From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:60021) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SeRye-0003oG-Fy for qemu-devel@nongnu.org; Tue, 12 Jun 2012 10:21:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SeRyT-0000Iw-8Q for qemu-devel@nongnu.org; Tue, 12 Jun 2012 10:21:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34472) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SeRyT-0000I8-0Z for qemu-devel@nongnu.org; Tue, 12 Jun 2012 10:21:37 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q5CELZJU027202 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 12 Jun 2012 10:21:35 -0400 Message-ID: <4FD7506C.1030606@redhat.com> Date: Tue, 12 Jun 2012 16:21:32 +0200 From: Kevin Wolf MIME-Version: 1.0 References: <1339508835-15108-1-git-send-email-kwolf@redhat.com> <4FD74B8D.9090800@redhat.com> In-Reply-To: <4FD74B8D.9090800@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] qcow2: Simplify calculation for COW area at the end List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: qemu-devel@nongnu.org Am 12.06.2012 16:00, schrieb Paolo Bonzini: > Il 12/06/2012 15:47, Kevin Wolf ha scritto: >> copy_sectors() always uses the sum (cluster_offset + n_start) or >> (start_sect + n_start), so if some value is added to both cluster_offset >> and start_sect, and subtracted from n_start, it's cancelled out anyway. >> >> Signed-off-by: Kevin Wolf >> --- >> block/qcow2-cluster.c | 5 ++--- >> 1 files changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c >> index 9aee9fc..763b724 100644 >> --- a/block/qcow2-cluster.c >> +++ b/block/qcow2-cluster.c >> @@ -640,11 +640,10 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m) >> } >> >> if (m->nb_available & (s->cluster_sectors - 1)) { >> - uint64_t end = m->nb_available & ~(uint64_t)(s->cluster_sectors - 1); >> cow = true; >> qemu_co_mutex_unlock(&s->lock); >> - ret = copy_sectors(bs, start_sect + end, cluster_offset + (end << 9), >> - m->nb_available - end, s->cluster_sectors); >> + ret = copy_sectors(bs, start_sect, cluster_offset, >> + m->nb_available, s->cluster_sectors); > > Do you need to add end to s->cluster_sectors too, so that "start_sect + > n_end" and "n_end - n_start" remain the same? You mean because n_end is now relative to start_sect instead of start_sect + end, right? I thought about it and I find this code is a bit confusing, but I think you're right that I need to replace n_end as well because it would be wrong for an allocating request than spans multiple clusters. I think this one should be right, would you agree? ret = copy_sectors(bs, start_sect, cluster_offset, m->nb_available, align_offset(m->nb_available, s->cluster_sectors)); The interesting question is why qemu-iotests doesn't catch it. Kevin