Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754329Ab3ISNJQ (ORCPT ); Thu, 19 Sep 2013 09:09:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32646 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754307Ab3ISNJM (ORCPT ); Thu, 19 Sep 2013 09:09:12 -0400 Date: Thu, 19 Sep 2013 08:59:24 -0400 From: Jeff Layton To: Eric Wong Cc: Zach Brown , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, Trond Myklebust , Bryan Schumaker , "Martin K. Petersen" , Jens Axboe , Mark Fasheh , Joel Becker Subject: Re: [RFC] extending splice for copy offloading Message-ID: <20130919085924.09b2a25c@tlielax.poochiereds.net> In-Reply-To: <20130911211722.GA9725@dcvr.yhbt.net> References: <1378919210-10372-1-git-send-email-zab@redhat.com> <20130911211722.GA9725@dcvr.yhbt.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2371 Lines: 62 On Wed, 11 Sep 2013 21:17:23 +0000 Eric Wong wrote: > Zach Brown wrote: > > Towards the end of that thread Eric Wong asked why we didn't just > > extend splice. I immediately replied with some dumb dismissive > > answer. Once I sat down and looked at it, though, it does make a > > lot of sense. So good job, Eric. +10 Dummie points for me. > > Thanks for revisiting that :> > > > Some things to talk about: > > - I really don't care about the naming here. If you do, holler. > > Exposing "DIRECT" to userspace now might confuse users into expecting > O_DIRECT behavior. I say this as an easily-confused user. > > In the future, perhaps O_DIRECT behavior can become per-splice (instead > of just per-open) and can save SPLICE_F_DIRECT for that. > > > - We might want different flags for file-to-file splicing and acceleration > > - We might want flags to require or forbid acceleration > Do we need new flags at all? If both fds refer to files, then perhaps we can just take it that SPLICE_F_DIRECT behavior is implied? I'd probably suggest that we not add any more flags than are necessary until use-cases for them become clear. > > - We might want to provide all these flags to sendfile, too > > Another syscall? I prefer not. Better to just maintain the sendfile > API as-is for compatibility reasons and nudge users towards splice. > Agreed. > > Thoughts? Objections? > > I'll try to test/comment more in a week or two (not much time for > computing until then). On the whole, the concept looks sound. I'll note too that by simply lifting the restriction that one of the fd's to splice must always be a pipe, that may also give us a relatively simple way to add recvfile() as well, even if only as a macro wrapper around splice(). That's been a long sought-after feature of the samba developers... Just allow userland to do a splice straight from a socket fd to a file. We may end up having to copy data if the alignment isn't right, but it'd still be valuable to do that directly in the kernel in a single syscall. -- Jeff Layton -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/