Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 1077 insertions, 0 deletions

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
new file mode 100644
index 000000000000..fd70509f0d53
--- /dev/null
+++ b/net/ipv4/tcp_minisocks.c
@@ -0,0 +1,1077 @@
+/*
+ * INET		An implementation of the TCP/IP protocol suite for the LINUX
+ *		operating system.  INET is implemented using the  BSD Socket
+ *		interface as the means of communication with the user level.
+ *
+ *		Implementation of the Transmission Control Protocol(TCP).
+ *
+ * Version:	$Id: tcp_minisocks.c,v 1.15 2002/02/01 22:01:04 davem Exp $
+ *
+ * Authors:	Ross Biro, <bir7@leland.Stanford.Edu>
+ *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
+ *		Mark Evans, <evansmp@uhura.aston.ac.uk>
+ *		Corey Minyard <wf-rch!minyard@relay.EU.net>
+ *		Florian La Roche, <flla@stud.uni-sb.de>
+ *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
+ *		Linus Torvalds, <torvalds@cs.helsinki.fi>
+ *		Alan Cox, <gw4pts@gw4pts.ampr.org>
+ *		Matthew Dillon, <dillon@apollo.west.oic.com>
+ *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
+ *		Jorge Cwik, <jorge@laser.satlink.net>
+ */
+
+#include <linux/config.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/sysctl.h>
+#include <linux/workqueue.h>
+#include <net/tcp.h>
+#include <net/inet_common.h>
+#include <net/xfrm.h>
+
+#ifdef CONFIG_SYSCTL
+#define SYNC_INIT 0 /* let the user enable it */
+#else
+#define SYNC_INIT 1
+#endif
+
+int sysctl_tcp_tw_recycle;
+int sysctl_tcp_max_tw_buckets = NR_FILE*2;
+
+int sysctl_tcp_syncookies = SYNC_INIT; 
+int sysctl_tcp_abort_on_overflow;
+
+static void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo);
+
+static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
+{
+	if (seq == s_win)
+		return 1;
+	if (after(end_seq, s_win) && before(seq, e_win))
+		return 1;
+	return (seq == e_win && seq == end_seq);
+}
+
+/* New-style handling of TIME_WAIT sockets. */
+
+int tcp_tw_count;
+
+
+/* Must be called with locally disabled BHs. */
+static void tcp_timewait_kill(struct tcp_tw_bucket *tw)
+{
+	struct tcp_ehash_bucket *ehead;
+	struct tcp_bind_hashbucket *bhead;
+	struct tcp_bind_bucket *tb;
+
+	/* Unlink from established hashes. */
+	ehead = &tcp_ehash[tw->tw_hashent];
+	write_lock(&ehead->lock);
+	if (hlist_unhashed(&tw->tw_node)) {
+		write_unlock(&ehead->lock);
+		return;
+	}
+	__hlist_del(&tw->tw_node);
+	sk_node_init(&tw->tw_node);
+	write_unlock(&ehead->lock);
+
+	/* Disassociate with bind bucket. */
+	bhead = &tcp_bhash[tcp_bhashfn(tw->tw_num)];
+	spin_lock(&bhead->lock);
+	tb = tw->tw_tb;
+	__hlist_del(&tw->tw_bind_node);
+	tw->tw_tb = NULL;
+	tcp_bucket_destroy(tb);
+	spin_unlock(&bhead->lock);
+
+#ifdef INET_REFCNT_DEBUG
+	if (atomic_read(&tw->tw_refcnt) != 1) {
+		printk(KERN_DEBUG "tw_bucket %p refcnt=%d\n", tw,
+		       atomic_read(&tw->tw_refcnt));
+	}
+#endif
+	tcp_tw_put(tw);
+}
+
+/* 
+ * * Main purpose of TIME-WAIT state is to close connection gracefully,
+ *   when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
+ *   (and, probably, tail of data) and one or more our ACKs are lost.
+ * * What is TIME-WAIT timeout? It is associated with maximal packet
+ *   lifetime in the internet, which results in wrong conclusion, that
+ *   it is set to catch "old duplicate segments" wandering out of their path.
+ *   It is not quite correct. This timeout is calculated so that it exceeds
+ *   maximal retransmission timeout enough to allow to lose one (or more)
+ *   segments sent by peer and our ACKs. This time may be calculated from RTO.
+ * * When TIME-WAIT socket receives RST, it means that another end
+ *   finally closed and we are allowed to kill TIME-WAIT too.
+ * * Second purpose of TIME-WAIT is catching old duplicate segments.
+ *   Well, certainly it is pure paranoia, but if we load TIME-WAIT
+ *   with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
+ * * If we invented some more clever way to catch duplicates
+ *   (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
+ *
+ * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
+ * When you compare it to RFCs, please, read section SEGMENT ARRIVES
+ * from the very beginning.
