src/parsec/disk-image/parsec/parsec-benchmark/pkgs/libs/uptcpip/src/freebsd.netinet/ip_fastfwd.c - public/gem5-resources - Git at Google

 /*-
  * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. The name of the author may not be used to endorse or promote
  *    products derived from this software without specific prior written
  *    permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */

 /*
  * ip_fastforward gets its speed from processing the forwarded packet to
  * completion (if_output on the other side) without any queues or netisr's.
  * The receiving interface DMAs the packet into memory, the upper half of
  * driver calls ip_fastforward, we do our routing table lookup and directly
  * send it off to the outgoing interface, which DMAs the packet to the
  * network card. The only part of the packet we touch with the CPU is the
  * IP header (unless there are complex firewall rules touching other parts
  * of the packet, but that is up to you). We are essentially limited by bus
  * bandwidth and how fast the network card/driver can set up receives and
  * transmits.
  *
  * We handle basic errors, IP header errors, checksum errors,
  * destination unreachable, fragmentation and fragmentation needed and
  * report them via ICMP to the sender.
  *
  * Else if something is not pure IPv4 unicast forwarding we fall back to
  * the normal ip_input processing path. We should only be called from
  * interfaces connected to the outside world.
  *
  * Firewalling is fully supported including divert, ipfw fwd and ipfilter
  * ipnat and address rewrite.
  *
  * IPSEC is not supported if this host is a tunnel broker. IPSEC is
  * supported for connections to/from local host.
  *
  * We try to do the least expensive (in CPU ops) checks and operations
  * first to catch junk with as little overhead as possible.
  *
  * We take full advantage of hardware support for IP checksum and
  * fragmentation offloading.
  *
  * We don't do ICMP redirect in the fast forwarding path. I have had my own
  * cases where two core routers with Zebra routing suite would send millions
  * ICMP redirects to connected hosts if the destination router was not the
  * default gateway. In one case it was filling the routing table of a host
  * with approximately 300.000 cloned redirect entries until it ran out of
  * kernel memory. However the networking code proved very robust and it didn't
  * crash or fail in other ways.
  */

 /*
  * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which
  * is being followed here.
  */

 #include <sys/bsd_cdefs.h>
 //__FBSDID("$FreeBSD$");

 #include "bsd_opt_ipfw.h"
 #include "bsd_opt_ipstealth.h"

 #include <sys/bsd_param.h>
 #include <sys/bsd_systm.h>
 #include <sys/bsd_kernel.h>
 #include <sys/bsd_malloc.h>
 #include <sys/bsd_mbuf.h>
 #include <sys/bsd_protosw.h>
 #include <sys/bsd_socket.h>
 //baoyg//#include <sys/bsd_sysctl.h>

 //#include <net/bsd_pfil.h>
 #include <net/bsd_if.h>
 #include <net/bsd_if_types.h>
 #include <net/bsd_if_var.h>
 #include <net/bsd_if_dl.h>
 #include <net/bsd_route.h>
 #include <net/bsd_vnet.h>

 #include <netinet/bsd_in.h>
 #include <netinet/bsd_in_systm.h>
 #include <netinet/bsd_in_var.h>
 #include <netinet/bsd_ip.h>
 #include <netinet/bsd_ip_var.h>
 #include <netinet/bsd_ip_icmp.h>
 #include <netinet/bsd_ip_options.h>

 #include <machine/bsd_in_cksum.h>

 static VNET_DEFINE(int, ipfastforward_active);
 #define	V_ipfastforward_active		VNET(ipfastforward_active)
 /*
 SYSCTL_VNET_INT(_net_inet_ip, OID_AUTO, fastforwarding, CTLFLAG_RW,
     &VNET_NAME(ipfastforward_active), 0, "Enable fast IP forwarding");
 */
 static struct sockaddr_in *
 ip_findroute(struct route *ro, struct in_addr dest, struct mbuf *m)
 {
 	struct sockaddr_in *dst;
 	struct rtentry *rt;

 	/*
 	 * Find route to destination.
 	 */
 	bzero(ro, sizeof(*ro));
 	dst = (struct sockaddr_in *)&ro->ro_dst;
 	dst->sin_family = AF_INET;
 	dst->sin_len = sizeof(*dst);
 	dst->sin_addr.s_addr = dest.s_addr;
 	in_rtalloc_ign(ro, 0, M_GETFIB(m));

