERR("Error registering to %s apps socket", sock_info->name);
 714                 prev_connect_failed = 1;
 715                 /*
 716                  * If we cannot register to the sessiond daemon, don't
 717                  * delay constructor execution.
 718                  */
 719                 ret = handle_register_done(sock_info);
 720                 assert(!ret);
 721                 ust_unlock();
 722                 goto restart;
 723         }
 724         ust_unlock();
 725
 726         for (;;) {
 727                 ssize_t len;
 728                 struct ustcomm_ust_msg lum;
 729
 730                 len = ustcomm_recv_unix_sock(sock, &lum, sizeof(lum));
 731                 switch (len) {
 732                 case 0: /* orderly shutdown */
 733                         DBG("%s ltt-sessiond has performed an orderly shutdown\n", sock_info->name);
 734                         ust_lock();
 735                         /*
 736                          * Either sessiond has shutdown or refused us by closing the socket.
 737                          * In either case, we don't want to delay construction execution,
 738                          * and we need to wait before retry.
 739                          */
 740                         prev_connect_failed = 1;
 741                         /*
 742                          * If we cannot register to the sessiond daemon, don't
 743                          * delay constructor execution.
 744                          */
 745                         ret = handle_register_done(sock_info);
 746                         assert(!ret);
 747                         ust_unlock();
 748                         goto end;
 749                 case sizeof(lum):
 750                         DBG("message received\n");
 751                         ret = handle_message(sock_info, sock, &lum);
 752                         if (ret < 0) {
 753                                 ERR("Error handling message for %s socket", sock_info->name);
 754                         }
 755                         continue;
 756                 case -1:
 757                         DBG("Receive failed from lttng-sessiond with errno %d", errno);
 758                         if (errno == ECONNRESET) {
 759                                 ERR("%s remote end closed connection\n", sock_info->name);
 760                                 goto end;
 761                         }
 762                         goto end;
 763                 default:
 764                         ERR("incorrect message size (%s socket): %zd\n", sock_info->name, len);
 765                         continue;
 766                 }
 767
 768         }
 769 end:
 770         goto restart;   /* try to reconnect */
 771 quit:
 772         return NULL;
 773 }
 774
 775 /*
 776  * Return values: -1: don't wait. 0: wait forever. 1: timeout wait.
 777  */
 778 static
 779 int get_timeout(struct timespec *constructor_timeout)
 780 {
 781         long constructor_delay_ms = LTTNG_UST_DEFAULT_CONSTRUCTOR_TIMEOUT_MS;
 782         char *str_delay;
 783         int ret;
 784
 785         str_delay = getenv("LTTNG_UST_REGISTER_TIMEOUT");
 786         if (str_delay) {
 787                 constructor_delay_ms = strtol(str_delay, NULL, 10);
 788         }
 789
 790         switch (constructor_delay_ms) {
 791         case -1:/* fall-through */
 792         case 0:
 793                 return constructor_delay_ms;
 794         default:
 795                 break;
 796         }
 797
 798         /*
 799          * If we are unable to find the current time, don't wait.
 800          */
 801         ret = clock_gettime(CLOCK_REALTIME, constructor_timeout);
 802         if (ret) {
 803                 return -1;
 804         }
 805         constructor_timeout->tv_sec += constructor_delay_ms / 1000UL;
 806         constructor_timeout->tv_nsec +=
 807                 (constructor_delay_ms % 1000UL) * 1000000UL;
 808         if (constructor_timeout->tv_nsec >= 1000000000UL) {
 809                 constructor_timeout->tv_sec++;
 810                 constructor_timeout->tv_nsec -= 1000000000UL;
 811         }
 812         return 1;
 813 }
 814
 815 /*
 816  * sessiond monitoring thread: monitor presence of global and per-user
 817  * sessiond by polling the application common named pipe.
 818  */
 819 /* TODO */
 820
 821 void __attribute__((constructor)) lttng_ust_init(void)
 822 {
 823         struct timespec constructor_timeout;
 824         int timeout_mode;
 825         int ret;
 826
 827         if (uatomic_xchg(&initialized, 1) == 1)
 828                 return;
 829
 830         /*
 831          * We want precise control over the order in which we construct
 832          * our sub-libraries vs starting to receive commands from
 833          * sessiond (otherwise leading to errors when trying to create
 834          * sessiond before the init functions are completed).
 835          */
 836         init_usterr();
 837         init_tracepoint();
 838         ltt_ring_buffer_metadata_client_init();
 839         ltt_ring_buffer_client_overwrite_init();
 840         ltt_ring_buffer_client_discard_init();
 841
 842         timeout_mode = get_timeout(&constructor_timeout);
 843
 844         ret = sem_init(&constructor_wait, 0, 0);
 845         assert(!ret);
 846
 847         ret = setup_local_apps();
 848         if (ret) {
 849                 ERR("Error setting up to local apps");
 850         }
 851         ret = pthread_create(&local_apps.ust_listener, NULL,
 852                         ust_listener_thread, &local_apps);
 853
 854         if (local_apps.allowed) {
 855                 ret = pthread_create(&global_apps.ust_listener, NULL,
 856                                 ust_listener_thread, &global_apps);
 857         } else {
 858                 handle_register_done(&local_apps);
 859         }
 860
 861         switch (timeout_mode) {
 862         case 1: /* timeout wait */
 863                 do {
 864                         ret = sem_timedwait(&constructor_wait,
 865                                         &constructor_timeout);
 866                 } while (ret < 0 && errno == EINTR);
 867                 if (ret < 0 && errno == ETIMEDOUT) {
 868                         ERR("Timed out waiting for ltt-sessiond");
 869                 } else {
 870                         assert(!ret);
 871                 }
 872                 break;
 873         case -1:/* wait forever */
 874                 do {
 875                         ret = sem_wait(&constructor_wait);
 876                 } while (ret < 0 && errno == EINTR);
 877                 assert(!ret);
 878                 break;
 879         case 0: /* no timeout */
 880                 break;
 881         }
 882 }
 883
 884 static
 885 void lttng_ust_cleanup(int exiting)
 886 {
 887         cleanup_sock_info(&global_apps, exiting);
 888         if (local_apps.allowed) {
 889                 cleanup_sock_info(&local_apps, exiting);
 890         }
 891         /*
 892          * The teardown in this function all affect data structures
 893          * accessed under the UST lock by the listener thread. This
 894          * lock, along with the lttng_ust_comm_should_quit flag, ensure
 895          * that none of these threads are accessing this data at this
 896          * point.