+ *
+ * NOTE. With recycling (and later with fin-wait-2) TW bucket
+ * is _not_ stateless. It means, that strictly speaking we must
+ * spinlock it. I do not want! Well, probability of misbehaviour
+ * is ridiculously low and, seems, we could use some mb() tricks
+ * to avoid misread sequence numbers, states etc.  --ANK
+ */
+enum tcp_tw_status
+tcp_timewait_state_process(struct tcp_tw_bucket *tw, struct sk_buff *skb,
+			   struct tcphdr *th, unsigned len)
+{
+	struct tcp_options_received tmp_opt;
+	int paws_reject = 0;
+
+	tmp_opt.saw_tstamp = 0;
+	if (th->doff > (sizeof(struct tcphdr) >> 2) && tw->tw_ts_recent_stamp) {
+		tcp_parse_options(skb, &tmp_opt, 0);
+
+		if (tmp_opt.saw_tstamp) {
+			tmp_opt.ts_recent	   = tw->tw_ts_recent;
+			tmp_opt.ts_recent_stamp = tw->tw_ts_recent_stamp;
+			paws_reject = tcp_paws_check(&tmp_opt, th->rst);
+		}
+	}
+
+	if (tw->tw_substate == TCP_FIN_WAIT2) {
+		/* Just repeat all the checks of tcp_rcv_state_process() */
+
+		/* Out of window, send ACK */
+		if (paws_reject ||
+		    !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
+				   tw->tw_rcv_nxt,
+				   tw->tw_rcv_nxt + tw->tw_rcv_wnd))
+			return TCP_TW_ACK;
+
+		if (th->rst)
+			goto kill;
+
+		if (th->syn && !before(TCP_SKB_CB(skb)->seq, tw->tw_rcv_nxt))
+			goto kill_with_rst;
+
+		/* Dup ACK? */
+		if (!after(TCP_SKB_CB(skb)->end_seq, tw->tw_rcv_nxt) ||
+		    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
+			tcp_tw_put(tw);
+			return TCP_TW_SUCCESS;
+		}
+
+		/* New data or FIN. If new data arrive after half-duplex close,
+		 * reset.
+		 */
+		if (!th->fin ||
+		    TCP_SKB_CB(skb)->end_seq != tw->tw_rcv_nxt + 1) {
+kill_with_rst:
+			tcp_tw_deschedule(tw);
+			tcp_tw_put(tw);
+			return TCP_TW_RST;
+		}
+
+		/* FIN arrived, enter true time-wait state. */
+		tw->tw_substate	= TCP_TIME_WAIT;
+		tw->tw_rcv_nxt	= TCP_SKB_CB(skb)->end_seq;
+		if (tmp_opt.saw_tstamp) {
+			tw->tw_ts_recent_stamp	= xtime.tv_sec;
+			tw->tw_ts_recent	= tmp_opt.rcv_tsval;
+		}
+
+		/* I am shamed, but failed to make it more elegant.
+		 * Yes, it is direct reference to IP, which is impossible
+		 * to generalize to IPv6. Taking into account that IPv6
+		 * do not undertsnad recycling in any case, it not
+		 * a big problem in practice. --ANK */
+		if (tw->tw_family == AF_INET &&
+		    sysctl_tcp_tw_recycle && tw->tw_ts_recent_stamp &&
+		    tcp_v4_tw_remember_stamp(tw))
+			tcp_tw_schedule(tw, tw->tw_timeout);
+		else
+			tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
+		return TCP_TW_ACK;
+	}
+
+	/*
+	 *	Now real TIME-WAIT state.
+	 *
+	 *	RFC 1122:
+	 *	"When a connection is [...] on TIME-WAIT state [...]
+	 *	[a TCP] MAY accept a new SYN from the remote TCP to
+	 *	reopen the connection directly, if it:
+	 *	
+	 *	(1)  assigns its initial sequence number for the new
+	 *	connection to be larger than the largest sequence
+	 *	number it used on the previous connection incarnation,
+	 *	and
+	 *
+	 *	(2)  returns to TIME-WAIT state if the SYN turns out 
+	 *	to be an old duplicate".
+	 */
+
+	if (!paws_reject &&
+	    (TCP_SKB_CB(skb)->seq == tw->tw_rcv_nxt &&
+	     (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
+		/* In window segment, it may be only reset or bare ack. */
+
+		if (th->rst) {
+			/* This is TIME_WAIT assasination, in two flavors.
+			 * Oh well... nobody has a sufficient solution to this
+			 * protocol bug yet.
+			 */
+			if (sysctl_tcp_rfc1337 == 0) {
+kill:
+				tcp_tw_deschedule(tw);
+				tcp_tw_put(tw);
+				return TCP_TW_SUCCESS;
+			}
+		}
+		tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
+
+		if (tmp_opt.saw_tstamp) {
+			tw->tw_ts_recent	= tmp_opt.rcv_tsval;
+			tw->tw_ts_recent_stamp	= xtime.tv_sec;
+		}
+
+		tcp_tw_put(tw);
+		return TCP_TW_SUCCESS;
+	}
+
+	/* Out of window segment.
+
+	   All the segments are ACKed immediately.
+
+	   The only exception is new SYN. We accept it, if it is
+	   not old duplicate and we are not in danger to be killed
+	   by delayed old duplicates. RFC check is that it has
+	   newer sequence number works at rates <40Mbit/sec.
+	   However, if paws works, it is reliable AND even more,
+	   we even may relax silly seq space cutoff.
+
+	   RED-PEN: we violate main RFC requirement, if this SYN will appear
+	   old duplicate (i.e. we receive RST in reply to SYN-ACK),
+	   we must return socket to time-wait state. It is not good,
+	   but not fatal yet.
+	 */
+
+	if (th->syn && !th->rst && !th->ack && !paws_reject &&
+	    (after(TCP_SKB_CB(skb)->seq, tw->tw_rcv_nxt) ||
+	     (tmp_opt.saw_tstamp && (s32)(tw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
+		u32 isn = tw->tw_snd_nxt + 65535 + 2;
+		if (isn == 0)
+			isn++;
+		TCP_SKB_CB(skb)->when = isn;
+		return TCP_TW_SYN;
+	}
+
+	if (paws_reject)
+		NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
+
+	if(!th->rst) {
+		/* In this case we must reset the TIMEWAIT timer.
