2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same mountpoint

2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same mountpoint

[Kevin P. Fleming]

Accidentally <G> I mounted a filesystem from my server onto my workstation
twice. Mount gave me no error....

Both machines are kernel 2.4.9-ac3, both have NFSv3 support, server is using
knfsd, mount is version 2.11b. I export /storage on the server, and mount it
on /storage on my workstation.

When I boot the workstation, it automatically mounts /storage, so
everything's fine. If I then issue a  "mount /storage" command, I don't get
any error. df then reports two identical mounts for /storage. I can continue
to multiple mount (tried up to five mounts). Each "umount /storage" takes
away the most recent mount, with the last one performing a real unmount.

I can't, however, multiple mount any local filesystems (hard disk or CD-ROM
based), and don't have anything else handy to try.

Re: 2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same mountpoint

[Trond Myklebust]

>>>>> " " == Kevin P Fleming <kevin@labsysgrp.com> writes:

     > Accidentally <G> I mounted a filesystem from my server onto my
     > workstation twice. Mount gave me no error....

That's right. The 2.4 VFS removed the global restriction on the number
of mounts on a single mountpoint. So?

If people expect this to be an error, then the correct thing is for
the VFS restriction to be reinstated. I see no reason why it should be
the responsibility of the filesystem to check for this sort of
thing. A mountpoint is after all the one place where the VFS is
actually *designed* to override the filesystem.

Cheers,
  Trond

Re: 2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same mountpoint

[Thiago Vinhas de Moraes]

Em Qui, 30 de Ago de 2001 16:12, Trond Myklebust escreveu:
> >>>>> " " == Kevin P Fleming <kevin@labsysgrp.com> writes:
>      > Accidentally <G> I mounted a filesystem from my server onto my
>      > workstation twice. Mount gave me no error....
>
> That's right. The 2.4 VFS removed the global restriction on the number
> of mounts on a single mountpoint. So?
>
> If people expect this to be an error, then the correct thing is for
> the VFS restriction to be reinstated. I see no reason why it should be
> the responsibility of the filesystem to check for this sort of
> thing. A mountpoint is after all the one place where the VFS is
> actually *designed* to override the filesystem.

I think it should be reinstated. We must have in mind, that currently, the 
most part of end-users are newbies, and if we want Linux to be a true Desktop 
Enviroment, we must allow people that do not want to understand it, to run it.

Just IMHO.

Regards,
Thiago Vinhas

Re: 2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same mountpoint

[Pascal Schmidt]

On Thu, 30 Aug 2001, Thiago Vinhas de Moraes wrote:

> I think it should be reinstated. We must have in mind, that currently, the
> most part of end-users are newbies, and if we want Linux to be a true Desktop
> Enviroment, we must allow people that do not want to understand it, to run it.
Couldn't this be implemented in mount instead of the kernel? Should be
easy to check /proc/mounts whether anything is already mounted on a given
mountpoint.

-- 
Ciao, Pascal

-<[ pharao90@tzi.de, netmail 2:241/215.72, home http://cobol.cjb.net/) ]>-

Re: 2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same mountpoint

[Kevin P. Fleming]

I was expecting it to be an error, but I'm not upset that it's not. Just
kind of weird to see five mounts with the exact same information in
/etc/mtab.

I can see why it would be useful to have multiple things mounted on the same
mountpoint, but is there any reason to allow the _same_ filesystem to be
mounted multiple times at the same mountpoint?

----- Original Message -----
From: "Trond Myklebust" <trond.myklebust@fys.uio.no>
To: "Kevin P. Fleming" <kevin@labsysgrp.com>
Cc: <linux-kernel@vger.kernel.org>
Sent: Thursday, August 30, 2001 12:12 PM
Subject: Re: 2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same
mountpoint


> >>>>> " " == Kevin P Fleming <kevin@labsysgrp.com> writes:
>
>      > Accidentally <G> I mounted a filesystem from my server onto my
>      > workstation twice. Mount gave me no error....
>
> That's right. The 2.4 VFS removed the global restriction on the number
> of mounts on a single mountpoint. So?
>
> If people expect this to be an error, then the correct thing is for
> the VFS restriction to be reinstated. I see no reason why it should be
> the responsibility of the filesystem to check for this sort of
> thing. A mountpoint is after all the one place where the VFS is
> actually *designed* to override the filesystem.
>
> Cheers,
>   Trond
>
>
>

Re: 2.4.9-ac1/2/3 allows multiple mounts of NFS filesystem on same mountpoint

[Alexander Viro]

On Thu, 30 Aug 2001, Kevin P. Fleming wrote:

> I was expecting it to be an error, but I'm not upset that it's not. Just
> kind of weird to see five mounts with the exact same information in
> /etc/mtab.
> 
> I can see why it would be useful to have multiple things mounted on the same
> mountpoint, but is there any reason to allow the _same_ filesystem to be
> mounted multiple times at the same mountpoint?

How do you tell if it's the same filesystem?  Frankly, I'd rather get rid of
mounting several things at one mountpoint, different or not - that would
make life much easier, but it means that we need to implement mount-traps
to make autofs folks happy.  It _may_ be doable in 2.4, but I susupect that
it will end up as 2.5 project.