 897          */
 898         lttng_ust_abi_exit();
 899         lttng_ust_events_exit();
 900         ltt_ring_buffer_client_discard_exit();
 901         ltt_ring_buffer_client_overwrite_exit();
 902         ltt_ring_buffer_metadata_client_exit();
 903         exit_tracepoint();
 904         if (!exiting) {
 905                 /* Reinitialize values for fork */
 906                 sem_count = 2;
 907                 lttng_ust_comm_should_quit = 0;
 908                 initialized = 0;
 909         }
 910 }
 911
 912 void __attribute__((destructor)) lttng_ust_exit(void)
 913 {
 914         int ret;
 915
 916         /*
 917          * Using pthread_cancel here because:
 918          * A) we don't want to hang application teardown.
 919          * B) the thread is not allocating any resource.
 920          */
 921
 922         /*
 923          * Require the communication thread to quit. Synchronize with
 924          * mutexes to ensure it is not in a mutex critical section when
 925          * pthread_cancel is later called.
 926          */
 927         ust_lock();
 928         lttng_ust_comm_should_quit = 1;
 929         ust_unlock();
 930
 931         /* cancel threads */
 932         ret = pthread_cancel(global_apps.ust_listener);
 933         if (ret) {
 934                 ERR("Error cancelling global ust listener thread");
 935         }
 936         if (local_apps.allowed) {
 937                 ret = pthread_cancel(local_apps.ust_listener);
 938                 if (ret) {
 939                         ERR("Error cancelling local ust listener thread");
 940                 }
 941         }
 942         /*
 943          * Do NOT join threads: use of sys_futex makes it impossible to
 944          * join the threads without using async-cancel, but async-cancel
 945          * is delivered by a signal, which could hit the target thread
 946          * anywhere in its code path, including while the ust_lock() is
 947          * held, causing a deadlock for the other thread. Let the OS
 948          * cleanup the threads if there are stalled in a syscall.
 949          */
 950         lttng_ust_cleanup(1);
 951 }
 952
 953 /*
 954  * We exclude the worker threads across fork and clone (except
 955  * CLONE_VM), because these system calls only keep the forking thread
 956  * running in the child.  Therefore, we don't want to call fork or clone
 957  * in the middle of an tracepoint or ust tracing state modification.
 958  * Holding this mutex protects these structures across fork and clone.
 959  */
 960 void ust_before_fork(sigset_t *save_sigset)
 961 {
 962         /*
 963          * Disable signals. This is to avoid that the child intervenes
 964          * before it is properly setup for tracing. It is safer to
 965          * disable all signals, because then we know we are not breaking
 966          * anything by restoring the original mask.
 967          */
 968         sigset_t all_sigs;
 969         int ret;
 970
 971         /* Disable signals */
 972         sigfillset(&all_sigs);
 973         ret = sigprocmask(SIG_BLOCK, &all_sigs, save_sigset);
 974         if (ret == -1) {
 975                 PERROR("sigprocmask");
 976         }
 977         ust_lock();
 978         rcu_bp_before_fork();
 979 }
 980
 981 static void ust_after_fork_common(sigset_t *restore_sigset)
 982 {
 983         int ret;
 984
 985         DBG("process %d", getpid());
 986         ust_unlock();
 987         /* Restore signals */
 988         ret = sigprocmask(SIG_SETMASK, restore_sigset, NULL);
 989         if (ret == -1) {
 990                 PERROR("sigprocmask");
 991         }
 992 }
 993
 994 void ust_after_fork_parent(sigset_t *restore_sigset)
 995 {
 996         DBG("process %d", getpid());
 997         rcu_bp_after_fork_parent();
 998         /* Release mutexes and reenable signals */
 999         ust_after_fork_common(restore_sigset);
1000 }
1001
1002 /*
1003  * After fork, in the child, we need to cleanup all the leftover state,
1004  * except the worker thread which already magically disappeared thanks
1005  * to the weird Linux fork semantics. After tyding up, we call
1006  * lttng_ust_init() again to start over as a new PID.
1007  *
1008  * This is meant for forks() that have tracing in the child between the
1009  * fork and following exec call (if there is any).
1010  */
1011 void ust_after_fork_child(sigset_t *restore_sigset)
1012 {
1013         DBG("process %d", getpid());
1014         /* Release urcu mutexes */
1015         rcu_bp_after_fork_child();
1016         lttng_ust_cleanup(0);
1017         lttng_context_vtid_reset();
1018         /* Release mutexes and reenable signals */
1019         ust_after_fork_common(restore_sigset);
1020         lttng_ust_init();
1021 }