Re: [issue1537] null mount does not accept -o update

[YONETANI Tomokazu <qhwt+dfly@xxxxxxxxxx>]

On Thu, Nov 19, 2009 at 08:40:46AM +0000, Stathis Kamperis (via DragonFly issue tracker) wrote:
> 
> Stathis Kamperis <ekamperi@gmail.com> added the comment:
> 
> Ping!
> 
> Anyone interested with time and clue to review the patch ?
> I'd like to push it at some point, before it gets too stale, but ain't gonna
> happen if at least someone else gives me a thumbs up.

I noticed that I can't remount nullfs by mount(8).  The patched
mount_null accepts only one argument (the mountpoint to be remounted)
when MNT_UPDATE is specified either by -u or by -o update, but
what mount(8) passes to filesystem-specific mount commands like this:
  # mount -ur /mnt/pt
  -> mount_${foo} -o ro -o update /path/to/special /mnt/pt
  # mount -uw /mnt/pt
  -> mount_${foo} -o noro -o update /path/to/special /mnt/pt

I think that the following patch on top of yours does this for you,
although I only tested it slightly.


diff --git a/sbin/mount_null/mount_null.c b/sbin/mount_null/mount_null.c
index b9c595a..9e02b6d 100644
--- a/sbin/mount_null/mount_null.c
+++ b/sbin/mount_null/mount_null.c
@@ -88,29 +88,20 @@ main(int argc, char **argv)
 	argv += optind;
 
 	/*
-	 * Only the mount point need be specified in update mode.
+	 * Resolve target and source with realpath(3).  Only the mount point
+	 * needs be specified in update mode, but mount(8) passes us two
+	 * arguments, the second of which is the source directory.
 	 */
-	if (mntflags & MNT_UPDATE) {
-		if (argc != 1) {
-			usage();
-			/* not reached */
-		}
+	if ((mntflags & MNT_UPDATE) && argc == 1) {
+		args.target = NULL;
 		checkpath(argv[0], source);
-		error = getvfsbyname("null", &vfc);
-		if (error)
-			err(1, "getvfsbyname");
-		if (mount(vfc.vfc_name, source, mntflags, &args))
-			err(1, "mount");
-		exit(0);
-	}
-
-	if (argc < 2)
+	} else if (argc == 2) {
+		args.target = target;
+		checkpath(argv[0], target);
+		checkpath(argv[1], source);
+	} else
 		usage();
 
-	/* resolve target and source with realpath(3) */
-	checkpath(argv[0], target);
-	checkpath(argv[1], source);
-
 	/*
 	 * Mount points that did not use distinct paths (e.g. / on /mnt)
 	 * used to be disallowed because mount linkages were stored in
@@ -118,7 +109,6 @@ main(int argc, char **argv)
 	 * stores mount linkages in the namecache topology and does not
 	 * have this problem, so paths no longer need to be distinct.
 	 */
-	args.target = target;
 
 	error = getvfsbyname("null", &vfc);
 	if (error && vfsisloadable("null")) {