 	/*
 	 * Route there and interface still up?
 	 */
 	rt = ro->ro_rt;
 	if (rt && (rt->rt_flags & RTF_UP) &&
 	    (rt->rt_ifp->if_flags & IFF_UP) &&
 	    (rt->rt_ifp->if_drv_flags & IFF_DRV_RUNNING)) {
 		if (rt->rt_flags & RTF_GATEWAY)
 			dst = (struct sockaddr_in *)rt->rt_gateway;
 	} else {
 		IPSTAT_INC(ips_noroute);
 		IPSTAT_INC(ips_cantforward);
 		if (rt)
 			RTFREE(rt);
 		icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
 		return NULL;
 	}
 	return dst;
 }

 /*
  * Try to forward a packet based on the destination address.
  * This is a fast path optimized for the plain forwarding case.
  * If the packet is handled (and consumed) here then we return 1;
  * otherwise 0 is returned and the packet should be delivered
  * to ip_input for full processing.
  */
 struct mbuf *
 ip_fastforward(struct mbuf *m)
 {
 	struct ip *ip;
 	struct mbuf *m0 = NULL;
 	struct route ro;
 	struct sockaddr_in *dst = NULL;
 	struct ifnet *ifp;
 	struct in_addr odest, dest;
 	u_short sum, ip_len;
 	int error = 0;
 	int hlen, mtu;
 #ifdef IPFIREWALL_FORWARD
 	struct m_tag *fwd_tag;
 #endif

 	/*
 	 * Are we active and forwarding packets?
 	 */
 	if (!V_ipfastforward_active || !V_ipforwarding)
 		return m;

 	M_ASSERTVALID(m);
 	M_ASSERTPKTHDR(m);

 	bzero(&ro, sizeof(ro));

 	/*
 	 * Step 1: check for packet drop conditions (and sanity checks)
 	 */

 	/*
 	 * Is entire packet big enough?
 	 */
 	if (m->m_pkthdr.len < sizeof(struct ip)) {
 		IPSTAT_INC(ips_tooshort);
 		goto drop;
 	}

 	/*
 	 * Is first mbuf large enough for ip header and is header present?
 	 */
 	if (m->m_len < sizeof (struct ip) &&
 	   (m = m_pullup(m, sizeof (struct ip))) == NULL) {
 		IPSTAT_INC(ips_toosmall);
 		return NULL;	/* mbuf already free'd */
 	}

 	ip = mtod(m, struct ip *);

 	/*
 	 * Is it IPv4?
 	 */
 	if (ip->ip_v != IPVERSION) {
 		IPSTAT_INC(ips_badvers);
 		goto drop;
 	}

 	/*
 	 * Is IP header length correct and is it in first mbuf?
 	 */
 	hlen = ip->ip_hl << 2;
 	if (hlen < sizeof(struct ip)) {	/* minimum header length */
 		IPSTAT_INC(ips_badlen);
 		goto drop;
 	}
 	if (hlen > m->m_len) {
 		if ((m = m_pullup(m, hlen)) == NULL) {
 			IPSTAT_INC(ips_badhlen);
 			return NULL;	/* mbuf already free'd */
 		}
 		ip = mtod(m, struct ip *);
 	}

 	/*
 	 * Checksum correct?
 	 */
 	if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED)
 		sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID);
 	else {
 		if (hlen == sizeof(struct ip))
 			sum = in_cksum_hdr(ip);
 		else
 			sum = in_cksum(m, hlen);
 	}
 	if (sum) {
 		IPSTAT_INC(ips_badsum);
 		goto drop;
 	}

 	/*
 	 * Remember that we have checked the IP header and found it valid.
 	 */
 	m->m_pkthdr.csum_flags |= (CSUM_IP_CHECKED | CSUM_IP_VALID);

 	ip_len = ntohs(ip->ip_len);

 	/*
 	 * Is IP length longer than packet we have got?
 	 */
 	if (m->m_pkthdr.len < ip_len) {
 		IPSTAT_INC(ips_tooshort);
 		goto drop;
 	}

 	/*
 	 * Is packet longer than IP header tells us? If yes, truncate packet.
 	 */
 	if (m->m_pkthdr.len > ip_len) {
 		if (m->m_len == m->m_pkthdr.len) {
 			m->m_len = ip_len;
 			m->m_pkthdr.len = ip_len;
 		} else
 			m_adj(m, ip_len - m->m_pkthdr.len);
 	}

 	/*
 	 * Is packet from or to 127/8?
 	 */
 	if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
 	    (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
 		IPSTAT_INC(ips_badaddr);
 		goto drop;
 	}

 #ifdef ALTQ
 	/*
 	 * Is packet dropped by traffic conditioner?
 	 */
 	if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
 		goto drop;
 #endif

