Re: OK to mount multiple FS in one dir?

["Thorsten Glaser Geuer" <eccesys@topmail.de>]

----- Original Message ----- 
From: "Peter Samuelson" <peter@cadcamlab.org>
To: "Michael D. Crawford" <crawford@goingware.com>
Cc: <linux-kernel@vger.kernel.org>
Sent: Tuesday, 6. February 2001 00:06
Subject: Re: OK to mount multiple FS in one dir?


> 
> [Michael D. Crawford]
> > I found I could mount three partitions on /mnt
> 
> Yes.  New feature, appeared in the 2.4.0test series, or shortly before.
> 
> > and they'd all show up as mounted at /mnt in the "mount" command, but
> > if I unmounted one of them (only tried with the currently visible
> > one), then it appeared that there were no filesystems mounted there,
> > but I could continue umounting until the other two were gone.
> 
> util-linux gets rather confused by this feature.  They say newer
> versions fix this.
> 
> > But I had the 2.10r util-linux sources on my machine and installed
> > mount and umount from it, and I find that it gets it right mostly
> > when I mount and unmount multiple things, with the exception that if
> > /dev/sda5 was mounted before /dev/sda1, then if I give the command
> > "umount /dev/sda5", sda1 is the one that gets unmounted rather than
> > sda5, so it takes the most recently mounted filesystem rather than
> > the one you specify.
> 
> I think this is a kernel limitation.  'umount' takes '/dev/sda5' and
> turns it into '/mnt/test' and calls umount("/mnt/test").  The kernel
> then unmounts whatever is on "top" of /mnt/test.
> 
> I don't think there's anything umount can do about this behavior.

What about userland umount checking which device is umounted and
refusing to umount it or at least issuing a printf warning?

> 
> Peter

-mirabilos

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