text: /*
   * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at:
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #include <config.h>
  #include "daemon.h"
  #include <assert.h>
  #include <errno.h>
  #include <fcntl.h>
  #include <signal.h>
  #include <stdlib.h>
  #include <string.h>
  #include <sys/resource.h>
  #include <sys/wait.h>
  #include <sys/stat.h>
  #include <unistd.h>
  #include "command-line.h"
  #include "fatal-signal.h"
  #include "dirs.h"
  #include "lockfile.h"
  #include "process.h"
  #include "socket-util.h"
  #include "timeval.h"
  #include "util.h"
  #include "vlog.h"
  
  VLOG_DEFINE_THIS_MODULE(daemon);
  
  /* --detach: Should we run in the background? */
  static bool detach;             /* Was --detach specified? */
  static bool detached;           /* Have we already detached? */
  
  /* --pidfile: Name of pidfile (null if none). */
  static char *pidfile;
  
  /* Device and inode of pidfile, so we can avoid reopening it. */
  static dev_t pidfile_dev;
  static ino_t pidfile_ino;
  
  /* --overwrite-pidfile: Create pidfile even if one already exists and is
     locked? */
  static bool overwrite_pidfile;
  
  /* --no-chdir: Should we chdir to "/"? */
  static bool chdir_ = true;
  
  /* File descriptor used by daemonize_start() and daemonize_complete(). */
  static int daemonize_fd = -1;
  
  /* --monitor: Should a supervisory process monitor the daemon and restart it if
   * it dies due to an error signal? */
  static bool monitor;
  
  /* For each of the standard file descriptors, whether to replace it by
   * /dev/null (if false) or keep it for the daemon to use (if true). */
  static bool save_fds[3];
  
  static void check_already_running(void);
  static int lock_pidfile(FILE *, int command);
  
  /* Returns the file name that would be used for a pidfile if 'name' were
   * provided to set_pidfile().  The caller must free the returned string. */
  char *
  make_pidfile_name(const char *name)
  {
  #ifndef _WIN32
      return (!name
              ? xasprintf("%s/%s.pid", ovs_rundir(), program_name)
              : abs_file_name(ovs_rundir(), name));
  #else
      return (!name
          ? xasprintf("%s.pid", ovs_rundir(), program_name)
          : abs_file_name(ovs_rundir(), name));
  #endif
  }
  
  /* Sets up a following call to daemonize() to create a pidfile named 'name'.
   * If 'name' begins with '/', then it is treated as an absolute path.
   * Otherwise, it is taken relative to RUNDIR, which is $(prefix)/var/run by
   * default.
   *
   * If 'name' is null, then program_name followed by ".pid" is used. */
  void
  set_pidfile(const char *name)
  {
      free(pidfile);
      pidfile = make_pidfile_name(name);
  }
  
  /* Returns an absolute path to the configured pidfile, or a null pointer if no
   * pidfile is configured.  The caller must not modify or free the returned
   * string. */
  const char *
  get_pidfile(void)
  {
      return pidfile;
  }
  
  /* Sets that we do not chdir to "/". */
  void
  set_no_chdir(void)
  {
      chdir_ = false;
  }
  
  /* Will we chdir to "/" as part of daemonizing? */
  bool
  is_chdir_enabled(void)
  {
      return chdir_;
  }
  
  /* Normally, daemonize() or damonize_start() will terminate the program with a
   * message if a locked pidfile already exists.  If this function is called, an
   * existing pidfile will be replaced, with a warning. */
  void
  ignore_existing_pidfile(void)
  {
      overwrite_pidfile = true;
  }
  
  /* Sets up a following call to daemonize() to detach from the foreground
   * session, running this process in the background.  */
  void
  set_detach(void)
  {
      detach = true;
  }
  
  /* Will daemonize() really detach? */
  bool
  get_detach(void)
  {
      return detach;
  }
  
  /* Sets up a following call to daemonize() to fork a supervisory process to
   * monitor the daemon and restart it if it dies due to an error signal.  */
  void
  daemon_set_monitor(void)
  {
      monitor = true;
  }
  
