virtio: event index interface

Define a new feature bit for the guest and host to utilize
an event index (like Xen) instead if a flag bit to enable/disable
interrupts and kicks.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index a813e5d460ebf320b2ebbb9d9fedd3117919edae..c4eef73deb3fc1642fd0c567d5758888ad04bd70 100644 (file)
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -52,6 +52,12 @@
 /* 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. */
+/* 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_EVENT_IDX                29
+
 /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
 struct vring_desc {
        /* Address (guest-physical). */
@@ -106,6 +112,7 @@ struct vring {
  *     __u16 avail_flags;
  *     __u16 avail_idx;
  *     __u16 available[num];
+ *     __u16 used_event_idx;
  *
  *     // Padding to the next align boundary.
  *     char pad[];
@@ -114,8 +121,14 @@ 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, 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)
 {
@@ -130,7 +143,7 @@ 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__