Add daemonising routines

src/daemonitor/000_TopSource.c

@@ -11,6 +11,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <dirent.h>
 #include <getopt.h>
 #include <limits.h>
 #include <signal.h>

src/daemonitor/103_daemon.c

@@ -0,0 +1,158 @@
+/* daemonitor/src/daemonitor/103_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).");
+        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
+*/