+		 *
+		 * If it is ACKless SYN it may be both old duplicate
+		 * and new good SYN with random sequence number <rcv_nxt.
+		 * Do not reschedule in the last case.
+		 */
+		if (paws_reject || th->ack)
+			tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
+
+		/* Send ACK. Note, we do not put the bucket,
+		 * it will be released by caller.
+		 */
+		return TCP_TW_ACK;
+	}
+	tcp_tw_put(tw);
+	return TCP_TW_SUCCESS;
+}
+
+/* Enter the time wait state.  This is called with locally disabled BH.
+ * Essentially we whip up a timewait bucket, copy the
+ * relevant info into it from the SK, and mess with hash chains
+ * and list linkage.
+ */
+static void __tcp_tw_hashdance(struct sock *sk, struct tcp_tw_bucket *tw)
+{
+	struct tcp_ehash_bucket *ehead = &tcp_ehash[sk->sk_hashent];
+	struct tcp_bind_hashbucket *bhead;
+
+	/* Step 1: Put TW into bind hash. Original socket stays there too.
+	   Note, that any socket with inet_sk(sk)->num != 0 MUST be bound in
+	   binding cache, even if it is closed.
+	 */
+	bhead = &tcp_bhash[tcp_bhashfn(inet_sk(sk)->num)];
+	spin_lock(&bhead->lock);
+	tw->tw_tb = tcp_sk(sk)->bind_hash;
+	BUG_TRAP(tcp_sk(sk)->bind_hash);
+	tw_add_bind_node(tw, &tw->tw_tb->owners);
+	spin_unlock(&bhead->lock);
+
+	write_lock(&ehead->lock);
+
+	/* Step 2: Remove SK from established hash. */
+	if (__sk_del_node_init(sk))
+		sock_prot_dec_use(sk->sk_prot);
+
+	/* Step 3: Hash TW into TIMEWAIT half of established hash table. */
+	tw_add_node(tw, &(ehead + tcp_ehash_size)->chain);
+	atomic_inc(&tw->tw_refcnt);
+
+	write_unlock(&ehead->lock);
+}
+
+/* 
+ * Move a socket to time-wait or dead fin-wait-2 state.
+ */ 
+void tcp_time_wait(struct sock *sk, int state, int timeo)
+{
+	struct tcp_tw_bucket *tw = NULL;
+	struct tcp_sock *tp = tcp_sk(sk);
+	int recycle_ok = 0;
+
+	if (sysctl_tcp_tw_recycle && tp->rx_opt.ts_recent_stamp)
+		recycle_ok = tp->af_specific->remember_stamp(sk);
+
+	if (tcp_tw_count < sysctl_tcp_max_tw_buckets)
+		tw = kmem_cache_alloc(tcp_timewait_cachep, SLAB_ATOMIC);
+
+	if(tw != NULL) {
+		struct inet_sock *inet = inet_sk(sk);
+		int rto = (tp->rto<<2) - (tp->rto>>1);
+
+		/* Give us an identity. */
+		tw->tw_daddr		= inet->daddr;
+		tw->tw_rcv_saddr	= inet->rcv_saddr;
+		tw->tw_bound_dev_if	= sk->sk_bound_dev_if;
+		tw->tw_num		= inet->num;
+		tw->tw_state		= TCP_TIME_WAIT;
+		tw->tw_substate		= state;
+		tw->tw_sport		= inet->sport;
+		tw->tw_dport		= inet->dport;
+		tw->tw_family		= sk->sk_family;
+		tw->tw_reuse		= sk->sk_reuse;
+		tw->tw_rcv_wscale	= tp->rx_opt.rcv_wscale;
+		atomic_set(&tw->tw_refcnt, 1);
+
+		tw->tw_hashent		= sk->sk_hashent;
+		tw->tw_rcv_nxt		= tp->rcv_nxt;
+		tw->tw_snd_nxt		= tp->snd_nxt;
+		tw->tw_rcv_wnd		= tcp_receive_window(tp);
+		tw->tw_ts_recent	= tp->rx_opt.ts_recent;
+		tw->tw_ts_recent_stamp	= tp->rx_opt.ts_recent_stamp;
+		tw_dead_node_init(tw);
+
+#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
+		if (tw->tw_family == PF_INET6) {
+			struct ipv6_pinfo *np = inet6_sk(sk);
+
+			ipv6_addr_copy(&tw->tw_v6_daddr, &np->daddr);
+			ipv6_addr_copy(&tw->tw_v6_rcv_saddr, &np->rcv_saddr);
+			tw->tw_v6_ipv6only = np->ipv6only;
+		} else {
+			memset(&tw->tw_v6_daddr, 0, sizeof(tw->tw_v6_daddr));
+			memset(&tw->tw_v6_rcv_saddr, 0, sizeof(tw->tw_v6_rcv_saddr));
+			tw->tw_v6_ipv6only = 0;
+		}
+#endif
+		/* Linkage updates. */
+		__tcp_tw_hashdance(sk, tw);
+
+		/* Get the TIME_WAIT timeout firing. */
+		if (timeo < rto)
+			timeo = rto;
+
+		if (recycle_ok) {
+			tw->tw_timeout = rto;
+		} else {
+			tw->tw_timeout = TCP_TIMEWAIT_LEN;
+			if (state == TCP_TIME_WAIT)
+				timeo = TCP_TIMEWAIT_LEN;
+		}
+
+		tcp_tw_schedule(tw, timeo);
+		tcp_tw_put(tw);
+	} else {
+		/* Sorry, if we're out of memory, just CLOSE this
+		 * socket up.  We've got bigger problems than
+		 * non-graceful socket closings.
