5.1-BETA umount problems

[Ian Dowse]

In message <20030519051855.GB4396 at HAL9000.homeunix.com>, David Schultz writes:
>umount -f can be extremely useful on a multiuser system when you
>*really* want to unmount a filesystem regardless of who might be
>trying to use it.  However, it also makes it easy to shoot
>yourself in the foot.  If it only fails in situations where you
>are absolutely guaranteed to shoot yourself in the foot, that's
>fine.  There's no reason it should allow someone to unmount a
>filesystem that contains a mountpoint for another mounted
>filesystem.

I've had some patches floating around for a while that change
unmount() so that filesystems can be unmounted by specifying the
filesystem ID instead of a path. This helps a lot in the unmounting
of NFS mounts from dead servers, as it avoids any lookups that might
hang indefinitely, but it should also make it possible to unmount
filesystems that get detached from the filesystem they were mounted
over. I was holding off on committing this in the hopes of finding
a cleaner way of passing a fsid_t through unmount()'s `const char
*dir' argument. Patch is at:

	http://www.maths.tcd.ie/~iedowse/FreeBSD/umount_by_fsid.diff

Ian