lib/daemon.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
   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 <errno.h>
  20 #include <fcntl.h>
  21 #include <signal.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <sys/resource.h>
  25 #include <sys/wait.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28 #include "command-line.h"
  29 #include "fatal-signal.h"
  30 #include "dirs.h"
  31 #include "lockfile.h"
  32 #include "process.h"
  33 #include "socket-util.h"
  34 #include "timeval.h"
  35 #include "util.h"
  36 #include "vlog.h"
  37
  38 VLOG_DEFINE_THIS_MODULE(daemon);
  39
  40 /* --detach: Should we run in the background? */
  41 static bool detach;
  42
  43 /* --pidfile: Name of pidfile (null if none). */
  44 static char *pidfile;
  45
  46 /* Device and inode of pidfile, so we can avoid reopening it. */
  47 static dev_t pidfile_dev;
  48 static ino_t pidfile_ino;
  49
  50 /* --overwrite-pidfile: Create pidfile even if one already exists and is
  51    locked? */
  52 static bool overwrite_pidfile;
  53
  54 /* --no-chdir: Should we chdir to "/"? */
  55 static bool chdir_ = true;
  56
  57 /* File descriptor used by daemonize_start() and daemonize_complete(). */
  58 static int daemonize_fd = -1;
  59
  60 /* --monitor: Should a supervisory process monitor the daemon and restart it if
  61  * it dies due to an error signal? */
  62 static bool monitor;
  63
  64 static void check_already_running(void);
  65 static int lock_pidfile(FILE *, int command);
  66
  67 /* Returns the file name that would be used for a pidfile if 'name' were
  68  * provided to set_pidfile().  The caller must free the returned string. */
  69 char *
  70 make_pidfile_name(const char *name)
  71 {
  72     return (!name
  73             ? xasprintf("%s/%s.pid", ovs_rundir(), program_name)
  74             : abs_file_name(ovs_rundir(), name));
  75 }
  76
  77 /* Sets up a following call to daemonize() to create a pidfile named 'name'.
  78  * If 'name' begins with '/', then it is treated as an absolute path.
  79  * Otherwise, it is taken relative to RUNDIR, which is $(prefix)/var/run by
  80  * default.
  81  *
  82  * If 'name' is null, then program_name followed by ".pid" is used. */
  83 void
  84 set_pidfile(const char *name)
  85 {
  86     free(pidfile);
  87     pidfile = make_pidfile_name(name);
  88 }
  89
  90 /* Returns an absolute path to the configured pidfile, or a null pointer if no
  91  * pidfile is configured.  The caller must not modify or free the returned
  92  * string. */
  93 const char *
  94 get_pidfile(void)
  95 {
  96     return pidfile;
  97 }
  98
  99 /* Sets that we do not chdir to "/". */
 100 void
 101 set_no_chdir(void)
 102 {
 103     chdir_ = false;
 104 }
 105
 106 /* Will we chdir to "/" as part of daemonizing? */
 107 bool
 108 is_chdir_enabled(void)
 109 {
 110     return chdir_;
 111 }
 112
 113 /* Normally, daemonize() or damonize_start() will terminate the program with a
 114  * message if a locked pidfile already exists.  If this function is called, an
 115  * existing pidfile will be replaced, with a warning. */
 116 void
 117 ignore_existing_pidfile(void)
 118 {
 119     overwrite_pidfile = true;
 120 }
 121
 122 /* Sets up a following call to daemonize() to detach from the foreground
 123  * session, running this process in the background.  */
 124 void
 125 set_detach(void)
 126 {
 127     detach = true;
 128 }
 129
 130 /* Will daemonize() really detach? */
 131 bool
 132 get_detach(void)
 133 {
 134     return detach;
 135 }
 136
 137 /* Sets up a following call to daemonize() to fork a supervisory process to
 138  * monitor the daemon and restart it if it dies due to an error signal.  */
 139 void
 140 daemon_set_monitor(void)
 141 {
 142     monitor = true;
 143 }
 144
 145 /* If a pidfile has been configured, creates it and stores the running
 146  * process's pid in it.  Ensures that the pidfile will be deleted when the
 147  * process exits. */
 148 static void
 149 make_pidfile(void)
 150 {
 151     long int pid = getpid();
