Re: [PATCH 2/2] hw/display: fail early when multiple virgl devices are requested

[Mark Cave-Ayland]

On 01/07/2021 08:18, marcandre.lureau@redhat.com wrote:

> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> This avoids failing to initialize virgl and crashing later on, and clear
> the user expectations.
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>   hw/display/virtio-gpu-gl.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c
> index d971b48080..c973d4824b 100644
> --- a/hw/display/virtio-gpu-gl.c
> +++ b/hw/display/virtio-gpu-gl.c
> @@ -25,6 +25,8 @@
>   
>   #include <virglrenderer.h>
>   
> +static int virgl_count = 0;
> +
>   static void virtio_gpu_gl_update_cursor_data(VirtIOGPU *g,
>                                                struct virtio_gpu_scanout *s,
>                                                uint32_t resource_id)
> @@ -113,6 +115,11 @@ static void virtio_gpu_gl_device_realize(DeviceState 
> *qdev, Error **errp)
>       return;
>   #endif
>   
> +    if (virgl_count++ > 0) {
> +        error_setg(errp, "multiple virgl devices aren't supported yet");
> +        return;
> +    }
> +
>       if (!display_opengl) {
>           error_setg(errp, "opengl is not available");
>           return;
> @@ -124,6 +131,10 @@ static void virtio_gpu_gl_device_realize(DeviceState 
> *qdev, Error **errp)
>   
>       virtio_gpu_device_realize(qdev, errp);
>   }
> +static void virtio_gpu_gl_device_unrealize(DeviceState *dev)
> +{
> +    virgl_count--;
> +}
>   
>   static Property virtio_gpu_gl_properties[] = {
>       DEFINE_PROP_BIT("stats", VirtIOGPU, parent_obj.conf.flags,
> @@ -144,6 +155,7 @@ static void virtio_gpu_gl_class_init(ObjectClass *klass, 
> void *data)
>       vgc->update_cursor_data = virtio_gpu_gl_update_cursor_data;
>   
>       vdc->realize = virtio_gpu_gl_device_realize;
> +    vdc->unrealize = virtio_gpu_gl_device_unrealize;
>       vdc->reset = virtio_gpu_gl_reset;
>       device_class_set_props(dc, virtio_gpu_gl_properties);
>   }

FWIW I think the best way to prevent instantiation of multiple devices is to use the 
QOM API to detect if more than one instance of a class exists within the QOM tree.

Have a look at fw_cfg_find() and its usage from fw_cfg_common_realize() in 
hw/nvram/fw_cfg.c for an example of this.


ATB,

Mark.