  /* A daemon doesn't normally have any use for the file descriptors for stdin,
   * stdout, and stderr after it detaches.  To keep these file descriptors from
   * e.g. holding an SSH session open, by default detaching replaces each of
   * these file descriptors by /dev/null.  But a few daemons expect the user to
   * redirect stdout or stderr to a file, in which case it is desirable to keep
   * these file descriptors.  This function, therefore, disables replacing 'fd'
   * by /dev/null when the daemon detaches. */
  void
  daemon_save_fd(int fd)
  {
      assert(fd == STDIN_FILENO || fd == STDOUT_FILENO || fd == STDERR_FILENO);
      save_fds[fd] = true;
  }
  
  /* If a pidfile has been configured, creates it and stores the running
   * process's pid in it.  Ensures that the pidfile will be deleted when the
   * process exits. */
  static void
  make_pidfile(void)
  {
      long int pid = getpid();
      struct stat s;
      char *tmpfile;
      FILE *file;
      int error;
  
      /* Create a temporary pidfile. */
      tmpfile = xasprintf("%s.tmp%ld", pidfile, pid);
      fatal_signal_add_file_to_unlink(tmpfile);
      file = fopen(tmpfile, "w+");
      if (!file) {
          VLOG_FATAL("%s: create failed (%s)", tmpfile, strerror(errno));
      }
  
      if (fstat(fileno(file), &s) == -1) {
          VLOG_FATAL("%s: fstat failed (%s)", tmpfile, strerror(errno));
      }
  
      fprintf(file, "%ld\n", pid);
      if (fflush(file) == EOF) {
          VLOG_FATAL("%s: write failed (%s)", tmpfile, strerror(errno));
      }
  
      error = lock_pidfile(file, F_SETLK);
      if (error) {
          VLOG_FATAL("%s: fcntl(F_SETLK) failed (%s)", tmpfile, strerror(error));
      }
  
      /* Rename or link it to the correct name. */
      if (overwrite_pidfile) {
          if (rename(tmpfile, pidfile) < 0) {
              VLOG_FATAL("failed to rename \"%s\" to \"%s\" (%s)",
                         tmpfile, pidfile, strerror(errno));
          }
      } else {
          do {
              error = link(tmpfile, pidfile) == -1 ? errno : 0;
              if (error == EEXIST) {
                  check_already_running();
              }
          } while (error == EINTR || error == EEXIST);
          if (error) {
              VLOG_FATAL("failed to link \"%s\" as \"%s\" (%s)",
                         tmpfile, pidfile, strerror(error));
          }
      }
  
      /* Ensure that the pidfile will get deleted on exit. */
      fatal_signal_add_file_to_unlink(pidfile);
  
      /* Delete the temporary pidfile if it still exists. */
      if (!overwrite_pidfile) {
          error = fatal_signal_unlink_file_now(tmpfile);
          if (error) {
              VLOG_FATAL("%s: unlink failed (%s)", tmpfile, strerror(error));
          }
      }
  
      /* Clean up.
       *
       * We don't close 'file' because its file descriptor must remain open to
       * hold the lock. */
      pidfile_dev = s.st_dev;
      pidfile_ino = s.st_ino;
      free(tmpfile);
      free(pidfile);
      pidfile = NULL;
  }
  
  /* If configured with set_pidfile() or set_detach(), creates the pid file and
   * detaches from the foreground session.  */
  void
  daemonize(void)
  {
      daemonize_start();
      daemonize_complete();
  }
  
  /* Calls fork() and on success returns its return value.  On failure, logs an
   * error and exits unsuccessfully.
   *
   * Post-fork, but before returning, this function calls a few other functions
   * that are generally useful if the child isn't planning to exec a new
   * process. */
  pid_t
  fork_and_clean_up(void)
  {
      pid_t pid;
  
  #ifndef _WIN32
      pid = fork();
  #endif
      if (pid > 0) {
          /* Running in parent process. */
          fatal_signal_fork();
      } else if (!pid) {
          /* Running in child process. */
          time_postfork();
          lockfile_postfork();
      } else {
          VLOG_FATAL("fork failed (%s)", strerror(errno));
      }
  
      return pid;
  }
  
  /* Forks, then:
   *
   *   - In the parent, waits for the child to signal that it has completed its
   *     startup sequence.  Then stores -1 in '*fdp' and returns the child's pid.
   *
   *   - In the child, stores a fd in '*fdp' and returns 0.  The caller should
   *     pass the fd to fork_notify_startup() after it finishes its startup
   *     sequence.
   *
   * If something goes wrong with the fork, logs a critical error and aborts the
   * process. */
  static pid_t
  fork_and_wait_for_startup(int *fdp)
  {
      int fds[2];
      pid_t pid;
  
