Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763239AbXJZADO (ORCPT ); Thu, 25 Oct 2007 20:03:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760568AbXJZAC5 (ORCPT ); Thu, 25 Oct 2007 20:02:57 -0400 Received: from ozlabs.org ([203.10.76.45]:48575 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756879AbXJZAC4 (ORCPT ); Thu, 25 Oct 2007 20:02:56 -0400 From: Rusty Russell To: Jens Axboe Subject: Re: [PATCH 09/10] Change table chaining layout Date: Fri, 26 Oct 2007 10:03:18 +1000 User-Agent: KMail/1.9.6 (enterprise 0.20070907.709405) Cc: Linus Torvalds , Boaz Harrosh , Alan Cox , Geert Uytterhoeven , Linux Kernel Development , mingo@elte.hu References: <1193076664-13652-10-git-send-email-jens.axboe@oracle.com> <20071025091140.GK5053@kernel.dk> <200710252154.45542.rusty@rustcorp.com.au> In-Reply-To: <200710252154.45542.rusty@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200710261003.19287.rusty@rustcorp.com.au> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1809 Lines: 43 On Thursday 25 October 2007 21:54:44 Rusty Russell wrote: > On Thursday 25 October 2007 19:11:40 Jens Axboe wrote: > > On Thu, Oct 25 2007, Rusty Russell wrote: > > > What irritates me more is that scatterlists aren't quite generically > > > useful. The virtio code wants to join a scatterlist created by > > > blk_rq_map_sg() with two others, yet it won't work because sg_chain() > > > doesn't remove the end marker from the first entry. > > > > That's a minor nit for your special purpose, we/you can change that. > > Well currently sg_chain() only joins "incomplete" (ie. unterminated) sg > chains. That works great for you, but it feels more like a special purpose > to me. > > > > If this patch weren't already included, I'd be strongly arguing for the > > > bio idea: I find the chained sg code tricksy and ugly (sorry Jens). > > > > What is the bio idea? A bio works in essentially the same way, the only > > difference is having a specific next pointer. It's still just a linked > > lists of arbitrarily sized sg tables (the bio_vec arrays). > > It was suggested by analogy earlier in this thread, to use a two-level > structure. > > In this case I would have first renamed struct scatterlist to struct > scatterelem. Then struct scatterlist looks like: > > struct scatterlist { > unsigned int num; > struct scatterelem elems[0]; > }; To correct my own thoughts, it'd be better to just put a "struct list_head list;" in there for chaining. That's more along standard kernel lines, and neatly handles the single-scatterlist case. Cheers, Rusty. - 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/