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vmdk: Fix partial overwrite of zero cluster 

When overwriting a zero cluster, we must not perform copy-on-write from
the backing file, but from a zeroed buffer.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200430133007.170335-4-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2020-04-30 15:30:04 +02:00
parent 2821c1cc0f
commit 4823cde58e
1 changed files with 12 additions and 6 deletions
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18
block/vmdk.c
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@ -1340,7 +1340,9 @@ static void vmdk_refresh_limits(BlockDriverState *bs, Error **errp)
* get_whole_cluster
*
* Copy backing file's cluster that covers @sector_num, otherwise write zero,
* to the cluster at @cluster_sector_num.
* to the cluster at @cluster_sector_num. If @zeroed is true, we're overwriting
* a zeroed cluster in the current layer and must not copy data from the
* backing file.
*
* If @skip_start_sector < @skip_end_sector, the relative range
* [@skip_start_sector, @skip_end_sector) is not copied or written, and leave
@ -1351,18 +1353,21 @@ static int get_whole_cluster(BlockDriverState *bs,
uint64_t cluster_offset,
uint64_t offset,
uint64_t skip_start_bytes,
uint64_t skip_end_bytes)
uint64_t skip_end_bytes,
bool zeroed)
{
int ret = VMDK_OK;
int64_t cluster_bytes;
uint8_t *whole_grain;
bool copy_from_backing;
/* For COW, align request sector_num to cluster start */
cluster_bytes = extent->cluster_sectors << BDRV_SECTOR_BITS;
offset = QEMU_ALIGN_DOWN(offset, cluster_bytes);
whole_grain = qemu_blockalign(bs, cluster_bytes);
copy_from_backing = bs->backing && !zeroed;
if (!bs->backing) {
if (!copy_from_backing) {
memset(whole_grain, 0, skip_start_bytes);
memset(whole_grain + skip_end_bytes, 0, cluster_bytes - skip_end_bytes);
}
@ -1377,7 +1382,7 @@ static int get_whole_cluster(BlockDriverState *bs,
/* Read backing data before skip range */
if (skip_start_bytes > 0) {
if (bs->backing) {
if (copy_from_backing) {
/* qcow2 emits this on bs->file instead of bs->backing */
BLKDBG_EVENT(extent->file, BLKDBG_COW_READ);
ret = bdrv_pread(bs->backing, offset, whole_grain,
@ -1397,7 +1402,7 @@ static int get_whole_cluster(BlockDriverState *bs,
}
/* Read backing data after skip range */
if (skip_end_bytes < cluster_bytes) {
if (bs->backing) {
if (copy_from_backing) {
/* qcow2 emits this on bs->file instead of bs->backing */
BLKDBG_EVENT(extent->file, BLKDBG_COW_READ);
ret = bdrv_pread(bs->backing, offset + skip_end_bytes,
@ -1631,7 +1636,8 @@ static int get_cluster_offset(BlockDriverState *bs,
* or inappropriate VM shutdown.
*/
ret = get_whole_cluster(bs, extent, cluster_sector * BDRV_SECTOR_SIZE,
offset, skip_start_bytes, skip_end_bytes);
offset, skip_start_bytes, skip_end_bytes,
zeroed);
if (ret) {
return ret;
}