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[linux-2.6.git] / net / ipv4 / tcp.c

/*
 * 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.c,v 1.216 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>
 *
 * Fixes:
 *              Alan Cox        :       Numerous verify_area() calls
 *              Alan Cox        :       Set the ACK bit on a reset
 *              Alan Cox        :       Stopped it crashing if it closed while
 *                                      sk->inuse=1 and was trying to connect
 *                                      (tcp_err()).
 *              Alan Cox        :       All icmp error handling was broken
 *                                      pointers passed where wrong and the
 *                                      socket was looked up backwards. Nobody
 *                                      tested any icmp error code obviously.
 *              Alan Cox        :       tcp_err() now handled properly. It
 *                                      wakes people on errors. poll
 *                                      behaves and the icmp error race
 *                                      has gone by moving it into sock.c
 *              Alan Cox        :       tcp_send_reset() fixed to work for
 *                                      everything not just packets for
 *                                      unknown sockets.
 *              Alan Cox        :       tcp option processing.
 *              Alan Cox        :       Reset tweaked (still not 100%) [Had
 *                                      syn rule wrong]
 *              Herp Rosmanith  :       More reset fixes
 *              Alan Cox        :       No longer acks invalid rst frames.
 *                                      Acking any kind of RST is right out.
 *              Alan Cox        :       Sets an ignore me flag on an rst
 *                                      receive otherwise odd bits of prattle
 *                                      escape still
 *              Alan Cox        :       Fixed another acking RST frame bug.
 *                                      Should stop LAN workplace lockups.
 *              Alan Cox        :       Some tidyups using the new skb list
 *                                      facilities
 *              Alan Cox        :       sk->keepopen now seems to work
 *              Alan Cox        :       Pulls options out correctly on accepts
 *              Alan Cox        :       Fixed assorted sk->rqueue->next errors
 *              Alan Cox        :       PSH doesn't end a TCP read. Switched a
 *                                      bit to skb ops.
 *              Alan Cox        :       Tidied tcp_data to avoid a potential
 *                                      nasty.
 *              Alan Cox        :       Added some better commenting, as the
 *                                      tcp is hard to follow
 *              Alan Cox        :       Removed incorrect check for 20 * psh
 *      Michael O'Reilly        :       ack < copied bug fix.
 *      Johannes Stille         :       Misc tcp fixes (not all in yet).
 *              Alan Cox        :       FIN with no memory -> CRASH
 *              Alan Cox        :       Added socket option proto entries.
 *                                      Also added awareness of them to accept.
 *              Alan Cox        :       Added TCP options (SOL_TCP)
 *              Alan Cox        :       Switched wakeup calls to callbacks,
 *                                      so the kernel can layer network
 *                                      sockets.
 *              Alan Cox        :       Use ip_tos/ip_ttl settings.
 *              Alan Cox        :       Handle FIN (more) properly (we hope).
 *              Alan Cox        :       RST frames sent on unsynchronised
 *                                      state ack error.
 *              Alan Cox        :       Put in missing check for SYN bit.
 *              Alan Cox        :       Added tcp_select_window() aka NET2E
 *                                      window non shrink trick.
 *              Alan Cox        :       Added a couple of small NET2E timer
 *                                      fixes
 *              Charles Hedrick :       TCP fixes
 *              Toomas Tamm     :       TCP window fixes
 *              Alan Cox        :       Small URG fix to rlogin ^C ack fight
 *              Charles Hedrick :       Rewrote most of it to actually work
 *              Linus           :       Rewrote tcp_read() and URG handling
 *                                      completely
 *              Gerhard Koerting:       Fixed some missing timer handling
 *              Matthew Dillon  :       Reworked TCP machine states as per RFC
 *              Gerhard Koerting:       PC/TCP workarounds
 *              Adam Caldwell   :       Assorted timer/timing errors
 *              Matthew Dillon  :       Fixed another RST bug
 *              Alan Cox        :       Move to kernel side addressing changes.
 *              Alan Cox        :       Beginning work on TCP fastpathing
 *                                      (not yet usable)
 *              Arnt Gulbrandsen:       Turbocharged tcp_check() routine.
 *              Alan Cox        :       TCP fast path debugging
 *              Alan Cox        :       Window clamping
 *              Michael Riepe   :       Bug in tcp_check()
 *              Matt Dillon     :       More TCP improvements and RST bug fixes
 *              Matt Dillon     :       Yet more small nasties remove from the
 *                                      TCP code (Be very nice to this man if
 *                                      tcp finally works 100%) 8)
 *              Alan Cox        :       BSD accept semantics.
 *              Alan Cox        :       Reset on closedown bug.
 *      Peter De Schrijver      :       ENOTCONN check missing in tcp_sendto().
 *              Michael Pall    :       Handle poll() after URG properly in
 *                                      all cases.
 *              Michael Pall    :       Undo the last fix in tcp_read_urg()
 *                                      (multi URG PUSH broke rlogin).
 *              Michael Pall    :       Fix the multi URG PUSH problem in
 *                                      tcp_readable(), poll() after URG
 *                                      works now.
 *              Michael Pall    :       recv(...,MSG_OOB) never blocks in the
 *                                      BSD api.
 *              Alan Cox        :       Changed the semantics of sk->socket to
 *                                      fix a race and a signal problem with
 *                                      accept() and async I/O.
 *              Alan Cox        :       Relaxed the rules on tcp_sendto().
 *              Yury Shevchuk   :       Really fixed accept() blocking problem.
 *              Craig I. Hagan  :       Allow for BSD compatible TIME_WAIT for
 *                                      clients/servers which listen in on
 *                                      fixed ports.
 *              Alan Cox        :       Cleaned the above up and shrank it to
 *                                      a sensible code size.
 *              Alan Cox        :       Self connect lockup fix.
 *              Alan Cox        :       No connect to multicast.
 *              Ross Biro       :       Close unaccepted children on master
 *                                      socket close.
 *              Alan Cox        :       Reset tracing code.
 *              Alan Cox        :       Spurious resets on shutdown.
 *              Alan Cox        :       Giant 15 minute/60 second timer error
 *              Alan Cox        :       Small whoops in polling before an
 *                                      accept.
 *              Alan Cox        :       Kept the state trace facility since
 *                                      it's handy for debugging.
 *              Alan Cox        :       More reset handler fixes.
 *              Alan Cox        :       Started rewriting the code based on
 *                                      the RFC's for other useful protocol
 *                                      references see: Comer, KA9Q NOS, and
 *                                      for a reference on the difference
 *                                      between specifications and how BSD
 *                                      works see the 4.4lite source.
 *              A.N.Kuznetsov   :       Don't time wait on completion of tidy
 *                                      close.
 *              Linus Torvalds  :       Fin/Shutdown & copied_seq changes.
 *              Linus Torvalds  :       Fixed BSD port reuse to work first syn
 *              Alan Cox        :       Reimplemented timers as per the RFC
 *                                      and using multiple timers for sanity.
 *              Alan Cox        :       Small bug fixes, and a lot of new
 *                                      comments.
 *              Alan Cox        :       Fixed dual reader crash by locking
 *                                      the buffers (much like datagram.c)
 *              Alan Cox        :       Fixed stuck sockets in probe. A probe
 *                                      now gets fed up of retrying without
 *                                      (even a no space) answer.
 *              Alan Cox        :       Extracted closing code better
 *              Alan Cox        :       Fixed the closing state machine to
 *                                      resemble the RFC.
 *              Alan Cox        :       More 'per spec' fixes.
 *              Jorge Cwik      :       Even faster checksumming.
 *              Alan Cox        :       tcp_data() doesn't ack illegal PSH
 *                                      only frames. At least one pc tcp stack
 *                                      generates them.
 *              Alan Cox        :       Cache last socket.
 *              Alan Cox        :       Per route irtt.
 *              Matt Day        :       poll()->select() match BSD precisely on error
 *              Alan Cox        :       New buffers
 *              Marc Tamsky     :       Various sk->prot->retransmits and
 *                                      sk->retransmits misupdating fixed.
 *                                      Fixed tcp_write_timeout: stuck close,
 *                                      and TCP syn retries gets used now.
 *              Mark Yarvis     :       In tcp_read_wakeup(), don't send an
 *                                      ack if state is TCP_CLOSED.
 *              Alan Cox        :       Look up device on a retransmit - routes may
 *                                      change. Doesn't yet cope with MSS shrink right
 *                                      but it's a start!
 *              Marc Tamsky     :       Closing in closing fixes.
 *              Mike Shaver     :       RFC1122 verifications.
 *              Alan Cox        :       rcv_saddr errors.
 *              Alan Cox        :       Block double connect().
 *              Alan Cox        :       Small hooks for enSKIP.
 *              Alexey Kuznetsov:       Path MTU discovery.
 *              Alan Cox        :       Support soft errors.
 *              Alan Cox        :       Fix MTU discovery pathological case
 *                                      when the remote claims no mtu!
 *              Marc Tamsky     :       TCP_CLOSE fix.
 *              Colin (G3TNE)   :       Send a reset on syn ack replies in
 *                                      window but wrong (fixes NT lpd problems)
 *              Pedro Roque     :       Better TCP window handling, delayed ack.
 *              Joerg Reuter    :       No modification of locked buffers in
 *                                      tcp_do_retransmit()
 *              Eric Schenk     :       Changed receiver side silly window
 *                                      avoidance algorithm to BSD style
 *                                      algorithm. This doubles throughput
 *                                      against machines running Solaris,
 *                                      and seems to result in general
 *                                      improvement.
 *      Stefan Magdalinski      :       adjusted tcp_readable() to fix FIONREAD
 *      Willy Konynenberg       :       Transparent proxying support.
 *      Mike McLagan            :       Routing by source
 *              Keith Owens     :       Do proper merging with partial SKB's in
 *                                      tcp_do_sendmsg to avoid burstiness.
 *              Eric Schenk     :       Fix fast close down bug with
 *                                      shutdown() followed by close().
 *              Andi Kleen      :       Make poll agree with SIGIO
 *      Salvatore Sanfilippo    :       Support SO_LINGER with linger == 1 and
 *                                      lingertime == 0 (RFC 793 ABORT Call)
 *      Hirokazu Takahashi      :       Use copy_from_user() instead of
 *                                      csum_and_copy_from_user() if possible.
 *
 *              This program is free software; you can redistribute it and/or
 *              modify it under the terms of the GNU General Public License
 *              as published by the Free Software Foundation; either version
 *              2 of the License, or(at your option) any later version.
 *
 * Description of States:
 *
 *      TCP_SYN_SENT            sent a connection request, waiting for ack
 *
 *      TCP_SYN_RECV            received a connection request, sent ack,
 *                              waiting for final ack in three-way handshake.
 *
 *      TCP_ESTABLISHED         connection established
 *
 *      TCP_FIN_WAIT1           our side has shutdown, waiting to complete
 *                              transmission of remaining buffered data
 *
 *      TCP_FIN_WAIT2           all buffered data sent, waiting for remote
 *                              to shutdown
 *
 *      TCP_CLOSING             both sides have shutdown but we still have
 *                              data we have to finish sending
 *
 *      TCP_TIME_WAIT           timeout to catch resent junk before entering
 *                              closed, can only be entered from FIN_WAIT2
 *                              or CLOSING.  Required because the other end
 *                              may not have gotten our last ACK causing it
 *                              to retransmit the data packet (which we ignore)
 *
 *      TCP_CLOSE_WAIT          remote side has shutdown and is waiting for
 *                              us to finish writing our data and to shutdown
 *                              (we have to close() to move on to LAST_ACK)
 *
 *      TCP_LAST_ACK            out side has shutdown after remote has
 *                              shutdown.  There may still be data in our
 *                              buffer that we have to finish sending
 *
 *      TCP_CLOSE               socket is finished
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/smp_lock.h>
#include <linux/fs.h>
#include <linux/random.h>