      xpipe(fds);
  
      pid = fork_and_clean_up();
      if (pid > 0) {
          /* Running in parent process. */
          size_t bytes_read;
          char c;
  
          close(fds[1]);
          if (read_fully(fds[0], &c, 1, &bytes_read) != 0) {
              int retval;
              int status;
  
              do {
                  retval = waitpid(pid, &status, 0);
              } while (retval == -1 && errno == EINTR);
  
              if (retval == pid) {
                  if (WIFEXITED(status) && WEXITSTATUS(status)) {
                      /* Child exited with an error.  Convey the same error
                       * to our parent process as a courtesy. */
                      exit(WEXITSTATUS(status));
                  } else {
                      char *status_msg = process_status_msg(status);
                      VLOG_FATAL("fork child died before signaling startup (%s)",
                                 status_msg);
                  }
              } else if (retval < 0) {
                  VLOG_FATAL("waitpid failed (%s)", strerror(errno));
              } else {
                  NOT_REACHED();
              }
          }
          close(fds[0]);
          *fdp = -1;
      } else if (!pid) {
          /* Running in child process. */
          close(fds[0]);
          *fdp = fds[1];
      }
  
      return pid;
  }
  
  static void
  fork_notify_startup(int fd)
  {
      if (fd != -1) {
          size_t bytes_written;
          int error;
  
          error = write_fully(fd, "", 1, &bytes_written);
          if (error) {
              VLOG_FATAL("pipe write failed (%s)", strerror(error));
          }
  
          close(fd);
      }
  }
  
  static bool
  should_restart(int status)
  {
      if (WIFSIGNALED(status)) {
          static const int error_signals[] = {
              SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV,
              SIGXCPU, SIGXFSZ
          };
  
          size_t i;
  
          for (i = 0; i < ARRAY_SIZE(error_signals); i++) {
              if (error_signals[i] == WTERMSIG(status)) {
                  return true;
              }
          }
      }
      return false;
  }
  
  static void
  monitor_daemon(pid_t daemon_pid)
  {
      /* XXX Should log daemon's stderr output at startup time. */
      time_t last_restart;
      char *status_msg;
      int crashes;
  
      subprogram_name = "monitor";
      status_msg = xstrdup("healthy");
      last_restart = TIME_MIN;
      crashes = 0;
      for (;;) {
          int retval;
          int status;
  
          proctitle_set("monitoring pid %lu (%s)",
                        (unsigned long int) daemon_pid, status_msg);
  
          do {
              retval = waitpid(daemon_pid, &status, 0);
          } while (retval == -1 && errno == EINTR);
  
          if (retval == -1) {
              VLOG_FATAL("waitpid failed (%s)", strerror(errno));
          } else if (retval == daemon_pid) {
              char *s = process_status_msg(status);
              if (should_restart(status)) {
                  free(status_msg);
                  status_msg = xasprintf("%d crashes: pid %lu died, %s",
                                         ++crashes,
                                         (unsigned long int) daemon_pid, s);
                  free(s);
  
                  if (WCOREDUMP(status)) {
                      /* Disable further core dumps to save disk space. */
                      struct rlimit r;
  
                      r.rlim_cur = 0;
                      r.rlim_max = 0;
  #ifndef _WIN32
                      if (setrlimit(RLIMIT_CORE, &r) == -1) {
                          VLOG_WARN("failed to disable core dumps: %s",
                                    strerror(errno));
                      }
  #endif
                  }
  
                  /* Throttle restarts to no more than once every 10 seconds. */
                  if (time(NULL) < last_restart + 10) {
                      VLOG_WARN("%s, waiting until 10 seconds since last "
                                "restart", status_msg);
                      for (;;) {
                          time_t now = time(NULL);
                          time_t wakeup = last_restart + 10;
                          if (now >= wakeup) {
                              break;
                          }
                          sleep(wakeup - now);
                      }
                  }
                  last_restart = time(NULL);
  
