virtio: basic structure for packed ring

Define packed ring structure according to Qemu nomenclature,
field data(wrap counter, etc) are also included.

Signed-off-by: Wei Xu <wexu@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
Message-Id: <20191025083527.30803-2-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio.c

@@ -43,6 +43,13 @@ typedef struct VRingDesc
     uint16_t next;
 } VRingDesc;
 
+typedef struct VRingPackedDesc {
+    uint64_t addr;
+    uint32_t len;
+    uint16_t id;
+    uint16_t flags;
+} VRingPackedDesc;
+
 typedef struct VRingAvail
 {
     uint16_t flags;
@@ -81,17 +88,25 @@ typedef struct VRing
     VRingMemoryRegionCaches *caches;
 } VRing;
 
+typedef struct VRingPackedDescEvent {
+    uint16_t off_wrap;
+    uint16_t flags;
+} VRingPackedDescEvent ;
+
 struct VirtQueue
 {
     VRing vring;
 
     /* Next head to pop */
     uint16_t last_avail_idx;
+    bool last_avail_wrap_counter;
 
     /* Last avail_idx read from VQ. */
     uint16_t shadow_avail_idx;
+    bool shadow_avail_wrap_counter;
 
     uint16_t used_idx;
+    bool used_wrap_counter;
 
     /* Last used index value we have signalled on */
     uint16_t signalled_used;