Simplify daemon and always close file descriptors

Use daemon(3) to daemonise rather than writing our own code. Since we
use the mode of daemon(3) which closes the standard 3 file descriptors,
if the user requests logging to one of those we dup(2) the original
first. We must also take care to always close any newly-opened file
descriptors before execve(2) of the child.

src/daemonitor/200_log.c

@@ -1,8 +1,8 @@
 /* daemonitor/src/daemonitor/200_log.c
  *
- *  (c)2007, Laurence Withers, <l@lwithers.me.uk>.
+ *  Copyright: ©2007–2012, Laurence Withers.
- *  Released under the GNU GPLv3. See file COPYING or
+ *  Author: Laurence Withers <l@lwithers.me.uk>
- *  http://www.gnu.org/copyleft/gpl.html for details.
+ *  License: GPLv3
  */
 
 
@@ -170,16 +170,25 @@ void log_func_syslog(int level, const char* fmt, ...)
 /* log_destination_set()
  *  Set `log_func' function pointer.
  */
-void log_destination_set(enum log_destination_t dest)
+void
+log_destination_set(enum log_destination_t dest)
 {
     switch(dest) {
     case log_destination_stdout:
-        log_func_fd = STDOUT_FILENO;
+        log_func_fd = dup(STDOUT_FILENO);
+        if(log_func_fd == -1) {
+            printf("dup() failed: %m.");
+            exit(1);
+        }
         log_func = log_func_file;
         break;
 
     case log_destination_stderr:
-        log_func_fd = STDERR_FILENO;
+        log_func_fd = dup(STDERR_FILENO);
+        if(log_func_fd == -1) {
+            fprintf(stderr, "dup() failed: %m.");
+            exit(1);
+        }
         log_func = log_func_file;
         break;
 
@@ -210,6 +219,5 @@ int log_destination_set_file(const char* filename)
 
 
 /* options for text editors
-kate: replace-trailing-space-save true; space-indent true; tab-width 4;
 vim: expandtab:ts=4:sw=4
 */

src/daemonitor/400_daemon.c

@@ -1,160 +0,0 @@
-/* daemonitor/src/daemonitor/400_daemon.c
- *
- *  (c)2007, Laurence Withers, <l@lwithers.me.uk>.
- *  Released under the GNU GPLv3. See file COPYING or
- *  http://www.gnu.org/copyleft/gpl.html for details.
-*/
-
-
-
-/* DAEMON ROUTINES ********************************************************************************
- *
- *  This file provides the daemonise() routine, which makes the process a daemon (fork() + setsid()
- *  so that the process lives in the background, also opens /dev/console). It also provides the
- *  close_file_descriptors() routine, which clears all file descriptors but 0, 1 and 2.
- */
-
-
-
-/* PUBLIC API ************************************************************************************/
-
-
-
-/* daemonise()
- *  Performs a fork() and setsid() so that the process lives in the background. It closes stdin,
- *  stdout and stderr and opens /dev/null and/or /dev/console instead, as appropriate. On error,
- *  this function exits the program.
- */
-void daemonise(void);
-
-
-
-/* close_file_descriptors()
- *  Closes all file descriptors but stdin, stdout and stderr. Should be called whether we are
- *  daemonising or not.
- */
-void close_file_descriptors(void);
-
-
-
-/* IMPLEMENTATION ********************************************************************************/
-
-
-
-void daemonise(void)
-{
-    int fd;
-    pid_t pid;
-
-    /* close stdin and reopen it as /dev/null */
-    TEMP_FAILURE_RETRY( close(STDIN_FILENO) );
-    fd = open("/dev/null", O_RDONLY);
-    switch(fd) {
-    case -1:
-        LOG(LOG_CRIT, "Could not open `/dev/null' (%m).");
-        exit(1);
-
-    case STDIN_FILENO:
-        break;
-
-    default:
-        LOG(LOG_CRIT, "Opened `/dev/null' for stdin, but got file descriptor %d instead.", fd);
-        exit(1);
-    }
-
-    /* close stdout and reopen it as /dev/console if possible, or /dev/null if not */
-    TEMP_FAILURE_RETRY( close(STDOUT_FILENO) );
-    fd = open("/dev/console", O_WRONLY | O_NOCTTY);
-    if(fd == -1) {
-        LOG(LOG_WARNING, "Could not open `/dev/console' for stdout (%m).");
-        fd = open("/dev/null", O_WRONLY);
-    }
-    switch(fd) {
-    case -1:
-        LOG(LOG_CRIT, "Could not open `/dev/null' (%m).");
-        exit(1);
-
-    case STDOUT_FILENO:
-        break;
-
-    default:
-        LOG(LOG_CRIT, "Opened `/dev/null' for stdout, but got file descriptor %d instead.", fd);
-        exit(1);
-    }
-
-    /* close stderr and reopen it as /dev/console if possible, or /dev/null if not */
-    TEMP_FAILURE_RETRY( close(STDERR_FILENO) );
-    fd = open("/dev/console", O_WRONLY | O_NOCTTY);
-    if(fd == -1) {
-        LOG(LOG_WARNING, "Could not open `/dev/console' for stderr (%m).");
-        /* force fd closed again, in case glibc kindly connected it to syslog for us */
-        TEMP_FAILURE_RETRY( close(STDERR_FILENO) );
-        fd = open("/dev/null", O_WRONLY);
-    }
-    switch(fd) {
-    case -1:
-        LOG(LOG_CRIT, "Could not open `/dev/null' (%m).");
-        exit(1);
-
-    case STDERR_FILENO:
-        break;
-
-    default:
-        LOG(LOG_CRIT, "Opened `/dev/null' for stderr, but got file descriptor %d instead.", fd);
-        exit(1);
-    }
-
-    /* daemonise */
-    pid = fork();
-    if(pid == (pid_t)-1) {
-        LOG(LOG_CRIT, "Could not fork daemonised process (%m).");
-        exit(1);
-    }
-
-    if(pid) {
-        /* parent */
-        _exit(0); /* don't call atexit() et al. in parent */
-    }
-
-    
-    setsid();
-    LOG(LOG_NOTICE, "Daemonised, PID %lu.", (unsigned long)getpid());
-}
-
-
-
-/* close_file_descriptors()
- *  Adapted from libgslutil (GPL-3).
- */
-void close_file_descriptors(void)
-{
-    DIR* d;
-    struct dirent* de;
-    int i, end, dfd;
-
-    d = opendir("/proc/self/fd");
-    if(!d) {
-        /* backup method */
-        for(i = STDERR_FILENO + 1, end = getdtablesize(); i < end; ++i) {
-            close(i);
-        }
-        return;
-    }
-    dfd = dirfd(d);
-
-    while( (de = readdir(d)) ) {
-        if(de->d_name[0] == '.') continue;
-        i = strtol(de->d_name, 0, 10);
-        if(i == dfd) continue; /* skip file descriptor associated with `DIR* d' */
-        if(i <= STDERR_FILENO) continue; /* leave stdin, stdout, stderr alone */
-        TEMP_FAILURE_RETRY( close(i) );
-    }
-    closedir(d);
-}
-
-
-
-/* options for text editors
-kate: replace-trailing-space-save true; space-indent true; tab-width 4;
-vim: expandtab:ts=4:sw=4
-*/

