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Subject[PATCH 06/18] virtio_ring: avail event index interface
Define a new feature bit for the host to
declare that it uses an avail_event index
(like Xen) instead of a feature bit
to enable/disable interrupts.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
include/linux/virtio_ring.h | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index f5c1b75..f791772 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -32,6 +32,9 @@
/* 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
+/* The Host publishes the avail index for which it expects a kick
+ * at the end of the used ring. Guest should ignore the used->flags field. */
+#define VIRTIO_RING_F_AVAIL_EVENT_IDX 32

/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
struct vring_desc {
@@ -96,11 +99,13 @@ struct vring {
* __u16 used_flags;
* __u16 used_idx;
* struct vring_used_elem used[num];
+ * __u16 avail_event_idx;
* };
*/
-/* We publish the used event index at the end of the available ring.
- * It is at the end for backwards compatibility. */
+/* We publish the used event index at the end of the available ring, and vice
+ * versa. They are at the end for backwards compatibility. */
#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
+#define vring_avail_event(vr) (*(__u16 *)&(vr)->used->ring[(vr)->num])

static inline void vring_init(struct vring *vr, unsigned int num, void *p,
unsigned long align)
@@ -116,7 +121,7 @@ static inline unsigned vring_size(unsigned int num, unsigned long align)
{
return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
+ align - 1) & ~(align - 1))
- + sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num;
+ + sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
}

#ifdef __KERNEL__
--
1.7.5.53.gc233e


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