xfs: multithreaded iwalk implementation

Create a parallel iwalk implementation and switch quotacheck to use it.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/xfs_sysctl.h

@@ -82,6 +82,9 @@ enum {
 extern xfs_param_t	xfs_params;
 
 struct xfs_globals {
+#ifdef DEBUG
+	int	pwork_threads;		/* parallel workqueue threads */
+#endif
 	int	log_recovery_delay;	/* log recovery delay (secs) */
 	int	mount_delay;		/* mount setup delay (secs) */
 	bool	bug_on_assert;		/* BUG() the kernel on assert failure */