On 22.12.19 12:36, Alberto Garcia wrote:
> Extended L2 entries are 128-bit wide: 64 bits for the entry itself and
> 64 bits for the subcluster allocation bitmap.
> 
> In order to support them correctly get/set_l2_entry() need to be
> updated so they take the entry width into account in order to
> calculate the correct offset.
> 
> This patch also adds the get/set_l2_bitmap() functions that are
> used to access the bitmaps. For convenience we allow calling
> get_l2_bitmap() on images without subclusters, although the caller
> does not need and should ignore the returned value.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 8be020bb76..64b0a814f4 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -518,15 +518,37 @@ static inline size_t l2_entry_size(BDRVQcow2State *s)

[...]

> +static inline uint64_t get_l2_bitmap(BDRVQcow2State *s, uint64_t *l2_slice,
> +                                     int idx)
> +{
> +    if (has_subclusters(s)) {
> +        idx *= l2_entry_size(s) / sizeof(uint64_t);
> +        return be64_to_cpu(l2_slice[idx + 1]);
> +    } else {
> +        /* For convenience only; the caller should ignore this value. */
> +        return 0;

Is there a reason you decided not to return the first subcluster as
allocated?  (As you had proposed in v2)

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

> +    }
> +}