new helper: ihold()

Clones an existing reference to inode; caller must already hold one.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index fac5229..fb2ca2e 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -500,7 +500,7 @@
 #define IHOLD(ip) \
 do { \
 	ASSERT(atomic_read(&VFS_I(ip)->i_count) > 0) ; \
-	atomic_inc(&(VFS_I(ip)->i_count)); \
+	ihold(VFS_I(ip)); \
 	trace_xfs_ihold(ip, _THIS_IP_); \
 } while (0)