#include <net/icmp.h>
#include <net/tcp.h>
#include <net/xfrm.h>
#include <net/ip.h>


#include <asm/uaccess.h>
#include <asm/ioctls.h>

int sysctl_tcp_fin_timeout = TCP_FIN_TIMEOUT;

DEFINE_SNMP_STAT(struct tcp_mib, tcp_statistics);

kmem_cache_t *tcp_openreq_cachep;
kmem_cache_t *tcp_bucket_cachep;
kmem_cache_t *tcp_timewait_cachep;

atomic_t tcp_orphan_count = ATOMIC_INIT(0);

int sysctl_tcp_default_win_scale;

int sysctl_tcp_mem[3];
int sysctl_tcp_wmem[3] = { 4 * 1024, 16 * 1024, 128 * 1024 };
int sysctl_tcp_rmem[3] = { 4 * 1024, 87380, 87380 * 2 };

atomic_t tcp_memory_allocated;  /* Current allocated memory. */
atomic_t tcp_sockets_allocated; /* Current number of TCP sockets. */

/* Pressure flag: try to collapse.
 * Technical note: it is used by multiple contexts non atomically.
 * All the tcp_mem_schedule() is of this nature: accounting
 * is strict, actions are advisory and have some latency. */
int tcp_memory_pressure;

#define TCP_PAGES(amt) (((amt) + TCP_MEM_QUANTUM - 1) / TCP_MEM_QUANTUM)

int tcp_mem_schedule(struct sock *sk, int size, int kind)
{
        int amt = TCP_PAGES(size);

        sk->sk_forward_alloc += amt * TCP_MEM_QUANTUM;
        atomic_add(amt, &tcp_memory_allocated);

        /* Under limit. */
        if (atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
                if (tcp_memory_pressure)
                        tcp_memory_pressure = 0;
                return 1;
        }

        /* Over hard limit. */
        if (atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[2]) {
                tcp_enter_memory_pressure();
                goto suppress_allocation;
        }

        /* Under pressure. */
        if (atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[1])
                tcp_enter_memory_pressure();

        if (kind) {
                if (atomic_read(&sk->sk_rmem_alloc) < sysctl_tcp_rmem[0])
                        return 1;
        } else if (sk->sk_wmem_queued < sysctl_tcp_wmem[0])
                return 1;

        if (!tcp_memory_pressure ||
            sysctl_tcp_mem[2] > atomic_read(&tcp_sockets_allocated) *
                                TCP_PAGES(sk->sk_wmem_queued +
                                          atomic_read(&sk->sk_rmem_alloc) +
                                          sk->sk_forward_alloc))
                return 1;

suppress_allocation:

        if (!kind) {
                tcp_moderate_sndbuf(sk);

                /* Fail only if socket is _under_ its sndbuf.
                 * In this case we cannot block, so that we have to fail.
                 */
                if (sk->sk_wmem_queued + size >= sk->sk_sndbuf)
                        return 1;
        }

        /* Alas. Undo changes. */
        sk->sk_forward_alloc -= amt * TCP_MEM_QUANTUM;
        atomic_sub(amt, &tcp_memory_allocated);
        return 0;
}

void __tcp_mem_reclaim(struct sock *sk)
{
        if (sk->sk_forward_alloc >= TCP_MEM_QUANTUM) {
                atomic_sub(sk->sk_forward_alloc / TCP_MEM_QUANTUM,
                           &tcp_memory_allocated);
                sk->sk_forward_alloc &= TCP_MEM_QUANTUM - 1;
                if (tcp_memory_pressure &&
                    atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0])
                        tcp_memory_pressure = 0;
        }
}

void tcp_rfree(struct sk_buff *skb)
{
        struct sock *sk = skb->sk;

        atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
        sk->sk_forward_alloc += skb->truesize;
}

/*
 * LISTEN is a special case for poll..
 */
static __inline__ unsigned int tcp_listen_poll(struct sock *sk,
                                               poll_table *wait)
{
        return tcp_sk(sk)->accept_queue ? (POLLIN | POLLRDNORM) : 0;
}

/*
 *      Wait for a TCP event.
 *
 *      Note that we don't need to lock the socket, as the upper poll layers
 *      take care of normal races (between the test and the event) and we don't
 *      go look at any of the socket buffers directly.
 */
unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
{
        unsigned int mask;
        struct sock *sk = sock->sk;
        struct tcp_opt *tp = tcp_sk(sk);

        poll_wait(file, sk->sk_sleep, wait);
        if (sk->sk_state == TCP_LISTEN)
                return tcp_listen_poll(sk, wait);

        /* Socket is not locked. We are protected from async events
           by poll logic and correct handling of state changes
           made by another threads is impossible in any case.
         */

        mask = 0;
        if (sk->sk_err)
                mask = POLLERR;

        /*
         * POLLHUP is certainly not done right. But poll() doesn't
         * have a notion of HUP in just one direction, and for a
         * socket the read side is more interesting.
         *
         * Some poll() documentation says that POLLHUP is incompatible
         * with the POLLOUT/POLLWR flags, so somebody should check this
         * all. But careful, it tends to be safer to return too many
         * bits than too few, and you can easily break real applications
         * if you don't tell them that something has hung up!
         *
         * Check-me.
         *
         * Check number 1. POLLHUP is _UNMASKABLE_ event (see UNIX98 and
         * our fs/select.c). It means that after we received EOF,
         * poll always returns immediately, making impossible poll() on write()
         * in state CLOSE_WAIT. One solution is evident --- to set POLLHUP
         * if and only if shutdown has been made in both directions.
         * Actually, it is interesting to look how Solaris and DUX
         * solve this dilemma. I would prefer, if PULLHUP were maskable,
         * then we could set it on SND_SHUTDOWN. BTW examples given
         * in Stevens' books assume exactly this behaviour, it explains
         * why PULLHUP is incompatible with POLLOUT.    --ANK
         *
         * NOTE. Check for TCP_CLOSE is added. The goal is to prevent
         * blocking on fresh not-connected or disconnected socket. --ANK
         */
        if (sk->sk_shutdown == SHUTDOWN_MASK || sk->sk_state == TCP_CLOSE)
                mask |= POLLHUP;
        if (sk->sk_shutdown & RCV_SHUTDOWN)
                mask |= POLLIN | POLLRDNORM;

        /* Connected? */
        if ((1 << sk->sk_state) & ~(TCPF_SYN_SENT | TCPF_SYN_RECV)) {
                /* Potential race condition. If read of tp below will
                 * escape above sk->sk_state, we can be illegally awaken
                 * in SYN_* states. */
                if ((tp->rcv_nxt != tp->copied_seq) &&
                    (tp->urg_seq != tp->copied_seq ||
                     tp->rcv_nxt != tp->copied_seq + 1 ||
                     sock_flag(sk, SOCK_URGINLINE) || !tp->urg_data))
                        mask |= POLLIN | POLLRDNORM;

                if (!(sk->sk_shutdown & SEND_SHUTDOWN)) {
                        if (tcp_wspace(sk) >= tcp_min_write_space(sk)) {
                                mask |= POLLOUT | POLLWRNORM;
                        } else {  /* send SIGIO later */
                                set_bit(SOCK_ASYNC_NOSPACE,
                                        &sk->sk_socket->flags);
                                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);

                                /* Race breaker. If space is freed after
                                 * wspace test but before the flags are set,
                                 * IO signal will be lost.
                                 */
                                if (tcp_wspace(sk) >= tcp_min_write_space(sk))
                                        mask |= POLLOUT | POLLWRNORM;
                        }
                }

                if (tp->urg_data & TCP_URG_VALID)
                        mask |= POLLPRI;
        }
        return mask;
}

/*
 *      TCP socket write_space callback.
 */
void tcp_write_space(struct sock *sk)
{
        struct socket *sock = sk->sk_socket;

        if (tcp_wspace(sk) >= tcp_min_write_space(sk) && sock) {
                clear_bit(SOCK_NOSPACE, &sock->flags);

                if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
                        wake_up_interruptible(sk->sk_sleep);

                if (sock->fasync_list && !(sk->sk_shutdown & SEND_SHUTDOWN))
                        sock_wake_async(sock, 2, POLL_OUT);
        }
}

int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
{
        struct tcp_opt *tp = tcp_sk(sk);
        int answ;

        switch (cmd) {
        case SIOCINQ:
                if (sk->sk_state == TCP_LISTEN)
                        return -EINVAL;

                lock_sock(sk);
                if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
                        answ = 0;
                else if (sock_flag(sk, SOCK_URGINLINE) ||
                         !tp->urg_data ||
                         before(tp->urg_seq, tp->copied_seq) ||
                         !before(tp->urg_seq, tp->rcv_nxt)) {
                        answ = tp->rcv_nxt - tp->copied_seq;

                        /* Subtract 1, if FIN is in queue. */
                        if (answ && !skb_queue_empty(&sk->sk_receive_queue))
                                answ -=
                       ((struct sk_buff *)sk->sk_receive_queue.prev)->h.th->fin;
                } else
                        answ = tp->urg_seq - tp->copied_seq;
                release_sock(sk);
                break;
        case SIOCATMARK:
                answ = tp->urg_data && tp->urg_seq == tp->copied_seq;
                break;
        case SIOCOUTQ:
                if (sk->sk_state == TCP_LISTEN)
                        return -EINVAL;

                if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
                        answ = 0;
                else
                        answ = tp->write_seq - tp->snd_una;
                break;
        default:
                return -ENOIOCTLCMD;
        };

        return put_user(answ, (int __user *)arg);
}


int tcp_listen_start(struct sock *sk)
{
        struct inet_opt *inet = inet_sk(sk);
        struct tcp_opt *tp = tcp_sk(sk);
        struct tcp_listen_opt *lopt;

        sk->sk_max_ack_backlog = 0;
        sk->sk_ack_backlog = 0;
        tp->accept_queue = tp->accept_queue_tail = NULL;
        tp->syn_wait_lock = RW_LOCK_UNLOCKED;
        tcp_delack_init(tp);

        lopt = kmalloc(sizeof(struct tcp_listen_opt), GFP_KERNEL);
        if (!lopt)
                return -ENOMEM;

        memset(lopt, 0, sizeof(struct tcp_listen_opt));
        for (lopt->max_qlen_log = 6; ; lopt->max_qlen_log++)
                if ((1 << lopt->max_qlen_log) >= sysctl_max_syn_backlog)
                        break;
        get_random_bytes(&lopt->hash_rnd, 4);

        write_lock_bh(&tp->syn_wait_lock);
        tp->listen_opt = lopt;
        write_unlock_bh(&tp->syn_wait_lock);

        /* There is race window here: we announce ourselves listening,
         * but this transition is still not validated by get_port().
         * It is OK, because this socket enters to hash table only
         * after validation is complete.
         */
        sk->sk_state = TCP_LISTEN;
        if (!sk->sk_prot->get_port(sk, inet->num)) {
                inet->sport = htons(inet->num);

                sk_dst_reset(sk);
                sk->sk_prot->hash(sk);

                return 0;
        }

        sk->sk_state = TCP_CLOSE;
        write_lock_bh(&tp->syn_wait_lock);
        tp->listen_opt = NULL;
        write_unlock_bh(&tp->syn_wait_lock);
        kfree(lopt);
        return -EADDRINUSE;
}