 152     struct stat s;
 153     char *tmpfile;
 154     FILE *file;
 155     int error;
 156
 157     /* Create a temporary pidfile. */
 158     tmpfile = xasprintf("%s.tmp%ld", pidfile, pid);
 159     fatal_signal_add_file_to_unlink(tmpfile);
 160     file = fopen(tmpfile, "w+");
 161     if (!file) {
 162         VLOG_FATAL("%s: create failed (%s)", tmpfile, strerror(errno));
 163     }
 164
 165     if (fstat(fileno(file), &s) == -1) {
 166         VLOG_FATAL("%s: fstat failed (%s)", tmpfile, strerror(errno));
 167     }
 168
 169     fprintf(file, "%ld\n", pid);
 170     if (fflush(file) == EOF) {
 171         VLOG_FATAL("%s: write failed (%s)", tmpfile, strerror(errno));
 172     }
 173
 174     error = lock_pidfile(file, F_SETLK);
 175     if (error) {
 176         VLOG_FATAL("%s: fcntl(F_SETLK) failed (%s)", tmpfile, strerror(error));
 177     }
 178
 179     /* Rename or link it to the correct name. */
 180     if (overwrite_pidfile) {
 181         if (rename(tmpfile, pidfile) < 0) {
 182             VLOG_FATAL("failed to rename \"%s\" to \"%s\" (%s)",
 183                        tmpfile, pidfile, strerror(errno));
 184         }
 185     } else {
 186         do {
 187             error = link(tmpfile, pidfile) == -1 ? errno : 0;
 188             if (error == EEXIST) {
 189                 check_already_running();
 190             }
 191         } while (error == EINTR || error == EEXIST);
 192         if (error) {
 193             VLOG_FATAL("failed to link \"%s\" as \"%s\" (%s)",
 194                        tmpfile, pidfile, strerror(error));
 195         }
 196     }
 197
 198     /* Ensure that the pidfile will get deleted on exit. */
 199     fatal_signal_add_file_to_unlink(pidfile);
 200
 201     /* Delete the temporary pidfile if it still exists. */
 202     if (!overwrite_pidfile) {
 203         error = fatal_signal_unlink_file_now(tmpfile);
 204         if (error) {
 205             VLOG_FATAL("%s: unlink failed (%s)", tmpfile, strerror(error));
 206         }
 207     }
 208
 209     /* Clean up.
 210      *
 211      * We don't close 'file' because its file descriptor must remain open to
 212      * hold the lock. */
 213     pidfile_dev = s.st_dev;
 214     pidfile_ino = s.st_ino;
 215     free(tmpfile);
 216     free(pidfile);
 217     pidfile = NULL;
 218 }
 219
 220 /* If configured with set_pidfile() or set_detach(), creates the pid file and
 221  * detaches from the foreground session.  */
 222 void
 223 daemonize(void)
 224 {
 225     daemonize_start();
 226     daemonize_complete();
 227 }
 228
 229 static pid_t
 230 fork_and_wait_for_startup(int *fdp)
 231 {
 232     int fds[2];
 233     pid_t pid;
 234
 235     xpipe(fds);
 236
 237     pid = fork();
 238     if (pid > 0) {
 239         /* Running in parent process. */
 240         size_t bytes_read;
 241         char c;
 242
 243         close(fds[1]);
 244         fatal_signal_fork();
 245         if (read_fully(fds[0], &c, 1, &bytes_read) != 0) {
 246             int retval;
 247             int status;
 248
 249             do {
 250                 retval = waitpid(pid, &status, 0);
 251             } while (retval == -1 && errno == EINTR);
 252
 253             if (retval == pid
 254                 && WIFEXITED(status)
 255                 && WEXITSTATUS(status)) {
 256                 /* Child exited with an error.  Convey the same error to
 257                  * our parent process as a courtesy. */
 258                 exit(WEXITSTATUS(status));
 259             }
 260
 261             VLOG_FATAL("fork child failed to signal startup (%s)",
 262                        strerror(errno));
 263         }
 264         close(fds[0]);
 265         *fdp = -1;
 266     } else if (!pid) {
 267         /* Running in child process. */
 268         close(fds[0]);
 269         time_postfork();
 270         lockfile_postfork();
 271         *fdp = fds[1];
 272     } else {
 273         VLOG_FATAL("fork failed (%s)", strerror(errno));
 274     }
 275
 276     return pid;
 277 }
 278
 279 static void
