Function ng_ppp_cutproto

freebsd/netgraph/ng_ppp.c:2434–2454

* Cut a possibly compressed PPP protocol number from the front of a frame. */

 * Cut a possibly compressed PPP protocol number from the front of a frame.
 */
static struct mbuf *
ng_ppp_cutproto(struct mbuf *m, uint16_t *proto)
{

	*proto = 0;
	if (m->m_len < 1 && (m = m_pullup(m, 1)) == NULL)
		return (NULL);

	*proto = *mtod(m, uint8_t *);
	m_adj(m, 1);

	if (!PROT_VALID(*proto)) {
		if (m->m_len < 1 && (m = m_pullup(m, 1)) == NULL)
			return (NULL);

		*proto = (*proto << 8) + *mtod(m, uint8_t *);
		m_adj(m, 1);
	}

	return (m);
}

/*
 * Prepend some bytes to an mbuf.