xfs: create wrappers for converting kuid_t to/from uid_t

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_linux.h

@@ -191,6 +191,32 @@ typedef __uint64_t __psunsigned_t;
 #define MAX(a,b)	(max(a,b))
 #define howmany(x, y)	(((x)+((y)-1))/(y))
 
+/* Kernel uid/gid conversion. These are used to convert to/from the on disk
+ * uid_t/gid_t types to the kuid_t/kgid_t types that the kernel uses internally.
+ * The conversion here is type only, the value will remain the same since we
+ * are converting to the init_user_ns. The uid is later mapped to a particular
+ * user namespace value when crossing the kernel/user boundary.
+ */
+static inline __uint32_t xfs_kuid_to_uid(kuid_t uid)
+{
+	return from_kuid(&init_user_ns, uid);
+}
+
+static inline kuid_t xfs_uid_to_kuid(__uint32_t uid)
+{
+	return make_kuid(&init_user_ns, uid);
+}
+
+static inline __uint32_t xfs_kgid_to_gid(kgid_t gid)
+{
+	return from_kgid(&init_user_ns, gid);
+}
+
+static inline kgid_t xfs_gid_to_kgid(__uint32_t gid)
+{
+	return make_kgid(&init_user_ns, gid);
+}
+
 /*
  * Various platform dependent calls that don't fit anywhere else
  */