t_buf
struct t_buf t_in; /* input buffer info */
struct t_buf t_out; /* output buffer info */
struct t_buf **meta; /* buffer metadata */
tbuf.meta = (struct t_buf **)kmem_alloc(tbuf.cnt * sizeof (*tbuf.meta),
sizeof (struct t_buf));
tbuf_data_size = tbuf.size - sizeof (struct t_buf);