Re: [PATCH 3/4] virtio-gpu: use a VMState variant for the scanout field

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, May 07, 2024 at 03:19:19PM +0400, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> Depending on the version, use v1 or v2 of the scanout VM state.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  hw/display/virtio-gpu.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
> index ae831b6b3e..4fd72caf3f 100644
> --- a/hw/display/virtio-gpu.c
> +++ b/hw/display/virtio-gpu.c
> @@ -1191,17 +1191,29 @@ static const VMStateDescription vmstate_virtio_gpu_scanout = {
>      },
>  };
>  
> +static bool vmstate_before_v2(void *opaque, int version)
> +{
> +    return version <= 1;
> +}
> +
>  static const VMStateDescription vmstate_virtio_gpu_scanouts = {
>      .name = "virtio-gpu-scanouts",
> -    .version_id = 1,
> +    .version_id = 2,
> +    .minimum_version_id = 1,
>      .fields = (const VMStateField[]) {
>          VMSTATE_INT32(parent_obj.enable, struct VirtIOGPU),
>          VMSTATE_UINT32_EQUAL(parent_obj.conf.max_outputs,
>                               struct VirtIOGPU, NULL),
> -        VMSTATE_STRUCT_VARRAY_UINT32(parent_obj.scanout, struct VirtIOGPU,
> -                                     parent_obj.conf.max_outputs, 1,
> -                                     vmstate_virtio_gpu_scanout,
> -                                     struct virtio_gpu_scanout),
> +        VMSTATE_VSTRUCT_TEST_VARRAY_UINT32(parent_obj.scanout, struct VirtIOGPU,
> +                                           vmstate_before_v2,
> +                                           parent_obj.conf.max_outputs, 1,
> +                                           vmstate_virtio_gpu_scanout,
> +                                           struct virtio_gpu_scanout, 1),
> +        VMSTATE_VSTRUCT_TEST_VARRAY_UINT32(parent_obj.scanout, struct VirtIOGPU,
> +                                           NULL,
> +                                           parent_obj.conf.max_outputs, 2,
> +                                           vmstate_virtio_gpu_scanout,
> +                                           struct virtio_gpu_scanout, 2),
>          VMSTATE_END_OF_LIST()
>      },


Just don't, please.
Add a property and add a conditional field based on property, set
from the compat machinery.


>  };
> -- 
> 2.41.0.28.gd7d8841f67