Re: [PKT_SCHED]: Add stateless NAT

--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig

@@ -447,6 +447,17 @@ config NET_ACT_IPT
 	  To compile this code as a module, choose M here: the
 	  module will be called ipt.

+config NET_ACT_NAT
+        tristate "Stateless NAT"
+        depends on NET_CLS_ACT
+        select NETFILTER

+        ---help---
+	  Say Y here to do stateless NAT on IPv4 packets.  You should use
+	  netfilter for NAT unless you know what you are doing.
+
+	  To compile this code as a module, choose M here: the
+	  module will be called ipt.
+

+++ b/net/sched/act_nat.c

+static struct tcf_common *tcf_nat_ht[NAT_TAB_MASK + 1];
+static u32 nat_idx_gen;
+static DEFINE_RWLOCK(nat_lock);

+static struct tcf_hashinfo nat_hash_info = {
+	.htab	=	tcf_nat_ht,
+	.hmask	=	NAT_TAB_MASK,
+	.lock	=	&nat_lock,
+};

+static int tcf_nat(struct sk_buff *skb, struct tc_action *a,
+		   struct tcf_result *res)
+{
+	struct tcf_nat *p = a->priv;
+	struct iphdr *iph;
+	__be32 old_addr;
+	__be32 new_addr;
+	__be32 mask;
+	__be32 addr;
+	int egress;
+	int action;
+	int ihl;
+
+	spin_lock(&p->tcf_lock);
+
+	p->tcf_tm.lastuse = jiffies;
+	old_addr = p->old_addr;
+	new_addr = p->new_addr;
+	mask = p->mask;
+	egress = p->flags & TCA_NAT_FLAG_EGRESS;
+	action = p->tcf_action;
+
+	p->tcf_bstats.bytes += skb->len;
+	p->tcf_bstats.packets++;
+
+	spin_unlock(&p->tcf_lock);
+
+	if (!pskb_may_pull(skb, sizeof(*iph)))
+		return TC_ACT_SHOT;
+
+	iph = ip_hdr(skb);
+
+	if (egress)
+		addr = iph->saddr;
+	else
+		addr = iph->daddr;
+
+	if (!((old_addr ^ addr) & mask)) {
+		if (skb_cloned(skb) &&
+		    !skb_clone_writable(skb, sizeof(*iph)) &&
+		    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+			return TC_ACT_SHOT;
+
+		new_addr &= mask;
+		new_addr |= addr & ~mask;
+
+		/* Rewrite IP header */
+		iph = ip_hdr(skb);
+		if (egress)
+			iph->saddr = new_addr;
+		else
+			iph->daddr = new_addr;
+
+		nf_csum_replace4(&iph->check, addr, new_addr);
+	}
+
+	ihl = iph->ihl * 4;
+
+	/* It would be nice to share code with stateful NAT. */
+	switch (iph->frag_off & htons(IP_OFFSET) ? 0 : iph->protocol) {
+	case IPPROTO_TCP:
+	{
+		struct tcphdr *tcph;
+
+		if (!pskb_may_pull(skb, ihl + sizeof(*tcph)) ||
+		    (skb_cloned(skb) &&
+		     !skb_clone_writable(skb, ihl + sizeof(*tcph)) &&
+		     pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
+			return TC_ACT_SHOT;
+
+		tcph = (void *)(skb_network_header(skb) + ihl);