FreeBSD/Linux Kernel Cross Reference
sys/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).
      *
      * Authors:     Ross Biro
      *              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
    */
   
   #define pr_fmt(fmt) "TCP: " fmt
   
   #include <linux/kernel.h>
   #include <linux/module.h>
   #include <linux/types.h>
   #include <linux/fcntl.h>
   #include <linux/poll.h>
   #include <linux/init.h>
   #include <linux/fs.h>
   #include <linux/skbuff.h>
   #include <linux/scatterlist.h>
   #include <linux/splice.h>
   #include <linux/net.h>
   #include <linux/socket.h>
   #include <linux/random.h>
   #include <linux/bootmem.h>
   #include <linux/highmem.h>
   #include <linux/swap.h>
   #include <linux/cache.h>
   #include <linux/err.h>
   #include <linux/crypto.h>
   #include <linux/time.h>
   #include <linux/slab.h>
   
   #include <net/icmp.h>
   #include <net/inet_common.h>
   #include <net/tcp.h>
   #include <net/xfrm.h>
   #include <net/ip.h>
   #include <net/netdma.h>
   #include <net/sock.h>
   
   #include <asm/uaccess.h>
   #include <asm/ioctls.h>
   
   int sysctl_tcp_fin_timeout __read_mostly = TCP_FIN_TIMEOUT;
   
   struct percpu_counter tcp_orphan_count;
   EXPORT_SYMBOL_GPL(tcp_orphan_count);
   
   int sysctl_tcp_wmem[3] __read_mostly;
   int sysctl_tcp_rmem[3] __read_mostly;
   
   EXPORT_SYMBOL(sysctl_tcp_rmem);
   EXPORT_SYMBOL(sysctl_tcp_wmem);
   
   atomic_long_t tcp_memory_allocated;     /* Current allocated memory. */
   EXPORT_SYMBOL(tcp_memory_allocated);
   
   /*
    * Current number of TCP sockets.
    */
   struct percpu_counter tcp_sockets_allocated;
   EXPORT_SYMBOL(tcp_sockets_allocated);
   
   /*
    * TCP splice context
    */
   struct tcp_splice_state {
           struct pipe_inode_info *pipe;
           size_t len;
           unsigned int flags;
   };
   
   /*
    * Pressure flag: try to collapse.
    * Technical note: it is used by multiple contexts non atomically.
    * All the __sk_mem_schedule() is of this nature: accounting
    * is strict, actions are advisory and have some latency.
    */
   int tcp_memory_pressure __read_mostly;
   EXPORT_SYMBOL(tcp_memory_pressure);
   
   void tcp_enter_memory_pressure(struct sock *sk)
   {
           if (!tcp_memory_pressure) {
                   NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMEMORYPRESSURES);
                   tcp_memory_pressure = 1;
           }
   }
   EXPORT_SYMBOL(tcp_enter_memory_pressure);
   
   /* Convert seconds to retransmits based on initial and max timeout */
   static u8 secs_to_retrans(int seconds, int timeout, int rto_max)
   {
           u8 res = 0;
   
           if (seconds > 0) {
                   int period = timeout;
   
                   res = 1;
                   while (seconds > period && res < 255) {
                           res++;
                           timeout <<= 1;
                           if (timeout > rto_max)
                                   timeout = rto_max;
                           period += timeout;
                   }
           }
           return res;
   }
   
   /* Convert retransmits to seconds based on initial and max timeout */
   static int retrans_to_secs(u8 retrans, int timeout, int rto_max)
   {
           int period = 0;
   
           if (retrans > 0) {
                   period = timeout;
                   while (--retrans) {
                           timeout <<= 1;
                           if (timeout > rto_max)
                                   timeout = rto_max;
                           period += timeout;
                   }
           }
           return period;
   }
   
