Date: Mon, 8 Mar 2010 19:59:33 -0800
From: Brad Boyer <flar@allandria.com>
To: James Morris <jmorris@namei.org>
Cc: linux-nfs@vger.kernel.org, linux-security-module@vger.kernel.org,
        Trond Myklebust <Trond.Myklebust@netapp.com>,
        "J. Bruce Fields" <bfields@fieldses.org>, Neil Brown <neilb@suse.de>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 0/6][v4][RFC] NFSv3: implement extended attribute protocol (XATTR)
Message-ID: <20100309035932.GA14237@cynthia.pants.nu>
References: <alpine.LRH.2.00.1002261457420.25193@tundra.namei.org> <alpine.LRH.2.00.1003082122340.6314@tundra.namei.org>
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On Mon, Mar 08, 2010 at 09:42:06PM +1100, James Morris wrote:
> Since the last version, I've incorporated feedback to add a new top-level 
> xattr namespace "nfsd", for storing client-origin xattrs on the server.  
> Support for the new namespace has been implemented on ext3 for testing 
> purposes.
> 
> Access to this namespace locally requires CAP_SYS_ADMIN, and it is not 
> accessible over the wire.  Note that there is still potential for 
> confusion between local and remote users, e.g.
> 
> $ setfattr -n user.foo -v bar file.txt
> 
> on an NFS mounted fs will create an xattr on the server called 
> nfsd.user.foo, and then if the user logs in locally, they will not see the 
> xattr at all.  Similarly, if they create xattrs locally, they will not be 
> exported via XATTR.
> 
> Comments welcome.

I personally think it's a bad idea to not map regular user xattr values
directly to what is local to the server. One common thing I've seen in
many places is to have local disks on various servers exported over
NFS to other servers, but the intent is that the user shouldn't care
which server physically hosts the storage. In this case, you want the
data to appear the same regardless of the use or non-use of NFS. In
this sort of situation, one system will see different data than the
others for the same files with the same access level. One possible
option would be to make it configurable, kind of like root_squash.

	Brad Boyer
	flar@allandria.com