 	/*
 	 * Step 2: fallback conditions to normal ip_input path processing
 	 */

 	/*
 	 * Only IP packets without options
 	 */
 	if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
 		if (ip_doopts == 1)
 			return m;
 		else if (ip_doopts == 2) {
 			icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
 				0, 0);
 			return NULL;	/* mbuf already free'd */
 		}
 		/* else ignore IP options and continue */
 	}

 	/*
 	 * Only unicast IP, not from loopback, no L2 or IP broadcast,
 	 * no multicast, no INADDR_ANY
 	 *
 	 * XXX: Probably some of these checks could be direct drop
 	 * conditions.  However it is not clear whether there are some
 	 * hacks or obscure behaviours which make it neccessary to
 	 * let ip_input handle it.  We play safe here and let ip_input
 	 * deal with it until it is proven that we can directly drop it.
 	 */
 	if ((m->m_flags & (M_BCAST|M_MCAST)) ||
 	    (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
 	    ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST ||
 	    ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST ||
 	    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 	    IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
 	    IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
 	    IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ||
 	    ip->ip_src.s_addr == INADDR_ANY ||
 	    ip->ip_dst.s_addr == INADDR_ANY )
 		return m;

 	/*
 	 * Is it for a local address on this host?
 	 */
 	if (in_localip(ip->ip_dst))
 		return m;

 	IPSTAT_INC(ips_total);

 	/*
 	 * Step 3: incoming packet firewall processing
 	 */

 	/*
 	 * Convert to host representation
 	 */
 	ip->ip_len = ntohs(ip->ip_len);
 	ip->ip_off = ntohs(ip->ip_off);

 	odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;

 	/*
 	 * Run through list of ipfilter hooks for input packets
 	 */
 //	if (!PFIL_HOOKED(&inet_pfil_hook))
 		goto passin;

 /*	if (pfil_run_hooks(&inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, NULL) ||
 	    m == NULL)
 		goto drop;
 */
 	M_ASSERTVALID(m);
 	M_ASSERTPKTHDR(m);

 	ip = mtod(m, struct ip *);	/* m may have changed by pfil hook */
 	dest.s_addr = ip->ip_dst.s_addr;

 	/*
 	 * Destination address changed?
 	 */
 	if (odest.s_addr != dest.s_addr) {
 		/*
 		 * Is it now for a local address on this host?
 		 */
 		if (in_localip(dest))
 			goto forwardlocal;
 		/*
 		 * Go on with new destination address
 		 */
 	}
 #ifdef IPFIREWALL_FORWARD
 	if (m->m_flags & M_FASTFWD_OURS) {
 		/*
 		 * ipfw changed it for a local address on this host.
 		 */
 		goto forwardlocal;
 	}
 #endif /* IPFIREWALL_FORWARD */

 passin:
 	/*
 	 * Step 4: decrement TTL and look up route
 	 */

 	/*
 	 * Check TTL
 	 */
 #ifdef IPSTEALTH
 	if (!V_ipstealth) {
 #endif
 	if (ip->ip_ttl <= IPTTLDEC) {
 		icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
 		return NULL;	/* mbuf already free'd */
 	}

 	/*
 	 * Decrement the TTL and incrementally change the IP header checksum.
 	 * Don't bother doing this with hw checksum offloading, it's faster
 	 * doing it right here.
 	 */
 	ip->ip_ttl -= IPTTLDEC;
 	if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
 		ip->ip_sum -= ~htons(IPTTLDEC << 8);
 	else
 		ip->ip_sum += htons(IPTTLDEC << 8);
 #ifdef IPSTEALTH
 	}
 #endif

 	/*
 	 * Find route to destination.
 	 */
 	if ((dst = ip_findroute(&ro, dest, m)) == NULL)
 		return NULL;	/* icmp unreach already sent */
 	ifp = ro.ro_rt->rt_ifp;

 	/*
 	 * Immediately drop blackholed traffic, and directed broadcasts
 	 * for either the all-ones or all-zero subnet addresses on
 	 * locally attached networks.
 	 */
 	if ((ro.ro_rt->rt_flags & (RTF_BLACKHOLE|RTF_BROADCAST)) != 0)
 		goto drop;

 	/*
 	 * Step 5: outgoing firewall packet processing
 	 */

 	/*
 	 * Run through list of hooks for output packets.
 	 */
 //	if (!PFIL_HOOKED(&inet_pfil_hook))
 		goto passout;

 /*	if (pfil_run_hooks(&inet_pfil_hook, &m, ifp, PFIL_OUT, NULL) || m == NULL) {
 		goto drop;
 	}
 */
 	M_ASSERTVALID(m);
 	M_ASSERTPKTHDR(m);

 	ip = mtod(m, struct ip *);
 	dest.s_addr = ip->ip_dst.s_addr;

