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 <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 "ovs-thread.h"
  33 #include "process.h"
  34 #include "socket-util.h"
  35 #include "timeval.h"
  36 #include "util.h"
  37 #include "vlog.h"
  38
  39 VLOG_DEFINE_THIS_MODULE(daemon_unix);
  40
  41 /* --detach: Should we run in the background? */
  42 static bool detach;             /* Was --detach specified? */
  43 static bool detached;           /* Have we already detached? */
  44
  45 /* --pidfile: Name of pidfile (null if none). */
  46 static char *pidfile;
  47
  48 /* Device and inode of pidfile, so we can avoid reopening it. */
  49 static dev_t pidfile_dev;
  50 static ino_t pidfile_ino;
  51
  52 /* --overwrite-pidfile: Create pidfile even if one already exists and is
  53    locked? */
  54 static bool overwrite_pidfile;
  55
  56 /* --no-chdir: Should we chdir to "/"? */
  57 static bool chdir_ = true;
  58
  59 /* File descriptor used by daemonize_start() and daemonize_complete(). */
  60 static int daemonize_fd = -1;
  61
  62 /* --monitor: Should a supervisory process monitor the daemon and restart it if
  63  * it dies due to an error signal? */
  64 static bool monitor;
  65
  66 static void check_already_running(void);
  67 static int lock_pidfile(FILE *, int command);
  68 static char *make_pidfile_name(const char *name);
  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 static 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 up a following call to daemonize() to create a pidfile named 'name'.
  83  * If 'name' begins with '/', then it is treated as an absolute path.
  84  * Otherwise, it is taken relative to RUNDIR, which is $(prefix)/var/run by
  85  * default.
  86  *
  87  * If 'name' is null, then program_name followed by ".pid" is used. */
  88 void
  89 set_pidfile(const char *name)
  90 {
  91     assert_single_threaded();
  92     free(pidfile);
  93     pidfile = make_pidfile_name(name);
  94 }
  95
  96 /* Sets that we do not chdir to "/". */
  97 void
  98 set_no_chdir(void)
  99 {
 100     chdir_ = false;
 101 }
 102
 103 /* Normally, daemonize() or damonize_start() will terminate the program with a
 104  * message if a locked pidfile already exists.  If this function is called, an
 105  * existing pidfile will be replaced, with a warning. */
 106 void
 107 ignore_existing_pidfile(void)
 108 {
 109     overwrite_pidfile = true;
 110 }
 111
 112 /* Sets up a following call to daemonize() to detach from the foreground
 113  * session, running this process in the background.  */
 114 void
 115 set_detach(void)
 116 {
 117     detach = true;
 118 }
 119
 120 /* Will daemonize() really detach? */
 121 bool
 122 get_detach(void)
 123 {
 124     return detach;
 125 }
 126
 127 /* Sets up a following call to daemonize() to fork a supervisory process to
 128  * monitor the daemon and restart it if it dies due to an error signal.  */
 129 void
 130 daemon_set_monitor(void)
 131 {
 132     monitor = true;
 133 }
 134
 135 /* If a pidfile has been configured, creates it and stores the running
 136  * process's pid in it.  Ensures that the pidfile will be deleted when the
 137  * process exits. */
 138 static void
 139 make_pidfile(void)
 140 {
 141     long int pid = getpid();
 142     struct stat s;
 143     char *tmpfile;
 144     FILE *file;
 145     int error;
 146
 147     /* Create a temporary pidfile. */
 148     if (overwrite_pidfile) {
 149         tmpfile = xasprintf("%s.tmp%ld", pidfile, pid);
 150         fatal_signal_add_file_to_unlink(tmpfile);
 151     } else {
 152         /* Everyone shares the same file which will be treated as a lock.  To