   /* Address-family independent initialization for a tcp_sock.
    *
    * NOTE: A lot of things set to zero explicitly by call to
    *       sk_alloc() so need not be done here.
    */
   void tcp_init_sock(struct sock *sk)
   {
           struct inet_connection_sock *icsk = inet_csk(sk);
           struct tcp_sock *tp = tcp_sk(sk);
   
           skb_queue_head_init(&tp->out_of_order_queue);
           tcp_init_xmit_timers(sk);
           tcp_prequeue_init(tp);
           INIT_LIST_HEAD(&tp->tsq_node);
   
           icsk->icsk_rto = TCP_TIMEOUT_INIT;
           tp->mdev = TCP_TIMEOUT_INIT;
   
           /* So many TCP implementations out there (incorrectly) count the
            * initial SYN frame in their delayed-ACK and congestion control
            * algorithms that we must have the following bandaid to talk
            * efficiently to them.  -DaveM
            */
           tp->snd_cwnd = TCP_INIT_CWND;
   
           /* See draft-stevens-tcpca-spec-01 for discussion of the
            * initialization of these values.
            */
           tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
           tp->snd_cwnd_clamp = ~0;
           tp->mss_cache = TCP_MSS_DEFAULT;
   
           tp->reordering = sysctl_tcp_reordering;
           tcp_enable_early_retrans(tp);
           icsk->icsk_ca_ops = &tcp_init_congestion_ops;
   
           sk->sk_state = TCP_CLOSE;
   
           sk->sk_write_space = sk_stream_write_space;
           sock_set_flag(sk, SOCK_USE_WRITE_QUEUE);
   
           icsk->icsk_sync_mss = tcp_sync_mss;
   
           /* TCP Cookie Transactions */
           if (sysctl_tcp_cookie_size > 0) {
                   /* Default, cookies without s_data_payload. */
                   tp->cookie_values =
                           kzalloc(sizeof(*tp->cookie_values),
                                   sk->sk_allocation);
                   if (tp->cookie_values != NULL)
                           kref_init(&tp->cookie_values->kref);
           }
           /* Presumed zeroed, in order of appearance:
            *      cookie_in_always, cookie_out_never,
            *      s_data_constant, s_data_in, s_data_out
            */
           sk->sk_sndbuf = sysctl_tcp_wmem[1];
           sk->sk_rcvbuf = sysctl_tcp_rmem[1];
   
           local_bh_disable();
           sock_update_memcg(sk);
           sk_sockets_allocated_inc(sk);
           local_bh_enable();
   }
   EXPORT_SYMBOL(tcp_init_sock);
   
   /*
    *      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;
           const struct tcp_sock *tp = tcp_sk(sk);
   
           sock_poll_wait(file, sk_sleep(sk), wait);
           if (sk->sk_state == TCP_LISTEN)
                   return inet_csk_listen_poll(sk);
   
           /* Socket is not locked. We are protected from async events
            * by poll logic and correct handling of state changes
            * made by other threads is impossible in any case.
            */
   
           mask = 0;
   
           /*
            * 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 POLLHUP were maskable,
            * then we could set it on SND_SHUTDOWN. BTW examples given
            * in Stevens' books assume exactly this behaviour, it explains
            * why POLLHUP 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 | POLLRDHUP;
   
           /* Connected or passive Fast Open socket? */
           if (sk->sk_state != TCP_SYN_SENT &&
               (sk->sk_state != TCP_SYN_RECV || tp->fastopen_rsk != NULL)) {
                   int target = sock_rcvlowat(sk, 0, INT_MAX);
   
                   if (tp->urg_seq == tp->copied_seq &&
                       !sock_flag(sk, SOCK_URGINLINE) &&
                       tp->urg_data)
                           target++;
   