                  VLOG_ERR("%s, restarting", status_msg);
                  daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
                  if (!daemon_pid) {
                      break;
                  }
              } else {
                  VLOG_INFO("pid %lu died, %s, exiting",
                            (unsigned long int) daemon_pid, s);
                  free(s);
                  exit(0);
              }
          }
      }
      free(status_msg);
  
      /* Running in new daemon process. */
      proctitle_restore();
      subprogram_name = "";
  }
  
  /* Close standard file descriptors (except any that the client has requested we
   * leave open by calling daemon_save_fd()).  If we're started from e.g. an SSH
   * session, then this keeps us from holding that session open artificially. */
  static void
  close_standard_fds(void)
  {
      int null_fd = get_null_fd();
      if (null_fd >= 0) {
          int fd;
  
          for (fd = 0; fd < 3; fd++) {
              if (!save_fds[fd]) {
                  dup2(null_fd, fd);
              }
          }
      }
  
      /* Disable logging to stderr to avoid wasting CPU time. */
      vlog_set_levels(NULL, VLF_CONSOLE, VLL_OFF);
  }
  
  /* If daemonization is configured, then starts daemonization, by forking and
   * returning in the child process.  The parent process hangs around until the
   * child lets it know either that it completed startup successfully (by calling
   * daemon_complete()) or that it failed to start up (by exiting with a nonzero
   * exit code). */
  void
  daemonize_start(void)
  {
      daemonize_fd = -1;
      
      if (detach) {
          if (fork_and_wait_for_startup(&daemonize_fd) > 0) {
              /* Running in parent process. */
              exit(0);
          }
  
          /* Running in daemon or monitor process. */
  #ifndef _WIN32
          setsid();
  #endif
      }
  
      if (monitor) {
          int saved_daemonize_fd = daemonize_fd;
          pid_t daemon_pid;
  
          daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
          if (daemon_pid > 0) {
              /* Running in monitor process. */
              fork_notify_startup(saved_daemonize_fd);
              close_standard_fds();
              monitor_daemon(daemon_pid);
          }
          /* Running in daemon process. */
      }
  
      if (pidfile) {
          make_pidfile();
      }
  
      /* Make sure that the unixctl commands for vlog get registered in a
       * daemon, even before the first log message. */
      vlog_init();
  }
  
  /* If daemonization is configured, then this function notifies the parent
   * process that the child process has completed startup successfully.  It also
   * call daemonize_post_detach().
   *
   * Calling this function more than once has no additional effect. */
  void
  daemonize_complete(void)
  {
      if (!detached) {
          detached = true;
  
          fork_notify_startup(daemonize_fd);
          daemonize_fd = -1;
          daemonize_post_detach();
      }
  }
  
  /* If daemonization is configured, then this function does traditional Unix
   * daemonization behavior: join a new session, chdir to the root (if not
   * disabled), and close the standard file descriptors.
   *
   * It only makes sense to call this function as part of an implementation of a
   * special daemon subprocess.  A normal daemon should just call
   * daemonize_complete(). */
  void
  daemonize_post_detach(void)
  {
      if (detach) {
          if (chdir_) {
  #ifndef _WIN32
              ignore(chdir("/"));
  #endif
          }
          close_standard_fds();
      }
  }
  
  void
  daemon_usage(void)
  {
      printf(
          "\nDaemon options:\n"
          "  --detach                run in background as daemon\n"
          "  --no-chdir              do not chdir to '/'\n"
          "  --pidfile[=FILE]        create pidfile (default: %s/%s.pid)\n"
          "  --overwrite-pidfile     with --pidfile, start even if already "
                                     "running\n",
          ovs_rundir(), program_name);
  }
  
  static int
  lock_pidfile__(FILE *file, int command, struct flock *lck)
  {
      int error;
  
      lck->l_type = F_WRLCK;
      lck->l_whence = SEEK_SET;
      lck->l_start = 0;
      lck->l_len = 0;
      lck->l_pid = 0;
  
      do {
          error = fcntl(fileno(file), command, lck) == -1 ? errno : 0;
      } while (error == EINTR); 
      return error;
  }
  
  static int
  lock_pidfile(FILE *file, int command)
  {
      struct flock lck;
  
      return lock_pidfile__(file, command, &lck);
  }
  
  static pid_t
  read_pidfile__(const char *pidfile, bool delete_if_stale)
  {
      struct stat s, s2;
      struct flock lck;
      char line[128];
      FILE *file;
      int error;
  