 153          * avoid some uncomfortable race conditions, we can't set up the fatal
 154          * signal unlink until we've acquired it. */
 155         tmpfile = xasprintf("%s.tmp", pidfile);
 156     }
 157
 158     file = fopen(tmpfile, "a+");
 159     if (!file) {
 160         VLOG_FATAL("%s: create failed (%s)", tmpfile, ovs_strerror(errno));
 161     }
 162
 163     error = lock_pidfile(file, F_SETLK);
 164     if (error) {
 165         /* Looks like we failed to acquire the lock.  Note that, if we failed
 166          * for some other reason (and '!overwrite_pidfile'), we will have
 167          * left 'tmpfile' as garbage in the file system. */
 168         VLOG_FATAL("%s: fcntl(F_SETLK) failed (%s)", tmpfile,
 169                    ovs_strerror(error));
 170     }
 171
 172     if (!overwrite_pidfile) {
 173         /* We acquired the lock.  Make sure to clean up on exit, and verify
 174          * that we're allowed to create the actual pidfile. */
 175         fatal_signal_add_file_to_unlink(tmpfile);
 176         check_already_running();
 177     }
 178
 179     if (fstat(fileno(file), &s) == -1) {
 180         VLOG_FATAL("%s: fstat failed (%s)", tmpfile, ovs_strerror(errno));
 181     }
 182
 183     if (ftruncate(fileno(file), 0) == -1) {
 184         VLOG_FATAL("%s: truncate failed (%s)", tmpfile, ovs_strerror(errno));
 185     }
 186
 187     fprintf(file, "%ld\n", pid);
 188     if (fflush(file) == EOF) {
 189         VLOG_FATAL("%s: write failed (%s)", tmpfile, ovs_strerror(errno));
 190     }
 191
 192     error = rename(tmpfile, pidfile);
 193
 194     /* Due to a race, 'tmpfile' may be owned by a different process, so we
 195      * shouldn't delete it on exit. */
 196     fatal_signal_remove_file_to_unlink(tmpfile);
 197
 198     if (error < 0) {
 199         VLOG_FATAL("failed to rename \"%s\" to \"%s\" (%s)",
 200                    tmpfile, pidfile, ovs_strerror(errno));
 201     }
 202
 203     /* Ensure that the pidfile will get deleted on exit. */
 204     fatal_signal_add_file_to_unlink(pidfile);
 205
 206     /* Clean up.
 207      *
 208      * We don't close 'file' because its file descriptor must remain open to
 209      * hold the lock. */
 210     pidfile_dev = s.st_dev;
 211     pidfile_ino = s.st_ino;
 212     free(tmpfile);
 213 }
 214
 215 /* If configured with set_pidfile() or set_detach(), creates the pid file and
 216  * detaches from the foreground session.  */
 217 void
 218 daemonize(void)
 219 {
 220     daemonize_start();
 221     daemonize_complete();
 222 }
 223
 224 /* Calls fork() and on success returns its return value.  On failure, logs an
 225  * error and exits unsuccessfully.
 226  *
 227  * Post-fork, but before returning, this function calls a few other functions
 228  * that are generally useful if the child isn't planning to exec a new
 229  * process. */
 230 static pid_t
 231 fork_and_clean_up(void)
 232 {
 233     pid_t pid = xfork();
 234     if (pid > 0) {
 235         /* Running in parent process. */
 236         fatal_signal_fork();
 237     } else if (!pid) {
 238         /* Running in child process. */
 239         lockfile_postfork();
 240     }
 241     return pid;
 242 }
 243
 244 /* Forks, then:
 245  *
 246  *   - In the parent, waits for the child to signal that it has completed its
 247  *     startup sequence.  Then stores -1 in '*fdp' and returns the child's pid.
 248  *
 249  *   - In the child, stores a fd in '*fdp' and returns 0.  The caller should
 250  *     pass the fd to fork_notify_startup() after it finishes its startup
 251  *     sequence.