+		 */
+		if (net_ratelimit())
+			printk(KERN_INFO "TCP: time wait bucket table overflow\n");
+	}
+
+	tcp_update_metrics(sk);
+	tcp_done(sk);
+}
+
+/* Kill off TIME_WAIT sockets once their lifetime has expired. */
+static int tcp_tw_death_row_slot;
+
+static void tcp_twkill(unsigned long);
+
+/* TIME_WAIT reaping mechanism. */
+#define TCP_TWKILL_SLOTS	8	/* Please keep this a power of 2. */
+#define TCP_TWKILL_PERIOD	(TCP_TIMEWAIT_LEN/TCP_TWKILL_SLOTS)
+
+#define TCP_TWKILL_QUOTA	100
+
+static struct hlist_head tcp_tw_death_row[TCP_TWKILL_SLOTS];
+static DEFINE_SPINLOCK(tw_death_lock);
+static struct timer_list tcp_tw_timer = TIMER_INITIALIZER(tcp_twkill, 0, 0);
+static void twkill_work(void *);
+static DECLARE_WORK(tcp_twkill_work, twkill_work, NULL);
+static u32 twkill_thread_slots;
+
+/* Returns non-zero if quota exceeded.  */
+static int tcp_do_twkill_work(int slot, unsigned int quota)
+{
+	struct tcp_tw_bucket *tw;
+	struct hlist_node *node;
+	unsigned int killed;
+	int ret;
+
+	/* NOTE: compare this to previous version where lock
+	 * was released after detaching chain. It was racy,
+	 * because tw buckets are scheduled in not serialized context
+	 * in 2.3 (with netfilter), and with softnet it is common, because
+	 * soft irqs are not sequenced.
+	 */
+	killed = 0;
+	ret = 0;
+rescan:
+	tw_for_each_inmate(tw, node, &tcp_tw_death_row[slot]) {
+		__tw_del_dead_node(tw);
+		spin_unlock(&tw_death_lock);
+		tcp_timewait_kill(tw);
+		tcp_tw_put(tw);
+		killed++;
+		spin_lock(&tw_death_lock);
+		if (killed > quota) {
+			ret = 1;
+			break;
+		}
+
+		/* While we dropped tw_death_lock, another cpu may have
+		 * killed off the next TW bucket in the list, therefore
+		 * do a fresh re-read of the hlist head node with the
+		 * lock reacquired.  We still use the hlist traversal
+		 * macro in order to get the prefetches.
+		 */
+		goto rescan;
+	}
+
+	tcp_tw_count -= killed;
+	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITED, killed);
+
+	return ret;
+}
+
+static void tcp_twkill(unsigned long dummy)
+{
+	int need_timer, ret;
+
+	spin_lock(&tw_death_lock);
+
+	if (tcp_tw_count == 0)
+		goto out;
+
+	need_timer = 0;
+	ret = tcp_do_twkill_work(tcp_tw_death_row_slot, TCP_TWKILL_QUOTA);
+	if (ret) {
+		twkill_thread_slots |= (1 << tcp_tw_death_row_slot);
+		mb();
+		schedule_work(&tcp_twkill_work);
+		need_timer = 1;
+	} else {
+		/* We purged the entire slot, anything left?  */
+		if (tcp_tw_count)
+			need_timer = 1;
+	}
+	tcp_tw_death_row_slot =
+		((tcp_tw_death_row_slot + 1) & (TCP_TWKILL_SLOTS - 1));
+	if (need_timer)
+		mod_timer(&tcp_tw_timer, jiffies + TCP_TWKILL_PERIOD);
+out:
+	spin_unlock(&tw_death_lock);
+}
+
+extern void twkill_slots_invalid(void);
+
+static void twkill_work(void *dummy)
+{
+	int i;
+
+	if ((TCP_TWKILL_SLOTS - 1) > (sizeof(twkill_thread_slots) * 8))
+		twkill_slots_invalid();
+
+	while (twkill_thread_slots) {
+		spin_lock_bh(&tw_death_lock);
+		for (i = 0; i < TCP_TWKILL_SLOTS; i++) {
+			if (!(twkill_thread_slots & (1 << i)))
+				continue;
+
+			while (tcp_do_twkill_work(i, TCP_TWKILL_QUOTA) != 0) {
+				if (need_resched()) {
+					spin_unlock_bh(&tw_death_lock);
+					schedule();
+					spin_lock_bh(&tw_death_lock);
+				}
+			}
+
+			twkill_thread_slots &= ~(1 << i);
+		}
+		spin_unlock_bh(&tw_death_lock);
+	}
+}
+
+/* These are always called from BH context.  See callers in
+ * tcp_input.c to verify this.
