btrfs: send: annotate struct name_cache_entry with __counted_by()

Add the __counted_by compiler attribute to the flexible array member
name to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: toblux

fs/btrfs/send.c

@@ -347,7 +347,7 @@ struct name_cache_entry {
 	int ret;
 	int need_later_update;
 	int name_len;
-	char name[];
+	char name[] __counted_by(name_len);
 };
 
 /* See the comment at lru_cache.h about struct btrfs_lru_cache_entry. */