/*
 *      This routine closes sockets which have been at least partially
 *      opened, but not yet accepted.
 */

static void tcp_listen_stop (struct sock *sk)
{
        struct tcp_opt *tp = tcp_sk(sk);
        struct tcp_listen_opt *lopt = tp->listen_opt;
        struct open_request *acc_req = tp->accept_queue;
        struct open_request *req;
        int i;

        tcp_delete_keepalive_timer(sk);

        /* make all the listen_opt local to us */
        write_lock_bh(&tp->syn_wait_lock);
        tp->listen_opt = NULL;
        write_unlock_bh(&tp->syn_wait_lock);
        tp->accept_queue = tp->accept_queue_tail = NULL;

        if (lopt->qlen) {
                for (i = 0; i < TCP_SYNQ_HSIZE; i++) {
                        while ((req = lopt->syn_table[i]) != NULL) {
                                lopt->syn_table[i] = req->dl_next;
                                lopt->qlen--;
                                tcp_openreq_free(req);

                /* Following specs, it would be better either to send FIN
                 * (and enter FIN-WAIT-1, it is normal close)
                 * or to send active reset (abort).
                 * Certainly, it is pretty dangerous while synflood, but it is
                 * bad justification for our negligence 8)
                 * To be honest, we are not able to make either
                 * of the variants now.                 --ANK
                 */
                        }
                }
        }
        BUG_TRAP(!lopt->qlen);

        kfree(lopt);

        while ((req = acc_req) != NULL) {
                struct sock *child = req->sk;

                acc_req = req->dl_next;

                local_bh_disable();
                bh_lock_sock(child);
                BUG_TRAP(!sock_owned_by_user(child));
                sock_hold(child);

                tcp_disconnect(child, O_NONBLOCK);

                sock_orphan(child);

                atomic_inc(&tcp_orphan_count);

                tcp_destroy_sock(child);

                bh_unlock_sock(child);
                local_bh_enable();
                sock_put(child);

                tcp_acceptq_removed(sk);
                tcp_openreq_fastfree(req);
        }
        BUG_TRAP(!sk->sk_ack_backlog);
}

/*
 *      Wait for a socket to get into the connected state
 *
 *      Note: Must be called with the socket locked.
 */
static int wait_for_tcp_connect(struct sock *sk, int flags, long *timeo_p)
{
        struct tcp_opt *tp = tcp_sk(sk);
        struct task_struct *tsk = current;
        DEFINE_WAIT(wait);

        while ((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
                if (sk->sk_err)
                        return sock_error(sk);
                if ((1 << sk->sk_state) & ~(TCPF_SYN_SENT | TCPF_SYN_RECV))
                        return -EPIPE;
                if (!*timeo_p)
                        return -EAGAIN;
                if (signal_pending(tsk))
                        return sock_intr_errno(*timeo_p);

                prepare_to_wait(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);
                tp->write_pending++;

                release_sock(sk);
                *timeo_p = schedule_timeout(*timeo_p);
                lock_sock(sk);

                finish_wait(sk->sk_sleep, &wait);
                tp->write_pending--;
        }
        return 0;
}

static inline int tcp_memory_free(struct sock *sk)
{
        return sk->sk_wmem_queued < sk->sk_sndbuf;
}

/*
 *      Wait for more memory for a socket
 */
static int wait_for_tcp_memory(struct sock *sk, long *timeo)
{
        struct tcp_opt *tp = tcp_sk(sk);
        int err = 0;
        long vm_wait = 0;
        long current_timeo = *timeo;
        DEFINE_WAIT(wait);

        if (tcp_memory_free(sk))
                current_timeo = vm_wait = (net_random() % (HZ / 5)) + 2;

        for (;;) {
                set_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);

                prepare_to_wait(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);

                if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
                        goto do_error;
                if (!*timeo)
                        goto do_nonblock;
                if (signal_pending(current))
                        goto do_interrupted;
                clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
                if (tcp_memory_free(sk) && !vm_wait)
                        break;

                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
                tp->write_pending++;
                release_sock(sk);
                if (!tcp_memory_free(sk) || vm_wait)
                        current_timeo = schedule_timeout(current_timeo);
                lock_sock(sk);
                tp->write_pending--;

                if (vm_wait) {
                        vm_wait -= current_timeo;
                        current_timeo = *timeo;
                        if (current_timeo != MAX_SCHEDULE_TIMEOUT &&
                            (current_timeo -= vm_wait) < 0)
                                current_timeo = 0;
                        vm_wait = 0;
                }
                *timeo = current_timeo;
        }
out:
        finish_wait(sk->sk_sleep, &wait);
        return err;

do_error:
        err = -EPIPE;
        goto out;
do_nonblock:
        err = -EAGAIN;
        goto out;
do_interrupted:
        err = sock_intr_errno(*timeo);
        goto out;
}

static inline int can_coalesce(struct sk_buff *skb, int i, struct page *page,
                               int off)
{
        if (i) {
                skb_frag_t *frag = &skb_shinfo(skb)->frags[i - 1];
                return page == frag->page &&
                       off == frag->page_offset + frag->size;
        }
        return 0;
}

static inline void fill_page_desc(struct sk_buff *skb, int i,
                                  struct page *page, int off, int size)
{
        skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
        frag->page = page;
        frag->page_offset = off;
        frag->size = size;
        skb_shinfo(skb)->nr_frags = i + 1;
}

static inline void tcp_mark_push(struct tcp_opt *tp, struct sk_buff *skb)
{
        TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
        tp->pushed_seq = tp->write_seq;
}

static inline int forced_push(struct tcp_opt *tp)
{
        return after(tp->write_seq, tp->pushed_seq + (tp->max_window >> 1));
}

static inline void skb_entail(struct sock *sk, struct tcp_opt *tp,
                              struct sk_buff *skb)
{
        skb->csum = 0;
        TCP_SKB_CB(skb)->seq = tp->write_seq;
        TCP_SKB_CB(skb)->end_seq = tp->write_seq;
        TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
        TCP_SKB_CB(skb)->sacked = 0;
        __skb_queue_tail(&sk->sk_write_queue, skb);
        tcp_charge_skb(sk, skb);
        if (!tp->send_head)
                tp->send_head = skb;
        else if (tp->nonagle&TCP_NAGLE_PUSH)
                tp->nonagle &= ~TCP_NAGLE_PUSH; 
}

static inline void tcp_mark_urg(struct tcp_opt *tp, int flags,
                                struct sk_buff *skb)
{
        if (flags & MSG_OOB) {
                tp->urg_mode = 1;
                tp->snd_up = tp->write_seq;
                TCP_SKB_CB(skb)->sacked |= TCPCB_URG;
        }
}

static inline void tcp_push(struct sock *sk, struct tcp_opt *tp, int flags,
                            int mss_now, int nonagle)
{
        if (tp->send_head) {
                struct sk_buff *skb = sk->sk_write_queue.prev;
                if (!(flags & MSG_MORE) || forced_push(tp))
                        tcp_mark_push(tp, skb);
                tcp_mark_urg(tp, flags, skb);
                __tcp_push_pending_frames(sk, tp, mss_now,
                                          (flags & MSG_MORE) ? TCP_NAGLE_CORK : nonagle);
        }
}

static int tcp_error(struct sock *sk, int flags, int err)
{
        if (err == -EPIPE)
                err = sock_error(sk) ? : -EPIPE;
        if (err == -EPIPE && !(flags & MSG_NOSIGNAL))
                send_sig(SIGPIPE, current, 0);
        return err;
}

static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffset,
                         size_t psize, int flags)
{
        struct tcp_opt *tp = tcp_sk(sk);
        int mss_now;
        int err;
        ssize_t copied;
        long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);

        /* Wait for a connection to finish. */
        if ((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
                if ((err = wait_for_tcp_connect(sk, 0, &timeo)) != 0)
                        goto out_err;

        clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);

        mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));
        copied = 0;

        err = -EPIPE;
        if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
                goto do_error;

        while (psize > 0) {
                struct sk_buff *skb = sk->sk_write_queue.prev;
                struct page *page = pages[poffset / PAGE_SIZE];
                int copy, i;
                int offset = poffset % PAGE_SIZE;
                int size = min_t(size_t, psize, PAGE_SIZE - offset);

                if (!tp->send_head || (copy = mss_now - skb->len) <= 0) {
new_segment:
                        if (!tcp_memory_free(sk))
                                goto wait_for_sndbuf;

                        skb = tcp_alloc_pskb(sk, 0, tp->mss_cache,
                                             sk->sk_allocation);
                        if (!skb)
                                goto wait_for_memory;

                        skb_entail(sk, tp, skb);
                        copy = mss_now;
                }

                if (copy > size)
                        copy = size;

                i = skb_shinfo(skb)->nr_frags;
                if (can_coalesce(skb, i, page, offset)) {
                        skb_shinfo(skb)->frags[i - 1].size += copy;
                } else if (i < MAX_SKB_FRAGS) {
                        get_page(page);
                        fill_page_desc(skb, i, page, offset, copy);
                } else {
                        tcp_mark_push(tp, skb);
                        goto new_segment;
                }

                skb->len += copy;
                skb->data_len += copy;
                skb->ip_summed = CHECKSUM_HW;
                tp->write_seq += copy;
                TCP_SKB_CB(skb)->end_seq += copy;

                if (!copied)
                        TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_PSH;

                copied += copy;
                poffset += copy;
                if (!(psize -= copy))
                        goto out;

                if (skb->len != mss_now || (flags & MSG_OOB))
                        continue;

                if (forced_push(tp)) {
                        tcp_mark_push(tp, skb);
                        __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_PUSH);
                } else if (skb == tp->send_head)
                        tcp_push_one(sk, mss_now);
                continue;

wait_for_sndbuf:
                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
wait_for_memory:
                if (copied)
                        tcp_push(sk, tp, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);

                if ((err = wait_for_tcp_memory(sk, &timeo)) != 0)
                        goto do_error;

                mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));
        }

out:
        if (copied)
                tcp_push(sk, tp, flags, mss_now, tp->nonagle);
        return copied;

do_error:
        if (copied)
                goto out;
out_err:
        return tcp_error(sk, flags, err);
}

ssize_t tcp_sendpage(struct socket *sock, struct page *page, int offset,
                     size_t size, int flags)
{
        ssize_t res;
        struct sock *sk = sock->sk;

#define TCP_ZC_CSUM_FLAGS (NETIF_F_IP_CSUM | NETIF_F_NO_CSUM | NETIF_F_HW_CSUM)

        if (!(sk->sk_route_caps & NETIF_F_SG) ||
            !(sk->sk_route_caps & TCP_ZC_CSUM_FLAGS))
                return sock_no_sendpage(sock, page, offset, size, flags);

#undef TCP_ZC_CSUM_FLAGS

        lock_sock(sk);
        TCP_CHECK_TIMER(sk);
        res = do_tcp_sendpages(sk, &page, offset, size, flags);
        TCP_CHECK_TIMER(sk);
        release_sock(sk);
        return res;
}

