Return-Path: linux-nfs-owner@vger.kernel.org Received: from mailgw02.dd24.net ([193.46.215.43]:55706 "EHLO mailgw02.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754507Ab3J1APA (ORCPT ); Sun, 27 Oct 2013 20:15:00 -0400 Message-ID: <1382919289.6932.35.camel@heisenberg.scientia.net> Subject: Re: XATTRs in NFS? From: Christoph Anton Mitterer To: "Myklebust, Trond" Cc: Eshel Marc , Dr Fields James Bruce , Mailing List Linux NFS , "linux-nfs-owner@vger.kernel.org" , Wheeler Ric Date: Mon, 28 Oct 2013 01:14:49 +0100 In-Reply-To: <4260556F-D57B-407E-A686-808D3D802137@netapp.com> 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> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: 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. Cheers, Chris. btw: Note that while I'm good friends with the dCache developers, I don't speak for them, nor do I know whether they'd really like this or not. [0] http://www.dcache.org/