                   /* 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 >= target)
                           mask |= POLLIN | POLLRDNORM;
   
                   if (!(sk->sk_shutdown & SEND_SHUTDOWN)) {
                           if (sk_stream_wspace(sk) >= sk_stream_min_wspace(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 (sk_stream_wspace(sk) >= sk_stream_min_wspace(sk))
                                           mask |= POLLOUT | POLLWRNORM;
                           }
                   } else
                           mask |= POLLOUT | POLLWRNORM;
   
                   if (tp->urg_data & TCP_URG_VALID)
                           mask |= POLLPRI;
           }
           /* This barrier is coupled with smp_wmb() in tcp_reset() */
           smp_rmb();
           if (sk->sk_err)
                   mask |= POLLERR;
   
           return mask;
   }
   EXPORT_SYMBOL(tcp_poll);
   
   int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
   {
           struct tcp_sock *tp = tcp_sk(sk);
           int answ;
           bool slow;
   
           switch (cmd) {
           case SIOCINQ:
                   if (sk->sk_state == TCP_LISTEN)
                           return -EINVAL;
   
                   slow = lock_sock_fast(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 was received */
                           if (answ && sock_flag(sk, SOCK_DONE))
                                   answ--;
                   } else
                           answ = tp->urg_seq - tp->copied_seq;
                   unlock_sock_fast(sk, slow);
                   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;
           case SIOCOUTQNSD:
                   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_nxt;
                   break;
           default:
                   return -ENOIOCTLCMD;
           }
   
           return put_user(answ, (int __user *)arg);
   }
   EXPORT_SYMBOL(tcp_ioctl);
   
   static inline void tcp_mark_push(struct tcp_sock *tp, struct sk_buff *skb)
   {
           TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
           tp->pushed_seq = tp->write_seq;
   }
   
   static inline bool forced_push(const struct tcp_sock *tp)
   {
           return after(tp->write_seq, tp->pushed_seq + (tp->max_window >> 1));
   }
   
   static inline void skb_entail(struct sock *sk, struct sk_buff *skb)
   {
           struct tcp_sock *tp = tcp_sk(sk);
           struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
   
           skb->csum    = 0;
           tcb->seq     = tcb->end_seq = tp->write_seq;
           tcb->tcp_flags = TCPHDR_ACK;
           tcb->sacked  = 0;
           skb_header_release(skb);
           tcp_add_write_queue_tail(sk, skb);
           sk->sk_wmem_queued += skb->truesize;
           sk_mem_charge(sk, skb->truesize);
           if (tp->nonagle & TCP_NAGLE_PUSH)
                   tp->nonagle &= ~TCP_NAGLE_PUSH;
   }
   
   static inline void tcp_mark_urg(struct tcp_sock *tp, int flags)
   {
           if (flags & MSG_OOB)
                   tp->snd_up = tp->write_seq;
   }
   
   static inline void tcp_push(struct sock *sk, int flags, int mss_now,
                               int nonagle)
   {
           if (tcp_send_head(sk)) {
                   struct tcp_sock *tp = tcp_sk(sk);
   
                   if (!(flags & MSG_MORE) || forced_push(tp))
                           tcp_mark_push(tp, tcp_write_queue_tail(sk));
   
                   tcp_mark_urg(tp, flags);
                   __tcp_push_pending_frames(sk, mss_now,
                                             (flags & MSG_MORE) ? TCP_NAGLE_CORK : nonagle);
           }
   }
   
   static int tcp_splice_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
                                   unsigned int offset, size_t len)
   {
           struct tcp_splice_state *tss = rd_desc->arg.data;
           int ret;
   
           ret = skb_splice_bits(skb, offset, tss->pipe, min(rd_desc->count, len),
                                 tss->flags);
           if (ret > 0)
                   rd_desc->count -= ret;
           return ret;
   }
   
   static int __tcp_splice_read(struct sock *sk, struct tcp_splice_state *tss)
   {
           /* Store TCP splice context information in read_descriptor_t. */
           read_descriptor_t rd_desc = {
                   .arg.data = tss,
                   .count    = tss->len,
           };
   
           return tcp_read_sock(sk, &rd_desc, tcp_splice_data_recv);
   }
   
   /**
    *  tcp_splice_read - splice data from TCP socket to a pipe
    * @sock:       socket to splice from
    * @ppos:       position (not valid)
    * @pipe:       pipe to splice to
    * @len:        number of bytes to splice
    * @flags:      splice modifier flags
    *
    * Description:
    *    Will read pages from given socket and fill them into a pipe.
    *
    **/
   ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
                           struct pipe_inode_info *pipe, size_t len,
                           unsigned int flags)
   {
           struct sock *sk = sock->sk;
           struct tcp_splice_state tss = {
                   .pipe = pipe,
                   .len = len,
                   .flags = flags,
           };
           long timeo;
           ssize_t spliced;
           int ret;
   
