restore '-d' (daemonise) flag

common.h

@@ -24,6 +24,7 @@ typedef struct {
     char *output_name;
     audio_output *output;
     int buffer_start_fill;
+    int daemonise;
 } shairport_cfg;
 
 extern int debuglev;

rtsp.c

@@ -758,6 +758,14 @@ void rtsp_listen_loop(void) {
 
     mdns_register();
 
+    if (config.daemonise) {
+        pid_t pid = fork();
+        if (pid) {
+            printf("%d\n", pid);
+            exit(0);
+        }
+    }
+
     printf("Listening for connections.\n");
 
     int acceptfd;

shairport.c

@@ -59,6 +59,8 @@ void usage(char *progname) {
            "    -o output   set audio output\n"
            "    -b fill     set how full the buffer must be before audio output starts\n"
            "                    This value is in frames; default %d\n"
+           "    -d          fork (daemonise)\n"
+           "                    The PID of the child process is written to stdout\n"
            "Run %s -o <output> -h to find the available options for a specific output\n"
            "\n", config.buffer_start_fill, progname);
 
@@ -74,13 +76,16 @@ void usage(char *progname) {
 
 int parse_options(int argc, char **argv) {
     int opt;
-    while ((opt = getopt(argc, argv, "+hvp:a:o:b:")) > 0) {
+    while ((opt = getopt(argc, argv, "+hdvp:a:o:b:")) > 0) {
         switch (opt) {
             default:
                 printf("Unknown argument -%c\n", optopt);
             case 'h':
                 usage(argv[0]);
                 exit(1);
+            case 'd':
+                config.daemonise = 1;
+                break;
             case 'v':
                 debuglev++;
                 break;