 	/*
 	 * Destination address changed?
 	 */
 #ifndef IPFIREWALL_FORWARD
 	if (odest.s_addr != dest.s_addr) {
 #else
 	fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
 	if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
 #endif /* IPFIREWALL_FORWARD */
 		/*
 		 * Is it now for a local address on this host?
 		 */
 #ifndef IPFIREWALL_FORWARD
 		if (in_localip(dest)) {
 #else
 		if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
 #endif /* IPFIREWALL_FORWARD */
 forwardlocal:
 			/*
 			 * Return packet for processing by ip_input().
 			 * Keep host byte order as expected at ip_input's
 			 * "ours"-label.
 			 */
 			m->m_flags |= M_FASTFWD_OURS;
 			if (ro.ro_rt)
 				RTFREE(ro.ro_rt);
 			return m;
 		}
 		/*
 		 * Redo route lookup with new destination address
 		 */
 #ifdef IPFIREWALL_FORWARD
 		if (fwd_tag) {
 			dest.s_addr = ((struct sockaddr_in *)
 				    (fwd_tag + 1))->sin_addr.s_addr;
 			m_tag_delete(m, fwd_tag);
 		}
 #endif /* IPFIREWALL_FORWARD */
 		RTFREE(ro.ro_rt);
 		if ((dst = ip_findroute(&ro, dest, m)) == NULL)
 			return NULL;	/* icmp unreach already sent */
 		ifp = ro.ro_rt->rt_ifp;
 	}

 passout:
 	/*
 	 * Step 6: send off the packet
 	 */

 	/*
 	 * Check if route is dampned (when ARP is unable to resolve)
 	 */
 	if ((ro.ro_rt->rt_flags & RTF_REJECT) &&
 	    (ro.ro_rt->rt_rmx.rmx_expire == 0 ||
 	    time_uptime < ro.ro_rt->rt_rmx.rmx_expire)) {
 		icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
 		goto consumed;
 	}

 #ifndef ALTQ
 	/*
 	 * Check if there is enough space in the interface queue
 	 */
 	if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >=
 	    ifp->if_snd.ifq_maxlen) {
 		IPSTAT_INC(ips_odropped);
 		/* would send source quench here but that is depreciated */
 		goto drop;
 	}
 #endif

 	/*
 	 * Check if media link state of interface is not down
 	 */
 	if (ifp->if_link_state == LINK_STATE_DOWN) {
 		icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
 		goto consumed;
 	}

 	/*
 	 * Check if packet fits MTU or if hardware will fragment for us
 	 */
 	if (ro.ro_rt->rt_rmx.rmx_mtu)
 		mtu = min(ro.ro_rt->rt_rmx.rmx_mtu, ifp->if_mtu);
 	else
 		mtu = ifp->if_mtu;

 	if (ip->ip_len <= mtu ||
 	    (ifp->if_hwassist & CSUM_FRAGMENT && (ip->ip_off & IP_DF) == 0)) {
 		/*
 		 * Restore packet header fields to original values
 		 */
 		ip->ip_len = htons(ip->ip_len);
 		ip->ip_off = htons(ip->ip_off);
 		/*
 		 * Send off the packet via outgoing interface
 		 */
 		error = (*ifp->if_output)(ifp, m,
 				(struct sockaddr *)dst, &ro);
 	} else {
 		/*
 		 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
 		 */
 		if (ip->ip_off & IP_DF) {
 			IPSTAT_INC(ips_cantfrag);
 			icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
 				0, mtu);
 			goto consumed;
 		} else {
 			/*
 			 * We have to fragment the packet
 			 */
 			m->m_pkthdr.csum_flags |= CSUM_IP;
 			/*
 			 * ip_fragment expects ip_len and ip_off in host byte
 			 * order but returns all packets in network byte order
 			 */
 			if (ip_fragment(ip, &m, mtu, ifp->if_hwassist,
 					(~ifp->if_hwassist & CSUM_DELAY_IP))) {
 				goto drop;
 			}
 			KASSERT(m != NULL, ("null mbuf and no error"));
 			/*
 			 * Send off the fragments via outgoing interface
 			 */
 			error = 0;
 			do {
 				m0 = m->m_nextpkt;
 				m->m_nextpkt = NULL;

 				error = (*ifp->if_output)(ifp, m,
 					(struct sockaddr *)dst, &ro);
 				if (error)
 					break;
 			} while ((m = m0) != NULL);
 			if (error) {
 				/* Reclaim remaining fragments */
 				for (m = m0; m; m = m0) {
 					m0 = m->m_nextpkt;
 					m_freem(m);
 				}
 			} else
 				IPSTAT_INC(ips_fragmented);
 		}
 	}

 	if (error != 0)
 		IPSTAT_INC(ips_odropped);
 	else {
 		ro.ro_rt->rt_rmx.rmx_pksent++;
 		IPSTAT_INC(ips_forward);
 		IPSTAT_INC(ips_fastforward);
 	}
 consumed:
 	RTFREE(ro.ro_rt);
 	return NULL;
 drop:
 	if (m)
 		m_freem(m);
 	if (ro.ro_rt)
 		RTFREE(ro.ro_rt);
 	return NULL;
 }
	/*-
	* Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	* 3. The name of the author may not be used to endorse or promote
	* products derived from this software without specific prior written
	* permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	* SUCH DAMAGE.
	*/