           sock_rps_record_flow(sk);
           /*
            * We can't seek on a socket input
            */
           if (unlikely(*ppos))
                   return -ESPIPE;
   
           ret = spliced = 0;
   
           lock_sock(sk);
   
           timeo = sock_rcvtimeo(sk, sock->file->f_flags & O_NONBLOCK);
           while (tss.len) {
                   ret = __tcp_splice_read(sk, &tss);
                   if (ret < 0)
                           break;
                   else if (!ret) {
                           if (spliced)
                                   break;
                           if (sock_flag(sk, SOCK_DONE))
                                   break;
                           if (sk->sk_err) {
                                   ret = sock_error(sk);
                                   break;
                           }
                           if (sk->sk_shutdown & RCV_SHUTDOWN)
                                   break;
                           if (sk->sk_state == TCP_CLOSE) {
                                   /*
                                    * This occurs when user tries to read
                                    * from never connected socket.
                                    */
                                   if (!sock_flag(sk, SOCK_DONE))
                                           ret = -ENOTCONN;
                                   break;
                           }
                           if (!timeo) {
                                   ret = -EAGAIN;
                                   break;
                           }
                           sk_wait_data(sk, &timeo);
                           if (signal_pending(current)) {
                                   ret = sock_intr_errno(timeo);
                                   break;
                           }
                           continue;
                   }
                   tss.len -= ret;
                   spliced += ret;
   
                   if (!timeo)
                           break;
                   release_sock(sk);
                   lock_sock(sk);
   
                   if (sk->sk_err || sk->sk_state == TCP_CLOSE ||
                       (sk->sk_shutdown & RCV_SHUTDOWN) ||
                       signal_pending(current))
                           break;
           }
   
           release_sock(sk);
   
           if (spliced)
                   return spliced;
   
           return ret;
   }
   EXPORT_SYMBOL(tcp_splice_read);
   
   struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp)
   {
           struct sk_buff *skb;
   
           /* The TCP header must be at least 32-bit aligned.  */
           size = ALIGN(size, 4);
   
           skb = alloc_skb_fclone(size + sk->sk_prot->max_header, gfp);
           if (skb) {
                   if (sk_wmem_schedule(sk, skb->truesize)) {
                           skb_reserve(skb, sk->sk_prot->max_header);
                           /*
                            * Make sure that we have exactly size bytes
                            * available to the caller, no more, no less.
                            */
                           skb->avail_size = size;
                           return skb;
                   }
                   __kfree_skb(skb);
           } else {
                   sk->sk_prot->enter_memory_pressure(sk);
                   sk_stream_moderate_sndbuf(sk);
           }
           return NULL;
   }
   
   static unsigned int tcp_xmit_size_goal(struct sock *sk, u32 mss_now,
                                          int large_allowed)
   {
           struct tcp_sock *tp = tcp_sk(sk);
           u32 xmit_size_goal, old_size_goal;
   
           xmit_size_goal = mss_now;
   
           if (large_allowed && sk_can_gso(sk)) {
                   xmit_size_goal = ((sk->sk_gso_max_size - 1) -
                                     inet_csk(sk)->icsk_af_ops->net_header_len -
                                     inet_csk(sk)->icsk_ext_hdr_len -
                                     tp->tcp_header_len);
   
