mdmon: remove switch-root functionality.

Using switch-root and then creating files in /var/run once
that location is writable is racing as most distro clean out
/var/run shortly after it is mounted.
This can cause the .pid and .sock files to be deleted shortly
after they are created.

This option doesn't seem to be used at all any, and the alternative
of communicating the pid etc in some preserved directory and then
restarting mdmon once all is settled seems simpler.

So remove the code for supporting switchroot and update man page
accordingly.

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

mdmon.8

@@ -5,7 +5,7 @@ mdmon \- monitor MD external metadata arrays
 
 .SH SYNOPSIS
 
-.BI mdmon " CONTAINER [NEWROOT | PID]"
+.BI mdmon " [--all] [--takeover] CONTAINER"
 
 .SH OVERVIEW
 The 2.6.27 kernel brings the ability to support external metadata arrays.
@@ -128,66 +128,35 @@ device>/<member index>" if the array is to remain readonly.
 CONTAINER
 The
 .B container
-device to monitor.  It can be a full path like /dev/md/container, a simple md
+device to monitor.  It can be a full path like /dev/md/container, or a
-device name like md127, or
+simple md device name like md127.
-.I \-\-all
- which tells
-.I mdmon
-to scan for containers and launch an
-.I mdmon
-instance for each one found.
 .TP
-[NEWROOT]
+.B \-\-takeover
-In order to support an external metadata raid array as the rootfs
+This instructs
 .I mdmon
-needs to be started in the initramfs environment.  Once the initramfs
+to replace any active
-environment mounts the final rootfs
 .I mdmon
-needs to be restarted in the new namespace.  When NEWROOT is specified
+which is currently monitoring the array.  This is primarily used late
+in the boot process to replace any
 .I mdmon
-will terminate any
+which was started from an
+.B initramfs
+before the root filesystem was mounted.  This avoids holding a
+reference on that
+.B initramfs
+indefinitely and ensures that the
+.I pid
+and
+.I sock
+files used to communicate with
 .I mdmon
-instances that are running in the current namespace,
+are in a standard place.
-.IR chroot (2)
-to NEWROOT, and continue monitoring the container.
-
-Alternately the new
-.I mdmon
-can be started after the new root has been installed with
-.I pivotroot
-by passing
-.B /
-as the NEWROOT.  For
-.I mdmon
-to be able to find and kill the old
-.I mdmon
-there must be some part of the filesystem that persists from before
-the
-.I pivotroot
-to afterwards.  This can be
-.B /var/run/mdadm
-or some other directory.  The default other directory is
-.B /lib/init/rw/mdadm
-but this can easily be changed when
-.I mdmon
-is compiled.
-If
-.I mdmon
-cannot store the pid file in
-.B /var/run/mdadm
-it will store it in the other directory until
-.B /var/run/mdadm
-becomes available, or until it is killed.
 .TP
-[PID]
+.B \-\-all
-If the second argument to
+This tells mdmon to find any active containers and start monitoring
-.I mdmon
+each of them if appropriate.  This is normally used with
-does not start with a slash it is assumed to be the pid of a previous
+.B \-\-takeover
-instance of
+late in the boot sequence.
-.I mdmon
-to kill.  This is used internally by
-.I mdmon
-to pass the pid across a chroot/exec and should not be used otherwise.
 
 .PP
 Note that
@@ -200,17 +169,16 @@ RAID arrays.  The only times it is run other that by
 is when the boot scripts need to restart it after mounting the new
 root filesystem.
 
-.SH EXMAPLES
+.SH EXAMPLES
 
-.B "  mdmon --all /"
+.B "  mdmon \-\-all \-\-takeover"
 .br
 Any
 .I mdmon
 which is currently running is killed and a new instance is started.
-This should be run early in the boot sequence after a
+This should be run late in the boot sequence and particularly after
-.I pivotroot
+.B /var
-to the final root filesystem, but before that filesystem is remounted
+is mounted and writable.
-read-write.
 .SH SEE ALSO
 .IR mdadm (8),
 .IR md (4).

mdmon.c

@@ -254,28 +254,31 @@ void usage(void)
 	exit(2);
 }
 
-static int mdmon(char *devname, int devnum, int must_fork, char *switchroot);
+static int mdmon(char *devname, int devnum, int must_fork, int takeover);
 
 int main(int argc, char *argv[])
 {
 	char *container_name = NULL;
-	char *switchroot = NULL;
 	int devnum;
 	char *devname;
 	int status = 0;
+	int arg;
+	int all = 0;
+	int takeover = 0;
 