#define TCP_PAGE(sk)    (inet_sk(sk)->sndmsg_page)
#define TCP_OFF(sk)     (inet_sk(sk)->sndmsg_off)

static inline int tcp_copy_to_page(struct sock *sk, char __user *from,
                                   struct sk_buff *skb, struct page *page,
                                   int off, int copy)
{
        int err = 0;
        unsigned int csum;

        if (skb->ip_summed == CHECKSUM_NONE) {
                csum = csum_and_copy_from_user(from, page_address(page) + off,
                                       copy, 0, &err);
                if (err) return err;
                skb->csum = csum_block_add(skb->csum, csum, skb->len);
        } else {
                if (copy_from_user(page_address(page) + off, from, copy))
                        return -EFAULT;
        }

        skb->len += copy;
        skb->data_len += copy;
        skb->truesize += copy;
        sk->sk_wmem_queued += copy;
        sk->sk_forward_alloc -= copy;
        return 0;
}

static inline int skb_add_data(struct sk_buff *skb, char __user *from, int copy)
{
        int err = 0;
        unsigned int csum;
        int off = skb->len;

        if (skb->ip_summed == CHECKSUM_NONE) {
                csum = csum_and_copy_from_user(from, skb_put(skb, copy),
                                       copy, 0, &err);
                if (!err) {
                        skb->csum = csum_block_add(skb->csum, csum, off);
                        return 0;
                }
        } else {
                if (!copy_from_user(skb_put(skb, copy), from, copy))
                        return 0;
        }

        __skb_trim(skb, off);
        return -EFAULT;
}

static inline int select_size(struct sock *sk, struct tcp_opt *tp)
{
        int tmp = tp->mss_cache_std;

        if (sk->sk_route_caps & NETIF_F_SG) {
                int pgbreak = SKB_MAX_HEAD(MAX_TCP_HEADER);

                if (tmp >= pgbreak &&
                    tmp <= pgbreak + (MAX_SKB_FRAGS - 1) * PAGE_SIZE)
                        tmp = pgbreak;
        }
        return tmp;
}

int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                size_t size)
{
        struct iovec *iov;
        struct tcp_opt *tp = tcp_sk(sk);
        struct sk_buff *skb;
        int iovlen, flags;
        int mss_now;
        int err, copied;
        long timeo;

        lock_sock(sk);
        TCP_CHECK_TIMER(sk);

        flags = msg->msg_flags;
        timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);

        /* Wait for a connection to finish. */
        if ((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
                if ((err = wait_for_tcp_connect(sk, flags, &timeo)) != 0)
                        goto out_err;

        /* This should be in poll */
        clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);

        mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));

        /* Ok commence sending. */
        iovlen = msg->msg_iovlen;
        iov = msg->msg_iov;
        copied = 0;

        err = -EPIPE;
        if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
                goto do_error;

        while (--iovlen >= 0) {
                int seglen = iov->iov_len;
                unsigned char __user *from = iov->iov_base;

                iov++;

                while (seglen > 0) {
                        int copy;

                        skb = sk->sk_write_queue.prev;

                        if (!tp->send_head ||
                            (copy = mss_now - skb->len) <= 0) {

new_segment:
                                /* Allocate new segment. If the interface is SG,
                                 * allocate skb fitting to single page.
                                 */
                                if (!tcp_memory_free(sk))
                                        goto wait_for_sndbuf;

                                skb = tcp_alloc_pskb(sk, select_size(sk, tp),
                                                     0, sk->sk_allocation);
                                if (!skb)
                                        goto wait_for_memory;

                                /*
                                 * Check whether we can use HW checksum.
                                 */
                                if (sk->sk_route_caps &
                                    (NETIF_F_IP_CSUM | NETIF_F_NO_CSUM |
                                     NETIF_F_HW_CSUM))
                                        skb->ip_summed = CHECKSUM_HW;

                                skb_entail(sk, tp, skb);
                                copy = mss_now;
                        }

                        /* Try to append data to the end of skb. */
                        if (copy > seglen)
                                copy = seglen;

                        /* Where to copy to? */
                        if (skb_tailroom(skb) > 0) {
                                /* We have some space in skb head. Superb! */
                                if (copy > skb_tailroom(skb))
                                        copy = skb_tailroom(skb);
                                if ((err = skb_add_data(skb, from, copy)) != 0)
                                        goto do_fault;
                        } else {
                                int merge = 0;
                                int i = skb_shinfo(skb)->nr_frags;
                                struct page *page = TCP_PAGE(sk);
                                int off = TCP_OFF(sk);

                                if (can_coalesce(skb, i, page, off) &&
                                    off != PAGE_SIZE) {
                                        /* We can extend the last page
                                         * fragment. */
                                        merge = 1;
                                } else if (i == MAX_SKB_FRAGS ||
                                           (!i &&
                                           !(sk->sk_route_caps & NETIF_F_SG))) {
                                        /* Need to add new fragment and cannot
                                         * do this because interface is non-SG,
                                         * or because all the page slots are
                                         * busy. */
                                        tcp_mark_push(tp, skb);
                                        goto new_segment;
                                } else if (page) {
                                        /* If page is cached, align
                                         * offset to L1 cache boundary
                                         */
                                        off = (off + L1_CACHE_BYTES - 1) &
                                              ~(L1_CACHE_BYTES - 1);
                                        if (off == PAGE_SIZE) {
                                                put_page(page);
                                                TCP_PAGE(sk) = page = NULL;
                                        }
                                }

                                if (!page) {
                                        /* Allocate new cache page. */
                                        if (!(page = tcp_alloc_page(sk)))
                                                goto wait_for_memory;
                                        off = 0;
                                }

                                if (copy > PAGE_SIZE - off)
                                        copy = PAGE_SIZE - off;

                                /* Time to copy data. We are close to
                                 * the end! */
                                err = tcp_copy_to_page(sk, from, skb, page,
                                                       off, copy);
                                if (err) {
                                        /* If this page was new, give it to the
                                         * socket so it does not get leaked.
                                         */
                                        if (!TCP_PAGE(sk)) {
                                                TCP_PAGE(sk) = page;
                                                TCP_OFF(sk) = 0;
                                        }
                                        goto do_error;
                                }

                                /* Update the skb. */
                                if (merge) {
                                        skb_shinfo(skb)->frags[i - 1].size +=
                                                                        copy;
                                } else {
                                        fill_page_desc(skb, i, page, off, copy);
                                        if (TCP_PAGE(sk)) {
                                                get_page(page);
                                        } else if (off + copy < PAGE_SIZE) {
                                                get_page(page);
                                                TCP_PAGE(sk) = page;
                                        }
                                }

                                TCP_OFF(sk) = off + copy;
                        }

                        if (!copied)
                                TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_PSH;

                        tp->write_seq += copy;
                        TCP_SKB_CB(skb)->end_seq += copy;

                        from += copy;
                        copied += copy;
                        if ((seglen -= copy) == 0 && iovlen == 0)
                                goto out;

                        if (skb->len != mss_now || (flags & MSG_OOB))
                                continue;

                        if (forced_push(tp)) {
                                tcp_mark_push(tp, skb);
                                __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_PUSH);
                        } else if (skb == tp->send_head)
                                tcp_push_one(sk, mss_now);
                        continue;

wait_for_sndbuf:
                        set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
wait_for_memory:
                        if (copied)
                                tcp_push(sk, tp, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);

                        if ((err = wait_for_tcp_memory(sk, &timeo)) != 0)
                                goto do_error;

                        mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));
                }
        }

out:
        if (copied)
                tcp_push(sk, tp, flags, mss_now, tp->nonagle);
        TCP_CHECK_TIMER(sk);
        release_sock(sk);
        return copied;

do_fault:
        if (!skb->len) {
                if (tp->send_head == skb)
                        tp->send_head = NULL;
                __skb_unlink(skb, skb->list);
                tcp_free_skb(sk, skb);
        }

do_error:
        if (copied)
                goto out;
out_err:
        err = tcp_error(sk, flags, err);
        TCP_CHECK_TIMER(sk);
        release_sock(sk);
        return err;
}

/*
 *      Handle reading urgent data. BSD has very simple semantics for
 *      this, no blocking and very strange errors 8)
 */

static int tcp_recv_urg(struct sock *sk, long timeo,
                        struct msghdr *msg, int len, int flags,
                        int *addr_len)
{
        struct tcp_opt *tp = tcp_sk(sk);

        /* No URG data to read. */
        if (sock_flag(sk, SOCK_URGINLINE) || !tp->urg_data ||
            tp->urg_data == TCP_URG_READ)
                return -EINVAL; /* Yes this is right ! */

        if (sk->sk_state == TCP_CLOSE && !sock_flag(sk, SOCK_DONE))
                return -ENOTCONN;

        if (tp->urg_data & TCP_URG_VALID) {
                int err = 0;
                char c = tp->urg_data;

                if (!(flags & MSG_PEEK))
                        tp->urg_data = TCP_URG_READ;

                /* Read urgent data. */
                msg->msg_flags |= MSG_OOB;

                if (len > 0) {
                        if (!(flags & MSG_TRUNC))
                                err = memcpy_toiovec(msg->msg_iov, &c, 1);
                        len = 1;
                } else
                        msg->msg_flags |= MSG_TRUNC;

                return err ? -EFAULT : len;
        }

        if (sk->sk_state == TCP_CLOSE || (sk->sk_shutdown & RCV_SHUTDOWN))
                return 0;

        /* Fixed the recv(..., MSG_OOB) behaviour.  BSD docs and
         * the available implementations agree in this case:
         * this call should never block, independent of the
         * blocking state of the socket.
         * Mike <pall@rz.uni-karlsruhe.de>
         */
        return -EAGAIN;
}

/*
 *      Release a skb if it is no longer needed. This routine
 *      must be called with interrupts disabled or with the
 *      socket locked so that the sk_buff queue operation is ok.
 */

static inline void tcp_eat_skb(struct sock *sk, struct sk_buff *skb)
{
        __skb_unlink(skb, &sk->sk_receive_queue);
        __kfree_skb(skb);
}

/* Clean up the receive buffer for full frames taken by the user,
 * then send an ACK if necessary.  COPIED is the number of bytes
 * tcp_recvmsg has given to the user so far, it speeds up the
 * calculation of whether or not we must ACK for the sake of
 * a window update.
 */
void cleanup_rbuf(struct sock *sk, int copied)
{
        struct tcp_opt *tp = tcp_sk(sk);
        int time_to_ack = 0;

#if TCP_DEBUG
        struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);

        BUG_TRAP(!skb || before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq));
#endif

        if (tcp_ack_scheduled(tp)) {
                   /* Delayed ACKs frequently hit locked sockets during bulk
                    * receive. */
                if (tp->ack.blocked ||
                    /* Once-per-two-segments ACK was not sent by tcp_input.c */
                    tp->rcv_nxt - tp->rcv_wup > tp->ack.rcv_mss ||
                    /*
                     * If this read emptied read buffer, we send ACK, if
                     * connection is not bidirectional, user drained
                     * receive buffer and there was a small segment
                     * in queue.
                     */
                    (copied > 0 && (tp->ack.pending & TCP_ACK_PUSHED) &&
                     !tp->ack.pingpong && !atomic_read(&sk->sk_rmem_alloc)))
                        time_to_ack = 1;
        }

        /* We send an ACK if we can now advertise a non-zero window
         * which has been raised "significantly".
         *
         * Even if window raised up to infinity, do not send window open ACK
         * in states, where we will not receive more. It is useless.
         */
        if (copied > 0 && !time_to_ack && !(sk->sk_shutdown & RCV_SHUTDOWN)) {
                __u32 rcv_window_now = tcp_receive_window(tp);