                   /* TSQ : try to have two TSO segments in flight */
                   xmit_size_goal = min_t(u32, xmit_size_goal,
                                          sysctl_tcp_limit_output_bytes >> 1);
   
                   xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
   
                   /* We try hard to avoid divides here */
                   old_size_goal = tp->xmit_size_goal_segs * mss_now;
   
                   if (likely(old_size_goal <= xmit_size_goal &&
                              old_size_goal + mss_now > xmit_size_goal)) {
                           xmit_size_goal = old_size_goal;
                   } else {
                           tp->xmit_size_goal_segs =
                                   min_t(u16, xmit_size_goal / mss_now,
                                         sk->sk_gso_max_segs);
                           xmit_size_goal = tp->xmit_size_goal_segs * mss_now;
                   }
           }
   
           return max(xmit_size_goal, mss_now);
   }
   
   static int tcp_send_mss(struct sock *sk, int *size_goal, int flags)
   {
           int mss_now;
   
           mss_now = tcp_current_mss(sk);
           *size_goal = tcp_xmit_size_goal(sk, mss_now, !(flags & MSG_OOB));
   
           return mss_now;
   }
   
   static ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
                                   size_t size, int flags)
   {
           struct tcp_sock *tp = tcp_sk(sk);
           int mss_now, size_goal;
           int err;
           ssize_t copied;
           long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
   
           /* Wait for a connection to finish. One exception is TCP Fast Open
            * (passive side) where data is allowed to be sent before a connection
            * is fully established.
            */
           if (((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) &&
               !tcp_passive_fastopen(sk)) {
                   if ((err = sk_stream_wait_connect(sk, &timeo)) != 0)
                           goto out_err;
           }
   
           clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
   
           mss_now = tcp_send_mss(sk, &size_goal, flags);
           copied = 0;
   
           err = -EPIPE;
           if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
                   goto out_err;
   
           while (size > 0) {
                   struct sk_buff *skb = tcp_write_queue_tail(sk);
                   int copy, i;
                   bool can_coalesce;
   
                   if (!tcp_send_head(sk) || (copy = size_goal - skb->len) <= 0) {
   new_segment:
                           if (!sk_stream_memory_free(sk))
                                   goto wait_for_sndbuf;
   
                           skb = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
                           if (!skb)
                                   goto wait_for_memory;
   
                           skb_entail(sk, skb);
                           copy = size_goal;
                   }
   
                   if (copy > size)
                           copy = size;
   
                   i = skb_shinfo(skb)->nr_frags;
                   can_coalesce = skb_can_coalesce(skb, i, page, offset);
                   if (!can_coalesce && i >= MAX_SKB_FRAGS) {
                           tcp_mark_push(tp, skb);
                           goto new_segment;
                   }
                   if (!sk_wmem_schedule(sk, copy))
                           goto wait_for_memory;
   
                   if (can_coalesce) {
                           skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
                   } else {
                           get_page(page);
                           skb_fill_page_desc(skb, i, page, offset, copy);
                   }
   
                   skb->len += copy;
                   skb->data_len += copy;
                   skb->truesize += copy;
                   sk->sk_wmem_queued += copy;
                   sk_mem_charge(sk, copy);
                   skb->ip_summed = CHECKSUM_PARTIAL;
                   tp->write_seq += copy;
                   TCP_SKB_CB(skb)->end_seq += copy;
                   skb_shinfo(skb)->gso_segs = 0;
   
                   if (!copied)
                           TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
   
                   copied += copy;
                   offset += copy;
                   if (!(size -= copy))
                           goto out;
   
                   if (skb->len < size_goal || (flags & MSG_OOB))
                           continue;
   
                   if (forced_push(tp)) {
                           tcp_mark_push(tp, skb);
                           __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_PUSH);
                   } else if (skb == tcp_send_head(sk))
                           tcp_push_one(sk, mss_now);
                   continue;
   
   wait_for_sndbuf:
                   set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
   wait_for_memory:
                   tcp_push(sk, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);
   
                   if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
                           goto do_error;
   
                   mss_now = tcp_send_mss(sk, &size_goal, flags);
           }
   
   out:
           if (copied && !(flags & MSG_SENDPAGE_NOTLAST))
                   tcp_push(sk, flags, mss_now, tp->nonagle);
           return copied;
   
   do_error:
           if (copied)
                   goto out;
   out_err:
           return sk_stream_error(sk, flags, err);
   }
   
   int tcp_sendpage(struct sock *sk, struct page *page, int offset,
                    size_t size, int flags)
   {
           ssize_t res;
   
