---

yaml --- r: 252947 b: refs/heads/master c: bf7035b h: refs/heads/master i: 252945: 5d47ede 252943: 83fff78 v: v3
git-mirror · May 30, 2011 · baaa85b · baaa85b
1 parent 583f5dd
commit baaa85b
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Showing 2 changed files with 15 additions and 1 deletion.
diff --git a/[refs] b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 770b31a85e000b0194974922f238a30ade4246b6
+refs/heads/master: bf7035bf20563a6cadcb9e870406e7b21daf5e30
diff --git a/trunk/include/linux/virtio_ring.h b/trunk/include/linux/virtio_ring.h
@@ -146,6 +146,20 @@ static inline unsigned vring_size(unsigned int num, unsigned long align)
 		+ sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
 }
 
+/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
+/* Assuming a given event_idx value from the other size, if
+ * we have just incremented index from old to new_idx,
+ * should we trigger an event? */
+static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
+{
+	/* Note: Xen has similar logic for notification hold-off
+	 * in include/xen/interface/io/ring.h with req_event and req_prod
+	 * corresponding to event_idx + 1 and new_idx respectively.
+	 * Note also that req_event and req_prod in Xen start at 1,
+	 * event indexes in virtio start at 0. */
+	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
+}
+
 #ifdef __KERNEL__
 #include <linux/irqreturn.h>
 struct virtio_device;