                /* Optimize, __tcp_select_window() is not cheap. */
                if (2*rcv_window_now <= tp->window_clamp) {
                        __u32 new_window = __tcp_select_window(sk);

                        /* Send ACK now, if this read freed lots of space
                         * in our buffer. Certainly, new_window is new window.
                         * We can advertise it now, if it is not less than current one.
                         * "Lots" means "at least twice" here.
                         */
                        if (new_window && new_window >= 2 * rcv_window_now)
                                time_to_ack = 1;
                }
        }
        if (time_to_ack)
                tcp_send_ack(sk);
}

/* Now socket state including sk->sk_err is changed only under lock,
 * hence we may omit checks after joining wait queue.
 * We check receive queue before schedule() only as optimization;
 * it is very likely that release_sock() added new data.
 */

static long tcp_data_wait(struct sock *sk, long timeo)
{
        DEFINE_WAIT(wait);

        prepare_to_wait(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);

        set_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags);
        release_sock(sk);

        if (skb_queue_empty(&sk->sk_receive_queue))
                timeo = schedule_timeout(timeo);

        lock_sock(sk);
        clear_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags);

        finish_wait(sk->sk_sleep, &wait);
        return timeo;
}

static void tcp_prequeue_process(struct sock *sk)
{
        struct sk_buff *skb;
        struct tcp_opt *tp = tcp_sk(sk);

        NET_ADD_STATS_USER(TCPPrequeued, skb_queue_len(&tp->ucopy.prequeue));

        /* RX process wants to run with disabled BHs, though it is not
         * necessary */
        local_bh_disable();
        while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
                sk->sk_backlog_rcv(sk, skb);
        local_bh_enable();

        /* Clear memory counter. */
        tp->ucopy.memory = 0;
}

static inline struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
{
        struct sk_buff *skb;
        u32 offset;

        skb_queue_walk(&sk->sk_receive_queue, skb) {
                offset = seq - TCP_SKB_CB(skb)->seq;
                if (skb->h.th->syn)
                        offset--;
                if (offset < skb->len || skb->h.th->fin) {
                        *off = offset;
                        return skb;
                }
        }
        return NULL;
}

/*
 * This routine provides an alternative to tcp_recvmsg() for routines
 * that would like to handle copying from skbuffs directly in 'sendfile'
 * fashion.
 * Note:
 *      - It is assumed that the socket was locked by the caller.
 *      - The routine does not block.
 *      - At present, there is no support for reading OOB data
 *        or for 'peeking' the socket using this routine
 *        (although both would be easy to implement).
 */
int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
                  sk_read_actor_t recv_actor)
{
        struct sk_buff *skb;
        struct tcp_opt *tp = tcp_sk(sk);
        u32 seq = tp->copied_seq;
        u32 offset;
        int copied = 0;

        if (sk->sk_state == TCP_LISTEN)
                return -ENOTCONN;
        while ((skb = tcp_recv_skb(sk, seq, &offset)) != NULL) {
                if (offset < skb->len) {
                        size_t used, len;

                        len = skb->len - offset;
                        /* Stop reading if we hit a patch of urgent data */
                        if (tp->urg_data) {
                                u32 urg_offset = tp->urg_seq - seq;
                                if (urg_offset < len)
                                        len = urg_offset;
                                if (!len)
                                        break;
                        }
                        used = recv_actor(desc, skb, offset, len);
                        if (used <= len) {
                                seq += used;
                                copied += used;
                                offset += used;
                        }
                        if (offset != skb->len)
                                break;
                }
                if (skb->h.th->fin) {
                        tcp_eat_skb(sk, skb);
                        ++seq;
                        break;
                }
                tcp_eat_skb(sk, skb);
                if (!desc->count)
                        break;
        }
        tp->copied_seq = seq;

        tcp_rcv_space_adjust(sk);

        /* Clean up data we have read: This will do ACK frames. */
        if (copied)
                cleanup_rbuf(sk, copied);
        return copied;
}

/*
 *      This routine copies from a sock struct into the user buffer.
 *
 *      Technical note: in 2.3 we work on _locked_ socket, so that
 *      tricks with *seq access order and skb->users are not required.
 *      Probably, code can be easily improved even more.
 */

int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                size_t len, int nonblock, int flags, int *addr_len)
{
        struct tcp_opt *tp = tcp_sk(sk);
        int copied = 0;
        u32 peek_seq;
        u32 *seq;
        unsigned long used;
        int err;
        int target;             /* Read at least this many bytes */
        long timeo;
        struct task_struct *user_recv = NULL;

        lock_sock(sk);

        TCP_CHECK_TIMER(sk);

        err = -ENOTCONN;
        if (sk->sk_state == TCP_LISTEN)
                goto out;

        timeo = sock_rcvtimeo(sk, nonblock);

        /* Urgent data needs to be handled specially. */
        if (flags & MSG_OOB)
                goto recv_urg;

        seq = &tp->copied_seq;
        if (flags & MSG_PEEK) {
                peek_seq = tp->copied_seq;
                seq = &peek_seq;
        }

        target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);

        do {
                struct sk_buff *skb;
                u32 offset;

                /* Are we at urgent data? Stop if we have read anything or have SIGURG pending. */
                if (tp->urg_data && tp->urg_seq == *seq) {
                        if (copied)
                                break;
                        if (signal_pending(current)) {
                                copied = timeo ? sock_intr_errno(timeo) : -EAGAIN;
                                break;
                        }
                }

                /* Next get a buffer. */

                skb = skb_peek(&sk->sk_receive_queue);
                do {
                        if (!skb)
                                break;

                        /* Now that we have two receive queues this
                         * shouldn't happen.
                         */
                        if (before(*seq, TCP_SKB_CB(skb)->seq)) {
                                printk(KERN_INFO "recvmsg bug: copied %X "
                                       "seq %X\n", *seq, TCP_SKB_CB(skb)->seq);
                                break;
                        }
                        offset = *seq - TCP_SKB_CB(skb)->seq;
                        if (skb->h.th->syn)
                                offset--;
                        if (offset < skb->len)
                                goto found_ok_skb;
                        if (skb->h.th->fin)
                                goto found_fin_ok;
                        BUG_TRAP(flags & MSG_PEEK);
                        skb = skb->next;
                } while (skb != (struct sk_buff *)&sk->sk_receive_queue);

                /* Well, if we have backlog, try to process it now yet. */

                if (copied >= target && !sk->sk_backlog.tail)
                        break;

                if (copied) {
                        if (sk->sk_err ||
                            sk->sk_state == TCP_CLOSE ||
                            (sk->sk_shutdown & RCV_SHUTDOWN) ||
                            !timeo ||
                            signal_pending(current) ||
                            (flags & MSG_PEEK))
                                break;
                } else {
                        if (sock_flag(sk, SOCK_DONE))
                                break;

                        if (sk->sk_err) {
                                copied = sock_error(sk);
                                break;
                        }

                        if (sk->sk_shutdown & RCV_SHUTDOWN)
                                break;

                        if (sk->sk_state == TCP_CLOSE) {
                                if (!sock_flag(sk, SOCK_DONE)) {
                                        /* This occurs when user tries to read
                                         * from never connected socket.
                                         */
                                        copied = -ENOTCONN;
                                        break;
                                }
                                break;
                        }

                        if (!timeo) {
                                copied = -EAGAIN;
                                break;
                        }

                        if (signal_pending(current)) {
                                copied = sock_intr_errno(timeo);
                                break;
                        }
                }

                cleanup_rbuf(sk, copied);

                if (tp->ucopy.task == user_recv) {
                        /* Install new reader */
                        if (!user_recv && !(flags & (MSG_TRUNC | MSG_PEEK))) {
                                user_recv = current;
                                tp->ucopy.task = user_recv;
                                tp->ucopy.iov = msg->msg_iov;
                        }

                        tp->ucopy.len = len;

                        BUG_TRAP(tp->copied_seq == tp->rcv_nxt ||
                                 (flags & (MSG_PEEK | MSG_TRUNC)));

                        /* Ugly... If prequeue is not empty, we have to
                         * process it before releasing socket, otherwise
                         * order will be broken at second iteration.
                         * More elegant solution is required!!!
                         *
                         * Look: we have the following (pseudo)queues:
                         *
                         * 1. packets in flight
                         * 2. backlog
                         * 3. prequeue
                         * 4. receive_queue
                         *
                         * Each queue can be processed only if the next ones
                         * are empty. At this point we have empty receive_queue.
                         * But prequeue _can_ be not empty after 2nd iteration,
                         * when we jumped to start of loop because backlog
                         * processing added something to receive_queue.
                         * We cannot release_sock(), because backlog contains
                         * packets arrived _after_ prequeued ones.
                         *
                         * Shortly, algorithm is clear --- to process all
                         * the queues in order. We could make it more directly,
                         * requeueing packets from backlog to prequeue, if
                         * is not empty. It is more elegant, but eats cycles,
                         * unfortunately.
                         */
                        if (skb_queue_len(&tp->ucopy.prequeue))
                                goto do_prequeue;

                        /* __ Set realtime policy in scheduler __ */
                }

                if (copied >= target) {
                        /* Do not sleep, just process backlog. */
                        release_sock(sk);
                        lock_sock(sk);
                } else {
                        timeo = tcp_data_wait(sk, timeo);
                }

                if (user_recv) {
                        int chunk;

                        /* __ Restore normal policy in scheduler __ */

                        if ((chunk = len - tp->ucopy.len) != 0) {
                                NET_ADD_STATS_USER(TCPDirectCopyFromBacklog, chunk);
                                len -= chunk;
                                copied += chunk;
                        }

                        if (tp->rcv_nxt == tp->copied_seq &&
                            skb_queue_len(&tp->ucopy.prequeue)) {
do_prequeue:
                                tcp_prequeue_process(sk);

                                if ((chunk = len - tp->ucopy.len) != 0) {
                                        NET_ADD_STATS_USER(TCPDirectCopyFromPrequeue, chunk);
                                        len -= chunk;
                                        copied += chunk;
                                }
                        }
                }
                if ((flags & MSG_PEEK) && peek_seq != tp->copied_seq) {
                        if (net_ratelimit())
                                printk(KERN_DEBUG "TCP(%s:%d): Application bug, race in MSG_PEEK.\n",
                                       current->comm, current->pid);
                        peek_seq = tp->copied_seq;
                }
                continue;

        found_ok_skb:
                /* Ok so how much can we use? */
                used = skb->len - offset;
                if (len < used)
                        used = len;

                /* Do we have urgent data here? */
                if (tp->urg_data) {
                        u32 urg_offset = tp->urg_seq - *seq;
                        if (urg_offset < used) {
                                if (!urg_offset) {
                                        if (!sock_flag(sk, SOCK_URGINLINE)) {
                                                ++*seq;
                                                offset++;
                                                used--;
                                                if (!used)
                                                        goto skip_copy;
                                        }
                                } else
                                        used = urg_offset;
                        }
                }

                if (!(flags & MSG_TRUNC)) {
                        err = skb_copy_datagram_iovec(skb, offset,
                                                      msg->msg_iov, used);
                        if (err) {
                                /* Exception. Bailout! */
                                if (!copied)
                                        copied = -EFAULT;
                                break;
                        }
                }