           if (!(sk->sk_route_caps & NETIF_F_SG) ||
               !(sk->sk_route_caps & NETIF_F_ALL_CSUM))
                   return sock_no_sendpage(sk->sk_socket, page, offset, size,
                                           flags);
   
           lock_sock(sk);
           res = do_tcp_sendpages(sk, page, offset, size, flags);
           release_sock(sk);
           return res;
   }
   EXPORT_SYMBOL(tcp_sendpage);
   
   static inline int select_size(const struct sock *sk, bool sg)
   {
           const struct tcp_sock *tp = tcp_sk(sk);
           int tmp = tp->mss_cache;
   
           if (sg) {
                   if (sk_can_gso(sk)) {
                           /* Small frames wont use a full page:
                            * Payload will immediately follow tcp header.
                            */
                           tmp = SKB_WITH_OVERHEAD(2048 - MAX_TCP_HEADER);
                   } else {
                           int pgbreak = SKB_MAX_HEAD(MAX_TCP_HEADER);
   
                           if (tmp >= pgbreak &&
                               tmp <= pgbreak + (MAX_SKB_FRAGS - 1) * PAGE_SIZE)
                                   tmp = pgbreak;
                   }
           }
   
           return tmp;
   }
   
   void tcp_free_fastopen_req(struct tcp_sock *tp)
   {
           if (tp->fastopen_req != NULL) {
                   kfree(tp->fastopen_req);
                   tp->fastopen_req = NULL;
           }
   }
   
   static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg, int *size)
   {
          struct tcp_sock *tp = tcp_sk(sk);
          int err, flags;
  
          if (!(sysctl_tcp_fastopen & TFO_CLIENT_ENABLE))
                  return -EOPNOTSUPP;
          if (tp->fastopen_req != NULL)
                  return -EALREADY; /* Another Fast Open is in progress */
  
          tp->fastopen_req = kzalloc(sizeof(struct tcp_fastopen_request),
                                     sk->sk_allocation);
          if (unlikely(tp->fastopen_req == NULL))
                  return -ENOBUFS;
          tp->fastopen_req->data = msg;
  
          flags = (msg->msg_flags & MSG_DONTWAIT) ? O_NONBLOCK : 0;
          err = __inet_stream_connect(sk->sk_socket, msg->msg_name,
                                      msg->msg_namelen, flags);
          *size = tp->fastopen_req->copied;
          tcp_free_fastopen_req(tp);
          return err;
  }
  
  int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                  size_t size)
  {
          struct iovec *iov;
          struct tcp_sock *tp = tcp_sk(sk);
          struct sk_buff *skb;
          int iovlen, flags, err, copied = 0;
          int mss_now = 0, size_goal, copied_syn = 0, offset = 0;
          bool sg;
          long timeo;
  
          lock_sock(sk);
  
          flags = msg->msg_flags;
          if (flags & MSG_FASTOPEN) {
                  err = tcp_sendmsg_fastopen(sk, msg, &copied_syn);
                  if (err == -EINPROGRESS && copied_syn > 0)
                          goto out;
                  else if (err)
                          goto out_err;
                  offset = copied_syn;
          }
  
          timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
  
          /* Wait for a connection to finish. One exception is TCP Fast Open
           * (passive side) where data is allowed to be sent before a connection
           * is fully established.
           */
          if (((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) &&
              !tcp_passive_fastopen(sk)) {
                  if ((err = sk_stream_wait_connect(sk, &timeo)) != 0)
                          goto do_error;
          }
  
          if (unlikely(tp->repair)) {
                  if (tp->repair_queue == TCP_RECV_QUEUE) {
                          copied = tcp_send_rcvq(sk, msg, size);
                          goto out;
                  }
  
                  err = -EINVAL;
                  if (tp->repair_queue == TCP_NO_QUEUE)
                          goto out_err;
  
                  /* 'common' sending to sendq */
          }
  
          /* This should be in poll */
          clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
  
          mss_now = tcp_send_mss(sk, &size_goal, flags);
  
