From: Trond Myklebust <Trond.Myklebust@netapp.com>
Subject: Re: inconsistent mount attributes (ro/rw), RHEL5 / Netapp
Date: Sat, 05 May 2007 14:49:20 -0400
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Cc: Paul Krizak <paul.krizak@amd.com>, nfs@lists.sourceforge.net
To: Ian Kent <raven@themaw.net>
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On Sun, 2007-05-06 at 02:27 +0800, Ian Kent wrote:
> On Sat, 2007-05-05 at 13:17 -0400, Trond Myklebust wrote:
> > Why are people arguing that NFS should be working in a completely
> > different fashion to all other filesystems? Fix the VFS to allow
> > read-only bind mounts, and NFS will work just fine with that.
> 
> Sorry, I don't follow.
> How does think affect a client doing two distinct mounts to a server.
> Are you suggesting that such a bind mount should be done on the server
> and then exported? I guess that would give us distinct super blocks.

No. People are arguing that the client should allow the _same_
filesystem to be mounted both read-only and read-write. That is not
currently permitted for any other filesystem. The reason is that the
read-only flag acts on a per-superblock basis, and hence on a
per-filesystem basis. This is why you cannot do

        mount --bind -oro /foo /bar

If you fix the VFS to allow the above by making the read-only flag a
per-mountpoint flag instead of a per-superblock flag, then NFS can
happily do the same.

Trond

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