lib/daemon-unix.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "daemon.h"
  19 #include "daemon-private.h"
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <signal.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/resource.h>
  26 #include <sys/wait.h>
  27 #include <sys/stat.h>
  28 #include <unistd.h>
  29 #include "command-line.h"
  30 #include "fatal-signal.h"
  31 #include "dirs.h"
  32 #include "lockfile.h"
  33 #include "ovs-thread.h"
  34 #include "process.h"
  35 #include "socket-util.h"
  36 #include "timeval.h"
  37 #include "util.h"
  38 #include "vlog.h"
  39
  40 VLOG_DEFINE_THIS_MODULE(daemon_unix);
  41
  42 /* --detach: Should we run in the background? */
  43 bool detach;                    /* Was --detach specified? */
  44 static bool detached;           /* Have we already detached? */
  45
  46 /* --pidfile: Name of pidfile (null if none). */
  47 char *pidfile;
  48
  49 /* Device and inode of pidfile, so we can avoid reopening it. */
  50 static dev_t pidfile_dev;
  51 static ino_t pidfile_ino;
  52
  53 /* --overwrite-pidfile: Create pidfile even if one already exists and is
  54    locked? */
  55 static bool overwrite_pidfile;
  56
  57 /* --no-chdir: Should we chdir to "/"? */
  58 static bool chdir_ = true;
  59
  60 /* File descriptor used by daemonize_start() and daemonize_complete(). */
  61 static int daemonize_fd = -1;
  62
  63 /* --monitor: Should a supervisory process monitor the daemon and restart it if
  64  * it dies due to an error signal? */
  65 static bool monitor;
  66
  67 static void check_already_running(void);
  68 static int lock_pidfile(FILE *, int command);
  69 static pid_t fork_and_clean_up(void);
  70 static void daemonize_post_detach(void);
  71
  72 /* Returns the file name that would be used for a pidfile if 'name' were
  73  * provided to set_pidfile().  The caller must free the returned string. */
  74 char *
  75 make_pidfile_name(const char *name)
  76 {
  77     return (!name
  78             ? xasprintf("%s/%s.pid", ovs_rundir(), program_name)
  79             : abs_file_name(ovs_rundir(), name));
  80 }
  81
  82 /* Sets that we do not chdir to "/". */
  83 void
  84 set_no_chdir(void)
  85 {
  86     chdir_ = false;
  87 }
  88
  89 /* Normally, daemonize() or damonize_start() will terminate the program with a
  90  * message if a locked pidfile already exists.  If this function is called, an
  91  * existing pidfile will be replaced, with a warning. */
  92 void
  93 ignore_existing_pidfile(void)
  94 {
  95     overwrite_pidfile = true;
  96 }
  97
  98 /* Sets up a following call to daemonize() to detach from the foreground
  99  * session, running this process in the background.  */
 100 void
 101 set_detach(void)
 102 {
 103     detach = true;
 104 }
 105
 106 /* Sets up a following call to daemonize() to fork a supervisory process to
 107  * monitor the daemon and restart it if it dies due to an error signal.  */
 108 void
 109 daemon_set_monitor(void)
 110 {
 111     monitor = true;
 112 }
 113
 114 /* If a pidfile has been configured, creates it and stores the running
 115  * process's pid in it.  Ensures that the pidfile will be deleted when the
 116  * process exits. */
 117 static void
 118 make_pidfile(void)
 119 {
 120     long int pid = getpid();
 121     struct stat s;
 122     char *tmpfile;
 123     FILE *file;
 124     int error;
 125
 126     /* Create a temporary pidfile. */
 127     if (overwrite_pidfile) {
 128         tmpfile = xasprintf("%s.tmp%ld", pidfile, pid);
