See bin/17673 (http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=17673)
I reported the same for mount_union. The answer was that you must not use the
mount_* stuff, but use the real mount program, which will do all necessary
sanity checks.

HTH



On Sat, 18 Jan 2003 00:17:49 -0500
Matthew Mondor <mmondor@gobot.ca> wrote:

> Hi all,
> 
> I wonder if anyone else have stumbled into this (and if -current perhaps
> also has this problem, or other releases. I run 1.6_STABLE):
> 
> Mounting a nullfs filesystem with an non-absolute mountpoint results in
> a parmanent mount entry which umount cannot handle anymore. To demonstrate
> this:
> 
> A /tmp directory exists in the / filesystem and it is mounted virtually
> using nullfs to an existing tmp directory under servroot.
> 
> # cd /servroot
> # mount_null -o noexec /tmp tmp
> # df
> /tmp            991262   185330    756368    19%    tmp
> # umount tmp
> umount: /servroot/tmp: not currently mounted
> # umount ./tmp
> umount: /servroot/tmp: not currently mounted
> # umount /servroot/tmp 
> umount: /servroot/tmp: not currently mounted
> # umount /tmp 
> umount: /tmp: not currently mounted
> 
> Additionally, if a / is appended to a mountpoint path, a similar problem
> exists:
> 
> # mount_null -o noexec /tmp/ /servroot/tmp/
> # df
> /tmp            991262   185330    756368    19%    /servroot/tmp/
> # umount /servroot/tmp/
> umount: /servroot/tmp: not currently mounted
> 
> So the problem seems to have to do with the sanity checking of the supplied
> mountpoint, which mount(2) performs, or the vfs nullfs call for mount(2)...
> Unfortunately I could not verify yet if this consists of a more general
> problem with other filesystems as well.
> 
> Because obviously both first and second tests should have translated the
> mountpoint to /servroot/tmp ... There is no problem when using the perfect
> path i.e.
> 
> # mount_null -o noexec /tmp /servroot/tmp
> 
> [ now off to reboot to get rid of my problematic mountpoints :) ]
> 
> Matt
> 


-- 
Julio M. Merino Vidal <jmmv@menta.net>
The NetBSD Project - http://www.NetBSD.org/