xfs: dynamically allocate btree scrub context structure

Reorganize struct xchk_btree so that we can dynamically size the context
structure to fit the type of btree cursor that we have.  This will
enable us to use memory more efficiently once we start adding very tall
btree types.  Right-size the lastkey array to match the number of *node*
levels in the tree so that we stop wasting space.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/fs/xfs/scrub/btree.h b/fs/xfs/scrub/btree.h
index 7671108f9f85..da61a53a0b61 100644
--- a/fs/xfs/scrub/btree.h
+++ b/fs/xfs/scrub/btree.h
@@ -39,9 +39,22 @@ struct xchk_btree {
 
 	/* internal scrub state */
 	union xfs_btree_rec		lastrec;
-	union xfs_btree_key		lastkey[XFS_BTREE_MAXLEVELS];
 	struct list_head		to_check;
+
+	/* this element must come last! */
+	union xfs_btree_key		lastkey[];
 };
+
+/*
+ * Calculate the size of a xchk_btree structure.  There are nlevels-1 slots for
+ * keys because we track leaf records separately in lastrec.
+ */
+static inline size_t
+xchk_btree_sizeof(unsigned int nlevels)
+{
+	return struct_size((struct xchk_btree *)NULL, lastkey, nlevels - 1);
+}
+
 int xchk_btree(struct xfs_scrub *sc, struct xfs_btree_cur *cur,
 		xchk_btree_rec_fn scrub_fn, const struct xfs_owner_info *oinfo,
 		void *private);