	/*
	* ip_fastforward gets its speed from processing the forwarded packet to
	* completion (if_output on the other side) without any queues or netisr's.
	* The receiving interface DMAs the packet into memory, the upper half of
	* driver calls ip_fastforward, we do our routing table lookup and directly
	* send it off to the outgoing interface, which DMAs the packet to the
	* network card. The only part of the packet we touch with the CPU is the
	* IP header (unless there are complex firewall rules touching other parts
	* of the packet, but that is up to you). We are essentially limited by bus
	* bandwidth and how fast the network card/driver can set up receives and
	* transmits.
	*
	* We handle basic errors, IP header errors, checksum errors,
	* destination unreachable, fragmentation and fragmentation needed and
	* report them via ICMP to the sender.
	*
	* Else if something is not pure IPv4 unicast forwarding we fall back to
	* the normal ip_input processing path. We should only be called from
	* interfaces connected to the outside world.
	*
	* Firewalling is fully supported including divert, ipfw fwd and ipfilter
	* ipnat and address rewrite.
	*
	* IPSEC is not supported if this host is a tunnel broker. IPSEC is
	* supported for connections to/from local host.
	*
	* We try to do the least expensive (in CPU ops) checks and operations
	* first to catch junk with as little overhead as possible.
	*
	* We take full advantage of hardware support for IP checksum and
	* fragmentation offloading.
	*
	* We don't do ICMP redirect in the fast forwarding path. I have had my own
	* cases where two core routers with Zebra routing suite would send millions
	* ICMP redirects to connected hosts if the destination router was not the
	* default gateway. In one case it was filling the routing table of a host
	* with approximately 300.000 cloned redirect entries until it ran out of
	* kernel memory. However the networking code proved very robust and it didn't
	* crash or fail in other ways.
	*/

	/*
	* Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which
	* is being followed here.
	*/

	#include <sys/bsd_cdefs.h>
	//__FBSDID("$FreeBSD$");

	#include "bsd_opt_ipfw.h"
	#include "bsd_opt_ipstealth.h"

	#include <sys/bsd_param.h>
	#include <sys/bsd_systm.h>
	#include <sys/bsd_kernel.h>
	#include <sys/bsd_malloc.h>
	#include <sys/bsd_mbuf.h>
	#include <sys/bsd_protosw.h>
	#include <sys/bsd_socket.h>
	//baoyg//#include <sys/bsd_sysctl.h>

	//#include <net/bsd_pfil.h>
	#include <net/bsd_if.h>
	#include <net/bsd_if_types.h>
	#include <net/bsd_if_var.h>
	#include <net/bsd_if_dl.h>
	#include <net/bsd_route.h>
	#include <net/bsd_vnet.h>

	#include <netinet/bsd_in.h>
	#include <netinet/bsd_in_systm.h>
	#include <netinet/bsd_in_var.h>
	#include <netinet/bsd_ip.h>
	#include <netinet/bsd_ip_var.h>
	#include <netinet/bsd_ip_icmp.h>
	#include <netinet/bsd_ip_options.h>

	#include <machine/bsd_in_cksum.h>

	static VNET_DEFINE(int, ipfastforward_active);
	#define V_ipfastforward_active VNET(ipfastforward_active)
	/*
	SYSCTL_VNET_INT(_net_inet_ip, OID_AUTO, fastforwarding, CTLFLAG_RW,
	&VNET_NAME(ipfastforward_active), 0, "Enable fast IP forwarding");
	*/
	static struct sockaddr_in *
	ip_findroute(struct route ro, struct in_addr dest, struct mbuf m)
	{
	struct sockaddr_in *dst;
	struct rtentry *rt;

	/*
	* Find route to destination.
	*/
	bzero(ro, sizeof(*ro));
	dst = (struct sockaddr_in *)&ro->ro_dst;
	dst->sin_family = AF_INET;
	dst->sin_len = sizeof(*dst);
	dst->sin_addr.s_addr = dest.s_addr;
	in_rtalloc_ign(ro, 0, M_GETFIB(m));