 252  *
 253  * If something goes wrong with the fork, logs a critical error and aborts the
 254  * process. */
 255 static pid_t
 256 fork_and_wait_for_startup(int *fdp)
 257 {
 258     int fds[2];
 259     pid_t pid;
 260
 261     xpipe(fds);
 262
 263     pid = fork_and_clean_up();
 264     if (pid > 0) {
 265         /* Running in parent process. */
 266         size_t bytes_read;
 267         char c;
 268
 269         close(fds[1]);
 270         if (read_fully(fds[0], &c, 1, &bytes_read) != 0) {
 271             int retval;
 272             int status;
 273
 274             do {
 275                 retval = waitpid(pid, &status, 0);
 276             } while (retval == -1 && errno == EINTR);
 277
 278             if (retval == pid) {
 279                 if (WIFEXITED(status) && WEXITSTATUS(status)) {
 280                     /* Child exited with an error.  Convey the same error
 281                      * to our parent process as a courtesy. */
 282                     exit(WEXITSTATUS(status));
 283                 } else {
 284                     char *status_msg = process_status_msg(status);
 285                     VLOG_FATAL("fork child died before signaling startup (%s)",
 286                                status_msg);
 287                 }
 288             } else if (retval < 0) {
 289                 VLOG_FATAL("waitpid failed (%s)", ovs_strerror(errno));
 290             } else {
 291                 OVS_NOT_REACHED();
 292             }
 293         }
 294         close(fds[0]);
 295         *fdp = -1;
 296     } else if (!pid) {
 297         /* Running in child process. */
 298         close(fds[0]);
 299         *fdp = fds[1];
 300     }
 301
 302     return pid;
 303 }
 304
 305 static void
 306 fork_notify_startup(int fd)
 307 {
 308     if (fd != -1) {
 309         size_t bytes_written;
 310         int error;
 311
 312         error = write_fully(fd, "", 1, &bytes_written);
 313         if (error) {
 314             VLOG_FATAL("pipe write failed (%s)", ovs_strerror(error));
 315         }
 316
 317         close(fd);
 318     }
 319 }
 320
 321 static bool
 322 should_restart(int status)
 323 {
 324     if (WIFSIGNALED(status)) {
 325         static const int error_signals[] = {
 326             /* This list of signals is documented in daemon.man.  If you
 327              * change the list, update the documentation too. */
 328             SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV,
 329             SIGXCPU, SIGXFSZ
 330         };
 331
 332         size_t i;
 333
 334         for (i = 0; i < ARRAY_SIZE(error_signals); i++) {
 335             if (error_signals[i] == WTERMSIG(status)) {
 336                 return true;
 337             }
 338         }
 339     }
 340     return false;
 341 }
 342
 343 static void
 344 monitor_daemon(pid_t daemon_pid)
 345 {
 346     /* XXX Should log daemon's stderr output at startup time. */
 347     time_t last_restart;
 348     char *status_msg;
 349     int crashes;
 350
 351     set_subprogram_name("monitor");
 352     status_msg = xstrdup("healthy");
 353     last_restart = TIME_MIN;
 354     crashes = 0;
 355     for (;;) {
 356         int retval;
 357         int status;
 358
 359         proctitle_set("monitoring pid %lu (%s)",
 360                       (unsigned long int) daemon_pid, status_msg);
 361
 362         do {
 363             retval = waitpid(daemon_pid, &status, 0);
 364         } while (retval == -1 && errno == EINTR);
 365
 366         if (retval == -1) {
 367             VLOG_FATAL("waitpid failed (%s)", ovs_strerror(errno));
 368         } else if (retval == daemon_pid) {
 369             char *s = process_status_msg(status);
 370             if (should_restart(status)) {
 371                 free(status_msg);
 372                 status_msg = xasprintf("%d crashes: pid %lu died, %s",
 373                                        ++crashes,
 374                                        (unsigned long int) daemon_pid, s);
 375                 free(s);
 376
 377                 if (WCOREDUMP(status)) {
 378                     /* Disable further core dumps to save disk space. */
 379                     struct rlimit r;
 380
 381                     r.rlim_cur = 0;
 382                     r.rlim_max = 0;
 383                     if (setrlimit(RLIMIT_CORE, &r) == -1) {
 384                         VLOG_WARN("failed to disable core dumps: %s",
 385                                   ovs_strerror(errno));
 386                     }
 387                 }
 388
 389                 /* Throttle restarts to no more than once every 10 seconds. */
 390                 if (time(NULL) < last_restart + 10) {
 391                     VLOG_WARN("%s, waiting until 10 seconds since last "
 392                               "restart", status_msg);
 393                     for (;;) {
 394                         time_t now = time(NULL);
 395                         time_t wakeup = last_restart + 10;
 396                         if (now >= wakeup) {
 397                             break;
 398                         }
 399                         xsleep(wakeup - now);
 400                     }
 401                 }
 402                 last_restart = time(NULL);
 403
 404                 VLOG_ERR("%s, restarting", status_msg);
 405                 daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
 406                 if (!daemon_pid) {
 407                     break;
 408                 }
 409             } else {
 410                 VLOG_INFO("pid %lu died, %s, exiting",
 411                           (unsigned long int) daemon_pid, s);
 412                 free(s);
 413                 exit(0);
 414             }
 415         }
 416     }
 417     free(status_msg);
 418
 419     /* Running in new daemon process. */
 420     proctitle_restore();
 421     set_subprogram_name("");
 422 }
 423
 424 /* If daemonization is configured, then starts daemonization, by forking and
 425  * returning in the child process.  The parent process hangs around until the
 426  * child lets it know either that it completed startup successfully (by calling
 427  * daemon_complete()) or that it failed to start up (by exiting with a nonzero
 428  * exit code). */
 429 void
 430 daemonize_start(void)
 431 {
 432     assert_single_threaded();
 433     daemonize_fd = -1;
 434
 435     if (detach) {
 436         if (fork_and_wait_for_startup(&daemonize_fd) > 0) {
 437             /* Running in parent process. */
 438             exit(0);
 439         }
 440
 441         /* Running in daemon or monitor process. */
 442         setsid();
 443     }
 444
 445     if (monitor) {
 446         int saved_daemonize_fd = daemonize_fd;
 447         pid_t daemon_pid;
 448
 449         daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
 450         if (daemon_pid > 0) {
 451             /* Running in monitor process. */
 452             fork_notify_startup(saved_daemonize_fd);
 453             close_standard_fds();
 454             monitor_daemon(daemon_pid);
 455         }
 456         /* Running in daemon process. */
 457     }
 458
 459     forbid_forking("running in daemon process");
 460
 461     if (pidfile) {
 462         make_pidfile();
 463     }
 464
 465     /* Make sure that the unixctl commands for vlog get registered in a
 466      * daemon, even before the first log message. */
 467     vlog_init();
 468 }
 469
 470 /* If daemonization is configured, then this function notifies the parent
 471  * process that the child process has completed startup successfully.  It also
 472  * call daemonize_post_detach().
