From 657db3c8995258f892c353e56eaee2c36c96eff8 Mon Sep 17 00:00:00 2001
From: Hajimu UMEMOTO <ume@FreeBSD.org>
Date: Fri, 31 Oct 2003 16:21:26 +0000
Subject: [PATCH] (icmp6_rip6_input) if the received data is small enough but
 in an mbuf cluster, copy the data to a separate mbuf that do not use a
 cluster.  this change will reduce the possiblity of packet loss in the socket
 layer.

Obtained from:	KAME
---
 sys/netinet6/icmp6.c | 48 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/sys/netinet6/icmp6.c b/sys/netinet6/icmp6.c
index 272e04647af..0eb037702a4 100644
--- a/sys/netinet6/icmp6.c
+++ b/sys/netinet6/icmp6.c
@@ -1941,8 +1941,36 @@ icmp6_rip6_input(mp, off)
 				 in6p->in6p_icmp6filt))
 			continue;
 		if (last) {
-			struct	mbuf *n;
-			if ((n = m_copy(m, 0, (int)M_COPYALL)) != NULL) {
+			struct	mbuf *n = NULL;
+
+			/*
+			 * Recent network drivers tend to allocate a single
+			 * mbuf cluster, rather than to make a couple of
+			 * mbufs without clusters.  Also, since the IPv6 code
+			 * path tries to avoid m_pullup(), it is highly
+			 * probable that we still have an mbuf cluster here
+			 * even though the necessary length can be stored in an
+			 * mbuf's internal buffer.
+			 * Meanwhile, the default size of the receive socket
+			 * buffer for raw sockets is not so large.  This means
+			 * the possibility of packet loss is relatively higher
+			 * than before.  To avoid this scenario, we copy the
+			 * received data to a separate mbuf that does not use
+			 * a cluster, if possible.
+			 * XXX: it is better to copy the data after stripping
+			 * intermediate headers.
+			 */
+			if ((m->m_flags & M_EXT) && m->m_next == NULL &&
+			    m->m_len <= MHLEN) {
+				MGET(n, M_DONTWAIT, m->m_type);
+				if (n != NULL) {
+					m_dup_pkthdr(n, m, M_NOWAIT);
+					bcopy(m->m_data, n->m_data, m->m_len);
+					n->m_len = m->m_len;
+				}
+			}
+			if (n != NULL ||
+			    (n = m_copy(m, 0, (int)M_COPYALL)) != NULL) {
 				if (last->in6p_flags & IN6P_CONTROLOPTS)
 					ip6_savecontrol(last, n, &opts);
 				/* strip intermediate headers */
@@ -1967,6 +1995,22 @@ icmp6_rip6_input(mp, off)
 			ip6_savecontrol(last, m, &opts);
 		/* strip intermediate headers */
 		m_adj(m, off);
+
+		/* avoid using mbuf clusters if possible (see above) */
+		if ((m->m_flags & M_EXT) && m->m_next == NULL &&
+		    m->m_len <= MHLEN) {
+			struct mbuf *n;
+
+			MGET(n, M_DONTWAIT, m->m_type);
+			if (n != NULL) {
+				m_dup_pkthdr(n, m, M_NOWAIT);
+				bcopy(m->m_data, n->m_data, m->m_len);
+				n->m_len = m->m_len;
+
+				m_freem(m);
+				m = n;
+			}
+		}
 		if (sbappendaddr(&last->in6p_socket->so_rcv,
 		    (struct sockaddr *)&fromsa, m, opts) == 0) {
 			m_freem(m);
-- 
2.45.2