umount: --types does not limit

[Benno Schulenberg <bensberg@justemail.net>]

On Tue, Jul 15, 2014, at 10:02, Karel Zak wrote:
>    umount -t <type>
> 
>  the <type> is filesystem type (so you can force umount to use for
>  example /sbin/umount.<type>).

Hmm.  But it's not working for me, the --types option does not limit
umount in any way.  In the man page it says: "Indicate  that the
actions should *only* be taken on filesystems of the specified type."

But, for example, here Suse is of type ext4 and gets mounted:

# ./mount -t ext4 /suse
# ./mount | grep suse
/dev/sda2 on /suse type ext4 (rw,noatime,noexec,nosuid,nodev,user)

Now I want to unmount all btrfs systems:

# ./umount -t btrfs /suse /zero /other
# ./mount | grep suse

It just unmounts everything that is mentioned, the -t has no
limiting effect.  So it is useful only with -a.

Benno

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