+ */
+
+/* This is for handling early-kills of TIME_WAIT sockets. */
+void tcp_tw_deschedule(struct tcp_tw_bucket *tw)
+{
+	spin_lock(&tw_death_lock);
+	if (tw_del_dead_node(tw)) {
+		tcp_tw_put(tw);
+		if (--tcp_tw_count == 0)
+			del_timer(&tcp_tw_timer);
+	}
+	spin_unlock(&tw_death_lock);
+	tcp_timewait_kill(tw);
+}
+
+/* Short-time timewait calendar */
+
+static int tcp_twcal_hand = -1;
+static int tcp_twcal_jiffie;
+static void tcp_twcal_tick(unsigned long);
+static struct timer_list tcp_twcal_timer =
+		TIMER_INITIALIZER(tcp_twcal_tick, 0, 0);
+static struct hlist_head tcp_twcal_row[TCP_TW_RECYCLE_SLOTS];
+
+static void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo)
+{
+	struct hlist_head *list;
+	int slot;
+
+	/* timeout := RTO * 3.5
+	 *
+	 * 3.5 = 1+2+0.5 to wait for two retransmits.
+	 *
+	 * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
+	 * our ACK acking that FIN can be lost. If N subsequent retransmitted
+	 * FINs (or previous seqments) are lost (probability of such event
+	 * is p^(N+1), where p is probability to lose single packet and
+	 * time to detect the loss is about RTO*(2^N - 1) with exponential
+	 * backoff). Normal timewait length is calculated so, that we
+	 * waited at least for one retransmitted FIN (maximal RTO is 120sec).
+	 * [ BTW Linux. following BSD, violates this requirement waiting
+	 *   only for 60sec, we should wait at least for 240 secs.
+	 *   Well, 240 consumes too much of resources 8)
+	 * ]
+	 * This interval is not reduced to catch old duplicate and
+	 * responces to our wandering segments living for two MSLs.
+	 * However, if we use PAWS to detect
+	 * old duplicates, we can reduce the interval to bounds required
+	 * by RTO, rather than MSL. So, if peer understands PAWS, we
+	 * kill tw bucket after 3.5*RTO (it is important that this number
+	 * is greater than TS tick!) and detect old duplicates with help
+	 * of PAWS.
+	 */
+	slot = (timeo + (1<<TCP_TW_RECYCLE_TICK) - 1) >> TCP_TW_RECYCLE_TICK;
+
+	spin_lock(&tw_death_lock);
+
+	/* Unlink it, if it was scheduled */
+	if (tw_del_dead_node(tw))
+		tcp_tw_count--;
+	else
+		atomic_inc(&tw->tw_refcnt);
+
+	if (slot >= TCP_TW_RECYCLE_SLOTS) {
+		/* Schedule to slow timer */
+		if (timeo >= TCP_TIMEWAIT_LEN) {
+			slot = TCP_TWKILL_SLOTS-1;
+		} else {
+			slot = (timeo + TCP_TWKILL_PERIOD-1) / TCP_TWKILL_PERIOD;
+			if (slot >= TCP_TWKILL_SLOTS)
+				slot = TCP_TWKILL_SLOTS-1;
+		}
+		tw->tw_ttd = jiffies + timeo;
+		slot = (tcp_tw_death_row_slot + slot) & (TCP_TWKILL_SLOTS - 1);
+		list = &tcp_tw_death_row[slot];
+	} else {
+		tw->tw_ttd = jiffies + (slot << TCP_TW_RECYCLE_TICK);
+
+		if (tcp_twcal_hand < 0) {
+			tcp_twcal_hand = 0;
+			tcp_twcal_jiffie = jiffies;
+			tcp_twcal_timer.expires = tcp_twcal_jiffie + (slot<<TCP_TW_RECYCLE_TICK);
+			add_timer(&tcp_twcal_timer);
+		} else {
+			if (time_after(tcp_twcal_timer.expires, jiffies + (slot<<TCP_TW_RECYCLE_TICK)))
+				mod_timer(&tcp_twcal_timer, jiffies + (slot<<TCP_TW_RECYCLE_TICK));
+			slot = (tcp_twcal_hand + slot)&(TCP_TW_RECYCLE_SLOTS-1);
+		}
+		list = &tcp_twcal_row[slot];
+	}
+
+	hlist_add_head(&tw->tw_death_node, list);
+
+	if (tcp_tw_count++ == 0)
+		mod_timer(&tcp_tw_timer, jiffies+TCP_TWKILL_PERIOD);
+	spin_unlock(&tw_death_lock);
+}
+
+void tcp_twcal_tick(unsigned long dummy)
+{
+	int n, slot;
+	unsigned long j;
+	unsigned long now = jiffies;
+	int killed = 0;
+	int adv = 0;
+
+	spin_lock(&tw_death_lock);
+	if (tcp_twcal_hand < 0)
+		goto out;
+
+	slot = tcp_twcal_hand;
+	j = tcp_twcal_jiffie;
+
+	for (n=0; n<TCP_TW_RECYCLE_SLOTS; n++) {
+		if (time_before_eq(j, now)) {
+			struct hlist_node *node, *safe;
+			struct tcp_tw_bucket *tw;
+
+			tw_for_each_inmate_safe(tw, node, safe,
+					   &tcp_twcal_row[slot]) {
+				__tw_del_dead_node(tw);
+				tcp_timewait_kill(tw);
+				tcp_tw_put(tw);
+				killed++;
+			}
+		} else {
+			if (!adv) {
+				adv = 1;
+				tcp_twcal_jiffie = j;
+				tcp_twcal_hand = slot;
+			}
+
+			if (!hlist_empty(&tcp_twcal_row[slot])) {
+				mod_timer(&tcp_twcal_timer, j);
+				goto out;
+			}
+		}
+		j += (1<<TCP_TW_RECYCLE_TICK);
+		slot = (slot+1)&(TCP_TW_RECYCLE_SLOTS-1);
+	}
+	tcp_twcal_hand = -1;
+
+out:
+	if ((tcp_tw_count -= killed) == 0)
+		del_timer(&tcp_tw_timer);
+	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITKILLED, killed);
+	spin_unlock(&tw_death_lock);
+}
+
+/* This is not only more efficient than what we used to do, it eliminates
+ * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
+ *
+ * Actually, we could lots of memory writes here. tp of listening
+ * socket contains all necessary default parameters.
