Unmounting by filesystem ID

[Dan Nelson]

In the last episode (Jul 05), Ian Dowse said:
> In message <1057413470.716.3.camel at localhost>, "Vladimir B. Grebenschikov" writes:
> >May be you fix issue of umounting by known vnode ? problem is in
> >mounting different devices under chroot. in list of mounts they
> >differ only by device id, and it is rather=20 difficult to umount
> >filesystem if I known absolute path but do not enter to chroot.
> 
> The MNT_BYFSID approach makes it always possible to indicate to the
> kernel which filesystem is to be unmounted, but some more work is
> needed in the umount(8) utility to handle unusual cases.

Can mount(8) be changed to print the fsid?   Maybe hide it under -v if
it's a long value?  This seems like the only solution that can cover
the case where you have stacked two identical NFS mounts, one on top of
the other.  I've done this occasionally to force the kernel to retry
access to a server that has just come back after a reboot.

amd could probably benefit from dismounting using fsid if possible,
too.  Although it'd have to try fsid then path for the case where root
has dismounted then remounted one of its filesystems behind its back
(I've done this too, to change nfsv2 mounts to v3, etc).

-- 
	Dan Nelson
	dnelson at allantgroup.com