 280 fork_notify_startup(int fd)
 281 {
 282     if (fd != -1) {
 283         size_t bytes_written;
 284         int error;
 285
 286         error = write_fully(fd, "", 1, &bytes_written);
 287         if (error) {
 288             VLOG_FATAL("pipe write failed (%s)", strerror(error));
 289         }
 290
 291         close(fd);
 292     }
 293 }
 294
 295 static bool
 296 should_restart(int status)
 297 {
 298     if (WIFSIGNALED(status)) {
 299         static const int error_signals[] = {
 300             SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV,
 301             SIGXCPU, SIGXFSZ
 302         };
 303
 304         size_t i;
 305
 306         for (i = 0; i < ARRAY_SIZE(error_signals); i++) {
 307             if (error_signals[i] == WTERMSIG(status)) {
 308                 return true;
 309             }
 310         }
 311     }
 312     return false;
 313 }
 314
 315 static void
 316 monitor_daemon(pid_t daemon_pid)
 317 {
 318     /* XXX Should log daemon's stderr output at startup time. */
 319     const char *saved_program_name;
 320     time_t last_restart;
 321     char *status_msg;
 322     int crashes;
 323
 324     saved_program_name = program_name;
 325     program_name = xasprintf("monitor(%s)", program_name);
 326     status_msg = xstrdup("healthy");
 327     last_restart = TIME_MIN;
 328     crashes = 0;
 329     for (;;) {
 330         int retval;
 331         int status;
 332
 333         proctitle_set("%s: monitoring pid %lu (%s)",
 334                       saved_program_name, (unsigned long int) daemon_pid,
 335                       status_msg);
 336
 337         do {
 338             retval = waitpid(daemon_pid, &status, 0);
 339         } while (retval == -1 && errno == EINTR);
 340
 341         if (retval == -1) {
 342             VLOG_FATAL("waitpid failed (%s)", strerror(errno));
 343         } else if (retval == daemon_pid) {
 344             char *s = process_status_msg(status);
 345             if (should_restart(status)) {
 346                 free(status_msg);
 347                 status_msg = xasprintf("%d crashes: pid %lu died, %s",
 348                                        ++crashes,
 349                                        (unsigned long int) daemon_pid, s);
 350                 free(s);
 351
 352                 if (WCOREDUMP(status)) {
 353                     /* Disable further core dumps to save disk space. */
 354                     struct rlimit r;
 355
 356                     r.rlim_cur = 0;
 357                     r.rlim_max = 0;
 358                     if (setrlimit(RLIMIT_CORE, &r) == -1) {
 359                         VLOG_WARN("failed to disable core dumps: %s",
 360                                   strerror(errno));
 361                     }
 362                 }
 363
 364                 /* Throttle restarts to no more than once every 10 seconds. */
 365                 if (time(NULL) < last_restart + 10) {
 366                     VLOG_WARN("%s, waiting until 10 seconds since last "
 367                               "restart", status_msg);
 368                     for (;;) {
 369                         time_t now = time(NULL);
 370                         time_t wakeup = last_restart + 10;
 371                         if (now >= wakeup) {
 372                             break;
 373                         }
 374                         sleep(wakeup - now);
 375                     }
 376                 }
 377                 last_restart = time(NULL);
 378
 379                 VLOG_ERR("%s, restarting", status_msg);
 380                 daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
 381                 if (!daemon_pid) {
 382                     break;
 383                 }
 384             } else {
 385                 VLOG_INFO("pid %lu died, %s, exiting",
 386                           (unsigned long int) daemon_pid, s);
 387                 free(s);
 388                 exit(0);
 389             }
 390         }
 391     }
 392     free(status_msg);
 393
 394     /* Running in new daemon process. */
