linux-kernel - Re: [PATCH] VFS: fix recent breakage of FS_REVAL

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Date:	Mon, 24 May 2010 12:21:22 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Neil Brown <neilb@...e.de>, Chuck Lever <chuck.lever@...cle.com>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VFS: fix recent breakage of FS_REVAL_DOT

On Mon, 2010-05-24 at 16:50 +0100, Al Viro wrote: 
> On Mon, May 24, 2010 at 12:59:03PM +0100, Al Viro wrote:
> 
> > BTW, here's a question for nfs client folks: is it true that for any two
> > pathnames on _client_ resolving to pairs (mnt1, dentry) and (mnt2, dentry)
> > resp., nfs_devname(mnt1, dentry, ...) and nfs_devname(mnt2, dentry, ...)
> > should yield the strings that do not differ past the ':' (i.e. that the
> > only possible difference is going to be in spelling the server name)?
> 
> Actually, there's a related one: suppose we have two mounts from the same
> server, with the same flags, etc., ending up sharing a dentry on client.
> What will we get from GETATTR asking for fs_locations, in fs_root field?
> 
> Can an nfs4 server e.g. have /x/y being a symlink that resolves to /a/b and
> allow mounting of both /x/y/c and /a/b/c?  Which path would it return to
> client that has mounted both, walked to some referral point and called
> nfs_do_refmount(), triggering nfs4_proc_fs_locations()?
> 
> Trond, Neil?

When mounting /x/y/c in your example above, the NFSv4 protocol requires
the client itself to resolve the symlink, and then walk down /a/b/c
(looking up component by component), so it will in practice not see
anything other than /a/b/c.

If it walks down to a referral, and then calls nfs_do_refmount, it will
do the same thing: obtain a path /e/f/g on the new server, and then walk
down that component by component while resolving any symlinks and/or
referrals that it crosses in the process.

Cheers
  Trond

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