lib/daemon.c

   1 /*
   2  * Copyright (c) 2008, 2009 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 <stdlib.h>
  22 #include <string.h>
  23 #include <sys/wait.h>
  24 #include <unistd.h>
  25 #include "fatal-signal.h"
  26 #include "dirs.h"
  27 #include "lockfile.h"
  28 #include "socket-util.h"
  29 #include "timeval.h"
  30 #include "util.h"
  31
  32 #define THIS_MODULE VLM_daemon
  33 #include "vlog.h"
  34
  35 /* Should we run in the background? */
  36 static bool detach;
  37
  38 /* Name of pidfile (null if none). */
  39 static char *pidfile;
  40
  41 /* Create pidfile even if one already exists and is locked? */
  42 static bool overwrite_pidfile;
  43
  44 /* Should we chdir to "/"? */
  45 static bool chdir_ = true;
  46
  47 /* File descriptors used by daemonize_start() and daemonize_complete(). */
  48 static int daemonize_fds[2];
  49
  50 /* Returns the file name that would be used for a pidfile if 'name' were
  51  * provided to set_pidfile().  The caller must free the returned string. */
  52 char *
  53 make_pidfile_name(const char *name)
  54 {
  55     return (!name ? xasprintf("%s/%s.pid", ovs_rundir, program_name)
  56             : *name == '/' ? xstrdup(name)
  57             : xasprintf("%s/%s", ovs_rundir, name));
  58 }
  59
  60 /* Sets up a following call to daemonize() to create a pidfile named 'name'.
  61  * If 'name' begins with '/', then it is treated as an absolute path.
  62  * Otherwise, it is taken relative to RUNDIR, which is $(prefix)/var/run by
  63  * default.
  64  *
  65  * If 'name' is null, then program_name followed by ".pid" is used. */
  66 void
  67 set_pidfile(const char *name)
  68 {
  69     free(pidfile);
  70     pidfile = make_pidfile_name(name);
  71 }
  72
  73 /* Returns an absolute path to the configured pidfile, or a null pointer if no
  74  * pidfile is configured.  The caller must not modify or free the returned
  75  * string. */
  76 const char *
  77 get_pidfile(void)
  78 {
  79     return pidfile;
  80 }
  81
  82 /* Sets that we do not chdir to "/". */
  83 void
  84 set_no_chdir(void)
  85 {
  86     chdir_ = false;
  87 }
  88
  89 /* Will we chdir to "/" as part of daemonizing? */
  90 bool
  91 is_chdir_enabled(void)
  92 {
  93     return chdir_;
  94 }
  95
  96 /* Normally, die_if_already_running() will terminate the program with a message
  97  * if a locked pidfile already exists.  If this function is called,
  98  * die_if_already_running() will merely log a warning. */
  99 void
 100 ignore_existing_pidfile(void)
 101 {
 102     overwrite_pidfile = true;
 103 }
 104
 105 /* Sets up a following call to daemonize() to detach from the foreground
 106  * session, running this process in the background.  */
 107 void
 108 set_detach(void)
 109 {
 110     detach = true;
 111 }
 112
 113 /* Will daemonize() really detach? */
 114 bool
 115 get_detach(void)
 116 {
 117     return detach;
 118 }
 119
 120 /* If a pidfile has been configured and that pidfile already exists and is
 121  * locked by a running process, returns the pid of the running process.
 122  * Otherwise, returns 0. */
 123 static pid_t
 124 already_running(void)
 125 {
 126     pid_t pid = 0;
 127     if (pidfile) {
 128         int fd = open(pidfile, O_RDWR);
 129         if (fd >= 0) {
 130             struct flock lck;
 131             lck.l_type = F_WRLCK;
 132             lck.l_whence = SEEK_SET;
 133             lck.l_start = 0;
 134             lck.l_len = 0;
 135             if (fcntl(fd, F_GETLK, &lck) != -1 && lck.l_type != F_UNLCK) {
 136                 pid = lck.l_pid;
 137             }
 138             close(fd);
 139         }
 140     }
 141     return pid;
 142 }
 143
 144 /* If a locked pidfile exists, issue a warning message and, unless
 145  * ignore_existing_pidfile() has been called, terminate the program. */
 146 void
 147 die_if_already_running(void)
 148 {
 149     pid_t pid = already_running();
 150     if (pid) {
 151         if (!overwrite_pidfile) {
 152             ovs_fatal(0, "%s: already running as pid %ld",
 153                       get_pidfile(), (long int) pid);
 154         } else {
 155             VLOG_WARN("%s: %s already running as pid %ld",
 156                       get_pidfile(), program_name, (long int) pid);
 157         }
 158     }
 159 }
 160
 161 /* If a pidfile has been configured, creates it and stores the running process'
 162  * pid init.  Ensures that the pidfile will be deleted when the process
 163  * exits. */
 164 static void
 165 make_pidfile(void)
 166 {
 167     if (pidfile) {
 168         /* Create pidfile via temporary file, so that observers never see an
 169          * empty pidfile or an unlocked pidfile. */
 170         long int pid = getpid();
 171         char *tmpfile;
 172         int fd;
 173
 174         tmpfile = xasprintf("%s.tmp%ld", pidfile, pid);
 175         fatal_signal_add_file_to_unlink(tmpfile);
 176         fd = open(tmpfile, O_CREAT | O_WRONLY | O_TRUNC, 0666);
 177         if (fd >= 0) {
 178             struct flock lck;
 179             lck.l_type = F_WRLCK;
 180             lck.l_whence = SEEK_SET;
 181             lck.l_start = 0;
 182             lck.l_len = 0;
 183             if (fcntl(fd, F_SETLK, &lck) != -1) {
 184                 char *text = xasprintf("%ld\n", pid);
 185                 if (write(fd, text, strlen(text)) == strlen(text)) {
 186                     fatal_signal_add_file_to_unlink(pidfile);
 187                     if (rename(tmpfile, pidfile) < 0) {
