xen/evtchn: fix ring resize when binding new events

[deliverable/linux.git] / drivers / xen / evtchn.c

diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index 38272ad245516c272ab571bed1a5c962f4a0e808..f4edd6df3df235c55aef1329cb8e17b5ae8cf9f7 100644 (file)
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -316,7 +316,6 @@ static int evtchn_resize_ring(struct per_user_data *u)
 {
        unsigned int new_size;
        evtchn_port_t *new_ring, *old_ring;
-       unsigned int p, c;
 
        /*
         * Ensure the ring is large enough to capture all possible
@@ -346,20 +345,17 @@ static int evtchn_resize_ring(struct per_user_data *u)
        /*
         * Copy the old ring contents to the new ring.
         *
-        * If the ring contents crosses the end of the current ring,
-        * it needs to be copied in two chunks.
+        * To take care of wrapping, a full ring, and the new index
+        * pointing into the second half, simply copy the old contents
+        * twice.
         *
         * +---------+    +------------------+
-        * |34567  12| -> |       1234567    |
-        * +-----p-c-+    +------------------+
+        * |34567  12| -> |34567  1234567  12|
+        * +-----p-c-+    +-------c------p---+
         */
-       p = evtchn_ring_offset(u, u->ring_prod);
-       c = evtchn_ring_offset(u, u->ring_cons);
-       if (p < c) {
-               memcpy(new_ring + c, u->ring + c, (u->ring_size - c) * sizeof(*u->ring));
-               memcpy(new_ring + u->ring_size, u->ring, p * sizeof(*u->ring));
-       } else
-               memcpy(new_ring + c, u->ring + c, (p - c) * sizeof(*u->ring));
+       memcpy(new_ring, old_ring, u->ring_size * sizeof(*u->ring));
+       memcpy(new_ring + u->ring_size, old_ring,
+              u->ring_size * sizeof(*u->ring));
 
        u->ring = new_ring;
        u->ring_size = new_size;