1 files changed, 13 insertions, 1 deletions
diff --git a/include/linux/crush/mapper.h b/include/linux/crush/mapper.h
index 3303c7fd8a31..c95e19e1ff11 100644
--- a/include/linux/crush/mapper.h
+++ b/include/linux/crush/mapper.h
@@ -15,7 +15,19 @@ extern int crush_do_rule(const struct crush_map *map,
 			 int ruleno,
 			 int x, int *result, int result_max,
 			 const __u32 *weights, int weight_max,
-			 void *cwin, int *scratch);
+			 void *cwin);
+
+/*
+ * Returns the exact amount of workspace that will need to be used
+ * for a given combination of crush_map and result_max. The caller can
+ * then allocate this much on its own, either on the stack, in a
+ * per-thread long-lived buffer, or however it likes.
+ */
+static inline size_t crush_work_size(const struct crush_map *map,
+				     int result_max)
+{
+	return map->working_size + result_max * 3 * sizeof(__u32);
+}
 
 void crush_init_workspace(const struct crush_map *map, void *v);