 473  *
 474  * Calling this function more than once has no additional effect. */
 475 void
 476 daemonize_complete(void)
 477 {
 478     if (pidfile) {
 479         free(pidfile);
 480         pidfile = NULL;
 481     }
 482
 483     if (!detached) {
 484         detached = true;
 485
 486         fork_notify_startup(daemonize_fd);
 487         daemonize_fd = -1;
 488         daemonize_post_detach();
 489     }
 490 }
 491
 492 /* If daemonization is configured, then this function does traditional Unix
 493  * daemonization behavior: join a new session, chdir to the root (if not
 494  * disabled), and close the standard file descriptors.
 495  *
 496  * It only makes sense to call this function as part of an implementation of a
 497  * special daemon subprocess.  A normal daemon should just call
 498  * daemonize_complete(). */
 499 static void
 500 daemonize_post_detach(void)
 501 {
 502     if (detach) {
 503         if (chdir_) {
 504             ignore(chdir("/"));
 505         }
 506         close_standard_fds();
 507     }
 508 }
 509
 510 void
 511 daemon_usage(void)
 512 {
 513     printf(
 514         "\nDaemon options:\n"
 515         "  --detach                run in background as daemon\n"
 516         "  --no-chdir              do not chdir to '/'\n"
 517         "  --pidfile[=FILE]        create pidfile (default: %s/%s.pid)\n"
 518         "  --overwrite-pidfile     with --pidfile, start even if already "
 519                                    "running\n",
 520         ovs_rundir(), program_name);
 521 }
 522
 523 static int
 524 lock_pidfile__(FILE *file, int command, struct flock *lck)
 525 {
 526     int error;
 527
 528     lck->l_type = F_WRLCK;
 529     lck->l_whence = SEEK_SET;
 530     lck->l_start = 0;
 531     lck->l_len = 0;
 532     lck->l_pid = 0;
 533
 534     do {
 535         error = fcntl(fileno(file), command, lck) == -1 ? errno : 0;
 536     } while (error == EINTR);
 537     return error;
 538 }
 539
 540 static int
 541 lock_pidfile(FILE *file, int command)
 542 {
 543     struct flock lck;
 544
 545     return lock_pidfile__(file, command, &lck);
 546 }
 547
 548 static pid_t
 549 read_pidfile__(const char *pidfile, bool delete_if_stale)
 550 {
 551     struct stat s, s2;
 552     struct flock lck;
 553     char line[128];
 554     FILE *file;
 555     int error;
 556
 557     if ((pidfile_ino || pidfile_dev)
 558         && !stat(pidfile, &s)
 559         && s.st_ino == pidfile_ino && s.st_dev == pidfile_dev) {
 560         /* It's our own pidfile.  We can't afford to open it, because closing
 561          * *any* fd for a file that a process has locked also releases all the
 562          * locks on that file.
