On 17.03.20 19:16, Alberto Garcia wrote:
> 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>
> ---
>  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/tests/qemu-iotests/061 b/tests/qemu-iotests/061
> index 36b040491f..66bfd23179 100755
> --- a/tests/qemu-iotests/061
> +++ b/tests/qemu-iotests/061
> @@ -266,6 +266,12 @@ $QEMU_IMG amend -o "compat=0.10" "$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 8b3091a412..5d009867a2 100644
> --- a/tests/qemu-iotests/061.out
> +++ b/tests/qemu-iotests/061.out
> @@ -498,6 +498,11 @@ Format specific information:
>      corrupt: 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

This test fails in this commit, because extended_l2 is only available
after the next commit.  The code changes and the test itself look good
to me, though.

Max