opal_get_chars
extern ssize_t opal_get_chars(uint32_t vtermno, u8 *buf, size_t count);
opal_get_chars, opal_put_chars_atomic,
rc = opal_get_chars(termno, &c, 1);
opal_get_chars, opal_put_chars_atomic,
opal_get_chars, opal_put_chars_atomic,
.get_chars = opal_get_chars,