src/common/daemonize.c

   1 /*
   2  * Copyright (C) 2013 - David Goulet <dgoulet@efficios.com>
   3  * Copyright (C) 2014 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License, version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
  12  * more details.
  13  *
  14  * You should have received a copy of the GNU General Public License along with
  15  * this program; if not, write to the Free Software Foundation, Inc., 51
  16  * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  17  */
  18
  19 #define _LGPL_SOURCE
  20 #include <unistd.h>
  21 #include <common/compat/paths.h>
  22 #include <fcntl.h>
  23 #include <wait.h>
  24 #include <stdlib.h>
  25
  26 #include <urcu/system.h>
  27
  28 #include <src/common/daemonize.h>
  29 #include <src/common/error.h>
  30
  31 LTTNG_HIDDEN
  32 int lttng_daemonize(pid_t *child_ppid, int *completion_flag,
  33                 int close_fds)
  34 {
  35         int ret;
  36         pid_t pid;
  37
  38         /* Get parent pid of this process. */
  39         *child_ppid = getppid();
  40
  41         pid = fork();
  42         if (pid < 0) {
  43                 PERROR("fork");
  44                 goto error;
  45         } else if (pid == 0) {
  46                 int fd;
  47                 pid_t sid;
  48
  49                 /* Child */
  50
  51                 /*
  52                  * Get the newly created parent pid so we can signal
  53                  * that process when we are ready to operate.
  54                  */
  55                 *child_ppid = getppid();
  56
  57                 sid = setsid();
  58                 if (sid < 0) {
  59                         PERROR("setsid");
  60                         goto error;
  61                 }
  62
  63                 /*
  64                  * Try to change directory to /. If we can't well at
  65                  * least notify.
  66                  */
  67                 ret = chdir("/");
  68                 if (ret < 0) {
  69                         PERROR("chdir");
  70                 }
  71
  72                 if (close_fds) {
  73                         fd = open(_PATH_DEVNULL, O_RDWR, 0);
  74                         if (fd < 0) {
  75                                 PERROR("open %s", _PATH_DEVNULL);
  76                                 /*
  77                                  * Let 0, 1 and 2 open since we can't
  78                                  * bind them to /dev/null.
  79                                  */
  80                         } else {
  81                                 (void) dup2(fd, STDIN_FILENO);
  82                                 (void) dup2(fd, STDOUT_FILENO);
  83                                 (void) dup2(fd, STDERR_FILENO);
  84                                 if (fd > 2) {
  85                                         ret = close(fd);
  86                                         if (ret < 0) {
  87                                                 PERROR("close");
  88                                         }
  89                                 }
  90                         }
  91                 }
  92                 goto end;
  93         } else {
  94                 /* Parent */
  95
  96                 /*
  97                  * Waiting for child to notify this parent that it can
  98                  * exit. Note that sleep() is interrupted before the 1
  99                  * second delay as soon as the signal is received, so it
 100                  * will not cause visible delay for the user.
 101                  */
 102                 while (!CMM_LOAD_SHARED(*completion_flag)) {
 103                         int status;
 104                         pid_t ret;
 105
 106                         /*
 107                          * Check if child exists without blocking. If
 108                          * so, we have to stop this parent process and
 109                          * return an error.
 110                          */
 111                         ret = waitpid(pid, &status, WNOHANG);
 112                         if (ret < 0 || (ret != 0 && WIFEXITED(status))) {
 113                                 /* The child exited somehow or was not valid. */
 114                                 goto error;
 115                         }
 116                         sleep(1);
 117                 }
 118
 119                 /*
 120                  * From this point on, the parent can exit and the child
 121                  * is now an operationnal session daemon ready to serve
 122                  * clients and applications.
 123                  */
 124                 exit(EXIT_SUCCESS);
 125         }
 126
 127 end:
 128         return 0;
 129
 130 error:
 131         return -1;
 132 }