	/*
	* Route there and interface still up?
	*/
	rt = ro->ro_rt;
	if (rt && (rt->rt_flags & RTF_UP) &&
	(rt->rt_ifp->if_flags & IFF_UP) &&
	(rt->rt_ifp->if_drv_flags & IFF_DRV_RUNNING)) {
	if (rt->rt_flags & RTF_GATEWAY)
	dst = (struct sockaddr_in *)rt->rt_gateway;
	} else {
	IPSTAT_INC(ips_noroute);
	IPSTAT_INC(ips_cantforward);
	if (rt)
	RTFREE(rt);
	icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
	return NULL;
	}
	return dst;
	}

	/*
	* Try to forward a packet based on the destination address.
	* This is a fast path optimized for the plain forwarding case.
	* If the packet is handled (and consumed) here then we return 1;
	* otherwise 0 is returned and the packet should be delivered
	* to ip_input for full processing.
	*/
	struct mbuf *
	ip_fastforward(struct mbuf *m)
	{
	struct ip *ip;
	struct mbuf *m0 = NULL;
	struct route ro;
	struct sockaddr_in *dst = NULL;
	struct ifnet *ifp;
	struct in_addr odest, dest;
	u_short sum, ip_len;
	int error = 0;
	int hlen, mtu;
	#ifdef IPFIREWALL_FORWARD
	struct m_tag *fwd_tag;
	#endif

	/*
	* Are we active and forwarding packets?
	*/
	if (!V_ipfastforward_active \|\| !V_ipforwarding)
	return m;

	M_ASSERTVALID(m);
	M_ASSERTPKTHDR(m);

	bzero(&ro, sizeof(ro));

	/*
	* Step 1: check for packet drop conditions (and sanity checks)
	*/

	/*
	* Is entire packet big enough?
	*/
	if (m->m_pkthdr.len < sizeof(struct ip)) {
	IPSTAT_INC(ips_tooshort);
	goto drop;
	}

	/*
	* Is first mbuf large enough for ip header and is header present?
	*/
	if (m->m_len < sizeof (struct ip) &&
	(m = m_pullup(m, sizeof (struct ip))) == NULL) {
	IPSTAT_INC(ips_toosmall);
	return NULL; /* mbuf already free'd */
	}

	ip = mtod(m, struct ip *);

	/*
	* Is it IPv4?
	*/
	if (ip->ip_v != IPVERSION) {
	IPSTAT_INC(ips_badvers);
	goto drop;
	}

	/*
	* Is IP header length correct and is it in first mbuf?
	*/
	hlen = ip->ip_hl << 2;
	if (hlen < sizeof(struct ip)) { /* minimum header length */
	IPSTAT_INC(ips_badlen);
	goto drop;
	}
	if (hlen > m->m_len) {
	if ((m = m_pullup(m, hlen)) == NULL) {
	IPSTAT_INC(ips_badhlen);
	return NULL; /* mbuf already free'd */
	}
	ip = mtod(m, struct ip *);
	}

	/*
	* Checksum correct?
	*/
	if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED)
	sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID);
	else {
	if (hlen == sizeof(struct ip))
	sum = in_cksum_hdr(ip);
	else
	sum = in_cksum(m, hlen);
	}
	if (sum) {
	IPSTAT_INC(ips_badsum);
	goto drop;
	}

	/*
	* Remember that we have checked the IP header and found it valid.
	*/
	m->m_pkthdr.csum_flags \|= (CSUM_IP_CHECKED \| CSUM_IP_VALID);

	ip_len = ntohs(ip->ip_len);

	/*
	* Is IP length longer than packet we have got?
	*/
	if (m->m_pkthdr.len < ip_len) {
	IPSTAT_INC(ips_tooshort);
	goto drop;
	}

	/*
	* Is packet longer than IP header tells us? If yes, truncate packet.
	*/
	if (m->m_pkthdr.len > ip_len) {
	if (m->m_len == m->m_pkthdr.len) {
	m->m_len = ip_len;
	m->m_pkthdr.len = ip_len;
	} else
	m_adj(m, ip_len - m->m_pkthdr.len);
	}

	/*
	* Is packet from or to 127/8?
	*/
	if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET \|\|
	(ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
	IPSTAT_INC(ips_badaddr);
	goto drop;
	}

	#ifdef ALTQ
	/*
	* Is packet dropped by traffic conditioner?
	*/
	if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
	goto drop;
	#endif

	/*
	* Step 2: fallback conditions to normal ip_input path processing
	*/

	/*
	* Only IP packets without options
	*/
	if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
	if (ip_doopts == 1)
	return m;
	else if (ip_doopts == 2) {
	icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
	0, 0);
	return NULL; /* mbuf already free'd */
	}
	/* else ignore IP options and continue */
	}

