mdmon: fork and run as a daemon.

start_mdmon now waits for mdmon to complete initialisation and,
importantly, listen on the socket, before continuing.

Signed-off-by: Neil Brown <neilb@suse.de>

mdmon.c

@@ -32,6 +32,7 @@
 #include	<sys/un.h>
 #include	<sys/mman.h>
 #include	<sys/syscall.h>
+#include	<sys/wait.h>
 #include	<stdio.h>
 #include	<errno.h>
 #include	<string.h>
@@ -175,6 +176,8 @@ int main(int argc, char *argv[])
 	struct supertype *container;
 	sigset_t set;
 	struct sigaction act;
+	int pfd[2];
+	int status;
 
 	if (argc != 2) {
 		fprintf(stderr, "Usage: md-manage /device/name/for/container\n");
@@ -192,6 +195,24 @@ int main(int argc, char *argv[])
 		exit(1);
 	}
 
+	/* Fork, and have the child tell us when they are ready */
+	pipe(pfd);
+	switch(fork()){
+	case -1:
+		fprintf(stderr, "mdmon: failed to fork: %s\n",
+			strerror(errno));
+		exit(1);
+	case 0: /* child */
+		close(pfd[0]);
+		break;
+	default: /* parent */
+		close(pfd[1]);
+		if (read(pfd[0], &status, sizeof(status)) != sizeof(status)) {
+			wait(&status);
+			status = WEXITSTATUS(status);
+		}
+		exit(status);
+	}
 	/* hopefully it is a container - we'll check later */
 
 	container = malloc(sizeof(*container));
@@ -268,6 +289,23 @@ int main(int argc, char *argv[])
 		exit(3);
 	}
 
+	/* Ok, this is close enough.  We can say goodbye to our parent now.
+	 */
+	status = 0;
+	write(pfd[1], &status, sizeof(status));
+	close(pfd[1]);
+
+	chdir("/");
+	setsid();
+	close(0);
+	open("/dev/null", O_RDWR);
+	close(1);
+	dup(0);
+#ifndef DEBUG
+	close(2);
+	dup(0);
+#endif
+
 	mlockall(MCL_FUTURE);
 
 	/* SIGUSR is sent between parent and child.  So both block it

util.c

@@ -31,6 +31,7 @@
 #include	"md_p.h"
 #include	<sys/socket.h>
 #include	<sys/utsname.h>
+#include	<sys/wait.h>
 #include	<sys/un.h>
 #include	<ctype.h>
 #include	<dirent.h>
@@ -1078,6 +1079,8 @@ int start_mdmon(int devnum)
 {
 	int i;
 	int len;
+	pid_t pid;	
+	int status;
 	char pathbuf[1024];
 	char *paths[4] = {
 		pathbuf,
@@ -1117,7 +1120,10 @@ int start_mdmon(int devnum)
 	case -1: fprintf(stderr, Name ": cannot run mdmon. "
 			 "Array remains readonly\n");
 		return -1;
-	default: ; /* parent - good */
+	default: /* parent - good */
+		pid = wait(&status);
+		if (pid < 0 || status != 0)
+			return -1;
 	}
 	return 0;
 }