 129         fatal_signal_add_file_to_unlink(tmpfile);
 130     } else {
 131         /* Everyone shares the same file which will be treated as a lock.  To
 132          * avoid some uncomfortable race conditions, we can't set up the fatal
 133          * signal unlink until we've acquired it. */
 134         tmpfile = xasprintf("%s.tmp", pidfile);
 135     }
 136
 137     file = fopen(tmpfile, "a+");
 138     if (!file) {
 139         VLOG_FATAL("%s: create failed (%s)", tmpfile, ovs_strerror(errno));
 140     }
 141
 142     error = lock_pidfile(file, F_SETLK);
 143     if (error) {
 144         /* Looks like we failed to acquire the lock.  Note that, if we failed
 145          * for some other reason (and '!overwrite_pidfile'), we will have
 146          * left 'tmpfile' as garbage in the file system. */
 147         VLOG_FATAL("%s: fcntl(F_SETLK) failed (%s)", tmpfile,
 148                    ovs_strerror(error));
 149     }
 150
 151     if (!overwrite_pidfile) {
 152         /* We acquired the lock.  Make sure to clean up on exit, and verify
 153          * that we're allowed to create the actual pidfile. */
 154         fatal_signal_add_file_to_unlink(tmpfile);
 155         check_already_running();
 156     }
 157
 158     if (fstat(fileno(file), &s) == -1) {
 159         VLOG_FATAL("%s: fstat failed (%s)", tmpfile, ovs_strerror(errno));
 160     }
 161
 162     if (ftruncate(fileno(file), 0) == -1) {
 163         VLOG_FATAL("%s: truncate failed (%s)", tmpfile, ovs_strerror(errno));
 164     }
 165
 166     fprintf(file, "%ld\n", pid);
 167     if (fflush(file) == EOF) {
 168         VLOG_FATAL("%s: write failed (%s)", tmpfile, ovs_strerror(errno));
 169     }
 170
 171     error = rename(tmpfile, pidfile);
 172
 173     /* Due to a race, 'tmpfile' may be owned by a different process, so we
 174      * shouldn't delete it on exit. */
 175     fatal_signal_remove_file_to_unlink(tmpfile);
 176
 177     if (error < 0) {
 178         VLOG_FATAL("failed to rename \"%s\" to \"%s\" (%s)",
 179                    tmpfile, pidfile, ovs_strerror(errno));
 180     }
 181
 182     /* Ensure that the pidfile will get deleted on exit. */
 183     fatal_signal_add_file_to_unlink(pidfile);
 184
 185     /* Clean up.
 186      *
 187      * We don't close 'file' because its file descriptor must remain open to
 188      * hold the lock. */
 189     pidfile_dev = s.st_dev;
 190     pidfile_ino = s.st_ino;
 191     free(tmpfile);
 192 }
 193
 194 /* Calls fork() and on success returns its return value.  On failure, logs an
 195  * error and exits unsuccessfully.
 196  *
 197  * Post-fork, but before returning, this function calls a few other functions
 198  * that are generally useful if the child isn't planning to exec a new
 199  * process. */
 200 static pid_t
 201 fork_and_clean_up(void)
 202 {
 203     pid_t pid = xfork();
 204     if (pid > 0) {
 205         /* Running in parent process. */
 206         fatal_signal_fork();
 207     } else if (!pid) {
 208         /* Running in child process. */
 209         lockfile_postfork();
 210     }
 211     return pid;
 212 }
 213
 214 /* Forks, then:
 215  *
 216  *   - In the parent, waits for the child to signal that it has completed its
 217  *     startup sequence.  Then stores -1 in '*fdp' and returns the child's
 218  *     pid in '*child_pid' argument.
 219  *
 220  *   - In the child, stores a fd in '*fdp' and returns 0 through '*child_pid'
 221  *     argument.  The caller should pass the fd to fork_notify_startup() after
 222  *     it finishes its startup sequence.
