On Wed, 2019-07-24 at 19:12 +0200, Max Reitz wrote:
> Fixed VHDX images cannot guarantee to be zero-initialized. If the image
> has the "fixed" subformat, forward the call to the underlying storage
> node.
>
> Reported-by: Stefano Garzarella <sgarz...@redhat.com>
> Signed-off-by: Max Reitz <mre...@redhat.com>
> ---
> block/vhdx.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/block/vhdx.c b/block/vhdx.c
> index a02d1c99a7..6a09d0a55c 100644
> --- a/block/vhdx.c
> +++ b/block/vhdx.c
> @@ -2075,6 +2075,30 @@ static int coroutine_fn vhdx_co_check(BlockDriverState
> *bs,
> return 0;
> }
>
> +static int vhdx_has_zero_init(BlockDriverState *bs)
> +{
> + BDRVVHDXState *s = bs->opaque;
> + int state;
> +
> + /*
> + * Check the subformat: Fixed images have all BAT entries present,
> + * dynamic images have none (right after creation). It is
> + * therefore enough to check the first BAT entry.
> + */
> + if (!s->bat_entries) {
> + return 1;
> + }
> +
> + state = s->bat[0] & VHDX_BAT_STATE_BIT_MASK;
> + if (state == PAYLOAD_BLOCK_FULLY_PRESENT) {
> + /* Fixed subformat */
> + return bdrv_has_zero_init(bs->file->bs);
> + }
> +
> + /* Dynamic subformat */
> + return 1;
> +}
> +
> static QemuOptsList vhdx_create_opts = {
> .name = "vhdx-create-opts",
> .head = QTAILQ_HEAD_INITIALIZER(vhdx_create_opts.head),
> @@ -2128,7 +2152,7 @@ static BlockDriver bdrv_vhdx = {
> .bdrv_co_create_opts = vhdx_co_create_opts,
> .bdrv_get_info = vhdx_get_info,
> .bdrv_co_check = vhdx_co_check,
> - .bdrv_has_zero_init = bdrv_has_zero_init_1,
> + .bdrv_has_zero_init = vhdx_has_zero_init,
>
> .create_opts = &vhdx_create_opts,
> };
I am not familiar with VHDX format to be honest too, but knowing that dynamic
format allows for growing
and static are preallocated this makes sense.
Its a bit amusing and not surprising that the the spec for this format is in
.docx.
I took a quick look to get a rough impression of the file format.
Reviewed-by: Maxim Levitsky <mlevi...@redhat.com>
Best regards,
Maxim Levitsky