 563          *
 564          * Fortunately, we know the associated pid anyhow: */
 565         return getpid();
 566     }
 567
 568     file = fopen(pidfile, "r+");
 569     if (!file) {
 570         if (errno == ENOENT && delete_if_stale) {
 571             return 0;
 572         }
 573         error = errno;
 574         VLOG_WARN("%s: open: %s", pidfile, ovs_strerror(error));
 575         goto error;
 576     }
 577
 578     error = lock_pidfile__(file, F_GETLK, &lck);
 579     if (error) {
 580         VLOG_WARN("%s: fcntl: %s", pidfile, ovs_strerror(error));
 581         goto error;
 582     }
 583     if (lck.l_type == F_UNLCK) {
 584         /* pidfile exists but it isn't locked by anyone.  We need to delete it
 585          * so that a new pidfile can go in its place.  But just calling
 586          * unlink(pidfile) makes a nasty race: what if someone else unlinks it
 587          * before we do and then replaces it by a valid pidfile?  We'd unlink
 588          * their valid pidfile.  We do a little dance to avoid the race, by
 589          * locking the invalid pidfile.  Only one process can have the invalid
 590          * pidfile locked, and only that process has the right to unlink it. */
 591         if (!delete_if_stale) {
 592             error = ESRCH;
 593             VLOG_DBG("%s: pid file is stale", pidfile);
 594             goto error;
 595         }
 596
 597         /* Get the lock. */
 598         error = lock_pidfile(file, F_SETLK);
 599         if (error) {
 600             /* We lost a race with someone else doing the same thing. */
 601             VLOG_WARN("%s: lost race to lock pidfile", pidfile);
 602             goto error;
 603         }
 604
 605         /* Is the file we have locked still named 'pidfile'? */
 606         if (stat(pidfile, &s) || fstat(fileno(file), &s2)
 607             || s.st_ino != s2.st_ino || s.st_dev != s2.st_dev) {
 608             /* No.  We lost a race with someone else who got the lock before
 609              * us, deleted the pidfile, and closed it (releasing the lock). */
 610             error = EALREADY;
 611             VLOG_WARN("%s: lost race to delete pidfile", pidfile);
 612             goto error;
 613         }
 614
 615         /* We won the right to delete the stale pidfile. */
 616         if (unlink(pidfile)) {
 617             error = errno;
 618             VLOG_WARN("%s: failed to delete stale pidfile (%s)",
 619                       pidfile, ovs_strerror(error));
 620             goto error;
 621         }
 622         VLOG_DBG("%s: deleted stale pidfile", pidfile);
 623         fclose(file);
 624         return 0;
 625     }
 626
 627     if (!fgets(line, sizeof line, file)) {
 628         if (ferror(file)) {
 629             error = errno;
 630             VLOG_WARN("%s: read: %s", pidfile, ovs_strerror(error));
 631         } else {
 632             error = ESRCH;
 633             VLOG_WARN("%s: read: unexpected end of file", pidfile);
 634         }
 635         goto error;
 636     }
 637
 638     if (lck.l_pid != strtoul(line, NULL, 10)) {
 639         /* The process that has the pidfile locked is not the process that
 640          * created it.  It must be stale, with the process that has it locked
 641          * preparing to delete it. */
 642         error = ESRCH;
 643         VLOG_WARN("%s: stale pidfile for pid %s being deleted by pid %ld",
 644                   pidfile, line, (long int) lck.l_pid);
 645         goto error;
 646     }
 647
 648     fclose(file);
 649     return lck.l_pid;
 650
 651 error:
 652     if (file) {
 653         fclose(file);
 654     }
 655     return -error;
 656 }
 657
 658 /* Opens and reads a PID from 'pidfile'.  Returns the positive PID if
 659  * successful, otherwise a negative errno value. */
 660 pid_t
 661 read_pidfile(const char *pidfile)
 662 {
 663     return read_pidfile__(pidfile, false);
 664 }
 665
 666 /* Checks whether a process with the given 'pidfile' is already running and,
 667  * if so, aborts.  If 'pidfile' is stale, deletes it. */
 668 static void
 669 check_already_running(void)
 670 {
 671     long int pid = read_pidfile__(pidfile, true);
 672     if (pid > 0) {
 673         VLOG_FATAL("%s: already running as pid %ld, aborting", pidfile, pid);
 674     } else if (pid < 0) {
 675         VLOG_FATAL("%s: pidfile check failed (%s), aborting",
 676                    pidfile, ovs_strerror(-pid));
 677     }
 678 }
 679
 680 \f
 681 /* stub functions for non-windows platform. */
 682
 683 void
 684 service_start(int *argc OVS_UNUSED, char **argv[] OVS_UNUSED)
 685 {
 686 }
 687
 688 void
 689 service_stop(void)
 690 {
 691 }
 692
 693 bool
 694 should_service_stop(void)
 695 {
 696     return false;
 697 }