xen: Add RING_COPY_REQUEST()

[firefly-linux-kernel-4.4.55.git] / include / xen / interface / io / ring.h

diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
index 7d28aff605c7eb600c4c3bfe93b8b5f1edbaebfe..7dc685b4057d33ad227d861a2a3115a5ca55cd3e 100644 (file)
--- a/include/xen/interface/io/ring.h
+++ b/include/xen/interface/io/ring.h
@@ -181,6 +181,20 @@ struct __name##_back_ring {                                                \
 #define RING_GET_REQUEST(_r, _idx)                                     \
     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 
+/*
+ * Get a local copy of a request.
+ *
+ * Use this in preference to RING_GET_REQUEST() so all processing is
+ * done on a local copy that cannot be modified by the other end.
+ *
+ * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
+ * to be ineffective where _req is a struct which consists of only bitfields.
+ */
+#define RING_COPY_REQUEST(_r, _idx, _req) do {                         \
+       /* Use volatile to force the copy into _req. */                 \
+       *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx);   \
+} while (0)
+
 #define RING_GET_RESPONSE(_r, _idx)                                    \
     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))