-	switch (argc) {
+	for (arg = 1; arg < argc; arg++) {
-	case 3:
+		if (strcmp(argv[arg], "--all") == 0 ||
-		switchroot = argv[2];
+		    strcmp(argv[arg], "/proc/mdstat") == 0)
-	case 2:
+			all = 1;
-		container_name = argv[1];
+		else if (strcmp(argv[arg], "--takeover") == 0)
-		break;
+			takeover = 1;
-	default:
+		else if (container_name == NULL)
-		usage();
+			container_name = argv[arg];
+		else
+			usage();
 	}
 
-	if (strcmp(container_name, "/proc/mdstat") == 0 ||
+	if (all) {
-	    strcmp(container_name, "--all") == 0) {
 		struct mdstat_ent *mdstat, *e;
 
 		/* launch an mdmon instance for each container found */
@@ -292,7 +295,7 @@ int main(int argc, char *argv[])
 					sprintf(container_name, "%s", devname);
 				}
 				status |= mdmon(devname, e->devnum, 1,
-						switchroot);
+						takeover);
 			}
 		}
 		free_mdstat(mdstat);
@@ -320,10 +323,10 @@ int main(int argc, char *argv[])
 			container_name);
 		exit(1);
 	}
-	return mdmon(devname, devnum, do_fork(), switchroot);
+	return mdmon(devname, devnum, do_fork(), takeover);
 }
 
-static int mdmon(char *devname, int devnum, int must_fork, char *switchroot)
+static int mdmon(char *devname, int devnum, int must_fork, int takeover)
 {
 	int mdfd;
 	struct mdinfo *mdi, *di;
@@ -336,50 +339,7 @@ static int mdmon(char *devname, int devnum, int must_fork, char *switchroot)
 	pid_t victim = -1;
 	int victim_sock = -1;
 
-	dprintf("starting mdmon for %s in %s\n",
+	dprintf("starting mdmon for %s\n", devname);
-		devname, switchroot ? : "/");
-
-	/* switchroot is either a path name starting with '/', or a
-	 * pid of the original mdmon (we have already done the chroot).
-	 * In the latter case, stdin is a socket connected to the original
-	 * mdmon.
-	 */
-
-	/* try to spawn mdmon instances from the target file system */
-	if (switchroot && switchroot[0] == '/' &&
-	    strcmp(switchroot, "/") != 0) {
-		pid_t pid;
-		char buf[20];
-
-		switch (fork()) {
-		case 0:
-			victim = mdmon_pid(devnum);
-			victim_sock = connect_monitor(devname);
-			if (chroot(switchroot) != 0) {
-				fprintf(stderr, "mdmon: failed to chroot to '%s': %s\n",
-					switchroot, strerror(errno));
-				exit(4);
-			}
-			ignore = chdir("/");
-			sprintf(buf, "%d", victim);
-			if (victim_sock) {
-				close(0);
-				dup(victim_sock);
-				close(victim_sock);
-			}
-			execl("/sbin/mdmon", "mdmon", devname, buf, NULL);
-			exit(1);
-		case -1:
-			return 1;
-		default:
-			pid = wait(&status);
-			if (pid > -1 && WIFEXITED(status) &&
-			    WEXITSTATUS(status) == 0)
-				return 0;
-			else
-				return 1;
-		}
-	}
 
 	mdfd = open_dev(devnum);
 	if (mdfd < 0) {
@@ -486,17 +446,9 @@ static int mdmon(char *devname, int devnum, int must_fork, char *switchroot)
 	act.sa_handler = SIG_IGN;
 	sigaction(SIGPIPE, &act, NULL);
 
-	if (switchroot) {
+	if (takeover) {
-		/* we assume we assume that /sys /proc /dev are available in
+		victim = mdmon_pid(container->devnum);
-		 * the new root
+		victim_sock = connect_monitor(container->devname);
-		 */
-		if (switchroot[0] == '/') {
-			victim = mdmon_pid(container->devnum);
-			victim_sock = connect_monitor(container->devname);
-		} else {
-			victim = atoi(switchroot);
-			victim_sock = 0;
-		}
 	}
 
 	ignore = chdir("/");