hammer_buf_peek_io
KKASSERT(hammer_buf_peek_io(bp) == NULL);
hammer_io_t io = hammer_buf_peek_io(bp);
hammer_io_t io = hammer_buf_peek_io(bp);
hammer_io_t io = hammer_buf_peek_io(bp);
KKASSERT(hammer_buf_peek_io(bp) == io);
if ((io = hammer_buf_peek_io(bp)) != NULL) {