/*
 * Copyright (c) 2007-2013 Nicira, Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA
 *
 * This code is derived from kernel flow_dissector.c
 */

#include <linux/version.h>
#if LINUX_VERSION_CODE < KERNEL_VERSION(3,8,0)
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/if_vlan.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <linux/igmp.h>
#include <linux/icmp.h>
#include <linux/sctp.h>
#include <linux/dccp.h>
#include <linux/if_tunnel.h>
#include <linux/if_pppox.h>
#include <linux/ppp_defs.h>
#include <net/flow_keys.h>


/* copy saddr & daddr, possibly using 64bit load/store
 * Equivalent to :	flow->src = iph->saddr;
 *			flow->dst = iph->daddr;
 */
static void iph_to_flow_copy_addrs(struct flow_keys *flow, const struct iphdr *iph)
{
	BUILD_BUG_ON(offsetof(typeof(*flow), dst) !=
		     offsetof(typeof(*flow), src) + sizeof(flow->src));
	memcpy(&flow->src, &iph->saddr, sizeof(flow->src) + sizeof(flow->dst));
}

static __be32 skb_flow_get_ports(const struct sk_buff *skb, int thoff, u8 ip_proto)
{
	int poff = proto_ports_offset(ip_proto);

	if (poff >= 0) {
		__be32 *ports, _ports;

		ports = skb_header_pointer(skb, thoff + poff,
				sizeof(_ports), &_ports);
		if (ports)
			return *ports;
	}

	return 0;
}

static bool skb_flow_dissect(const struct sk_buff *skb, struct flow_keys *flow)
{
	int nhoff = skb_network_offset(skb);
	u8 ip_proto;
	__be16 proto = skb->protocol;

	memset(flow, 0, sizeof(*flow));

again:
	switch (proto) {
	case __constant_htons(ETH_P_IP): {
		const struct iphdr *iph;
		struct iphdr _iph;
ip:
		iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
		if (!iph)
			return false;

		if (ip_is_fragment(iph))
			ip_proto = 0;
		else
			ip_proto = iph->protocol;
		iph_to_flow_copy_addrs(flow, iph);
		nhoff += iph->ihl * 4;
		break;
	}
	case __constant_htons(ETH_P_IPV6): {
		const struct ipv6hdr *iph;
		struct ipv6hdr _iph;
ipv6:
		iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
		if (!iph)
			return false;

		ip_proto = iph->nexthdr;
		flow->src = (__force __be32)ipv6_addr_hash(&iph->saddr);
		flow->dst = (__force __be32)ipv6_addr_hash(&iph->daddr);
		nhoff += sizeof(struct ipv6hdr);
		break;
	}
	case __constant_htons(ETH_P_8021AD):
	case __constant_htons(ETH_P_8021Q): {
		const struct vlan_hdr *vlan;
		struct vlan_hdr _vlan;

		vlan = skb_header_pointer(skb, nhoff, sizeof(_vlan), &_vlan);
		if (!vlan)
			return false;

		proto = vlan->h_vlan_encapsulated_proto;
		nhoff += sizeof(*vlan);
		goto again;
	}
	case __constant_htons(ETH_P_PPP_SES): {
		struct {
			struct pppoe_hdr hdr;
			__be16 proto;
		} *hdr, _hdr;
		hdr = skb_header_pointer(skb, nhoff, sizeof(_hdr), &_hdr);
		if (!hdr)
			return false;
		proto = hdr->proto;
		nhoff += PPPOE_SES_HLEN;
		switch (proto) {
		case __constant_htons(PPP_IP):
			goto ip;
		case __constant_htons(PPP_IPV6):
			goto ipv6;
		default:
			return false;
		}
	}
	default:
		return false;
	}

	switch (ip_proto) {
	case IPPROTO_GRE: {
		struct gre_hdr {
			__be16 flags;
			__be16 proto;
		} *hdr, _hdr;

		hdr = skb_header_pointer(skb, nhoff, sizeof(_hdr), &_hdr);
		if (!hdr)
			return false;
		/*
		 * Only look inside GRE if version zero and no
		 * routing
		 */
		if (!(hdr->flags & (GRE_VERSION|GRE_ROUTING))) {
			proto = hdr->proto;
			nhoff += 4;
			if (hdr->flags & GRE_CSUM)
				nhoff += 4;
			if (hdr->flags & GRE_KEY)
				nhoff += 4;
			if (hdr->flags & GRE_SEQ)
				nhoff += 4;
			if (proto == htons(ETH_P_TEB)) {
				const struct ethhdr *eth;
				struct ethhdr _eth;

				eth = skb_header_pointer(skb, nhoff,
							 sizeof(_eth), &_eth);
				if (!eth)
					return false;
				proto = eth->h_proto;
				nhoff += sizeof(*eth);
			}
			goto again;
		}
		break;
	}
	case IPPROTO_IPIP:
		goto again;
	case IPPROTO_IPV6:
		proto = htons(ETH_P_IPV6);
		goto ipv6;
	default:
		break;
	}

	flow->ip_proto = ip_proto;
	flow->ports = skb_flow_get_ports(skb, nhoff, ip_proto);
	flow->thoff = (u16) nhoff;

	return true;
}

static u32 hashrnd __read_mostly;
static __always_inline void __flow_hash_secret_init(void)
{
	net_get_random_once(&hashrnd, sizeof(hashrnd));
}

static __always_inline u32 __flow_hash_3words(u32 a, u32 b, u32 c)
{
	__flow_hash_secret_init();
	return jhash_3words(a, b, c, hashrnd);
}

u32 __skb_get_hash(struct sk_buff *skb)
{
	struct flow_keys keys;
	u32 hash;

	if (!skb_flow_dissect(skb, &keys))
		return 0;

	/* get a consistent hash (same value on both flow directions) */
	if (((__force u32)keys.dst < (__force u32)keys.src) ||
	    (((__force u32)keys.dst == (__force u32)keys.src) &&
	     ((__force u16)keys.port16[1] < (__force u16)keys.port16[0]))) {
		swap(keys.dst, keys.src);
		swap(keys.port16[0], keys.port16[1]);
	}

	hash = __flow_hash_3words((__force u32)keys.dst,
				  (__force u32)keys.src,
				  (__force u32)keys.ports);
	if (!hash)
		hash = 1;

#ifdef HAVE_RXHASH
	skb->rxhash = hash;
#endif
	return hash;
}
#endif