                *seq += used;
                copied += used;
                len -= used;

                tcp_rcv_space_adjust(sk);

skip_copy:
                if (tp->urg_data && after(tp->copied_seq, tp->urg_seq)) {
                        tp->urg_data = 0;
                        tcp_fast_path_check(sk, tp);
                }
                if (used + offset < skb->len)
                        continue;

                if (skb->h.th->fin)
                        goto found_fin_ok;
                if (!(flags & MSG_PEEK))
                        tcp_eat_skb(sk, skb);
                continue;

        found_fin_ok:
                /* Process the FIN. */
                ++*seq;
                if (!(flags & MSG_PEEK))
                        tcp_eat_skb(sk, skb);
                break;
        } while (len > 0);

        if (user_recv) {
                if (skb_queue_len(&tp->ucopy.prequeue)) {
                        int chunk;

                        tp->ucopy.len = copied > 0 ? len : 0;

                        tcp_prequeue_process(sk);

                        if (copied > 0 && (chunk = len - tp->ucopy.len) != 0) {
                                NET_ADD_STATS_USER(TCPDirectCopyFromPrequeue, chunk);
                                len -= chunk;
                                copied += chunk;
                        }
                }

                tp->ucopy.task = NULL;
                tp->ucopy.len = 0;
        }

        /* According to UNIX98, msg_name/msg_namelen are ignored
         * on connected socket. I was just happy when found this 8) --ANK
         */

        /* Clean up data we have read: This will do ACK frames. */
        cleanup_rbuf(sk, copied);

        TCP_CHECK_TIMER(sk);
        release_sock(sk);
        return copied;

out:
        TCP_CHECK_TIMER(sk);
        release_sock(sk);
        return err;

recv_urg:
        err = tcp_recv_urg(sk, timeo, msg, len, flags, addr_len);
        goto out;
}

/*
 *      State processing on a close. This implements the state shift for
 *      sending our FIN frame. Note that we only send a FIN for some
 *      states. A shutdown() may have already sent the FIN, or we may be
 *      closed.
 */

static unsigned char new_state[16] = {
  /* current state:        new state:      action:      */
  /* (Invalid)          */ TCP_CLOSE,
  /* TCP_ESTABLISHED    */ TCP_FIN_WAIT1 | TCP_ACTION_FIN,
  /* TCP_SYN_SENT       */ TCP_CLOSE,
  /* TCP_SYN_RECV       */ TCP_FIN_WAIT1 | TCP_ACTION_FIN,
  /* TCP_FIN_WAIT1      */ TCP_FIN_WAIT1,
  /* TCP_FIN_WAIT2      */ TCP_FIN_WAIT2,
  /* TCP_TIME_WAIT      */ TCP_CLOSE,
  /* TCP_CLOSE          */ TCP_CLOSE,
  /* TCP_CLOSE_WAIT     */ TCP_LAST_ACK  | TCP_ACTION_FIN,
  /* TCP_LAST_ACK       */ TCP_LAST_ACK,
  /* TCP_LISTEN         */ TCP_CLOSE,
  /* TCP_CLOSING        */ TCP_CLOSING,
};

static int tcp_close_state(struct sock *sk)
{
        int next = (int)new_state[sk->sk_state];
        int ns = next & TCP_STATE_MASK;

        tcp_set_state(sk, ns);

        return next & TCP_ACTION_FIN;
}

/*
 *      Shutdown the sending side of a connection. Much like close except
 *      that we don't receive shut down or set_sock_flag(sk, SOCK_DEAD).
 */

void tcp_shutdown(struct sock *sk, int how)
{
        /*      We need to grab some memory, and put together a FIN,
         *      and then put it into the queue to be sent.
         *              Tim MacKenzie(tym@dibbler.cs.monash.edu.au) 4 Dec '92.
         */
        if (!(how & SEND_SHUTDOWN))
                return;

        /* If we've already sent a FIN, or it's a closed state, skip this. */
        if ((1 << sk->sk_state) &
            (TCPF_ESTABLISHED | TCPF_SYN_SENT |
             TCPF_SYN_RECV | TCPF_CLOSE_WAIT)) {
                /* Clear out any half completed packets.  FIN if needed. */
                if (tcp_close_state(sk))
                        tcp_send_fin(sk);
        }
}


/*
 *      Return 1 if we still have things to send in our buffers.
 */

static inline int closing(struct sock *sk)
{
        return (1 << sk->sk_state) &
               (TCPF_FIN_WAIT1 | TCPF_CLOSING | TCPF_LAST_ACK);
}

static __inline__ void tcp_kill_sk_queues(struct sock *sk)
{
        /* First the read buffer. */
        __skb_queue_purge(&sk->sk_receive_queue);

        /* Next, the error queue. */
        __skb_queue_purge(&sk->sk_error_queue);

        /* Next, the write queue. */
        BUG_TRAP(skb_queue_empty(&sk->sk_write_queue));

        /* Account for returned memory. */
        tcp_mem_reclaim(sk);

        BUG_TRAP(!sk->sk_wmem_queued);
        BUG_TRAP(!sk->sk_forward_alloc);

        /* It is _impossible_ for the backlog to contain anything
         * when we get here.  All user references to this socket
         * have gone away, only the net layer knows can touch it.
         */
}

/*
 * At this point, there should be no process reference to this
 * socket, and thus no user references at all.  Therefore we
 * can assume the socket waitqueue is inactive and nobody will
 * try to jump onto it.
 */
void tcp_destroy_sock(struct sock *sk)
{
        BUG_TRAP(sk->sk_state == TCP_CLOSE);
        BUG_TRAP(sock_flag(sk, SOCK_DEAD));

        /* It cannot be in hash table! */
        BUG_TRAP(sk_unhashed(sk));

        /* If it has not 0 inet_sk(sk)->num, it must be bound */
        BUG_TRAP(!inet_sk(sk)->num || tcp_sk(sk)->bind_hash);

#ifdef TCP_DEBUG
        if (sk->sk_zapped) {
                printk(KERN_DEBUG "TCP: double destroy sk=%p\n", sk);
                sock_hold(sk);
        }
        sk->sk_zapped = 1;
#endif

        sk->sk_prot->destroy(sk);

        tcp_kill_sk_queues(sk);

        xfrm_sk_free_policy(sk);

#ifdef INET_REFCNT_DEBUG
        if (atomic_read(&sk->sk_refcnt) != 1) {
                printk(KERN_DEBUG "Destruction TCP %p delayed, c=%d\n",
                       sk, atomic_read(&sk->sk_refcnt));
        }
#endif

        atomic_dec(&tcp_orphan_count);
        sock_put(sk);
}

void tcp_close(struct sock *sk, long timeout)
{
        struct sk_buff *skb;
        int data_was_unread = 0;

        lock_sock(sk);
        sk->sk_shutdown = SHUTDOWN_MASK;

        if (sk->sk_state == TCP_LISTEN) {
                tcp_set_state(sk, TCP_CLOSE);

                /* Special case. */
                tcp_listen_stop(sk);

                goto adjudge_to_death;
        }

        /*  We need to flush the recv. buffs.  We do this only on the
         *  descriptor close, not protocol-sourced closes, because the
         *  reader process may not have drained the data yet!
         */
        while ((skb = __skb_dequeue(&sk->sk_receive_queue)) != NULL) {
                u32 len = TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq -
                          skb->h.th->fin;
                data_was_unread += len;
                __kfree_skb(skb);
        }

        tcp_mem_reclaim(sk);

        /* As outlined in draft-ietf-tcpimpl-prob-03.txt, section
         * 3.10, we send a RST here because data was lost.  To
         * witness the awful effects of the old behavior of always
         * doing a FIN, run an older 2.1.x kernel or 2.0.x, start
         * a bulk GET in an FTP client, suspend the process, wait
         * for the client to advertise a zero window, then kill -9
         * the FTP client, wheee...  Note: timeout is always zero
         * in such a case.
         */
        if (data_was_unread) {
                /* Unread data was tossed, zap the connection. */
                NET_INC_STATS_USER(TCPAbortOnClose);
                tcp_set_state(sk, TCP_CLOSE);
                tcp_send_active_reset(sk, GFP_KERNEL);
        } else if (sock_flag(sk, SOCK_LINGER) && !sk->sk_lingertime) {
                /* Check zero linger _after_ checking for unread data. */
                sk->sk_prot->disconnect(sk, 0);
                NET_INC_STATS_USER(TCPAbortOnData);
        } else if (tcp_close_state(sk)) {
                /* We FIN if the application ate all the data before
                 * zapping the connection.
                 */

                /* RED-PEN. Formally speaking, we have broken TCP state
                 * machine. State transitions:
                 *
                 * TCP_ESTABLISHED -> TCP_FIN_WAIT1
                 * TCP_SYN_RECV -> TCP_FIN_WAIT1 (forget it, it's impossible)
                 * TCP_CLOSE_WAIT -> TCP_LAST_ACK
                 *
                 * are legal only when FIN has been sent (i.e. in window),
                 * rather than queued out of window. Purists blame.
                 *
                 * F.e. "RFC state" is ESTABLISHED,
                 * if Linux state is FIN-WAIT-1, but FIN is still not sent.
                 *
                 * The visible declinations are that sometimes
                 * we enter time-wait state, when it is not required really
                 * (harmless), do not send active resets, when they are
                 * required by specs (TCP_ESTABLISHED, TCP_CLOSE_WAIT, when
                 * they look as CLOSING or LAST_ACK for Linux)
                 * Probably, I missed some more holelets.
                 *                                              --ANK
                 */
                tcp_send_fin(sk);
        }

        if (timeout) {
                struct task_struct *tsk = current;
                DEFINE_WAIT(wait);

                do {
                        prepare_to_wait(sk->sk_sleep, &wait,
                                        TASK_INTERRUPTIBLE);
                        if (!closing(sk))
                                break;
                        release_sock(sk);
                        timeout = schedule_timeout(timeout);
                        lock_sock(sk);
                } while (!signal_pending(tsk) && timeout);

                finish_wait(sk->sk_sleep, &wait);
        }

adjudge_to_death:
        /* It is the last release_sock in its life. It will remove backlog. */
        release_sock(sk);


        /* Now socket is owned by kernel and we acquire BH lock
           to finish close. No need to check for user refs.
         */
        local_bh_disable();
        bh_lock_sock(sk);
        BUG_TRAP(!sock_owned_by_user(sk));

        sock_hold(sk);
        sock_orphan(sk);

        /*      This is a (useful) BSD violating of the RFC. There is a
         *      problem with TCP as specified in that the other end could
         *      keep a socket open forever with no application left this end.
         *      We use a 3 minute timeout (about the same as BSD) then kill
         *      our end. If they send after that then tough - BUT: long enough
         *      that we won't make the old 4*rto = almost no time - whoops
         *      reset mistake.
         *
         *      Nope, it was not mistake. It is really desired behaviour
         *      f.e. on http servers, when such sockets are useless, but
         *      consume significant resources. Let's do it with special
         *      linger2 option.                                 --ANK
         */

        if (sk->sk_state == TCP_FIN_WAIT2) {
                struct tcp_opt *tp = tcp_sk(sk);
                if (tp->linger2 < 0) {
                        tcp_set_state(sk, TCP_CLOSE);
                        tcp_send_active_reset(sk, GFP_ATOMIC);
                        NET_INC_STATS_BH(TCPAbortOnLinger);
                } else {
                        int tmo = tcp_fin_time(tp);

