From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45269) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WFPSF-0003nj-Gg for qemu-devel@nongnu.org; Mon, 17 Feb 2014 09:46:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WFPS9-0005Qy-8e for qemu-devel@nongnu.org; Mon, 17 Feb 2014 09:45:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59858) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WFPS9-0005Qo-0k for qemu-devel@nongnu.org; Mon, 17 Feb 2014 09:45:49 -0500 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 s1HEjlm0008542 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Mon, 17 Feb 2014 09:45:47 -0500 From: Kevin Wolf Date: Mon, 17 Feb 2014 15:45:47 +0100 Message-Id: <1392648347-4981-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PATCH v2] qcow2: Set zero flag for discarded clusters List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, stefanha@redhat.com, mreitz@redhat.com 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 ++++++++++++++++++++-- tests/qemu-iotests/046 | 18 ++++++++++++++---- 2 files changed, 34 insertions(+), 6 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index cd2dcfa..f404ef1 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1332,13 +1332,31 @@ 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->qcow_version >= 3) { + 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); diff --git a/tests/qemu-iotests/046 b/tests/qemu-iotests/046 index 2d44bbb..e0be46c 100755 --- a/tests/qemu-iotests/046 +++ b/tests/qemu-iotests/046 @@ -193,6 +193,16 @@ echo "== Verify image content ==" function verify_io() { + if ($QEMU_IMG info -f "$IMGFMT" "$TEST_IMG" | grep "compat: 0.10" > /dev/null); then + # For v2 images, discarded clusters are read from the backing file + # Keep the variable empty so that the backing file value can be used as + # the default below + discarded= + else + # Discarded clusters are zeroed for v3 or later + discarded=0 + fi + echo read -P 0 0 0x10000 echo read -P 1 0x10000 0x2000 @@ -221,16 +231,16 @@ function verify_io() echo read -P 70 0x78000 0x6000 echo read -P 7 0x7e000 0x2000 - echo read -P 8 0x80000 0x6000 + echo read -P ${discarded:-8} 0x80000 0x6000 echo read -P 80 0x86000 0x2000 - echo read -P 8 0x88000 0x2000 + echo read -P ${discarded:-8} 0x88000 0x2000 echo read -P 81 0x8a000 0xe000 echo read -P 90 0x98000 0x6000 echo read -P 9 0x9e000 0x2000 - echo read -P 10 0xa0000 0x6000 + echo read -P ${discarded:-10} 0xa0000 0x6000 echo read -P 100 0xa6000 0x2000 - echo read -P 10 0xa8000 0x2000 + echo read -P ${discarded:-10} 0xa8000 0x2000 echo read -P 101 0xaa000 0xe000 echo read -P 110 0xb8000 0x8000 -- 1.8.1.4