xfs: create block pointer check functions

Create some helper functions to check that a block pointer points
within the filesystem (or AG) and doesn't point at static metadata.
We will use this for scrub.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h
index ef26edc..7ba2d12 100644
--- a/fs/xfs/libxfs/xfs_alloc.h
+++ b/fs/xfs/libxfs/xfs_alloc.h
@@ -232,5 +232,9 @@ int xfs_alloc_query_range(struct xfs_btree_cur *cur,
 		xfs_alloc_query_range_fn fn, void *priv);
 int xfs_alloc_query_all(struct xfs_btree_cur *cur, xfs_alloc_query_range_fn fn,
 		void *priv);
+xfs_agblock_t xfs_ag_block_count(struct xfs_mount *mp, xfs_agnumber_t agno);
+bool xfs_verify_agbno(struct xfs_mount *mp, xfs_agnumber_t agno,
+		xfs_agblock_t agbno);
+bool xfs_verify_fsbno(struct xfs_mount *mp, xfs_fsblock_t fsbno);
 
 #endif	/* __XFS_ALLOC_H__ */