	/*
	* Only unicast IP, not from loopback, no L2 or IP broadcast,
	* no multicast, no INADDR_ANY
	*
	* XXX: Probably some of these checks could be direct drop
	* conditions. However it is not clear whether there are some
	* hacks or obscure behaviours which make it neccessary to
	* let ip_input handle it. We play safe here and let ip_input
	* deal with it until it is proven that we can directly drop it.
	*/
	if ((m->m_flags & (M_BCAST\|M_MCAST)) \|\|
	(m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) \|\|
	ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST \|\|
	ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST \|\|
	IN_MULTICAST(ntohl(ip->ip_src.s_addr)) \|\|
	IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) \|\|
	IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) \|\|
	IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) \|\|
	ip->ip_src.s_addr == INADDR_ANY \|\|
	ip->ip_dst.s_addr == INADDR_ANY )
	return m;

	/*
	* Is it for a local address on this host?
	*/
	if (in_localip(ip->ip_dst))
	return m;

	IPSTAT_INC(ips_total);

	/*
	* Step 3: incoming packet firewall processing
	*/

	/*
	* Convert to host representation
	*/
	ip->ip_len = ntohs(ip->ip_len);
	ip->ip_off = ntohs(ip->ip_off);

	odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;

	/*
	* Run through list of ipfilter hooks for input packets
	*/
	// if (!PFIL_HOOKED(&inet_pfil_hook))
	goto passin;

	/* if (pfil_run_hooks(&inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, NULL) \|\|
	m == NULL)
	goto drop;
	*/
	M_ASSERTVALID(m);
	M_ASSERTPKTHDR(m);

	ip = mtod(m, struct ip ); / m may have changed by pfil hook */
	dest.s_addr = ip->ip_dst.s_addr;

	/*
	* Destination address changed?
	*/
	if (odest.s_addr != dest.s_addr) {
	/*
	* Is it now for a local address on this host?
	*/
	if (in_localip(dest))
	goto forwardlocal;
	/*
	* Go on with new destination address
	*/
	}
	#ifdef IPFIREWALL_FORWARD
	if (m->m_flags & M_FASTFWD_OURS) {
	/*
	* ipfw changed it for a local address on this host.
	*/
	goto forwardlocal;
	}
	#endif /* IPFIREWALL_FORWARD */

	passin:
	/*
	* Step 4: decrement TTL and look up route
	*/

	/*
	* Check TTL
	*/
	#ifdef IPSTEALTH
	if (!V_ipstealth) {
	#endif
	if (ip->ip_ttl <= IPTTLDEC) {
	icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
	return NULL; /* mbuf already free'd */
	}

	/*
	* Decrement the TTL and incrementally change the IP header checksum.
	* Don't bother doing this with hw checksum offloading, it's faster
	* doing it right here.
	*/
	ip->ip_ttl -= IPTTLDEC;
	if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
	ip->ip_sum -= ~htons(IPTTLDEC << 8);
	else
	ip->ip_sum += htons(IPTTLDEC << 8);
	#ifdef IPSTEALTH
	}
	#endif

	/*
	* Find route to destination.
	*/
	if ((dst = ip_findroute(&ro, dest, m)) == NULL)
	return NULL; /* icmp unreach already sent */
	ifp = ro.ro_rt->rt_ifp;

	/*
	* Immediately drop blackholed traffic, and directed broadcasts
	* for either the all-ones or all-zero subnet addresses on
	* locally attached networks.
	*/
	if ((ro.ro_rt->rt_flags & (RTF_BLACKHOLE\|RTF_BROADCAST)) != 0)
	goto drop;

	/*
	* Step 5: outgoing firewall packet processing
	*/

	/*
	* Run through list of hooks for output packets.
	*/
	// if (!PFIL_HOOKED(&inet_pfil_hook))
	goto passout;

	/* if (pfil_run_hooks(&inet_pfil_hook, &m, ifp, PFIL_OUT, NULL) \|\| m == NULL) {
	goto drop;
	}
	*/
	M_ASSERTVALID(m);
	M_ASSERTPKTHDR(m);

	ip = mtod(m, struct ip *);
	dest.s_addr = ip->ip_dst.s_addr;

