Re: [RFC PATCH 10/27] vhost: Allocate shadow vring

[Stefan Hajnoczi]

On Fri, Nov 20, 2020 at 07:50:48PM +0100, Eugenio Pérez wrote:
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  hw/virtio/vhost-sw-lm-ring.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/vhost-sw-lm-ring.c b/hw/virtio/vhost-sw-lm-ring.c
> index cbf53965cd..cd7b5ba772 100644
> --- a/hw/virtio/vhost-sw-lm-ring.c
> +++ b/hw/virtio/vhost-sw-lm-ring.c
> @@ -16,8 +16,11 @@
>  #include "qemu/event_notifier.h"
>  
>  typedef struct VhostShadowVirtqueue {
> +    struct vring vring;
>      EventNotifier hdev_notifier;
>      VirtQueue *vq;
> +
> +    vring_desc_t descs[];
>  } VhostShadowVirtqueue;

VhostShadowVirtqueue is starting to look like VirtQueue. Can the shadow
vq code simply use the VirtIODevice's VirtQueues instead of duplicating
this?

What I mean is:

1. Disable the vhost hdev vq and sync the avail index back to the
   VirtQueue.
2. Move the irq fd to the VirtQueue as its guest notifier.
3. Install the shadow_vq_handler() as the VirtQueue's handle_output
   function.
4. Move the call fd to the VirtQueue as its host notifier.

Now we can process requests from the VirtIODevice's VirtQueue using
virtqueue_pop() and friends. We're also in sync and ready for vmstate
save/load.

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