+ */
+struct sock *tcp_create_openreq_child(struct sock *sk, struct open_request *req, struct sk_buff *skb)
+{
+	/* allocate the newsk from the same slab of the master sock,
+	 * if not, at sk_free time we'll try to free it from the wrong
+	 * slabcache (i.e. is it TCPv4 or v6?), this is handled thru sk->sk_prot -acme */
+	struct sock *newsk = sk_alloc(PF_INET, GFP_ATOMIC, sk->sk_prot, 0);
+
+	if(newsk != NULL) {
+		struct tcp_sock *newtp;
+		struct sk_filter *filter;
+
+		memcpy(newsk, sk, sizeof(struct tcp_sock));
+		newsk->sk_state = TCP_SYN_RECV;
+
+		/* SANITY */
+		sk_node_init(&newsk->sk_node);
+		tcp_sk(newsk)->bind_hash = NULL;
+
+		/* Clone the TCP header template */
+		inet_sk(newsk)->dport = req->rmt_port;
+
+		sock_lock_init(newsk);
+		bh_lock_sock(newsk);
+
+		rwlock_init(&newsk->sk_dst_lock);
+		atomic_set(&newsk->sk_rmem_alloc, 0);
+		skb_queue_head_init(&newsk->sk_receive_queue);
+		atomic_set(&newsk->sk_wmem_alloc, 0);
+		skb_queue_head_init(&newsk->sk_write_queue);
+		atomic_set(&newsk->sk_omem_alloc, 0);
+		newsk->sk_wmem_queued = 0;
+		newsk->sk_forward_alloc = 0;
+
+		sock_reset_flag(newsk, SOCK_DONE);
+		newsk->sk_userlocks = sk->sk_userlocks & ~SOCK_BINDPORT_LOCK;
+		newsk->sk_backlog.head = newsk->sk_backlog.tail = NULL;
+		newsk->sk_send_head = NULL;
+		rwlock_init(&newsk->sk_callback_lock);
+		skb_queue_head_init(&newsk->sk_error_queue);
+		newsk->sk_write_space = sk_stream_write_space;
+
+		if ((filter = newsk->sk_filter) != NULL)
+			sk_filter_charge(newsk, filter);
+
+		if (unlikely(xfrm_sk_clone_policy(newsk))) {
+			/* It is still raw copy of parent, so invalidate
+			 * destructor and make plain sk_free() */
+			newsk->sk_destruct = NULL;
+			sk_free(newsk);
+			return NULL;
+		}
+
+		/* Now setup tcp_sock */
+		newtp = tcp_sk(newsk);
+		newtp->pred_flags = 0;
+		newtp->rcv_nxt = req->rcv_isn + 1;
+		newtp->snd_nxt = req->snt_isn + 1;
+		newtp->snd_una = req->snt_isn + 1;
+		newtp->snd_sml = req->snt_isn + 1;
+
+		tcp_prequeue_init(newtp);
+
+		tcp_init_wl(newtp, req->snt_isn, req->rcv_isn);
+
+		newtp->retransmits = 0;
+		newtp->backoff = 0;
+		newtp->srtt = 0;
+		newtp->mdev = TCP_TIMEOUT_INIT;
+		newtp->rto = TCP_TIMEOUT_INIT;
+
+		newtp->packets_out = 0;
+		newtp->left_out = 0;
+		newtp->retrans_out = 0;
+		newtp->sacked_out = 0;
+		newtp->fackets_out = 0;
+		newtp->snd_ssthresh = 0x7fffffff;
+
+		/* So many TCP implementations out there (incorrectly) count the
+		 * initial SYN frame in their delayed-ACK and congestion control
+		 * algorithms that we must have the following bandaid to talk
+		 * efficiently to them.  -DaveM
+		 */
+		newtp->snd_cwnd = 2;
+		newtp->snd_cwnd_cnt = 0;
+
+		newtp->frto_counter = 0;
+		newtp->frto_highmark = 0;
+
+		tcp_set_ca_state(newtp, TCP_CA_Open);
+		tcp_init_xmit_timers(newsk);
+		skb_queue_head_init(&newtp->out_of_order_queue);
+		newtp->rcv_wup = req->rcv_isn + 1;
+		newtp->write_seq = req->snt_isn + 1;
+		newtp->pushed_seq = newtp->write_seq;
+		newtp->copied_seq = req->rcv_isn + 1;
+
+		newtp->rx_opt.saw_tstamp = 0;
+
+		newtp->rx_opt.dsack = 0;
+		newtp->rx_opt.eff_sacks = 0;
+
+		newtp->probes_out = 0;
+		newtp->rx_opt.num_sacks = 0;
+		newtp->urg_data = 0;
+		newtp->listen_opt = NULL;
+		newtp->accept_queue = newtp->accept_queue_tail = NULL;
+		/* Deinitialize syn_wait_lock to trap illegal accesses. */
+		memset(&newtp->syn_wait_lock, 0, sizeof(newtp->syn_wait_lock));
+
+		/* Back to base struct sock members. */
+		newsk->sk_err = 0;
+		newsk->sk_priority = 0;
+		atomic_set(&newsk->sk_refcnt, 2);
+#ifdef INET_REFCNT_DEBUG
+		atomic_inc(&inet_sock_nr);
+#endif
+		atomic_inc(&tcp_sockets_allocated);
+
+		if (sock_flag(newsk, SOCK_KEEPOPEN))
+			tcp_reset_keepalive_timer(newsk,
+						  keepalive_time_when(newtp));
+		newsk->sk_socket = NULL;
+		newsk->sk_sleep = NULL;
