xfs: add parent pointer ioctls

This patch adds a pair of new file ioctls to retrieve the parent pointer
of a given inode.  They both return the same results, but one operates
on the file descriptor passed to ioctl() whereas the other allows the
caller to specify a file handle for which the caller wants results.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_trace.c

@@ -41,6 +41,7 @@
 #include "xfs_bmap.h"
 #include "xfs_exchmaps.h"
 #include "xfs_exchrange.h"
+#include "xfs_parent.h"
 
 /*
  * We include this last to have the helpers above available for the trace