sin: add daemon mode for forked processes

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Iefbc9a8ac320f6a8898dc4b00cdb08316a6a6964

main.c

@@ -45,6 +45,7 @@ static const char *valid_mode[] = {"block", "delay", NULL};
 static volatile sig_atomic_t running = 1;
 static volatile sig_atomic_t cleanup_requested = 0;
 static int quiet = 0;
+static int daemonize = 0;
 
 static void handle_sig(int sig) {
   (void)sig;
@@ -347,7 +348,7 @@ static void usage(FILE *f, const char *prog) {
   fprintf(f,
           "Usage: %s -n <pattern> [-n <pattern> ...] "
           "[--what=WHAT] [--mode=MODE]\n"
-          "       [--who=WHO] [--why=WHY] [--poll=SECONDS] [-q]\n"
+          "       [--who=WHO] [--why=WHY] [--poll=SECONDS] [-d] [-q]\n"
           "\n"
           "Options:\n"
           "  -n, --name PATTERN    Process command-line substring to watch "
@@ -365,6 +366,7 @@ static void usage(FILE *f, const char *prog) {
           "system idle...)\n"
           "  --poll SECONDS        Poll interval in seconds (%.1f-%.1f, "
           "default: %.1f)\n"
+          "  -d, --daemon          Run as daemon (fork to background)\n"
           "  -q, --quiet           Suppress informational output\n"
           "  -h, --help            Show this help\n"
           "  -v, --version         Show version\n",
@@ -394,6 +396,63 @@ static void *safe_realloc(void *ptr, size_t new_size) {
   return new_ptr;
 }
 
+// Daemonize the process
+static int do_daemonize(void) {
+  pid_t pid = fork();
+  if (pid < 0) {
+    fprintf(stderr, "fork failed: %s\n", strerror(errno));
+    return -1;
+  }
+
+  if (pid > 0) {
+    // Parent exits
+    exit(EXIT_OK);
+  }
+
+  // Child continues
+  if (setsid() < 0) {
+    fprintf(stderr, "setsid failed: %s\n", strerror(errno));
+    return -1;
+  }
+
+  // Ignore SIGHUP
+  signal(SIGHUP, SIG_IGN);
+
+  // Fork again to ensure we're not a session leader
+  pid = fork();
+  if (pid < 0) {
+    fprintf(stderr, "second fork failed: %s\n", strerror(errno));
+    return -1;
+  }
+
+  if (pid > 0) {
+    // First child exits
+    exit(EXIT_OK);
+  }
+
+  // Change to root directory
+  if (chdir("/") < 0) {
+    fprintf(stderr, "chdir failed: %s\n", strerror(errno));
+    return -1;
+  }
+
+  close(STDIN_FILENO);
+  close(STDOUT_FILENO);
+  close(STDERR_FILENO);
+
+  int fd = open("/dev/null", O_RDWR);
+  if (fd >= 0) {
+    dup2(fd, STDIN_FILENO);
+    dup2(fd, STDOUT_FILENO);
+    dup2(fd, STDERR_FILENO);
+    if (fd > STDERR_FILENO) {
+      close(fd);
+    }
+  }
+
+  return 0;
+}
+
 int main(int argc, char **argv) {
   double poll = DEFAULT_POLL_INTERVAL;
   const char *what = "idle";
@@ -497,6 +556,9 @@ int main(int argc, char **argv) {
     } else if (strcmp(argv[i], "--quiet") == 0 || strcmp(argv[i], "-q") == 0) {
       quiet = 1;
 
+    } else if (strcmp(argv[i], "--daemon") == 0 || strcmp(argv[i], "-d") == 0) {
+      daemonize = 1;
+
     } else if (argv[i][0] == '-' && argv[i][1] == 'n' && argv[i][2] != '\0') {
       // Support "-npattern" form
       if (npats >= MAX_PATTERNS) {
@@ -550,6 +612,15 @@ int main(int argc, char **argv) {
             strerror(errno));
   }
 
+  // Daemonize before initializing inhibitor (must happen before D-Bus
+  // connection)
+  if (daemonize) {
+    if (do_daemonize() < 0) {
+      free(patterns);
+      return EXIT_INIT;
+    }
+  }
+
   struct Inhibitor inh;
   if (inhibitor_init(&inh, what, who, why, mode) < 0) {
     free(patterns);