[dm-devel] improved daemon setup

[Benjamin Marzinski]

If you log into a machine and start the multipathd daemon, you will hang on
logout, because multipathd doesn't fully detach itself from the calling
processes. Also, occasionally the device mapper library functions will print
error messages to stdout.  These appear in the terminal that was used to
start multipathd, if it was started by hand (not by init scripts).  To fix these
I added some code to fully daemonize multipathd, and redirect stdout and
stderr to /dev/console.
-------------- next part --------------
diff -urpN a/multipathd/main.c b/multipathd/main.c
--- a/multipathd/main.c	2005-11-07 12:13:07.000000000 -0600
+++ b/multipathd/main.c	2005-11-09 14:52:36.000000000 -0600
@@ -3,6 +3,9 @@
 #include <libdevmapper.h>
 #include <wait.h>
 #include <sys/mman.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <errno.h>
 
 /*
  * libsysfs
@@ -1559,6 +1562,53 @@ child (void * param)
 	exit(0);
 }
 
+static int
+daemonize(void)
+{
+	int pid, i;
+	int in_fd, out_fd;
+
+	if( (pid = fork()) < 0){
+		fprintf(stderr, "Failed first fork : %s\n", strerror(errno));
+		return -1;
+	}
+	else if (pid != 0)
+		return pid;
+
+	setsid();
+
+	if ( (pid = fork()) < 0)
+		fprintf(stderr, "Failed second fork : %s\n", strerror(errno));
+	else if (pid != 0)
+		_exit(0);
+
+	in_fd = open("/dev/null", O_RDONLY);
+	if (in_fd < 0){
+		fprintf(stderr, "cannot open /dev/null for input : %s\n",
+			strerror(errno));
+		_exit(0);
+	}
+	out_fd = open("/dev/console", O_WRONLY);
+	if (out_fd < 0){
+		fprintf(stderr, "cannot open /dev/console for output : %s\n",
+			strerror(errno));
+		_exit(0);
+	}
+
+	close(STDIN_FILENO);
+	dup(in_fd);
+	close(STDOUT_FILENO);
+	dup(out_fd);
+	close(STDERR_FILENO);
+	dup(out_fd);
+
+	close(in_fd);
+	close(out_fd);
+	chdir("/");
+	umask(0);
+	return 0;
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -1607,7 +1657,7 @@ main (int argc, char *argv[])
 	if (!logsink)
 		err = 0;
 	else
-		err = fork();
+		err = daemonize();
 	
 	if (err < 0)
 		/* error */