Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:55269 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751452Ab1LORoh (ORCPT ); Thu, 15 Dec 2011 12:44:37 -0500 Date: Thu, 15 Dec 2011 12:44:27 -0500 From: "J. Bruce Fields" To: Trond Myklebust Cc: Ric Wheeler , Al Viro , "linux-scsi@vger.kernel.org" , linux-fsdevel , Hannes Reinecke , Andrew Morton , linux-nfs@vger.kernel.org, Joel Becker , James Bottomley Subject: Re: copy offload support in Linux - new system call needed? Message-ID: <20111215174427.GA14614@fieldses.org> References: <4EE8F75F.6070800@gmail.com> <20111214192739.GN2203@ZenIV.linux.org.uk> <4EE8FC2E.3010207@gmail.com> <20111214222723.GD7623@fieldses.org> <1323961140.14317.2.camel@lade.trondhjem.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1323961140.14317.2.camel@lade.trondhjem.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, Dec 15, 2011 at 09:59:00AM -0500, Trond Myklebust wrote: > On Wed, 2011-12-14 at 17:27 -0500, J. Bruce Fields wrote: > > On Wed, Dec 14, 2011 at 02:42:38PM -0500, Ric Wheeler wrote: > > > On 12/14/2011 02:27 PM, Al Viro wrote: > > > >On Wed, Dec 14, 2011 at 02:22:07PM -0500, Ric Wheeler wrote: > > > > > > > >>We had an active thread a couple of years back that came out of the > > > >>reflink work and, at the time, there seemed to be moderately > > > >>positive support for adding a new system call that would fit this > > > >>use case (Joel Becker's copyfile()). > > > >> > > > >>Can we resurrect this effort? Is copyfile() still a good way to go, > > > >>or should we look at other hooks? > > > >copyfile(2) is probably a good way to go, provided that we do _not_ > > > >go baroque as it had happened the last time syscall had been discussed. > > > > > > > >IOW, to hell with progress reports, etc. - just a fastpath kind of > > > >thing, in the same kind of relationship to cp(1) as rename(2) is to mv(1). > > > >If it works - fine, if not - caller has to be ready to deal with handling > > > >cross-device case anyway. > > > > > > I think that this approach makes a lot of sense. Most of the > > > devices/targets that support the copy offload, will do it in very > > > reasonable amounts of time. > > > > The current NFSv4.2 draft rolls both the "fast" and "slow" cases into > > one operation: > > > > http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion2-06#section-2 > > > > Perhaps we should ask for separate operations for the two cases. (Or at > > least a "please don't bother if this is going to take 8 hours" flag....) > > How would the server know? Sorry, "8 hours" was a joke--no, you can't require the server to predict whether an operation will take more or less than some precise duration. I'm assuming the "fast" case that Al's proposing we do as a first step cover CoW operations? (So O(1) or close to it, users typically won't be asking for progress reports, operation may be atomic (with no partial-failure case), ?) --b.