From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49787) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WCAYR-0007k5-3B for qemu-devel@nongnu.org; Sat, 08 Feb 2014 11:15:02 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WCAYJ-0007ag-Dx for qemu-devel@nongnu.org; Sat, 08 Feb 2014 11:14:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36576) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WCAYJ-0007aW-5F for qemu-devel@nongnu.org; Sat, 08 Feb 2014 11:14:47 -0500 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s18GEkhU020674 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sat, 8 Feb 2014 11:14:46 -0500 Message-ID: <52F65880.9000307@redhat.com> Date: Sat, 08 Feb 2014 17:17:04 +0100 From: Max Reitz MIME-Version: 1.0 References: <1391873296-23451-1-git-send-email-kwolf@redhat.com> In-Reply-To: <1391873296-23451-1-git-send-email-kwolf@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] qcow2: Set zero flag for discarded clusters List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf , qemu-devel@nongnu.org Cc: pbonzini@redhat.com, stefanha@redhat.com On 08.02.2014 16:28, Kevin Wolf wrote: > Instead of making the backing file contents visible again after a discard > request, set the zero flag if possible (i.e. on version >= 3). > > Signed-off-by: Kevin Wolf > --- > block/qcow2-cluster.c | 22 ++++++++++++++++++++-- > 1 file changed, 20 insertions(+), 2 deletions(-) > > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index 25d45d1..008bc04 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -1333,13 +1333,31 @@ static int discard_single_l2(BlockDriverState *bs, uint64_t offset, > uint64_t old_offset; > > old_offset = be64_to_cpu(l2_table[l2_index + i]); > - if ((old_offset & L2E_OFFSET_MASK) == 0) { > + > + /* > + * Make sure that a discarded area reads back as zeroes for v3 images > + * (we cannot do it for v2 without actually writing a zero-filled > + * buffer). We can skip the operation if the cluster is already marked > + * as zero, or if it's unallocated and we don't have a backing file. > + * > + * TODO We might want to use bdrv_get_block_status(bs) here, but we're > + * holding s->lock, so that doesn't work today. > + */ > + if (!!(old_offset & QCOW_OFLAG_ZERO)) { > + continue; > + } > + > + if ((old_offset & L2E_OFFSET_MASK) == 0 && !bs->backing_hd) { > continue; > } > > /* First remove L2 entries */ > qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table); > - l2_table[l2_index + i] = cpu_to_be64(0); > + if (s->version >= 3) { Oh, I revoke my reviewed-by from earlier. This should probably be "s->qcow_version"; otherwise, it won't compile. Max > + l2_table[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO); > + } else { > + l2_table[l2_index + i] = cpu_to_be64(0); > + } > > /* Then decrease the refcount */ > qcow2_free_any_clusters(bs, old_offset, 1, type);