	/*
	* Destination address changed?
	*/
	#ifndef IPFIREWALL_FORWARD
	if (odest.s_addr != dest.s_addr) {
	#else
	fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
	if (odest.s_addr != dest.s_addr \|\| fwd_tag != NULL) {
	#endif /* IPFIREWALL_FORWARD */
	/*
	* Is it now for a local address on this host?
	*/
	#ifndef IPFIREWALL_FORWARD
	if (in_localip(dest)) {
	#else
	if (m->m_flags & M_FASTFWD_OURS \|\| in_localip(dest)) {
	#endif /* IPFIREWALL_FORWARD */
	forwardlocal:
	/*
	* Return packet for processing by ip_input().
	* Keep host byte order as expected at ip_input's
	* "ours"-label.
	*/
	m->m_flags \|= M_FASTFWD_OURS;
	if (ro.ro_rt)
	RTFREE(ro.ro_rt);
	return m;
	}
	/*
	* Redo route lookup with new destination address
	*/
	#ifdef IPFIREWALL_FORWARD
	if (fwd_tag) {
	dest.s_addr = ((struct sockaddr_in *)
	(fwd_tag + 1))->sin_addr.s_addr;
	m_tag_delete(m, fwd_tag);
	}
	#endif /* IPFIREWALL_FORWARD */
	RTFREE(ro.ro_rt);
	if ((dst = ip_findroute(&ro, dest, m)) == NULL)
	return NULL; /* icmp unreach already sent */
	ifp = ro.ro_rt->rt_ifp;
	}

	passout:
	/*
	* Step 6: send off the packet
	*/

	/*
	* Check if route is dampned (when ARP is unable to resolve)
	*/
	if ((ro.ro_rt->rt_flags & RTF_REJECT) &&
	(ro.ro_rt->rt_rmx.rmx_expire == 0 \|\|
	time_uptime < ro.ro_rt->rt_rmx.rmx_expire)) {
	icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
	goto consumed;
	}

	#ifndef ALTQ
	/*
	* Check if there is enough space in the interface queue
	*/
	if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >=
	ifp->if_snd.ifq_maxlen) {
	IPSTAT_INC(ips_odropped);
	/* would send source quench here but that is depreciated */
	goto drop;
	}
	#endif

	/*
	* Check if media link state of interface is not down
	*/
	if (ifp->if_link_state == LINK_STATE_DOWN) {
	icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
	goto consumed;
	}

	/*
	* Check if packet fits MTU or if hardware will fragment for us
	*/
	if (ro.ro_rt->rt_rmx.rmx_mtu)
	mtu = min(ro.ro_rt->rt_rmx.rmx_mtu, ifp->if_mtu);
	else
	mtu = ifp->if_mtu;

	if (ip->ip_len <= mtu \|\|
	(ifp->if_hwassist & CSUM_FRAGMENT && (ip->ip_off & IP_DF) == 0)) {
	/*
	* Restore packet header fields to original values
	*/
	ip->ip_len = htons(ip->ip_len);
	ip->ip_off = htons(ip->ip_off);
	/*
	* Send off the packet via outgoing interface
	*/
	error = (*ifp->if_output)(ifp, m,
	(struct sockaddr *)dst, &ro);
	} else {
	/*
	* Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
	*/
	if (ip->ip_off & IP_DF) {
	IPSTAT_INC(ips_cantfrag);
	icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
	0, mtu);
	goto consumed;
	} else {
	/*
	* We have to fragment the packet
	*/
	m->m_pkthdr.csum_flags \|= CSUM_IP;
	/*
	* ip_fragment expects ip_len and ip_off in host byte
	* order but returns all packets in network byte order
	*/
	if (ip_fragment(ip, &m, mtu, ifp->if_hwassist,
	(~ifp->if_hwassist & CSUM_DELAY_IP))) {
	goto drop;
	}
	KASSERT(m != NULL, ("null mbuf and no error"));
	/*
	* Send off the fragments via outgoing interface
	*/
	error = 0;
	do {
	m0 = m->m_nextpkt;
	m->m_nextpkt = NULL;

	error = (*ifp->if_output)(ifp, m,
	(struct sockaddr *)dst, &ro);
	if (error)
	break;
	} while ((m = m0) != NULL);
	if (error) {
	/* Reclaim remaining fragments */
	for (m = m0; m; m = m0) {
	m0 = m->m_nextpkt;
	m_freem(m);
	}
	} else
	IPSTAT_INC(ips_fragmented);
	}
	}

	if (error != 0)
	IPSTAT_INC(ips_odropped);
	else {
	ro.ro_rt->rt_rmx.rmx_pksent++;
	IPSTAT_INC(ips_forward);
	IPSTAT_INC(ips_fastforward);
	}
	consumed:
	RTFREE(ro.ro_rt);
	return NULL;
	drop:
	if (m)
	m_freem(m);
	if (ro.ro_rt)
	RTFREE(ro.ro_rt);
	return NULL;
	}