          /* 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 out_err;
  
          sg = !!(sk->sk_route_caps & NETIF_F_SG);
  
          while (--iovlen >= 0) {
                  size_t seglen = iov->iov_len;
                  unsigned char __user *from = iov->iov_base;
  
                  iov++;
                  if (unlikely(offset > 0)) {  /* Skip bytes copied in SYN */
                          if (offset >= seglen) {
                                  offset -= seglen;
                                  continue;
                          }
                          seglen -= offset;
                          from += offset;
                          offset = 0;
                  }
  
                  while (seglen > 0) {
                          int copy = 0;
                          int max = size_goal;
  
                          skb = tcp_write_queue_tail(sk);
                          if (tcp_send_head(sk)) {
                                  if (skb->ip_summed == CHECKSUM_NONE)
                                          max = mss_now;
                                  copy = max - skb->len;
                          }
  
                          if (copy <= 0) {
  new_segment:
                                  /* Allocate new segment. If the interface is SG,
                                   * allocate skb fitting to single page.
                                   */
                                  if (!sk_stream_memory_free(sk))
                                          goto wait_for_sndbuf;
  
                                  skb = sk_stream_alloc_skb(sk,
                                                            select_size(sk, sg),
                                                            sk->sk_allocation);
                                  if (!skb)
                                          goto wait_for_memory;
  
                                  /*
                                   * Check whether we can use HW checksum.
                                   */
                                  if (sk->sk_route_caps & NETIF_F_ALL_CSUM)
                                          skb->ip_summed = CHECKSUM_PARTIAL;
  
                                  skb_entail(sk, skb);
                                  copy = size_goal;
                                  max = size_goal;
                          }
  
                          /* Try to append data to the end of skb. */
                          if (copy > seglen)
                                  copy = seglen;
  
                          /* Where to copy to? */
                          if (skb_availroom(skb) > 0) {
                                  /* We have some space in skb head. Superb! */
                                  copy = min_t(int, copy, skb_availroom(skb));
                                  err = skb_add_data_nocache(sk, skb, from, copy);
                                  if (err)
                                          goto do_fault;
                          } else {
                                  bool merge = true;
                                  int i = skb_shinfo(skb)->nr_frags;
                                  struct page_frag *pfrag = sk_page_frag(sk);
  
                                  if (!sk_page_frag_refill(sk, pfrag))
                                          goto wait_for_memory;
  
                                  if (!skb_can_coalesce(skb, i, pfrag->page,
                                                        pfrag->offset)) {
                                          if (i == MAX_SKB_FRAGS || !sg) {
                                                  tcp_mark_push(tp, skb);
                                                  goto new_segment;
                                          }
                                          merge = false;
                                  }
  
                                  copy = min_t(int, copy, pfrag->size - pfrag->offset);
  
                                  if (!sk_wmem_schedule(sk, copy))
                                          goto wait_for_memory;
  
                                  err = skb_copy_to_page_nocache(sk, from, skb,
                                                                 pfrag->page,
                                                                 pfrag->offset,
                                                                 copy);
                                  if (err)
                                          goto do_error;
  
                                  /* Update the skb. */
                                  if (merge) {
                                          skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
                                  } else {
                                          skb_fill_page_desc(skb, i, pfrag->page,
                                                             pfrag->offset, copy);
                                          get_page(pfrag->page);
                                  }
                                  pfrag->offset += copy;
                          }
  
                          if (!copied)
                                  TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
  
                          tp->write_seq += copy;
                          TCP_SKB_CB(skb)->end_seq += copy;
                          skb_shinfo(skb)->gso_segs = 0;
  
                          from += copy;
                          copied += copy;
                          if ((seglen -= copy) == 0 && iovlen == 0)
                                  goto out;
  
                          if (skb->len < max || (flags & MSG_OOB) || unlikely(tp->repair))
                                  continue;
  
                          if (forced_push(tp)) {
                                  tcp_mark_push(tp, skb);
                                  __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_PUSH);
                          } else if (skb == tcp_send_head(sk))
                                  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, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);
  
                          if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
                                  goto do_error;
  
