From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33395) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ctigZ-00073t-Rz for qemu-devel@nongnu.org; Thu, 30 Mar 2017 18:36:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ctigY-0000qn-RS for qemu-devel@nongnu.org; Thu, 30 Mar 2017 18:36:55 -0400 From: Eric Blake Date: Thu, 30 Mar 2017 17:36:45 -0500 Message-Id: <20170330223645.349-4-eblake@redhat.com> In-Reply-To: <20170330223645.349-1-eblake@redhat.com> References: <20170330223645.349-1-eblake@redhat.com> Subject: [Qemu-devel] [PATCH v7 3/3] qcow2: Discard unaligned tail when wiping image List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, qemu-block@nongnu.org, mreitz@redhat.com The previous commit pointed out a subtle difference between the fast and slow path of qcow2_make_empty(), where we failed to discard the final (partial) cluster of an unaligned image. The problem stems from the fact that qcow2_discard_clusters() was silently ignoring sub-cluster head and tail on unaligned requests. A quick audit of all callers shows that qcow2_snapshot_create() has always passed a cluster-aligned request since the call was added in commit 1ebf561; qcow2_co_pdiscard() has passed a cluster-aligned request since commit ecdbead taught the block layer about preferred discard alignment; and qcow2_make_empty() was fixed to pass an aligned start (but not necessarily end) in commit a3e1505. Asserting that the start is always aligned also points out that we now have a dead check: rounding the end offset down can never result in a value less than the aligned start offset (the check was rendered dead with commit ecdbead). Meanwhile, we do not want to round the end cluster down in the one case of the end offset matching the (unaligned) file size - that final partial cluster should still be discarded. With those fixes in place, we can adjust the testsuite so that qemu-iotests 97 and 176 are once again identical for qcow2, showing that fast and slow paths are back in sync. Signed-off-by: Eric Blake --- v7: new patch --- block/qcow2-cluster.c | 10 ++++------ tests/qemu-iotests/176.out | 2 +- 2 files changed, 5 insertions(+), 7 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 78c11d4..100398c 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1519,12 +1519,10 @@ int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset, end_offset = offset + (nb_sectors << BDRV_SECTOR_BITS); - /* Round start up and end down */ - offset = align_offset(offset, s->cluster_size); - end_offset = start_of_cluster(s, end_offset); - - if (offset > end_offset) { - return 0; + /* The caller must cluster-align start; round end down except at EOF */ + assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); + if (end_offset != bs->total_sectors * BDRV_SECTOR_SIZE) { + end_offset = start_of_cluster(s, end_offset); } nb_clusters = size_to_clusters(s, end_offset - offset); diff --git a/tests/qemu-iotests/176.out b/tests/qemu-iotests/176.out index 990a41c..6271fa7 100644 --- a/tests/qemu-iotests/176.out +++ b/tests/qemu-iotests/176.out @@ -35,7 +35,7 @@ Offset Length File Offset Length File 0x7ffd0000 0x10000 TEST_DIR/t.IMGFMT.base 0x7ffe0000 0x20000 TEST_DIR/t.IMGFMT.itmd -0x83400000 0x200 TEST_DIR/t.IMGFMT +0x83400000 0x200 TEST_DIR/t.IMGFMT.itmd === Test pass 1 === -- 2.9.3