                        if (tmo > TCP_TIMEWAIT_LEN) {
                                tcp_reset_keepalive_timer(sk, tcp_fin_time(tp));
                        } else {
                                atomic_inc(&tcp_orphan_count);
                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
                                goto out;
                        }
                }
        }
        if (sk->sk_state != TCP_CLOSE) {
                tcp_mem_reclaim(sk);
                if (atomic_read(&tcp_orphan_count) > sysctl_tcp_max_orphans ||
                    (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
                     atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[2])) {
                        if (net_ratelimit())
                                printk(KERN_INFO "TCP: too many of orphaned "
                                       "sockets\n");
                        tcp_set_state(sk, TCP_CLOSE);
                        tcp_send_active_reset(sk, GFP_ATOMIC);
                        NET_INC_STATS_BH(TCPAbortOnMemory);
                }
        }
        atomic_inc(&tcp_orphan_count);

        if (sk->sk_state == TCP_CLOSE)
                tcp_destroy_sock(sk);
        /* Otherwise, socket is reprieved until protocol close. */

out:
        bh_unlock_sock(sk);
        local_bh_enable();
        sock_put(sk);
}

/* These states need RST on ABORT according to RFC793 */

static inline int tcp_need_reset(int state)
{
        return (1 << state) &
               (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT | TCPF_FIN_WAIT1 |
                TCPF_FIN_WAIT2 | TCPF_SYN_RECV);
}

int tcp_disconnect(struct sock *sk, int flags)
{
        struct inet_opt *inet = inet_sk(sk);
        struct tcp_opt *tp = tcp_sk(sk);
        int err = 0;
        int old_state = sk->sk_state;

        if (old_state != TCP_CLOSE)
                tcp_set_state(sk, TCP_CLOSE);

        /* ABORT function of RFC793 */
        if (old_state == TCP_LISTEN) {
                tcp_listen_stop(sk);
        } else if (tcp_need_reset(old_state) ||
                   (tp->snd_nxt != tp->write_seq &&
                    (1 << old_state) & (TCPF_CLOSING | TCPF_LAST_ACK))) {
                /* The last check adjusts for discrepance of Linux wrt. RFC
                 * states
                 */
                tcp_send_active_reset(sk, gfp_any());
                sk->sk_err = ECONNRESET;
        } else if (old_state == TCP_SYN_SENT)
                sk->sk_err = ECONNRESET;

        tcp_clear_xmit_timers(sk);
        __skb_queue_purge(&sk->sk_receive_queue);
        tcp_writequeue_purge(sk);
        __skb_queue_purge(&tp->out_of_order_queue);

        inet->dport = 0;

        if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
                inet_reset_saddr(sk);

        sk->sk_shutdown = 0;
        sock_reset_flag(sk, SOCK_DONE);
        tp->srtt = 0;
        if ((tp->write_seq += tp->max_window + 2) == 0)
                tp->write_seq = 1;
        tp->backoff = 0;
        tp->snd_cwnd = 2;
        tp->probes_out = 0;
        tp->packets_out = 0;
        tp->snd_ssthresh = 0x7fffffff;
        tp->snd_cwnd_cnt = 0;
        tcp_set_ca_state(tp, TCP_CA_Open);
        tcp_clear_retrans(tp);
        tcp_delack_init(tp);
        tp->send_head = NULL;
        tp->saw_tstamp = 0;
        tcp_sack_reset(tp);
        __sk_dst_reset(sk);

        BUG_TRAP(!inet->num || tp->bind_hash);

        sk->sk_error_report(sk);
        return err;
}

/*
 *      Wait for an incoming connection, avoid race
 *      conditions. This must be called with the socket locked.
 */
static int wait_for_connect(struct sock *sk, long timeo)
{
        struct tcp_opt *tp = tcp_sk(sk);
        DEFINE_WAIT(wait);
        int err;

        /*
         * True wake-one mechanism for incoming connections: only
         * one process gets woken up, not the 'whole herd'.
         * Since we do not 'race & poll' for established sockets
         * anymore, the common case will execute the loop only once.
         *
         * Subtle issue: "add_wait_queue_exclusive()" will be added
         * after any current non-exclusive waiters, and we know that
         * it will always _stay_ after any new non-exclusive waiters
         * because all non-exclusive waiters are added at the
         * beginning of the wait-queue. As such, it's ok to "drop"
         * our exclusiveness temporarily when we get woken up without
         * having to remove and re-insert us on the wait queue.
         */
        for (;;) {
                prepare_to_wait_exclusive(sk->sk_sleep, &wait,
                                          TASK_INTERRUPTIBLE);
                release_sock(sk);
                if (!tp->accept_queue)
                        timeo = schedule_timeout(timeo);
                lock_sock(sk);
                err = 0;
                if (tp->accept_queue)
                        break;
                err = -EINVAL;
                if (sk->sk_state != TCP_LISTEN)
                        break;
                err = sock_intr_errno(timeo);
                if (signal_pending(current))
                        break;
                err = -EAGAIN;
                if (!timeo)
                        break;
        }
        finish_wait(sk->sk_sleep, &wait);
        return err;
}

/*
 *      This will accept the next outstanding connection.
 */

struct sock *tcp_accept(struct sock *sk, int flags, int *err)
{
        struct tcp_opt *tp = tcp_sk(sk);
        struct open_request *req;
        struct sock *newsk;
        int error;

        lock_sock(sk);

        /* We need to make sure that this socket is listening,
         * and that it has something pending.
         */
        error = -EINVAL;
        if (sk->sk_state != TCP_LISTEN)
                goto out;

        /* Find already established connection */
        if (!tp->accept_queue) {
                long timeo = sock_rcvtimeo(sk, flags & O_NONBLOCK);

                /* If this is a non blocking socket don't sleep */
                error = -EAGAIN;
                if (!timeo)
                        goto out;

                error = wait_for_connect(sk, timeo);
                if (error)
                        goto out;
        }

        req = tp->accept_queue;
        if ((tp->accept_queue = req->dl_next) == NULL)
                tp->accept_queue_tail = NULL;

        newsk = req->sk;
        tcp_acceptq_removed(sk);
        tcp_openreq_fastfree(req);
        BUG_TRAP(newsk->sk_state != TCP_SYN_RECV);
        release_sock(sk);
        return newsk;

out:
        release_sock(sk);
        *err = error;
        return NULL;
}

/*
 *      Socket option code for TCP.
 */
int tcp_setsockopt(struct sock *sk, int level, int optname, char __user *optval,
                   int optlen)
{
        struct tcp_opt *tp = tcp_sk(sk);
        int val;
        int err = 0;

        if (level != SOL_TCP)
                return tp->af_specific->setsockopt(sk, level, optname,
                                                   optval, optlen);

        if (optlen < sizeof(int))
                return -EINVAL;

        if (get_user(val, (int __user *)optval))
                return -EFAULT;

        lock_sock(sk);

        switch (optname) {
        case TCP_MAXSEG:
                /* Values greater than interface MTU won't take effect. However
                 * at the point when this call is done we typically don't yet
                 * know which interface is going to be used */
                if (val < 8 || val > MAX_TCP_WINDOW) {
                        err = -EINVAL;
                        break;
                }
                tp->user_mss = val;
                break;

        case TCP_NODELAY:
                if (val) {
                        /* TCP_NODELAY is weaker than TCP_CORK, so that
                         * this option on corked socket is remembered, but
                         * it is not activated until cork is cleared.
                         *
                         * However, when TCP_NODELAY is set we make
                         * an explicit push, which overrides even TCP_CORK
                         * for currently queued segments.
                         */
                        tp->nonagle |= TCP_NAGLE_OFF|TCP_NAGLE_PUSH;
                        tcp_push_pending_frames(sk, tp);
                } else {
                        tp->nonagle &= ~TCP_NAGLE_OFF;
                }
                break;

        case TCP_CORK:
                /* When set indicates to always queue non-full frames.
                 * Later the user clears this option and we transmit
                 * any pending partial frames in the queue.  This is
                 * meant to be used alongside sendfile() to get properly
                 * filled frames when the user (for example) must write
                 * out headers with a write() call first and then use
                 * sendfile to send out the data parts.
                 *
                 * TCP_CORK can be set together with TCP_NODELAY and it is
                 * stronger than TCP_NODELAY.
                 */
                if (val) {
                        tp->nonagle |= TCP_NAGLE_CORK;
                } else {
                        tp->nonagle &= ~TCP_NAGLE_CORK;
                        if (tp->nonagle&TCP_NAGLE_OFF)
                                tp->nonagle |= TCP_NAGLE_PUSH;
                        tcp_push_pending_frames(sk, tp);
                }
                break;

        case TCP_KEEPIDLE:
                if (val < 1 || val > MAX_TCP_KEEPIDLE)
                        err = -EINVAL;
                else {
                        tp->keepalive_time = val * HZ;
                        if (sock_flag(sk, SOCK_KEEPOPEN) &&
                            !((1 << sk->sk_state) &
                              (TCPF_CLOSE | TCPF_LISTEN))) {
                                __u32 elapsed = tcp_time_stamp - tp->rcv_tstamp;
                                if (tp->keepalive_time > elapsed)
                                        elapsed = tp->keepalive_time - elapsed;
                                else
                                        elapsed = 0;
                                tcp_reset_keepalive_timer(sk, elapsed);
                        }
                }
                break;
        case TCP_KEEPINTVL:
                if (val < 1 || val > MAX_TCP_KEEPINTVL)
                        err = -EINVAL;
                else
                        tp->keepalive_intvl = val * HZ;
                break;
        case TCP_KEEPCNT:
                if (val < 1 || val > MAX_TCP_KEEPCNT)
                        err = -EINVAL;
                else
                        tp->keepalive_probes = val;
                break;
        case TCP_SYNCNT:
                if (val < 1 || val > MAX_TCP_SYNCNT)
                        err = -EINVAL;
                else
                        tp->syn_retries = val;
                break;

        case TCP_LINGER2:
                if (val < 0)
                        tp->linger2 = -1;
                else if (val > sysctl_tcp_fin_timeout / HZ)
                        tp->linger2 = 0;
                else
                        tp->linger2 = val * HZ;
                break;

        case TCP_DEFER_ACCEPT:
                tp->defer_accept = 0;
                if (val > 0) {
                        /* Translate value in seconds to number of
                         * retransmits */
                        while (tp->defer_accept < 32 &&
                               val > ((TCP_TIMEOUT_INIT / HZ) <<
                                       tp->defer_accept))
                                tp->defer_accept++;
                        tp->defer_accept++;
                }
                break;

        case TCP_WINDOW_CLAMP:
                if (!val) {
                        if (sk->sk_state != TCP_CLOSE) {
                                err = -EINVAL;
                                break;
                        }
                        tp->window_clamp = 0;
                } else
                        tp->window_clamp = val < SOCK_MIN_RCVBUF / 2 ?
                                                SOCK_MIN_RCVBUF / 2 : val;
                break;

        case TCP_QUICKACK:
                if (!val) {
                        tp->ack.pingpong = 1;
                } else {
                        tp->ack.pingpong = 0;
                        if ((1 << sk->sk_state) &
                            (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT) &&
                            tcp_ack_scheduled(tp)) {
                                tp->ack.pending |= TCP_ACK_PUSHED;
                                cleanup_rbuf(sk, 1);
                                if (!(val & 1))
                                        tp->ack.pingpong = 1;
                        }
                }
                break;

        default:
                err = -ENOPROTOOPT;
                break;
        };
        release_sock(sk);
        return err;
}

