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)
{
--
1.7.5.53.gc233e
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