 223  *
 224  * Returns 0 on success.  If something goes wrong and child process was not
 225  * able to signal its readiness by calling fork_notify_startup(), then this
 226  * function returns -1. However, even in case of failure it still sets child
 227  * process id in '*child_pid'. */
 228 static int
 229 fork_and_wait_for_startup(int *fdp, pid_t *child_pid)
 230 {
 231     int fds[2];
 232     pid_t pid;
 233     int ret = 0;
 234
 235     xpipe(fds);
 236
 237     pid = fork_and_clean_up();
 238     if (pid > 0) {
 239         /* Running in parent process. */
 240         size_t bytes_read;
 241         char c;
 242
 243         close(fds[1]);
 244         if (read_fully(fds[0], &c, 1, &bytes_read) != 0) {
 245             int retval;
 246             int status;
 247
 248             do {
 249                 retval = waitpid(pid, &status, 0);
 250             } while (retval == -1 && errno == EINTR);
 251
 252             if (retval == pid) {
 253                 if (WIFEXITED(status) && WEXITSTATUS(status)) {
 254                     /* Child exited with an error.  Convey the same error
 255                      * to our parent process as a courtesy. */
 256                     exit(WEXITSTATUS(status));
 257                 } else {
 258                     char *status_msg = process_status_msg(status);
 259                     VLOG_ERR("fork child died before signaling startup (%s)",
 260                              status_msg);
 261                     ret = -1;
 262                 }
 263             } else if (retval < 0) {
 264                 VLOG_FATAL("waitpid failed (%s)", ovs_strerror(errno));
 265             } else {
 266                 OVS_NOT_REACHED();
 267             }
 268         }
 269         close(fds[0]);
 270         *fdp = -1;
 271     } else if (!pid) {
 272         /* Running in child process. */
 273         close(fds[0]);
 274         *fdp = fds[1];
 275     }
 276     *child_pid = pid;
 277     return ret;
 278 }
 279
 280 static void
 281 fork_notify_startup(int fd)
 282 {
 283     if (fd != -1) {
 284         size_t bytes_written;
 285         int error;
 286
 287         error = write_fully(fd, "", 1, &bytes_written);
 288         if (error) {
 289             VLOG_FATAL("pipe write failed (%s)", ovs_strerror(error));
 290         }
 291
 292         close(fd);
 293     }
 294 }
 295
 296 static bool
 297 should_restart(int status)
 298 {
 299     if (WIFSIGNALED(status)) {
 300         static const int error_signals[] = {
 301             /* This list of signals is documented in daemon.man.  If you
 302              * change the list, update the documentation too. */
 303             SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV,
 304             SIGXCPU, SIGXFSZ
 305         };
 306
 307         size_t i;
 308
 309         for (i = 0; i < ARRAY_SIZE(error_signals); i++) {
 310             if (error_signals[i] == WTERMSIG(status)) {
 311                 return true;
 312             }
 313         }
 314     }
 315     return false;
 316 }
 317
 318 static void
 319 monitor_daemon(pid_t daemon_pid)
 320 {
 321     /* XXX Should log daemon's stderr output at startup time. */
 322     time_t last_restart;
 323     char *status_msg;
 324     int crashes;
 325     bool child_ready = true;
 326
 327     set_subprogram_name("monitor");
 328     status_msg = xstrdup("healthy");
 329     last_restart = TIME_MIN;
 330     crashes = 0;
 331     for (;;) {
 332         int retval;
 333         int status;
 334
 335         proctitle_set("monitoring pid %lu (%s)",
 336                       (unsigned long int) daemon_pid, status_msg);
 337
 338         if (child_ready) {
 339             do {
 340                 retval = waitpid(daemon_pid, &status, 0);
 341             } while (retval == -1 && errno == EINTR);
 342             if (retval == -1) {
 343                 VLOG_FATAL("waitpid failed (%s)", ovs_strerror(errno));
 344             }
 345         }
 346
 347         if (!child_ready || retval == daemon_pid) {
 348             char *s = process_status_msg(status);
 349             if (should_restart(status)) {
 350                 free(status_msg);
 351                 status_msg = xasprintf("%d crashes: pid %lu died, %s",
