On Wednesday, May 04, 2011 03:51:09 PM Michael S. Tsirkin wrote:
> Define a new feature bit for the guest to utilize a used_event index
> (like Xen) instead if a flag bit to enable/disable interrupts.
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> include/linux/virtio_ring.h | 9 +++++++++
> 1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> index e4d144b..f5c1b75 100644
> --- a/include/linux/virtio_ring.h
> +++ b/include/linux/virtio_ring.h
> @@ -29,6 +29,10 @@
> /* We support indirect buffer descriptors */
> #define VIRTIO_RING_F_INDIRECT_DESC 28
>
> +/* The Guest publishes the used index for which it expects an interrupt
> + * at the end of the avail ring. Host should ignore the avail->flags
> field. */ +#define VIRTIO_RING_F_USED_EVENT_IDX 29
> +
> /* Virtio ring descriptors: 16 bytes. These can chain together via
> "next". */ struct vring_desc {
> /* Address (guest-physical). */
> @@ -83,6 +87,7 @@ struct vring {
> * __u16 avail_flags;
> * __u16 avail_idx;
> * __u16 available[num];
> + * __u16 used_event_idx;
> *
> * // Padding to the next align boundary.
> * char pad[];
> @@ -93,6 +98,10 @@ struct vring {
> * struct vring_used_elem used[num];
> * };
> */
> +/* We publish the used event index at the end of the available ring.
> + * It is at the end for backwards compatibility. */
> +#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
> +
> static inline void vring_init(struct vring *vr, unsigned int num, void *p,
> unsigned long align)
> {
You should update the vring_size procedure to account for the extra field at
the end of the available ring by change the "(2 + num)" to "(3 + num)":
return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num)
Tom
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