 395     proctitle_restore();
 396     free((char *) program_name);
 397     program_name = saved_program_name;
 398 }
 399
 400 /* Close stdin, stdout, stderr.  If we're started from e.g. an SSH session,
 401  * then this keeps us from holding that session open artificially. */
 402 static void
 403 close_standard_fds(void)
 404 {
 405     int null_fd = get_null_fd();
 406     if (null_fd >= 0) {
 407         dup2(null_fd, STDIN_FILENO);
 408         dup2(null_fd, STDOUT_FILENO);
 409         dup2(null_fd, STDERR_FILENO);
 410     }
 411
 412     /* Disable logging to stderr to avoid wasting CPU time. */
 413     vlog_set_levels(NULL, VLF_CONSOLE, VLL_EMER);
 414 }
 415
 416 /* If daemonization is configured, then starts daemonization, by forking and
 417  * returning in the child process.  The parent process hangs around until the
 418  * child lets it know either that it completed startup successfully (by calling
 419  * daemon_complete()) or that it failed to start up (by exiting with a nonzero
 420  * exit code). */
 421 void
 422 daemonize_start(void)
 423 {
 424     daemonize_fd = -1;
 425
 426     if (detach) {
 427         if (fork_and_wait_for_startup(&daemonize_fd) > 0) {
 428             /* Running in parent process. */
 429             exit(0);
 430         }
 431         /* Running in daemon or monitor process. */
 432     }
 433
 434     if (monitor) {
 435         int saved_daemonize_fd = daemonize_fd;
 436         pid_t daemon_pid;
 437
 438         daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
 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     if (pidfile) {
 449         make_pidfile();
 450     }
 451
 452     /* Make sure that the unixctl commands for vlog get registered in a
 453      * daemon, even before the first log message. */
 454     vlog_init();
 455 }
 456
 457 /* If daemonization is configured, then this function notifies the parent
 458  * process that the child process has completed startup successfully.
 459  *
 460  * Calling this function more than once has no additional effect. */
 461 void
 462 daemonize_complete(void)
 463 {
 464     fork_notify_startup(daemonize_fd);
 465     daemonize_fd = -1;
 466
 467     if (detach) {
 468         setsid();
 469         if (chdir_) {
 470             ignore(chdir("/"));
 471         }
 472         close_standard_fds();
 473         detach = false;
 474     }
 475 }
 476
 477 void
 478 daemon_usage(void)
 479 {
 480     printf(
 481         "\nDaemon options:\n"
 482         "  --detach                run in background as daemon\n"
 483         "  --no-chdir              do not chdir to '/'\n"
 484         "  --pidfile[=FILE]        create pidfile (default: %s/%s.pid)\n"
 485         "  --overwrite-pidfile     with --pidfile, start even if already "
 486                                    "running\n",
 487         ovs_rundir(), program_name);
 488 }
 489
 490 static int
 491 lock_pidfile__(FILE *file, int command, struct flock *lck)
 492 {
 493     int error;
 494
 495     lck->l_type = F_WRLCK;
 496     lck->l_whence = SEEK_SET;
 497     lck->l_start = 0;
 498     lck->l_len = 0;
 499     lck->l_pid = 0;
 500
 501     do {
 502         error = fcntl(fileno(file), command, lck) == -1 ? errno : 0;
 503     } while (error == EINTR);
 504     return error;
 505 }
 506
 507 static int
 508 lock_pidfile(FILE *file, int command)
 509 {
 510     struct flock lck;
 511
 512     return lock_pidfile__(file, command, &lck);
 513 }
 514
 515 static pid_t
 516 read_pidfile__(const char *pidfile, bool delete_if_stale)
 517 {
 518     struct stat s, s2;
 519     struct flock lck;
 520     char line[128];
 521     FILE *file;
 522     int error;
 523
 524     if ((pidfile_ino || pidfile_dev)
 525         && !stat(pidfile, &s)
 526         && s.st_ino == pidfile_ino && s.st_dev == pidfile_dev) {
 527         /* It's our own pidfile.  We can't afford to open it, because closing
 528          * *any* fd for a file that a process has locked also releases all the
 529          * locks on that file.