src/daemonitor/600_run_program.c

@@ -1,8 +1,8 @@
 /* daemonitor/src/daemonitor/600_run_program.c
  *
- *  (c)2007, Laurence Withers, <l@lwithers.me.uk>.
+ *  Copyright: ©2007–2012, Laurence Withers.
- *  Released under the GNU GPLv3. See file COPYING or
+ *  Author: Laurence Withers <l@lwithers.me.uk>
- *  http://www.gnu.org/copyleft/gpl.html for details.
+ *  License: GPLv3
  */
 
 
@@ -45,8 +45,8 @@ volatile int sigterm_received = 0;
 
 
 /* close_file_descriptors()
- *  Closes all file descriptors but stdin, stdout and stderr. Should be called whether we are
+ *  Closes all file descriptors but stdin, stdout and stderr (which it leaves
- *  daemonising or not.
+ *  unchanged).
  */
 void close_file_descriptors(void);
 
@@ -56,6 +56,38 @@ void close_file_descriptors(void);
 
 
 
+/* close_file_descriptors()
+ *  Adapted from libgslutil (GPL-3).
+ */
+void
+close_file_descriptors(void)
+{
+    DIR* d;
+    struct dirent* de;
+    int i, end, dfd;
+
+    d = opendir("/proc/self/fd");
+    if(!d) {
+        /* backup method */
+        for(i = STDERR_FILENO + 1, end = getdtablesize(); i < end; ++i) {
+            close(i);
+        }
+        return;
+    }
+    dfd = dirfd(d);
+
+    while( (de = readdir(d)) ) {
+        if(de->d_name[0] == '.') continue;
+        i = strtol(de->d_name, 0, 10);
+        if(i == dfd) continue; /* skip file descriptor associated with `DIR* d' */
+        if(i <= STDERR_FILENO) continue; /* leave stdin, stdout, stderr alone */
+        TEMP_FAILURE_RETRY( close(i) );
+    }
+    closedir(d);
+}
+
+
+
 /* crash()
  *  Crash the program. This is better than just calling exit() because it doesn't clean up. We
  *  should leave our PID file lying around to look like we crashed. This function is paranoid.
@@ -113,6 +145,8 @@ void run_program(const char* exe_path, char** argv)
 
     /* child -- execute new process */
     if(pid == 0) {
+        close_file_descriptors();
+
         /* clear the child's signal mask */
         sigemptyset(&ss);
         sigprocmask(SIG_SETMASK, &ss, 0);
@@ -203,6 +237,5 @@ void run_program(const char* exe_path, char** argv)
 
 
 /* options for text editors
-kate: replace-trailing-space-save true; space-indent true; tab-width 4;
 vim: expandtab:ts=4:sw=4
 */

src/daemonitor/999_main.c

@@ -79,7 +79,7 @@ int main(int argc, char* argv[])
 {
     char* endp;
     const char* log_argument = 0, * pidfile_argument = 0, * restart_argument = 0;
-    int daemon = 0, restart_interval = DEFAULT_RESTART_INTERVAL;
+    int do_daemon = 0, restart_interval = DEFAULT_RESTART_INTERVAL;
 
     /* safety */
     close_file_descriptors(); /* leaves stdout etc. open */
@@ -91,7 +91,7 @@ int main(int argc, char* argv[])
         case '?': LOG_ANYWHERE("Invalid commandline options."); return 1;
         case 'h': usage(); return 1;
         case 'V': fputs("daemonitor " VERSION "\n", stderr); return 1;
-        case 'd': ++daemon; break;
+        case 'd': ++do_daemon; break;
         case 'l': log_argument = optarg; break;
         case 'p': pidfile_argument = optarg; break;
         case 'R': restart_argument = optarg; break;
@@ -136,7 +136,12 @@ int main(int argc, char* argv[])
     if(load_child_environ()) return 1;
 
     /* daemonise? */
-    if(daemon) daemonise();
+    if(do_daemon) {
+        if(daemon(0, 0)) {
+            LOG(LOG_CRIT, "daemon() failed: %m.");
+            return 1;
+        }
+    }
 
     /* write a PID file */
     if(pidfile_argument) {