/proc/mounts: two different loop devices mounted on same mountpoint?!

/proc/mounts: two different loop devices mounted on same mountpoint?!

[Pavel Machek]

Hi!

Kernel 2.4.17:

pavel@amd:~/misc$ cat /proc/mounts
/dev/root / ext2 rw 0 0
/dev/hda3 /suse ext2 rw 0 0
none /proc proc rw 0 0
none /proc/bus/usb usbdevfs rw 0 0
/dev/cfs0 /overlay coda rw 0 0
/dev/loop0 /mnt ext2 rw 0 0
/dev/loop1 /mnt ext2 rw 0 0
pavel@amd:~/misc$

Both /dev/loop0 *and* /dev/loop1 mounted on /mnt at same time? Oops?
What's the semantics of that? [And I guess it should not be allowed)

									Pavel
-- 
(about SSSCA) "I don't say this lightly.  However, I really think that the U.S.
no longer is classifiable as a democracy, but rather as a plutocracy." --hpa

Re: /proc/mounts: two different loop devices mounted on same mountpoint?!

[Davidovac Zoran]

I think that is normal behaviour in 2.4.X
that one can mount more than once
on same mount point.

Zoran

On Thu, 28 Feb 2002, Pavel Machek wrote:

> Date: Thu, 28 Feb 2002 10:59:48 +0100
> From: Pavel Machek <pavel@ucw.cz>
> To: Alexander Viro <viro@math.psu.edu>
> Cc: kernel list <linux-kernel@vger.kernel.org>
> Subject: /proc/mounts: two different loop devices mounted on same
>     mountpoint?!
>
> Hi!
>
> Kernel 2.4.17:
>
> pavel@amd:~/misc$ cat /proc/mounts
> /dev/root / ext2 rw 0 0
> /dev/hda3 /suse ext2 rw 0 0
> none /proc proc rw 0 0
> none /proc/bus/usb usbdevfs rw 0 0
> /dev/cfs0 /overlay coda rw 0 0
> /dev/loop0 /mnt ext2 rw 0 0
> /dev/loop1 /mnt ext2 rw 0 0
> pavel@amd:~/misc$
>
> Both /dev/loop0 *and* /dev/loop1 mounted on /mnt at same time? Oops?
> What's the semantics of that? [And I guess it should not be allowed)
>
> 									Pavel
> --
> (about SSSCA) "I don't say this lightly.  However, I really think that the U.S.
> no longer is classifiable as a democracy, but rather as a plutocracy." --hpa
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>

Re: /proc/mounts: two different loop devices mounted on same mountpoint?!

[Pavel Machek]

Hi!

> I think that is normal behaviour in 2.4.X
> that one can mount more than once
> on same mount point.

But two different devices? What's the semantics, then?
> > Hi!
> >
> > Kernel 2.4.17:
> >
> > pavel@amd:~/misc$ cat /proc/mounts
> > /dev/root / ext2 rw 0 0
> > /dev/hda3 /suse ext2 rw 0 0
> > none /proc proc rw 0 0
> > none /proc/bus/usb usbdevfs rw 0 0
> > /dev/cfs0 /overlay coda rw 0 0
> > /dev/loop0 /mnt ext2 rw 0 0
> > /dev/loop1 /mnt ext2 rw 0 0
> > pavel@amd:~/misc$
> >
> > Both /dev/loop0 *and* /dev/loop1 mounted on /mnt at same time? Oops?
> > What's the semantics of that? [And I guess it should not be allowed)
Casualities in World Trade Center: ~3k dead inside the building,
cryptography in U.S.A. and free speech in Czech Republic.

Re: /proc/mounts: two different loop devices mounted on same mountpoint?!

[Andreas Ferber]

On Thu, Feb 28, 2002 at 02:44:55PM +0100, Pavel Machek wrote:
> 
> > I think that is normal behaviour in 2.4.X
> > that one can mount more than once
> > on same mount point.
> But two different devices? What's the semantics, then?

All accesses go to the filesystem mounted last. The one mounted first
is inaccessible until you unmount the filesystem covering it. Well,
not really inaccessible, if any process happened to have a working
directory or an open file on the first filesystem at the time you
mounted the second, it can still access it.

There is nothing special involved, after all, it's the same as if you
mount a single filesystem to /mnt, the only difference is that the
second mount this time doesn't cover a single dirtree on the root
partition, but instead it covers a complete other filesystem.

Andreas
-- 
       Andreas Ferber - dev/consulting GmbH - Bielefeld, FRG
     ---------------------------------------------------------
         +49 521 1365800 - af@devcon.net - www.devcon.net