ftl: compute length after determining the offset

source/ftl/ftl.c

@@ -28,11 +28,10 @@ size_t ftl_read(struct ftl_map *map, void *data, size_t len, uint32_t va)
 	if (!data)
 		return 0;
 
-	len = min(len, (1 << map->log2_page_size) - offset);
-
 	mask = ((1 << map->log2_page_size) - 1);
 	offset = va & mask;
 	va >>= map->log2_page_size;
+	len = min(len, (1 << map->log2_page_size) - offset);
 
 	if ((ret = trace_path(map, NULL, &page, va)) < 0) {
 		memset(data, 0, len);