+
+		newtp->rx_opt.tstamp_ok = req->tstamp_ok;
+		if((newtp->rx_opt.sack_ok = req->sack_ok) != 0) {
+			if (sysctl_tcp_fack)
+				newtp->rx_opt.sack_ok |= 2;
+		}
+		newtp->window_clamp = req->window_clamp;
+		newtp->rcv_ssthresh = req->rcv_wnd;
+		newtp->rcv_wnd = req->rcv_wnd;
+		newtp->rx_opt.wscale_ok = req->wscale_ok;
+		if (newtp->rx_opt.wscale_ok) {
+			newtp->rx_opt.snd_wscale = req->snd_wscale;
+			newtp->rx_opt.rcv_wscale = req->rcv_wscale;
+		} else {
+			newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
+			newtp->window_clamp = min(newtp->window_clamp, 65535U);
+		}
+		newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->rx_opt.snd_wscale;
+		newtp->max_window = newtp->snd_wnd;
+
+		if (newtp->rx_opt.tstamp_ok) {
+			newtp->rx_opt.ts_recent = req->ts_recent;
+			newtp->rx_opt.ts_recent_stamp = xtime.tv_sec;
+			newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
+		} else {
+			newtp->rx_opt.ts_recent_stamp = 0;
+			newtp->tcp_header_len = sizeof(struct tcphdr);
+		}
+		if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len)
+			newtp->ack.last_seg_size = skb->len-newtp->tcp_header_len;
+		newtp->rx_opt.mss_clamp = req->mss;
+		TCP_ECN_openreq_child(newtp, req);
+		if (newtp->ecn_flags&TCP_ECN_OK)
+			sock_set_flag(newsk, SOCK_NO_LARGESEND);
+
+		tcp_ca_init(newtp);
+
+		TCP_INC_STATS_BH(TCP_MIB_PASSIVEOPENS);
+	}
+	return newsk;
+}
+
+/* 
+ *	Process an incoming packet for SYN_RECV sockets represented
+ *	as an open_request.
+ */
+
+struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
+			   struct open_request *req,
+			   struct open_request **prev)
+{
+	struct tcphdr *th = skb->h.th;
+	struct tcp_sock *tp = tcp_sk(sk);
+	u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
+	int paws_reject = 0;
+	struct tcp_options_received tmp_opt;
+	struct sock *child;
+
+	tmp_opt.saw_tstamp = 0;
+	if (th->doff > (sizeof(struct tcphdr)>>2)) {
+		tcp_parse_options(skb, &tmp_opt, 0);
+
+		if (tmp_opt.saw_tstamp) {
+			tmp_opt.ts_recent = req->ts_recent;
+			/* We do not store true stamp, but it is not required,
+			 * it can be estimated (approximately)
+			 * from another data.
+			 */
+			tmp_opt.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
+			paws_reject = tcp_paws_check(&tmp_opt, th->rst);
+		}
+	}
+
+	/* Check for pure retransmitted SYN. */
+	if (TCP_SKB_CB(skb)->seq == req->rcv_isn &&
+	    flg == TCP_FLAG_SYN &&
+	    !paws_reject) {
+		/*
+		 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
+		 * this case on figure 6 and figure 8, but formal
+		 * protocol description says NOTHING.
+		 * To be more exact, it says that we should send ACK,
+		 * because this segment (at least, if it has no data)
+		 * is out of window.
+		 *
+		 *  CONCLUSION: RFC793 (even with RFC1122) DOES NOT
+		 *  describe SYN-RECV state. All the description
+		 *  is wrong, we cannot believe to it and should
+		 *  rely only on common sense and implementation
+		 *  experience.
+		 *
+		 * Enforce "SYN-ACK" according to figure 8, figure 6
+		 * of RFC793, fixed by RFC1122.
+		 */
+		req->class->rtx_syn_ack(sk, req, NULL);
+		return NULL;
+	}
+
+	/* Further reproduces section "SEGMENT ARRIVES"
+	   for state SYN-RECEIVED of RFC793.
+	   It is broken, however, it does not work only
+	   when SYNs are crossed.
+
+	   You would think that SYN crossing is impossible here, since
+	   we should have a SYN_SENT socket (from connect()) on our end,
+	   but this is not true if the crossed SYNs were sent to both
+	   ends by a malicious third party.  We must defend against this,
+	   and to do that we first verify the ACK (as per RFC793, page
+	   36) and reset if it is invalid.  Is this a true full defense?
+	   To convince ourselves, let us consider a way in which the ACK
+	   test can still pass in this 'malicious crossed SYNs' case.