      if ((pidfile_ino || pidfile_dev)
          && !stat(pidfile, &s)
          && s.st_ino == pidfile_ino && s.st_dev == pidfile_dev) {
          /* It's our own pidfile.  We can't afford to open it, because closing
           * *any* fd for a file that a process has locked also releases all the
           * locks on that file.
           *
           * Fortunately, we know the associated pid anyhow: */
          return getpid();
      }
  
      file = fopen(pidfile, "r+");
      if (!file) {
          if (errno == ENOENT && delete_if_stale) {
              return 0;
          }
          error = errno;
          VLOG_WARN("%s: open: %s", pidfile, strerror(error));
          goto error;
      }
  
      error = lock_pidfile__(file, F_GETLK, &lck);
      if (error) {
          VLOG_WARN("%s: fcntl: %s", pidfile, strerror(error));
          goto error;
      }
      if (lck.l_type == F_UNLCK) {
          /* pidfile exists but it isn't locked by anyone.  We need to delete it
           * so that a new pidfile can go in its place.  But just calling
           * unlink(pidfile) makes a nasty race: what if someone else unlinks it
           * before we do and then replaces it by a valid pidfile?  We'd unlink
           * their valid pidfile.  We do a little dance to avoid the race, by
           * locking the invalid pidfile.  Only one process can have the invalid
           * pidfile locked, and only that process has the right to unlink it. */
          if (!delete_if_stale) {
              error = ESRCH;
              VLOG_DBG("%s: pid file is stale", pidfile);
              goto error;
          }
  
          /* Get the lock. */
          error = lock_pidfile(file, F_SETLK);
          if (error) {
              /* We lost a race with someone else doing the same thing. */
              VLOG_WARN("%s: lost race to lock pidfile", pidfile);
              goto error;
          }
  
          /* Is the file we have locked still named 'pidfile'? */
          if (stat(pidfile, &s) || fstat(fileno(file), &s2)
              || s.st_ino != s2.st_ino || s.st_dev != s2.st_dev) {
              /* No.  We lost a race with someone else who got the lock before
               * us, deleted the pidfile, and closed it (releasing the lock). */
              error = EALREADY;
              VLOG_WARN("%s: lost race to delete pidfile", pidfile);
              goto error;
          }
  
          /* We won the right to delete the stale pidfile. */
          if (unlink(pidfile)) {
              error = errno;
              VLOG_WARN("%s: failed to delete stale pidfile (%s)",
                        pidfile, strerror(error));
              goto error;
          }
          VLOG_DBG("%s: deleted stale pidfile", pidfile);
          fclose(file);
          return 0;
      }
  
      if (!fgets(line, sizeof line, file)) {
          if (ferror(file)) {
              error = errno;
              VLOG_WARN("%s: read: %s", pidfile, strerror(error));
          } else {
              error = ESRCH;
              VLOG_WARN("%s: read: unexpected end of file", pidfile);
          }
          goto error;
      }
  
      if (lck.l_pid != strtoul(line, NULL, 10)) {
          /* The process that has the pidfile locked is not the process that
           * created it.  It must be stale, with the process that has it locked
           * preparing to delete it. */
          error = ESRCH;
          VLOG_WARN("%s: stale pidfile for pid %s being deleted by pid %ld",
                    pidfile, line, (long int) lck.l_pid);
          goto error;
      }
  
      fclose(file);
      return lck.l_pid;
  
  error:
      if (file) {
          fclose(file);
      }
      return -error;
  }
  
  /* Opens and reads a PID from 'pidfile'.  Returns the positive PID if
   * successful, otherwise a negative errno value. */
  pid_t
  read_pidfile(const char *pidfile)
  {
      return read_pidfile__(pidfile, false);
  }
  
  /* Checks whether a process with the given 'pidfile' is already running and,
   * if so, aborts.  If 'pidfile' is stale, deletes it. */
  static void
  check_already_running(void)
  {
      long int pid = read_pidfile__(pidfile, true);
      if (pid > 0) {
          VLOG_FATAL("%s: already running as pid %ld, aborting", pidfile, pid);
      } else if (pid < 0) {
          VLOG_FATAL("%s: pidfile check failed (%s), aborting",
                     pidfile, strerror(-pid));
      }
  }
  