Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx12.netapp.com ([216.240.18.77]:32963 "EHLO mx12.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754507Ab3J1ATM convert rfc822-to-8bit (ORCPT ); Sun, 27 Oct 2013 20:19:12 -0400 From: "Myklebust, Trond" To: Christoph Anton Mitterer CC: Eshel Marc , Dr Fields James Bruce , Mailing List Linux NFS , "linux-nfs-owner@vger.kernel.org" , "Wheeler Ric" Subject: Re: XATTRs in NFS? Date: Mon, 28 Oct 2013 00:19:10 +0000 Message-ID: References: <1382560643.6924.12.camel@heisenberg.scientia.net> <1382624000.6907.8.camel@heisenberg.scientia.net> <1382630468.6907.58.camel@heisenberg.scientia.net> <625CAA34-BD6C-4283-86D0-3F8B460D54D0@netapp.com> <1382635350.6907.83.camel@heisenberg.scientia.net> <20131025140846.GB20497@fieldses.org> <526A8D9A.8090008@gmail.com> <7C1323EE-D63F-4F93-A44D-E7DDB0C61BF0@netapp.com> <4260556F-D57B-407E-A686-808D3D802137@netapp.com> <1382919289.6932.35.camel@heisenberg.scientia.net> In-Reply-To: <1382919289.6932.35.camel@heisenberg.scientia.net> Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Oct 27, 2013, at 8:14 PM, Christoph Anton Mitterer wrote: > On Sun, 2013-10-27 at 12:48 +0000, Myklebust, Trond wrote: >> Let's get the basic discussion of motivation right first. > Actually I might know another use case. > > dCache[0] which implements a (p)NFS 4.1 server and is heavily used > within the high energy physics community, could benefit from XATTRs as > well. > > Ever since, dCache has had a concept called PNFS tags (where the PNFS > had nothing to do with parallel NFS, but is called so for other > historical reasons), which are basically key/value pairs belonging to > some file (well at least directory, I don't remember where PNFS tags > exist for regular files). > > These tags are used to control several things, indirectly, e.g. to which > data pool node a file may go, and via that whether it may be moved to > tape, whether it is duplicated, etc. pp. > > Since there were no XATTRs (at least I guess that's the historical > reason), they used special files for this having the name: > ".(tag)(key)" and the content of the file is the value. > > So for a path, > /data/foo/bar/ > one can set the key "sGroup" (aka storage group) to a value say > "ATLAS" (which (very simplified) will tell dCache in the end that this > is storage belonging to the ATLAS experiment) by creating a file > echo "ATLAS" > '/data/foo/bar/.(tag)(sGroup)' > > > Obviously having such special files isn't that nice, and having real > XATTRs would be the better solution. Ordinary groups can do the same. Trond