ulist_del        2556 fs/btrfs/qgroup.c 				ulist_del(new_roots, qgroup_to_skip, 0);
ulist_del        2557 fs/btrfs/qgroup.c 				ulist_del(record->old_roots, qgroup_to_skip,
ulist_del          53 fs/btrfs/ulist.h int ulist_del(struct ulist *ulist, u64 val, u64 aux);