xen: fix const warning

* xen/public/io/ring.h (__CONST_RING_SIZE): Add macro from upstream
* xen/net.c (WINDOW): Use __CONST_RING_SIZE instead of __RING_SIZE.

2 files changed, 7 insertions, 1 deletions

diff --git a/xen/net.c b/xen/net.c
index 1dc2209e..4507ead3 100644
--- a/xen/net.c
+++ b/xen/net.c
@@ -47,7 +47,7 @@
 /* Hypervisor part */
 
 #define ADDRESS_SIZE 6
-#define WINDOW __RING_SIZE((netif_rx_sring_t*)0, PAGE_SIZE)
+#define WINDOW __CONST_RING_SIZE(netif_rx, PAGE_SIZE)
 
 struct net_data {
 	struct device	device;
diff --git a/xen/public/io/ring.h b/xen/public/io/ring.h
index 6ce1d0d4..8669564b 100644
--- a/xen/public/io/ring.h
+++ b/xen/public/io/ring.h
@@ -50,6 +50,12 @@ typedef unsigned int RING_IDX;
  * A ring contains as many entries as will fit, rounded down to the nearest 
  * power of two (so we can mask with (size-1) to loop around).
  */
+#define __CONST_RING_SIZE(_s, _sz) \
+    (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
+	    sizeof(((struct _s##_sring *)0)->ring[0])))
+/*
+ * The same for passing in an actual pointer instead of a name tag.
+ */
 #define __RING_SIZE(_s, _sz) \
     (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))