int tcp_getsockopt(struct sock *sk, int level, int optname, char __user *optval,
                   int __user *optlen)
{
        struct tcp_opt *tp = tcp_sk(sk);
        int val, len;

        if (level != SOL_TCP)
                return tp->af_specific->getsockopt(sk, level, optname,
                                                   optval, optlen);

        if (get_user(len, optlen))
                return -EFAULT;

        len = min_t(unsigned int, len, sizeof(int));

        if (len < 0)
                return -EINVAL;

        switch (optname) {
        case TCP_MAXSEG:
                val = tp->mss_cache_std;
                if (!val && ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
                        val = tp->user_mss;
                break;
        case TCP_NODELAY:
                val = !!(tp->nonagle&TCP_NAGLE_OFF);
                break;
        case TCP_CORK:
                val = !!(tp->nonagle&TCP_NAGLE_CORK);
                break;
        case TCP_KEEPIDLE:
                val = (tp->keepalive_time ? : sysctl_tcp_keepalive_time) / HZ;
                break;
        case TCP_KEEPINTVL:
                val = (tp->keepalive_intvl ? : sysctl_tcp_keepalive_intvl) / HZ;
                break;
        case TCP_KEEPCNT:
                val = tp->keepalive_probes ? : sysctl_tcp_keepalive_probes;
                break;
        case TCP_SYNCNT:
                val = tp->syn_retries ? : sysctl_tcp_syn_retries;
                break;
        case TCP_LINGER2:
                val = tp->linger2;
                if (val >= 0)
                        val = (val ? : sysctl_tcp_fin_timeout) / HZ;
                break;
        case TCP_DEFER_ACCEPT:
                val = !tp->defer_accept ? 0 : ((TCP_TIMEOUT_INIT / HZ) <<
                                               (tp->defer_accept - 1));
                break;
        case TCP_WINDOW_CLAMP:
                val = tp->window_clamp;
                break;
        case TCP_INFO: {
                struct tcp_info info;
                u32 now = tcp_time_stamp;

                if (get_user(len, optlen))
                        return -EFAULT;
                info.tcpi_state = sk->sk_state;
                info.tcpi_ca_state = tp->ca_state;
                info.tcpi_retransmits = tp->retransmits;
                info.tcpi_probes = tp->probes_out;
                info.tcpi_backoff = tp->backoff;
                info.tcpi_options = 0;
                if (tp->tstamp_ok)
                        info.tcpi_options |= TCPI_OPT_TIMESTAMPS;
                if (tp->sack_ok)
                        info.tcpi_options |= TCPI_OPT_SACK;
                if (tp->wscale_ok) {
                        info.tcpi_options |= TCPI_OPT_WSCALE;
                        info.tcpi_snd_wscale = tp->snd_wscale;
                        info.tcpi_rcv_wscale = tp->rcv_wscale;
                } else {
                        info.tcpi_snd_wscale = 0;
                        info.tcpi_rcv_wscale = 0;
                }
                if (tp->ecn_flags & TCP_ECN_OK)
                        info.tcpi_options |= TCPI_OPT_ECN;

                info.tcpi_rto = (1000000 * tp->rto) / HZ;
                info.tcpi_ato = (1000000 * tp->ack.ato) / HZ;
                info.tcpi_snd_mss = tp->mss_cache_std;
                info.tcpi_rcv_mss = tp->ack.rcv_mss;

                info.tcpi_unacked = tp->packets_out;
                info.tcpi_sacked = tp->sacked_out;
                info.tcpi_lost = tp->lost_out;
                info.tcpi_retrans = tp->retrans_out;
                info.tcpi_fackets = tp->fackets_out;

                info.tcpi_last_data_sent = ((now - tp->lsndtime) * 1000) / HZ;
                info.tcpi_last_ack_sent = 0;
                info.tcpi_last_data_recv = ((now -
                                             tp->ack.lrcvtime) * 1000) / HZ;
                info.tcpi_last_ack_recv = ((now - tp->rcv_tstamp) * 1000) / HZ;

                info.tcpi_pmtu = tp->pmtu_cookie;
                info.tcpi_rcv_ssthresh = tp->rcv_ssthresh;
                info.tcpi_rtt = ((1000000 * tp->srtt) / HZ) >> 3;
                info.tcpi_rttvar = ((1000000 * tp->mdev) / HZ) >> 2;
                info.tcpi_snd_ssthresh = tp->snd_ssthresh;
                info.tcpi_snd_cwnd = tp->snd_cwnd;
                info.tcpi_advmss = tp->advmss;
                info.tcpi_reordering = tp->reordering;

                len = min_t(unsigned int, len, sizeof(info));
                if (put_user(len, optlen))
                        return -EFAULT;
                if (copy_to_user(optval, &info, len))
                        return -EFAULT;
                return 0;
        }
        case TCP_QUICKACK:
                val = !tp->ack.pingpong;
                break;
        default:
                return -ENOPROTOOPT;
        };

        if (put_user(len, optlen))
                return -EFAULT;
        if (copy_to_user(optval, &val, len))
                return -EFAULT;
        return 0;
}


extern void __skb_cb_too_small_for_tcp(int, int);
extern void tcpdiag_init(void);

static __initdata unsigned long thash_entries;
static int __init set_thash_entries(char *str)
{
        if (!str)
                return 0;
        thash_entries = simple_strtoul(str, &str, 0);
        return 1;
}
__setup("thash_entries=", set_thash_entries);

void __init tcp_init(void)
{
        struct sk_buff *skb = NULL;
        unsigned long goal;
        int order, i;

        if (sizeof(struct tcp_skb_cb) > sizeof(skb->cb))
                __skb_cb_too_small_for_tcp(sizeof(struct tcp_skb_cb),
                                           sizeof(skb->cb));

        tcp_openreq_cachep = kmem_cache_create("tcp_open_request",
                                                   sizeof(struct open_request),
                                               0, SLAB_HWCACHE_ALIGN,
                                               NULL, NULL);
        if (!tcp_openreq_cachep)
                panic("tcp_init: Cannot alloc open_request cache.");

        tcp_bucket_cachep = kmem_cache_create("tcp_bind_bucket",
                                              sizeof(struct tcp_bind_bucket),
                                              0, SLAB_HWCACHE_ALIGN,
                                              NULL, NULL);
        if (!tcp_bucket_cachep)
                panic("tcp_init: Cannot alloc tcp_bind_bucket cache.");

        tcp_timewait_cachep = kmem_cache_create("tcp_tw_bucket",
                                                sizeof(struct tcp_tw_bucket),
                                                0, SLAB_HWCACHE_ALIGN,
                                                NULL, NULL);
        if (!tcp_timewait_cachep)
                panic("tcp_init: Cannot alloc tcp_tw_bucket cache.");

        /* Size and allocate the main established and bind bucket
         * hash tables.
         *
         * The methodology is similar to that of the buffer cache.
         */
        if (num_physpages >= (128 * 1024))
                goal = num_physpages >> (21 - PAGE_SHIFT);
        else
                goal = num_physpages >> (23 - PAGE_SHIFT);

        if (thash_entries)
                goal = (thash_entries * sizeof(struct tcp_ehash_bucket)) >> PAGE_SHIFT;
        for (order = 0; (1UL << order) < goal; order++)
                ;
        do {
                tcp_ehash_size = (1UL << order) * PAGE_SIZE /
                        sizeof(struct tcp_ehash_bucket);
                tcp_ehash_size >>= 1;
                while (tcp_ehash_size & (tcp_ehash_size - 1))
                        tcp_ehash_size--;
                tcp_ehash = (struct tcp_ehash_bucket *)
                        __get_free_pages(GFP_ATOMIC, order);
        } while (!tcp_ehash && --order > 0);

        if (!tcp_ehash)
                panic("Failed to allocate TCP established hash table\n");
        for (i = 0; i < (tcp_ehash_size << 1); i++) {
                tcp_ehash[i].lock = RW_LOCK_UNLOCKED;
                INIT_HLIST_HEAD(&tcp_ehash[i].chain);
        }

        do {
                tcp_bhash_size = (1UL << order) * PAGE_SIZE /
                        sizeof(struct tcp_bind_hashbucket);
                if ((tcp_bhash_size > (64 * 1024)) && order > 0)
                        continue;
                tcp_bhash = (struct tcp_bind_hashbucket *)
                        __get_free_pages(GFP_ATOMIC, order);
        } while (!tcp_bhash && --order >= 0);

        if (!tcp_bhash)
                panic("Failed to allocate TCP bind hash table\n");
        for (i = 0; i < tcp_bhash_size; i++) {
                tcp_bhash[i].lock = SPIN_LOCK_UNLOCKED;
                INIT_HLIST_HEAD(&tcp_bhash[i].chain);
        }

        /* Try to be a bit smarter and adjust defaults depending
         * on available memory.
         */
        if (order > 4) {
                sysctl_local_port_range[0] = 32768;
                sysctl_local_port_range[1] = 61000;
                sysctl_tcp_max_tw_buckets = 180000;
                sysctl_tcp_max_orphans = 4096 << (order - 4);
                sysctl_max_syn_backlog = 1024;
        } else if (order < 3) {
                sysctl_local_port_range[0] = 1024 * (3 - order);
                sysctl_tcp_max_tw_buckets >>= (3 - order);
                sysctl_tcp_max_orphans >>= (3 - order);
                sysctl_max_syn_backlog = 128;
        }
        tcp_port_rover = sysctl_local_port_range[0] - 1;

        sysctl_tcp_mem[0] =  768 << order;
        sysctl_tcp_mem[1] = 1024 << order;
        sysctl_tcp_mem[2] = 1536 << order;

        if (order < 3) {
                sysctl_tcp_wmem[2] = 64 * 1024;
                sysctl_tcp_rmem[0] = PAGE_SIZE;
                sysctl_tcp_rmem[1] = 43689;
                sysctl_tcp_rmem[2] = 2 * 43689;
        }

        printk(KERN_INFO "TCP: Hash tables configured "
               "(established %d bind %d)\n",
               tcp_ehash_size << 1, tcp_bhash_size);

        tcpdiag_init();
}

EXPORT_SYMBOL(__tcp_mem_reclaim);
EXPORT_SYMBOL(sysctl_tcp_rmem);
EXPORT_SYMBOL(sysctl_tcp_wmem);
EXPORT_SYMBOL(tcp_accept);
EXPORT_SYMBOL(tcp_close);
EXPORT_SYMBOL(tcp_close_state);
EXPORT_SYMBOL(tcp_destroy_sock);
EXPORT_SYMBOL(tcp_disconnect);
EXPORT_SYMBOL(tcp_getsockopt);
EXPORT_SYMBOL(tcp_ioctl);
EXPORT_SYMBOL(tcp_openreq_cachep);
EXPORT_SYMBOL(tcp_poll);
EXPORT_SYMBOL(tcp_read_sock);
EXPORT_SYMBOL(tcp_recvmsg);
EXPORT_SYMBOL(tcp_sendmsg);
EXPORT_SYMBOL(tcp_sendpage);
EXPORT_SYMBOL(tcp_setsockopt);
EXPORT_SYMBOL(tcp_shutdown);
EXPORT_SYMBOL(tcp_sockets_allocated);
EXPORT_SYMBOL(tcp_statistics);
EXPORT_SYMBOL(tcp_timewait_cachep);
EXPORT_SYMBOL(tcp_write_space);
EXPORT_SYMBOL_GPL(cleanup_rbuf);