 352                                        ++crashes,
 353                                        (unsigned long int) daemon_pid, s);
 354                 free(s);
 355
 356                 if (WCOREDUMP(status)) {
 357                     /* Disable further core dumps to save disk space. */
 358                     struct rlimit r;
 359
 360                     r.rlim_cur = 0;
 361                     r.rlim_max = 0;
 362                     if (setrlimit(RLIMIT_CORE, &r) == -1) {
 363                         VLOG_WARN("failed to disable core dumps: %s",
 364                                   ovs_strerror(errno));
 365                     }
 366                 }
 367
 368                 /* Throttle restarts to no more than once every 10 seconds. */
 369                 if (time(NULL) < last_restart + 10) {
 370                     VLOG_WARN("%s, waiting until 10 seconds since last "
 371                               "restart", status_msg);
 372                     for (;;) {
 373                         time_t now = time(NULL);
 374                         time_t wakeup = last_restart + 10;
 375                         if (now >= wakeup) {
 376                             break;
 377                         }
 378                         xsleep(wakeup - now);
 379                     }
 380                 }
 381                 last_restart = time(NULL);
 382
 383                 VLOG_ERR("%s, restarting", status_msg);
 384                 child_ready = !fork_and_wait_for_startup(&daemonize_fd,
 385                                                          &daemon_pid);
 386                 if (child_ready && !daemon_pid) {
 387                     /* Child process needs to break out of monitoring
 388                      * loop. */
 389                     break;
 390                 }
 391             } else {
 392                 VLOG_INFO("pid %lu died, %s, exiting",
 393                           (unsigned long int) daemon_pid, s);
 394                 free(s);
 395                 exit(0);
 396             }
 397         }
 398     }
 399     free(status_msg);
 400
 401     /* Running in new daemon process. */
 402     proctitle_restore();
 403     set_subprogram_name("");
 404 }
 405
 406 /* If daemonization is configured, then starts daemonization, by forking and
 407  * returning in the child process.  The parent process hangs around until the
 408  * child lets it know either that it completed startup successfully (by calling
 409  * daemon_complete()) or that it failed to start up (by exiting with a nonzero
 410  * exit code). */
 411 void
 412 daemonize_start(void)
 413 {
 414     assert_single_threaded();
 415     daemonize_fd = -1;
 416
 417     if (detach) {
 418         pid_t pid;
 419
 420         if (fork_and_wait_for_startup(&daemonize_fd, &pid)) {
 421             VLOG_FATAL("could not detach from foreground session");
 422         }
 423         if (pid > 0) {
 424             /* Running in parent process. */
 425             exit(0);
 426         }
 427
 428         /* Running in daemon or monitor process. */
 429         setsid();
 430     }
 431
 432     if (monitor) {
 433         int saved_daemonize_fd = daemonize_fd;
 434         pid_t daemon_pid;
 435
 436         if (fork_and_wait_for_startup(&daemonize_fd, &daemon_pid)) {
 437             VLOG_FATAL("could not initiate process monitoring");
 438         }
 439         if (daemon_pid > 0) {
 440             /* Running in monitor process. */
 441             fork_notify_startup(saved_daemonize_fd);
 442             close_standard_fds();
 443             monitor_daemon(daemon_pid);
 444         }
 445         /* Running in daemon process. */
 446     }
 447
 448     forbid_forking("running in daemon process");
 449
 450     if (pidfile) {
 451         make_pidfile();
 452     }
 453
 454     /* Make sure that the unixctl commands for vlog get registered in a
 455      * daemon, even before the first log message. */
 456     vlog_init();
 457 }
 458
 459 /* If daemonization is configured, then this function notifies the parent
 460  * process that the child process has completed startup successfully.  It also
 461  * call daemonize_post_detach().
