bcache: Abstract out stuff needed for sorting

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/btree.c

@@ -23,6 +23,7 @@
 #include "bcache.h"
 #include "btree.h"
 #include "debug.h"
+#include "extents.h"
 #include "writeback.h"
 
 #include <linux/slab.h>
@@ -931,6 +932,11 @@ out:
 	b->level	= level;
 	b->parent	= (void *) ~0UL;
 
+	if (!b->level)
+		b->ops	= &bch_extent_keys_ops;
+	else
+		b->ops	= &bch_btree_keys_ops;
+
 	mca_reinit(b);
 
 	return b;