Add util.h for kernel helpers

Add a little header for inline convenience functions.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/util.h

@@ -0,0 +1,20 @@
+#ifndef _SCOUTFS_UTIL_H_
+#define _SCOUTFS_UTIL_H_
+
+/*
+ * Little utility helpers that probably belong upstream.
+ */
+
+static inline void down_write_two(struct rw_semaphore *a,
+				  struct rw_semaphore *b)
+{
+	BUG_ON(a == b);
+
+	if (a > b)
+		swap(a, b);
+
+	down_write(a);
+	down_write_nested(b, SINGLE_DEPTH_NESTING);
+}
+
+#endif