linux-kernel - Re: [PATCH 00/32] VFS based Union Mount (V3)

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Date:	Wed, 17 Jun 2009 23:23:57 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	Jan Rekorajski <baggins@...h.mimuw.edu.pl>,
	Jan Blunck <jblunck@...e.de>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
	bharata@...ibm.com, dwmw2@...radead.org, mszeredi@...e.cz
Subject: Re: [PATCH 00/32] VFS based Union Mount (V3)

On Mon, Jun 15, 2009 at 11:55:28AM +0200, Jan Rekorajski wrote:
> On Mon, 08 Jun 2009, Valerie Aurora wrote:
> 
> > On Tue, Jun 09, 2009 at 12:44:06AM +0200, Jan Rekorajski wrote:
> > > On Mon, 08 Jun 2009, Valerie Aurora wrote:
> > > 
> > > > You'll get -EBUSY on the second mount of any NFS file system over
> > > > another - try it again with the --union flag.  Support for NFS on NFS
> > > > union mount would have to change this.
> > > 
> > > I did just that, --union didn't change standard NFS behaviour.
> > 
> > Er, excuse me - I mean to type "try it again WITHOUT the --union
> > flag."  My apologies!
> 
> I did, see below.
> 
> > > 
> > > mount -t nfs server:/export/system /mnt
> > > mount --union -t nfs server:/export/profile /mnt
> > > mount.nfs: /mnt is busy or already mounted
> > > 
> > > I did an experiment by using different IP of the server (same machine)
> > > when mounting the second fs, mount worked then, but 'ls -1 /mnt' oopsed.
> > > I can reproduce this and send you the oops next week.
> > 
> > Interesting!  Does this happen without the --union flag?
> 
> Filesystems are exported ro, all mounts nfs3,ro,tcp.
> 
> Without --union:
> 
> mount -t nfs 10.1.0.4:/nfs/system /mnt -oro,nolock,vers=3,tcp
> OK
> 
> mount -t nfs 10.1.0.4:/nfs/profile /mnt -oro,nolock,vers=3,tcp
> -EBUSY (as expected)
> 
> mount -t nfs 10.1.0.3:/nfs/profile /mnt -oro,nolock,vers=3,tcp
>  (notice different IP - but it's the same machine)
> Works, just overmounts /mnt, ls shown contents of /nfs/profile
> 
> Now, --union:
> 
> mount -t nfs 10.1.0.4:/nfs/system /mnt -oro,nolock,vers=3,tcp
> OK
> 
> mount --union -t nfs 10.1.0.4:/nfs/profile /mnt -oro,nolock,vers=3,tcp
> -EBUSY (/mnt busy or already mounted)
> 
> mount --union -t nfs 10.1.0.3:/nfs/profile /mnt -oro,nolock,vers=3,tcp
>  (notice different IP - but it's the same machine)
> mount command works, ls Oopses:

Sorry for the delay in reply!  This is on our to-do list, thanks for
doing a little more testing.

-VAL
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