[PATCH v6 31/32] qcow2: Assert that expand_zero_clusters_in_l1() does not support subclusters

[Alberto Garcia <berto@igalia.com>]

This function is only used by qcow2_expand_zero_clusters() to
downgrade a qcow2 image to a previous version. It is however not
possible to downgrade an image with extended L2 entries because older
versions of qcow2 do not have this feature.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 block/qcow2-cluster.c      | 8 +++++++-
 tests/qemu-iotests/061     | 6 ++++++
 tests/qemu-iotests/061.out | 5 +++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index b808d6ad95..608e785dd6 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -2156,6 +2156,9 @@ static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
     int ret;
     int i, j;
 
+    /* qcow2_downgrade() is not allowed in images with subclusters */
+    assert(!has_subclusters(s));
+
     slice_size2 = s->l2_slice_size * l2_entry_size(s);
     n_slices = s->cluster_size / slice_size2;
 
@@ -2224,7 +2227,8 @@ static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
                 if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
                     if (!bs->backing) {
                         /* not backed; therefore we can simply deallocate the
-                         * cluster */
+                         * cluster. No need to call set_l2_bitmap(), this
+                         * function doesn't support images with subclusters. */
                         set_l2_entry(s, l2_slice, j, 0);
                         l2_dirty = true;
                         continue;
@@ -2295,6 +2299,8 @@ static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
                 } else {
                     set_l2_entry(s, l2_slice, j, offset);
                 }
+                /* No need to call set_l2_bitmap() after set_l2_entry() because
+                 * this function doesn't support images with subclusters. */
                 l2_dirty = true;
             }
 
diff --git a/tests/qemu-iotests/061 b/tests/qemu-iotests/061
index 10eb243164..23add2dfe3 100755
--- a/tests/qemu-iotests/061
+++ b/tests/qemu-iotests/061
@@ -303,6 +303,12 @@ $QEMU_IMG amend -o "compat=0.10" "$TEST_IMG"
 _img_info --format-specific
 _check_test_img
 
+echo
+echo "=== Testing version downgrade with extended L2 entries ==="
+echo
+_make_test_img -o "compat=1.1,extended_l2=on" 64M
+$QEMU_IMG amend -o "compat=0.10" "$TEST_IMG"
+
 echo
 echo "=== Try changing the external data file ==="
 echo
diff --git a/tests/qemu-iotests/061.out b/tests/qemu-iotests/061.out
index 39812d8cf8..c1acdbd751 100644
--- a/tests/qemu-iotests/061.out
+++ b/tests/qemu-iotests/061.out
@@ -528,6 +528,11 @@ Format specific information:
     extended l2: false
 No errors were found on the image.
 
+=== Testing version downgrade with extended L2 entries ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
+qemu-img: Cannot downgrade an image with incompatible features 0x10 set
+
 === Try changing the external data file ===
 
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
-- 
2.20.1