 530          *
 531          * Fortunately, we know the associated pid anyhow: */
 532         return getpid();
 533     }
 534
 535     file = fopen(pidfile, "r+");
 536     if (!file) {
 537         if (errno == ENOENT && delete_if_stale) {
 538             return 0;
 539         }
 540         error = errno;
 541         VLOG_WARN("%s: open: %s", pidfile, strerror(error));
 542         goto error;
 543     }
 544
 545     error = lock_pidfile__(file, F_GETLK, &lck);
 546     if (error) {
 547         VLOG_WARN("%s: fcntl: %s", pidfile, strerror(error));
 548         goto error;
 549     }
 550     if (lck.l_type == F_UNLCK) {
 551         /* pidfile exists but it isn't locked by anyone.  We need to delete it
 552          * so that a new pidfile can go in its place.  But just calling
 553          * unlink(pidfile) makes a nasty race: what if someone else unlinks it
 554          * before we do and then replaces it by a valid pidfile?  We'd unlink
 555          * their valid pidfile.  We do a little dance to avoid the race, by
 556          * locking the invalid pidfile.  Only one process can have the invalid
 557          * pidfile locked, and only that process has the right to unlink it. */
 558         if (!delete_if_stale) {
 559             error = ESRCH;
 560             VLOG_DBG("%s: pid file is stale", pidfile);
 561             goto error;
 562         }
 563
 564         /* Get the lock. */
 565         error = lock_pidfile(file, F_SETLK);
 566         if (error) {
 567             /* We lost a race with someone else doing the same thing. */
 568             VLOG_WARN("%s: lost race to lock pidfile", pidfile);
 569             goto error;
 570         }
 571
 572         /* Is the file we have locked still named 'pidfile'? */
 573         if (stat(pidfile, &s) || fstat(fileno(file), &s2)
 574             || s.st_ino != s2.st_ino || s.st_dev != s2.st_dev) {
 575             /* No.  We lost a race with someone else who got the lock before
 576              * us, deleted the pidfile, and closed it (releasing the lock). */
 577             error = EALREADY;
 578             VLOG_WARN("%s: lost race to delete pidfile", pidfile);
 579             goto error;
 580         }
 581
 582         /* We won the right to delete the stale pidfile. */
 583         if (unlink(pidfile)) {
 584             error = errno;
 585             VLOG_WARN("%s: failed to delete stale pidfile (%s)",
 586                       pidfile, strerror(error));
 587             goto error;
 588         }
 589         VLOG_DBG("%s: deleted stale pidfile", pidfile);
 590         fclose(file);
 591         return 0;
 592     }
 593
 594     if (!fgets(line, sizeof line, file)) {
 595         if (ferror(file)) {
 596             error = errno;
 597             VLOG_WARN("%s: read: %s", pidfile, strerror(error));
 598         } else {
 599             error = ESRCH;
 600             VLOG_WARN("%s: read: unexpected end of file", pidfile);
 601         }
 602         goto error;
 603     }
 604
 605     if (lck.l_pid != strtoul(line, NULL, 10)) {
 606         /* The process that has the pidfile locked is not the process that
 607          * created it.  It must be stale, with the process that has it locked
 608          * preparing to delete it. */
 609         error = ESRCH;
 610         VLOG_WARN("%s: stale pidfile for pid %s being deleted by pid %ld",
 611                   pidfile, line, (long int) lck.l_pid);
 612         goto error;
 613     }
 614
 615     fclose(file);
 616     return lck.l_pid;
 617
 618 error:
 619     if (file) {
 620         fclose(file);
 621     }
 622     return -error;
 623 }
 624
 625 /* Opens and reads a PID from 'pidfile'.  Returns the positive PID if
 626  * successful, otherwise a negative errno value. */
 627 pid_t
 628 read_pidfile(const char *pidfile)
 629 {
 630     return read_pidfile__(pidfile, false);
 631 }
 632
 633 /* Checks whether a process with the given 'pidfile' is already running and,
 634  * if so, aborts.  If 'pidfile' is stale, deletes it. */
 635 static void
 636 check_already_running(void)
 637 {
 638     long int pid = read_pidfile__(pidfile, true);
 639     if (pid > 0) {
 640         VLOG_FATAL("%s: already running as pid %ld, aborting", pidfile, pid);
 641     } else if (pid < 0) {
 642         VLOG_FATAL("%s: pidfile check failed (%s), aborting",
 643                    pidfile, strerror(-pid));
 644     }
 645 }