+	   Malicious sender sends identical SYNs (and thus identical sequence
+	   numbers) to both A and B:
+
+		A: gets SYN, seq=7
+		B: gets SYN, seq=7
+
+	   By our good fortune, both A and B select the same initial
+	   send sequence number of seven :-)
+
+		A: sends SYN|ACK, seq=7, ack_seq=8
+		B: sends SYN|ACK, seq=7, ack_seq=8
+
+	   So we are now A eating this SYN|ACK, ACK test passes.  So
+	   does sequence test, SYN is truncated, and thus we consider
+	   it a bare ACK.
+
+	   If tp->defer_accept, we silently drop this bare ACK.  Otherwise,
+	   we create an established connection.  Both ends (listening sockets)
+	   accept the new incoming connection and try to talk to each other. 8-)
+
+	   Note: This case is both harmless, and rare.  Possibility is about the
+	   same as us discovering intelligent life on another plant tomorrow.
+
+	   But generally, we should (RFC lies!) to accept ACK
+	   from SYNACK both here and in tcp_rcv_state_process().
+	   tcp_rcv_state_process() does not, hence, we do not too.
+
+	   Note that the case is absolutely generic:
+	   we cannot optimize anything here without
+	   violating protocol. All the checks must be made
+	   before attempt to create socket.
+	 */
+
+	/* RFC793 page 36: "If the connection is in any non-synchronized state ...
+	 *                  and the incoming segment acknowledges something not yet
+	 *                  sent (the segment carries an unaccaptable ACK) ...
+	 *                  a reset is sent."
+	 *
+	 * Invalid ACK: reset will be sent by listening socket
+	 */
+	if ((flg & TCP_FLAG_ACK) &&
+	    (TCP_SKB_CB(skb)->ack_seq != req->snt_isn+1))
+		return sk;
+
+	/* Also, it would be not so bad idea to check rcv_tsecr, which
+	 * is essentially ACK extension and too early or too late values
+	 * should cause reset in unsynchronized states.
+	 */
+
+	/* RFC793: "first check sequence number". */
+
+	if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
+					  req->rcv_isn+1, req->rcv_isn+1+req->rcv_wnd)) {
+		/* Out of window: send ACK and drop. */
+		if (!(flg & TCP_FLAG_RST))
+			req->class->send_ack(skb, req);
+		if (paws_reject)
+			NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
+		return NULL;
+	}
+
+	/* In sequence, PAWS is OK. */
+
+	if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, req->rcv_isn+1))
+			req->ts_recent = tmp_opt.rcv_tsval;
+
+		if (TCP_SKB_CB(skb)->seq == req->rcv_isn) {
+			/* Truncate SYN, it is out of window starting
+			   at req->rcv_isn+1. */
+			flg &= ~TCP_FLAG_SYN;
+		}
+
+		/* RFC793: "second check the RST bit" and
+		 *	   "fourth, check the SYN bit"
+		 */
+		if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN))
+			goto embryonic_reset;
+
+		/* ACK sequence verified above, just make sure ACK is
+		 * set.  If ACK not set, just silently drop the packet.
+		 */
+		if (!(flg & TCP_FLAG_ACK))
+			return NULL;
+
+		/* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
+		if (tp->defer_accept && TCP_SKB_CB(skb)->end_seq == req->rcv_isn+1) {
+			req->acked = 1;
+			return NULL;
+		}
+
+		/* OK, ACK is valid, create big socket and
+		 * feed this segment to it. It will repeat all
+		 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
+		 * ESTABLISHED STATE. If it will be dropped after
+		 * socket is created, wait for troubles.
+		 */
+		child = tp->af_specific->syn_recv_sock(sk, skb, req, NULL);
+		if (child == NULL)
+			goto listen_overflow;
+
+		tcp_synq_unlink(tp, req, prev);
+		tcp_synq_removed(sk, req);
+
+		tcp_acceptq_queue(sk, req, child);
+		return child;
+
+	listen_overflow:
+		if (!sysctl_tcp_abort_on_overflow) {
+			req->acked = 1;
+			return NULL;
+		}
+
+	embryonic_reset:
+		NET_INC_STATS_BH(LINUX_MIB_EMBRYONICRSTS);
+		if (!(flg & TCP_FLAG_RST))
+			req->class->send_reset(skb);
+
+		tcp_synq_drop(sk, req, prev);
+		return NULL;
+}
+
+/*
+ * Queue segment on the new socket if the new socket is active,
+ * otherwise we just shortcircuit this and continue with
+ * the new socket.
+ */
+
+int tcp_child_process(struct sock *parent, struct sock *child,
+		      struct sk_buff *skb)
+{
+	int ret = 0;
+	int state = child->sk_state;
+
+	if (!sock_owned_by_user(child)) {
+		ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len);
+
+		/* Wakeup parent, send SIGIO */
+		if (state == TCP_SYN_RECV && child->sk_state != state)
+			parent->sk_data_ready(parent, 0);
+	} else {
+		/* Alas, it is possible again, because we do lookup
+		 * in main socket hash table and lock on listening
+		 * socket does not protect us more.
+		 */
+		sk_add_backlog(child, skb);
+	}
+
+	bh_unlock_sock(child);
+	sock_put(child);
+	return ret;
+}
+
+EXPORT_SYMBOL(tcp_check_req);
+EXPORT_SYMBOL(tcp_child_process);
+EXPORT_SYMBOL(tcp_create_openreq_child);
+EXPORT_SYMBOL(tcp_timewait_state_process);
+EXPORT_SYMBOL(tcp_tw_deschedule);