From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomohiro Kusumi Subject: Re: [PATCH] fix hard-coded disk header chunk size for persistent snapshot Date: Wed, 12 May 2010 14:57:34 +0900 Message-ID: <4BEA434E.3030403@jp.fujitsu.com> References: <4BEA0472.1060300@jp.fujitsu.com> <20100512013909.GD2377@agk-dp.fab.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Mikulas Patocka , Alasdair G Kergon , dm-devel@redhat.com Cc: linux-kernel@vger.kernel.org, kusumi.tomohiro@jp.fujitsu.com List-Id: dm-devel.ids (2010/05/12 13:58), Mikulas Patocka wrote: > > > On Wed, 12 May 2010, Alasdair G Kergon wrote: > >> On Wed, May 12, 2010 at 10:29:22AM +0900, Tomohiro Kusumi wrote: >>> This patch fixes hard-coded value for the size of a chunk that includes >>> disk header for persistent snapshot. It should be changed to existing >>> macro NUM_SNAPSHOT_HDR_CHUNKS instead of using hard-coded value 1. >> >> Any more places too? (E.g. persistent_commit_merge) >> >> Alasdair > > I think the expression in persistent_commit_merge should be changed to: > ps->next_free = area_location(ps, ps->current_area) + > ps->current_committed + 1; > > It is numerically the same, but will avoid trouble if > NUM_SNAPSHOT_HDR_CHUNKS is increased. > > Mikulas > > agree, a single chunk is large enough to contain 16byte disk header which does not seem necessary to increase NUM_SNAPSHOT_HDR_CHUNKS in the future (unless whole structure get totally changed), but it should also get fixed to avoid trouble. I merged it to the patch with your names signed off. Thanks, Tomohiro Kusumi Signed-off-by: Tomohiro Kusumi Signed-off-by: Alasdair G Kergon Signed-off-by: Mikulas Patocka --- diff -aNur linux-2.6.34-rc7.org/drivers/md/dm-snap-persistent.c linux-2.6.34-rc7/drivers/md/dm-snap-persistent.c --- linux-2.6.34-rc7.org/drivers/md/dm-snap-persistent.c 2010-05-10 10:36:28.000000000 +0900 +++ linux-2.6.34-rc7/drivers/md/dm-snap-persistent.c 2010-05-12 14:49:13.000000000 +0900 @@ -266,7 +266,7 @@ */ static chunk_t area_location(struct pstore *ps, chunk_t area) { - return 1 + ((ps->exceptions_per_area + 1) * area); + return NUM_SNAPSHOT_HDR_CHUNKS + ((ps->exceptions_per_area + 1) * area); } /* @@ -780,8 +780,8 @@ * ps->current_area does not get reduced by prepare_merge() until * after commit_merge() has removed the nr_merged previous exceptions. */ - ps->next_free = (area_location(ps, ps->current_area) - 1) + - (ps->current_committed + 1) + NUM_SNAPSHOT_HDR_CHUNKS; + ps->next_free = area_location(ps, ps->current_area) + + ps->current_committed + 1; return 0; }