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 <unistd.h>
  24 #include "fatal-signal.h"
  25 #include "dirs.h"
  26 #include "util.h"
  27
  28 #define THIS_MODULE VLM_daemon
  29 #include "vlog.h"
  30
  31 /* Should we run in the background? */
  32 static bool detach;
  33
  34 /* Name of pidfile (null if none). */
  35 static char *pidfile;
  36
  37 /* Create pidfile even if one already exists and is locked? */
  38 static bool overwrite_pidfile;
  39
  40 /* Should we chdir to "/". */
  41 static bool chdir_ = true;
  42
  43 /* Returns the file name that would be used for a pidfile if 'name' were
  44  * provided to set_pidfile().  The caller must free the returned string. */
  45 char *
  46 make_pidfile_name(const char *name)
  47 {
  48     return (!name ? xasprintf("%s/%s.pid", ovs_rundir, program_name)
  49             : *name == '/' ? xstrdup(name)
  50             : xasprintf("%s/%s", ovs_rundir, name));
  51 }
  52
  53 /* Sets up a following call to daemonize() to create a pidfile named 'name'.
  54  * If 'name' begins with '/', then it is treated as an absolute path.
  55  * Otherwise, it is taken relative to RUNDIR, which is $(prefix)/var/run by
  56  * default.
  57  *
  58  * If 'name' is null, then program_name followed by ".pid" is used. */
  59 void
  60 set_pidfile(const char *name)
  61 {
  62     free(pidfile);
  63     pidfile = make_pidfile_name(name);
  64 }
  65
  66 /* Returns an absolute path to the configured pidfile, or a null pointer if no
  67  * pidfile is configured.  The caller must not modify or free the returned
  68  * string. */
  69 const char *
  70 get_pidfile(void)
  71 {
  72     return pidfile;
  73 }
  74
  75 /* Sets that we do not chdir to "/". */
  76 void
  77 set_no_chdir(void)
  78 {
  79     chdir_ = false;
  80 }
  81
  82 /* Normally, die_if_already_running() will terminate the program with a message
  83  * if a locked pidfile already exists.  If this function is called,
  84  * die_if_already_running() will merely log a warning. */
  85 void
  86 ignore_existing_pidfile(void)
  87 {
  88     overwrite_pidfile = true;
  89 }
  90
  91 /* Sets up a following call to daemonize() to detach from the foreground
  92  * session, running this process in the background.  */
  93 void
  94 set_detach(void)
  95 {
  96     detach = true;
  97 }
  98
  99 /* If a pidfile has been configured and that pidfile already exists and is
 100  * locked by a running process, returns the pid of the running process.
 101  * Otherwise, returns 0. */
 102 static pid_t
 103 already_running(void)
 104 {
 105     pid_t pid = 0;
 106     if (pidfile) {
 107         int fd = open(pidfile, O_RDWR);
 108         if (fd >= 0) {
 109             struct flock lck;
 110             lck.l_type = F_WRLCK;
 111             lck.l_whence = SEEK_SET;
 112             lck.l_start = 0;
 113             lck.l_len = 0;
 114             if (fcntl(fd, F_GETLK, &lck) != -1 && lck.l_type != F_UNLCK) {
 115                 pid = lck.l_pid;
 116             }
 117             close(fd);
 118         }
 119     }
 120     return pid;
 121 }
 122
 123 /* If a locked pidfile exists, issue a warning message and, unless
 124  * ignore_existing_pidfile() has been called, terminate the program. */
 125 void
 126 die_if_already_running(void)
 127 {
 128     pid_t pid = already_running();
 129     if (pid) {
 130         if (!overwrite_pidfile) {
 131             ovs_fatal(0, "%s: already running as pid %ld",
 132                       get_pidfile(), (long int) pid);
 133         } else {
 134             VLOG_WARN("%s: %s already running as pid %ld",
 135                       get_pidfile(), program_name, (long int) pid);
 136         }
 137     }
 138 }
 139
 140 /* If a pidfile has been configured, creates it and stores the running process'
 141  * pid init.  Ensures that the pidfile will be deleted when the process
 142  * exits. */
 143 static void
 144 make_pidfile(void)
 145 {
 146     if (pidfile) {
 147         /* Create pidfile via temporary file, so that observers never see an
 148          * empty pidfile or an unlocked pidfile. */
 149         long int pid = getpid();
 150         char *tmpfile;
 151         int fd;
 152
 153         tmpfile = xasprintf("%s.tmp%ld", pidfile, pid);
 154         fatal_signal_add_file_to_unlink(tmpfile);
 155         fd = open(tmpfile, O_CREAT | O_WRONLY | O_TRUNC, 0666);
 156         if (fd >= 0) {
 157             struct flock lck;
 158             lck.l_type = F_WRLCK;
 159             lck.l_whence = SEEK_SET;
 160             lck.l_start = 0;
 161             lck.l_len = 0;
 162             if (fcntl(fd, F_SETLK, &lck) != -1) {
 163                 char *text = xasprintf("%ld\n", pid);
