Return-Path: Received: from mx2.netapp.com ([216.240.18.37]:30680 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754245Ab1HDQLA convert rfc822-to-8bit (ORCPT ); Thu, 4 Aug 2011 12:11:00 -0400 Subject: Re: State of NFSv4 VolatileFilehandles From: Trond Myklebust To: "J. Bruce Fields" Cc: Venkateswararao Jujjuri , Chuck Lever , linux-nfs@vger.kernel.org Date: Thu, 04 Aug 2011 12:10:44 -0400 In-Reply-To: <20110804160344.GC12445@fieldses.org> References: <4E37E66D.90102@linux.vnet.ibm.com> <45F4FC20-ED44-4430-A5A9-E06459A194F3@oracle.com> <4E38F894.4070003@linux.vnet.ibm.com> <2DD1BC2B-6113-4D00-9DD4-C5D431EA1F8A@oracle.com> <4E3A8225.1020309@linux.vnet.ibm.com> <20110804160344.GC12445@fieldses.org> Content-Type: text/plain; charset="UTF-8" Message-ID: <1312474244.5806.4.camel@lade.trondhjem.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Thu, 2011-08-04 at 12:03 -0400, J. Bruce Fields wrote: > On Thu, Aug 04, 2011 at 04:27:33AM -0700, Venkateswararao Jujjuri wrote: > > One of the usecase is rsync between two physical filesystems; but in > > this particular use case the export > > is readonly (rootfs). As trond mentioned Volatile FHs are fine in > > the case of readonly exports. > > Is it something we can consider for upstream? VFH only for readonly > > exports.? > > The client has no way of knowing that an export is read only. (Or that > the server guarantees the safety of looking up names again in the more > general cases Neil describes.) Unless we decide that a server is making > an implicit guarantee of that just by exposing volatile filehandles at > all. Doesn't sound like the existing spec really says that, though. NFSv4.1 introduces the 'fs_status' recommended attribute (see section 11.11 in RFC5661), which does, in fact, allow the client to deduce that an export is read-only/won't ever change. > If an examination of existing implementations and/or some sort of new > spec language could reassure us that servers will only ever expose > volatile filehandles when it's safe to do so, then maybe it would make > sense for the client to implement volatile filehandle recovery? > > But if there's a chance of "unsafe" servers out there, then it would > seem like a trap for the unwary user.... > > Your rootfs's probably aren't terribly large--could you copy around > compressed block-level images instead of doing rsync? Agreed. -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@netapp.com www.netapp.com