From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Monakhov Subject: Re: [PATCH 1/2] blkdev: fix merge_bvec_fn return value checks Date: Wed, 03 Mar 2010 22:42:17 +0300 Message-ID: <87lje9kx9i.fsf@openvz.org> References: <1267292113-12900-1-git-send-email-dmonakhov@openvz.org> <20100228184634.GI5768@kernel.dk> <874okyf4iw.fsf@openvz.org> <170fa0d21003031020x5b71b492vd733cf0d7c9b83d4@mail.gmail.com> <87wrxtkzwu.fsf@openvz.org> <20100303191613.GB18480@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <20100303191613.GB18480@redhat.com> (Mike Snitzer's message of "Wed, 3 Mar 2010 14:16:13 -0500") Sender: linux-kernel-owner@vger.kernel.org To: Mike Snitzer Cc: Jens Axboe , linux-kernel@vger.kernel.org, dm-devel@redhat.com List-Id: dm-devel.ids Mike Snitzer writes: > Linux has all sorts of internal interfaces that are "odd"... the current > 'q->merge_bvec_fn' interface included. But odd is not a problem (nor is > it "broken") unless you make changes that don't consider how the current > interface is defined. Ok. then cant you please explain more historical questions 1) Why bio_add_page() can not add less data than requested? Seems that it doesn't make caller's code much complicate Off course barrier bio is special case. I don't consider it here. 2) What statement "bio_add_page() must accept at least one page" exactly means? IMHO this means that bio_add_page() must accept at least one page with len (PAGE_SIZE - offset). Or more restricted statemnt that first bio_add_page() must be always successfull. But currently in some places this rule treated as what all bio which has size less whan PAGE_SIZE are accepted. And in x86 such bio may has up to 8 pages/bvecs. > > But I digress... > > Mike