 164                 if (write(fd, text, strlen(text)) == strlen(text)) {
 165                     fatal_signal_add_file_to_unlink(pidfile);
 166                     if (rename(tmpfile, pidfile) < 0) {
 167                         VLOG_ERR("failed to rename \"%s\" to \"%s\": %s",
 168                                  tmpfile, pidfile, strerror(errno));
 169                         fatal_signal_remove_file_to_unlink(pidfile);
 170                         close(fd);
 171                     } else {
 172                         /* Keep 'fd' open to retain the lock. */
 173                     }
 174                     free(text);
 175                 } else {
 176                     VLOG_ERR("%s: write failed: %s", tmpfile, strerror(errno));
 177                     close(fd);
 178                 }
 179             } else {
 180                 VLOG_ERR("%s: fcntl failed: %s", tmpfile, strerror(errno));
 181                 close(fd);
 182             }
 183         } else {
 184             VLOG_ERR("%s: create failed: %s", tmpfile, strerror(errno));
 185         }
 186         fatal_signal_remove_file_to_unlink(tmpfile);
 187         free(tmpfile);
 188     }
 189     free(pidfile);
 190     pidfile = NULL;
 191 }
 192
 193 /* If configured with set_pidfile() or set_detach(), creates the pid file and
 194  * detaches from the foreground session.  */
 195 void
 196 daemonize(void)
 197 {
 198     if (detach) {
 199         char c = 0;
 200         int fds[2];
 201         if (pipe(fds) < 0) {
 202             ovs_fatal(errno, "pipe failed");
 203         }
 204
 205         switch (fork()) {
 206         default:
 207             /* Parent process: wait for child to create pidfile, then exit. */
 208             close(fds[1]);
 209             fatal_signal_fork();
 210             if (read(fds[0], &c, 1) != 1) {
 211                 ovs_fatal(errno, "daemon child failed to signal startup");
 212             }
 213             exit(0);
 214
 215         case 0:
 216             /* Child process. */
 217             close(fds[0]);
 218             make_pidfile();
 219             write(fds[1], &c, 1);
 220             close(fds[1]);
 221             setsid();
 222             if (chdir_) {
 223                 chdir("/");
 224             }
 225             break;
 226
 227         case -1:
 228             /* Error. */
 229             ovs_fatal(errno, "could not fork");
 230             break;
 231         }
 232     } else {
 233         make_pidfile();
 234     }
 235 }
 236
 237 void
 238 daemon_usage(void)
 239 {
 240     printf(
 241         "\nDaemon options:\n"
 242         "  --detach                run in background as daemon\n"
 243         "  --no-chdir              do not chdir to '/'\n"
 244         "  --pidfile[=FILE]        create pidfile (default: %s/%s.pid)\n"
 245         "  --overwrite-pidfile     with --pidfile, start even if already "
 246                                    "running\n",
 247         ovs_rundir, program_name);
 248 }
 249
 250 /* Opens and reads a PID from 'pidfile'.  Returns the nonnegative PID if
 251  * successful, otherwise a negative errno value. */
 252 pid_t
 253 read_pidfile(const char *pidfile)
 254 {
 255     char line[128];
 256     struct flock lck;
 257     FILE *file;
 258     int error;
 259
 260     file = fopen(pidfile, "r");
 261     if (!file) {
 262         error = errno;
 263         VLOG_WARN("%s: open: %s", pidfile, strerror(error));
 264         goto error;
 265     }
 266
 267     lck.l_type = F_WRLCK;
 268     lck.l_whence = SEEK_SET;
 269     lck.l_start = 0;
 270     lck.l_len = 0;
 271     if (fcntl(fileno(file), F_GETLK, &lck)) {
 272         error = errno;
 273         VLOG_WARN("%s: fcntl: %s", pidfile, strerror(error));
 274         goto error;
 275     }
 276     if (lck.l_type == F_UNLCK) {
 277         error = ESRCH;
 278         VLOG_WARN("%s: pid file is not locked", pidfile);
 279         goto error;
 280     }
 281
 282     if (!fgets(line, sizeof line, file)) {
 283         if (ferror(file)) {
 284             error = errno;
 285             VLOG_WARN("%s: read: %s", pidfile, strerror(error));
 286         } else {
 287             error = ESRCH;
 288             VLOG_WARN("%s: read: unexpected end of file", pidfile);
 289         }
 290         goto error;
 291     }
 292
 293     if (lck.l_pid != strtoul(line, NULL, 10)) {
 294         error = ESRCH;
 295         VLOG_WARN("l_pid (%ld) != %s pid (%s)",
 296                    (long int) lck.l_pid, pidfile, line);
 297         goto error;
 298     }
 299
 300     fclose(file);
 301     return lck.l_pid;
 302
 303 error:
 304     if (file) {
 305         fclose(file);
 306     }
 307     return -error;
 308 }