 188                         VLOG_ERR("failed to rename \"%s\" to \"%s\": %s",
 189                                  tmpfile, pidfile, strerror(errno));
 190                         fatal_signal_remove_file_to_unlink(pidfile);
 191                         close(fd);
 192                     } else {
 193                         /* Keep 'fd' open to retain the lock. */
 194                     }
 195                     free(text);
 196                 } else {
 197                     VLOG_ERR("%s: write failed: %s", tmpfile, strerror(errno));
 198                     close(fd);
 199                 }
 200             } else {
 201                 VLOG_ERR("%s: fcntl failed: %s", tmpfile, strerror(errno));
 202                 close(fd);
 203             }
 204         } else {
 205             VLOG_ERR("%s: create failed: %s", tmpfile, strerror(errno));
 206         }
 207         fatal_signal_remove_file_to_unlink(tmpfile);
 208         free(tmpfile);
 209     }
 210     free(pidfile);
 211     pidfile = NULL;
 212 }
 213
 214 /* If configured with set_pidfile() or set_detach(), creates the pid file and
 215  * detaches from the foreground session.  */
 216 void
 217 daemonize(void)
 218 {
 219     daemonize_start();
 220     daemonize_complete();
 221 }
 222
 223 /* If daemonization is configured, then starts daemonization, by forking and
 224  * returning in the child process.  The parent process hangs around until the
 225  * child lets it know either that it completed startup successfully (by calling
 226  * daemon_complete()) or that it failed to start up (by exiting with a nonzero
 227  * exit code). */
 228 void
 229 daemonize_start(void)
 230 {
 231     if (detach) {
 232         pid_t pid;
 233
 234         if (pipe(daemonize_fds) < 0) {
 235             ovs_fatal(errno, "pipe failed");
 236         }
 237
 238         pid = fork();
 239         if (pid > 0) {
 240             /* Running in parent process. */
 241             char c;
 242
 243             close(daemonize_fds[1]);
 244             fatal_signal_fork();
 245             if (read(daemonize_fds[0], &c, 1) != 1) {
 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                 ovs_fatal(errno, "daemon child failed to signal startup");
 262             }
 263             exit(0);
 264         } else if (!pid) {
 265             /* Running in child process. */
 266             close(daemonize_fds[0]);
 267             make_pidfile();
 268             time_postfork();
 269             lockfile_postfork();
 270         } else {
 271             ovs_fatal(errno, "could not fork");
 272         }
 273     } else {
 274         make_pidfile();
 275     }
 276 }
 277
 278 /* If daemonization is configured, then this function notifies the parent
 279  * process that the child process has completed startup successfully. */
 280 void
 281 daemonize_complete(void)
 282 {
 283     if (detach) {
 284         size_t bytes_written;
 285         int error;
 286
 287         error = write_fully(daemonize_fds[1], "", 1, &bytes_written);
 288         if (error) {
 289             ovs_fatal(error, "could not write to pipe");
 290         }
 291
 292         close(daemonize_fds[1]);
 293         setsid();
 294         if (chdir_) {
 295             ignore(chdir("/"));
 296         }
 297     }
 298 }
 299
 300 void
 301 daemon_usage(void)
 302 {
 303     printf(
 304         "\nDaemon options:\n"
 305         "  --detach                run in background as daemon\n"
 306         "  --no-chdir              do not chdir to '/'\n"
 307         "  --pidfile[=FILE]        create pidfile (default: %s/%s.pid)\n"
 308         "  --overwrite-pidfile     with --pidfile, start even if already "
 309                                    "running\n",
 310         ovs_rundir, program_name);
 311 }
 312
 313 /* Opens and reads a PID from 'pidfile'.  Returns the nonnegative PID if
 314  * successful, otherwise a negative errno value. */
 315 pid_t
 316 read_pidfile(const char *pidfile)
 317 {
 318     char line[128];
 319     struct flock lck;
 320     FILE *file;
 321     int error;
 322
 323     file = fopen(pidfile, "r");
 324     if (!file) {
 325         error = errno;
 326         VLOG_WARN("%s: open: %s", pidfile, strerror(error));
 327         goto error;
 328     }
 329
 330     lck.l_type = F_WRLCK;
 331     lck.l_whence = SEEK_SET;
 332     lck.l_start = 0;
 333     lck.l_len = 0;
 334     if (fcntl(fileno(file), F_GETLK, &lck)) {
 335         error = errno;
 336         VLOG_WARN("%s: fcntl: %s", pidfile, strerror(error));
 337         goto error;
 338     }
 339     if (lck.l_type == F_UNLCK) {
 340         error = ESRCH;
 341         VLOG_WARN("%s: pid file is not locked", pidfile);
 342         goto error;
 343     }
 344
 345     if (!fgets(line, sizeof line, file)) {
 346         if (ferror(file)) {
 347             error = errno;
 348             VLOG_WARN("%s: read: %s", pidfile, strerror(error));
 349         } else {
 350             error = ESRCH;
 351             VLOG_WARN("%s: read: unexpected end of file", pidfile);
 352         }
 353         goto error;
 354     }
 355
 356     if (lck.l_pid != strtoul(line, NULL, 10)) {
 357         error = ESRCH;
 358         VLOG_WARN("l_pid (%ld) != %s pid (%s)",
 359                    (long int) lck.l_pid, pidfile, line);
 360         goto error;
 361     }
 362
 363     fclose(file);
 364     return lck.l_pid;
 365
 366 error:
 367     if (file) {
 368         fclose(file);
 369     }
 370     return -error;
 371 }