From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34638) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VF1m4-00049W-4N for qemu-devel@nongnu.org; Thu, 29 Aug 2013 08:56:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VF1lt-0002xD-Qs for qemu-devel@nongnu.org; Thu, 29 Aug 2013 08:56:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31856) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VF1lt-0002x0-IG for qemu-devel@nongnu.org; Thu, 29 Aug 2013 08:56:21 -0400 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r7TCuKBS007400 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Thu, 29 Aug 2013 08:56:20 -0400 Message-ID: <521F44F2.5050700@redhat.com> Date: Thu, 29 Aug 2013 14:56:18 +0200 From: Max Reitz MIME-Version: 1.0 References: <1377771363-5198-1-git-send-email-mreitz@redhat.com> <20130829123343.GH2961@dhcp-200-207.str.redhat.com> <521F40D3.8000302@redhat.com> <20130829125301.GJ2961@dhcp-200-207.str.redhat.com> In-Reply-To: <20130829125301.GJ2961@dhcp-200-207.str.redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] qcow2-refcount: Snapshot update for zero clusters List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org, Stefan Hajnoczi Am 29.08.2013 14:53, schrieb Kevin Wolf: > Am 29.08.2013 um 14:38 hat Max Reitz geschrieben: >> Am 29.08.2013 14:33, schrieb Kevin Wolf: >>> Am 29.08.2013 um 12:16 hat Max Reitz geschrieben: >>>> Do not try to update the refcount for zero clusters in >>>> qcow2_update_snapshot_refcount. >>>> >>>> Signed-off-by: Max Reitz >>>> --- >>>> block/qcow2-refcount.c | 16 +++++++++++++--- >>>> 1 file changed, 13 insertions(+), 3 deletions(-) >>> Please don't forget to add a test case for v2. >> Okay. >> >>>> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c >>>> index 1244693..7555242 100644 >>>> --- a/block/qcow2-refcount.c >>>> +++ b/block/qcow2-refcount.c >>>> @@ -863,9 +863,13 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs, >>>> for(j = 0; j < s->l2_size; j++) { >>>> offset = be64_to_cpu(l2_table[j]); >>>> if (offset != 0) { >>>> + uint64_t cluster_index; >>>> + >>>> old_offset = offset; >>>> offset &= ~QCOW_OFLAG_COPIED; >>>> - if (offset & QCOW_OFLAG_COMPRESSED) { >>>> + >>>> + switch (qcow2_get_cluster_type(offset)) { >>>> + case QCOW2_CLUSTER_COMPRESSED: >>>> nb_csectors = ((offset >> s->csize_shift) & >>>> s->csize_mask) + 1; >>>> if (addend != 0) { >>>> @@ -880,8 +884,10 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs, >>>> } >>>> /* compressed clusters are never modified */ >>>> refcount = 2; >>>> - } else { >>>> - uint64_t cluster_index = (offset & L2E_OFFSET_MASK) >> s->cluster_bits; >>>> + break; >>>> + >>>> + case QCOW2_CLUSTER_NORMAL: >>>> + cluster_index = (offset & L2E_OFFSET_MASK) >> s->cluster_bits; >>>> if (addend != 0) { >>>> refcount = update_cluster_refcount(bs, cluster_index, addend, >>>> QCOW2_DISCARD_SNAPSHOT); >>>> @@ -893,6 +899,10 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs, >>>> ret = refcount; >>>> goto fail; >>>> } >>>> + break; >>> I think this part isn't quite right. Even zero clusters can have an >>> allocated offset, so I think what's really needed is that the same code >>> runs from QCOW2_CLUSTER_ZERO. However, add an if (cluster_index == 0) >>> case for the unallocated case. >> So then it would be enough to change: >> >> - if (offset != 0) { >> + if ((offset & L2E_OFFSET_MASK) != 0) { >> >> and just execute the same code for QCOW2_CLUSTER_NORMAL and >> QCOW2_CLUSTER_ZERO? > Doing only this change in the original code might happen to work, but > it's not really clean as the L2 entry format is different for compressed > clusters (L2E_OFFSET_MASK isn't valid for it). So having the switch for > the cluster type is a good thing, but the implementation for normal and > zero clusters should be shared indeed. Yes, of course I meant to include the switch as well. > The offset != 0 check ends up redundant when you introduce the switch, > so in theory it could as well be removed. > Well, I don't know; for zero clusters, the if statement is required anyway (since qcow2_get_cluster_type does not distinguish between allocated and non-allocated zero clusters), so I though we might as well just leave it where it is (just slightly adjusted in the way I proposed). Max