 462  *
 463  * Calling this function more than once has no additional effect. */
 464 void
 465 daemonize_complete(void)
 466 {
 467     if (pidfile) {
 468         free(pidfile);
 469         pidfile = NULL;
 470     }
 471
 472     if (!detached) {
 473         detached = true;
 474
 475         fork_notify_startup(daemonize_fd);
 476         daemonize_fd = -1;
 477         daemonize_post_detach();
 478     }
 479 }
 480
 481 /* If daemonization is configured, then this function does traditional Unix
 482  * daemonization behavior: join a new session, chdir to the root (if not
 483  * disabled), and close the standard file descriptors.
 484  *
 485  * It only makes sense to call this function as part of an implementation of a
 486  * special daemon subprocess.  A normal daemon should just call
 487  * daemonize_complete(). */
 488 static void
 489 daemonize_post_detach(void)
 490 {
 491     if (detach) {
 492         if (chdir_) {
 493             ignore(chdir("/"));
 494         }
 495         close_standard_fds();
 496     }
 497 }
 498
 499 void
 500 daemon_usage(void)
 501 {
 502     printf(
 503         "\nDaemon options:\n"
 504         "  --detach                run in background as daemon\n"
 505         "  --no-chdir              do not chdir to '/'\n"
 506         "  --pidfile[=FILE]        create pidfile (default: %s/%s.pid)\n"
 507         "  --overwrite-pidfile     with --pidfile, start even if already "
 508                                    "running\n",
 509         ovs_rundir(), program_name);
 510 }
 511
 512 static int
 513 lock_pidfile__(FILE *file, int command, struct flock *lck)
 514 {
 515     int error;
 516
 517     lck->l_type = F_WRLCK;
 518     lck->l_whence = SEEK_SET;
 519     lck->l_start = 0;
 520     lck->l_len = 0;
 521     lck->l_pid = 0;
 522
 523     do {
 524         error = fcntl(fileno(file), command, lck) == -1 ? errno : 0;
 525     } while (error == EINTR);
 526     return error;
 527 }
 528
 529 static int
 530 lock_pidfile(FILE *file, int command)
 531 {
 532     struct flock lck;
 533
 534     return lock_pidfile__(file, command, &lck);
 535 }
 536
 537 static pid_t
 538 read_pidfile__(const char *pidfile, bool delete_if_stale)
 539 {
 540     struct stat s, s2;
 541     struct flock lck;
 542     char line[128];
 543     FILE *file;
 544     int error;
 545
 546     if ((pidfile_ino || pidfile_dev)
 547         && !stat(pidfile, &s)
 548         && s.st_ino == pidfile_ino && s.st_dev == pidfile_dev) {
 549         /* It's our own pidfile.  We can't afford to open it, because closing
 550          * *any* fd for a file that a process has locked also releases all the
 551          * locks on that file.
