Setting the QCOW_OFLAG_ZERO bit of the L2 entry is forbidden if an
image has subclusters. Instead, the individual 'all zeroes' bits must
be used.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2-refcount.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index de85ed29a4..65f4fc27c3 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1685,8 +1685,13 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
                         int ign = active ? QCOW2_OL_ACTIVE_L2 :
                                            QCOW2_OL_INACTIVE_L2;
 
-                        l2_entry = QCOW_OFLAG_ZERO;
-                        set_l2_entry(s, l2_table, i, l2_entry);
+                        if (has_subclusters(s)) {
+                            set_l2_entry(s, l2_table, i, 0);
+                            set_l2_bitmap(s, l2_table, i,
+                                          QCOW_L2_BITMAP_ALL_ZEROES);
+                        } else {
+                            set_l2_entry(s, l2_table, i, QCOW_OFLAG_ZERO);
+                        }
                         ret = qcow2_pre_write_overlap_check(bs, ign,
                                 l2e_offset, l2_entry_size(s), false);
                         if (ret < 0) {
-- 
2.20.1

On 22.12.19 12:36, Alberto Garcia wrote:
> Setting the QCOW_OFLAG_ZERO bit of the L2 entry is forbidden if an
> image has subclusters. Instead, the individual 'all zeroes' bits must
> be used.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2-refcount.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>