[Qemu-devel] [PATCH] qcow2: Fix qcow2_make_empty() with external data file

[Kevin Wolf <kwolf@redhat.com>]

make_completely_empty() is an optimisated path for bdrv_make_empty()
where completely new metadata is created inside the image file instead
of going through all clusters and discarding them. For an external data
file, however, we actually need to do discard operations on the data
file; just overwriting the qcow2 file doesn't get rid of the data.

The necessary slow path with an explicit discard operation already
exists for other cases. Use it for external data files, too.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 7fbef97aab..097fde56f9 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4384,7 +4384,8 @@ static int qcow2_make_empty(BlockDriverState *bs)
 
     if (s->qcow_version >= 3 && !s->snapshots && !s->nb_bitmaps &&
         3 + l1_clusters <= s->refcount_block_size &&
-        s->crypt_method_header != QCOW_CRYPT_LUKS) {
+        s->crypt_method_header != QCOW_CRYPT_LUKS &&
+        !has_data_file(bs)) {
         /* The following function only works for qcow2 v3 images (it
          * requires the dirty flag) and only as long as there are no
          * features that reserve extra clusters (such as snapshots,
-- 
2.20.1