 552          *
 553          * Fortunately, we know the associated pid anyhow: */
 554         return getpid();
 555     }
 556
 557     file = fopen(pidfile, "r+");
 558     if (!file) {
 559         if (errno == ENOENT && delete_if_stale) {
 560             return 0;
 561         }
 562         error = errno;
 563         VLOG_WARN("%s: open: %s", pidfile, ovs_strerror(error));
 564         goto error;
 565     }
 566
 567     error = lock_pidfile__(file, F_GETLK, &lck);
 568     if (error) {
 569         VLOG_WARN("%s: fcntl: %s", pidfile, ovs_strerror(error));
 570         goto error;
 571     }
 572     if (lck.l_type == F_UNLCK) {
 573         /* pidfile exists but it isn't locked by anyone.  We need to delete it
 574          * so that a new pidfile can go in its place.  But just calling
 575          * unlink(pidfile) makes a nasty race: what if someone else unlinks it
 576          * before we do and then replaces it by a valid pidfile?  We'd unlink
 577          * their valid pidfile.  We do a little dance to avoid the race, by
 578          * locking the invalid pidfile.  Only one process can have the invalid
 579          * pidfile locked, and only that process has the right to unlink it. */
 580         if (!delete_if_stale) {
 581             error = ESRCH;
 582             VLOG_DBG("%s: pid file is stale", pidfile);
 583             goto error;
 584         }
 585
 586         /* Get the lock. */
 587         error = lock_pidfile(file, F_SETLK);
 588         if (error) {
 589             /* We lost a race with someone else doing the same thing. */
 590             VLOG_WARN("%s: lost race to lock pidfile", pidfile);
 591             goto error;
 592         }
 593
 594         /* Is the file we have locked still named 'pidfile'? */
 595         if (stat(pidfile, &s) || fstat(fileno(file), &s2)
 596             || s.st_ino != s2.st_ino || s.st_dev != s2.st_dev) {
 597             /* No.  We lost a race with someone else who got the lock before
 598              * us, deleted the pidfile, and closed it (releasing the lock). */
 599             error = EALREADY;
 600             VLOG_WARN("%s: lost race to delete pidfile", pidfile);
 601             goto error;
 602         }
 603
 604         /* We won the right to delete the stale pidfile. */
 605         if (unlink(pidfile)) {
 606             error = errno;
 607             VLOG_WARN("%s: failed to delete stale pidfile (%s)",
 608                       pidfile, ovs_strerror(error));
 609             goto error;
 610         }
 611         VLOG_DBG("%s: deleted stale pidfile", pidfile);
 612         fclose(file);
 613         return 0;
 614     }
 615
 616     if (!fgets(line, sizeof line, file)) {
 617         if (ferror(file)) {
 618             error = errno;
 619             VLOG_WARN("%s: read: %s", pidfile, ovs_strerror(error));
 620         } else {
 621             error = ESRCH;
 622             VLOG_WARN("%s: read: unexpected end of file", pidfile);
 623         }
 624         goto error;
 625     }
 626
 627     if (lck.l_pid != strtoul(line, NULL, 10)) {
 628         /* The process that has the pidfile locked is not the process that
 629          * created it.  It must be stale, with the process that has it locked
 630          * preparing to delete it. */
 631         error = ESRCH;
 632         VLOG_WARN("%s: stale pidfile for pid %s being deleted by pid %ld",
 633                   pidfile, line, (long int) lck.l_pid);
 634         goto error;
 635     }
 636
 637     fclose(file);
 638     return lck.l_pid;
 639
 640 error:
 641     if (file) {
 642         fclose(file);
 643     }
 644     return -error;
 645 }
 646
 647 /* Opens and reads a PID from 'pidfile'.  Returns the positive PID if
 648  * successful, otherwise a negative errno value. */
 649 pid_t
 650 read_pidfile(const char *pidfile)
 651 {
 652     return read_pidfile__(pidfile, false);
 653 }
 654
 655 /* Checks whether a process with the given 'pidfile' is already running and,
 656  * if so, aborts.  If 'pidfile' is stale, deletes it. */
 657 static void
 658 check_already_running(void)
 659 {
 660     long int pid = read_pidfile__(pidfile, true);
 661     if (pid > 0) {
 662         VLOG_FATAL("%s: already running as pid %ld, aborting", pidfile, pid);
 663     } else if (pid < 0) {
 664         VLOG_FATAL("%s: pidfile check failed (%s), aborting",
 665                    pidfile, ovs_strerror(-pid));
 666     }
 667 }
 668
 669 \f
 670 /* stub functions for non-windows platform. */
 671
 672 void
 673 service_start(int *argc OVS_UNUSED, char **argv[] OVS_UNUSED)
 674 {
 675 }
 676
 677 void
 678 service_stop(void)
 679 {
 680 }
 681
 682 bool
 683 should_service_stop(void)
 684 {
 685     return false;
 686 }