                          mss_now = tcp_send_mss(sk, &size_goal, flags);
                  }
          }
  
  out:
          if (copied)
                  tcp_push(sk, flags, mss_now, tp->nonagle);
          release_sock(sk);
          return copied + copied_syn;
  
  do_fault:
          if (!skb->len) {
                  tcp_unlink_write_queue(skb, sk);
                  /* It is the one place in all of TCP, except connection
                   * reset, where we can be unlinking the send_head.
                   */
                  tcp_check_send_head(sk, skb);
                  sk_wmem_free_skb(sk, skb);
          }
  
  do_error:
          if (copied + copied_syn)
                  goto out;
  out_err:
          err = sk_stream_error(sk, flags, err);
          release_sock(sk);
          return err;
  }
  EXPORT_SYMBOL(tcp_sendmsg);
  
  /*
   *      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, struct msghdr *msg, int len, int flags)
  {
          struct tcp_sock *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;
  }
  
  static int tcp_peek_sndq(struct sock *sk, struct msghdr *msg, int len)
  {
          struct sk_buff *skb;
          int copied = 0, err = 0;
  
          /* XXX -- need to support SO_PEEK_OFF */
  
          skb_queue_walk(&sk->sk_write_queue, skb) {
                  err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, skb->len);
                  if (err)
                          break;
  
                  copied += skb->len;
          }
  
          return err ?: copied;
  }
  
  /* 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 tcp_cleanup_rbuf(struct sock *sk, int copied)
  {
          struct tcp_sock *tp = tcp_sk(sk);
          bool time_to_ack = false;
  
          struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
  
          WARN(skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq),
               "cleanup rbuf bug: copied %X seq %X rcvnxt %X\n",
               tp->copied_seq, TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt);
  
          if (inet_csk_ack_scheduled(sk)) {
                  const struct inet_connection_sock *icsk = inet_csk(sk);
                     /* Delayed ACKs frequently hit locked sockets during bulk
                      * receive. */
                  if (icsk->icsk_ack.blocked ||
                      /* Once-per-two-segments ACK was not sent by tcp_input.c */
                      tp->rcv_nxt - tp->rcv_wup > icsk->icsk_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 &&
                       ((icsk->icsk_ack.pending & ICSK_ACK_PUSHED2) ||
                        ((icsk->icsk_ack.pending & ICSK_ACK_PUSHED) &&
                         !icsk->icsk_ack.pingpong)) &&
                        !atomic_read(&sk->sk_rmem_alloc)))
                          time_to_ack = true;
          }
  
          /* 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 = true;
                  }
          }
          if (time_to_ack)
                  tcp_send_ack(sk);
  }
  
  static void tcp_prequeue_process(struct sock *sk)
  {
          struct sk_buff *skb;
          struct tcp_sock *tp = tcp_sk(sk);
  
          NET_INC_STATS_USER(sock_net(sk), LINUX_MIB_TCPPREQUEUED);
  
          /* 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_backlog_rcv(sk, skb);
          local_bh_enable();
  
          /* Clear memory counter. */
          tp->ucopy.memory = 0;
  }
  
  #ifdef CONFIG_NET_DMA
  static void tcp_service_net_dma(struct sock *sk, bool wait)
  {
          dma_cookie_t done, used;
          dma_cookie_t last_issued;
          struct tcp_sock *tp = tcp_sk(sk);
  
          if (!tp->ucopy.dma_chan)
                  return;
  
          last_issued = tp->ucopy.dma_cookie;
          dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);
  
          do {
                  if (dma_async_memcpy_complete(tp->ucopy.dma_chan,
                                                last_issued, &done,
                                                &used) == DMA_SUCCESS) {
                          /* Safe to free early-copied skbs now */
                          __skb_queue_purge(&sk->sk_async_wait_queue);
                          break;
                  } else {
                          struct sk_buff *skb;
                          while ((skb = skb_peek(&sk->sk_async_wait_queue)) &&
                                 (dma_async_is_complete(skb->dma_cookie, done,
                                                        used) == DMA_SUCCESS)) {
                                  __skb_dequeue(&sk->sk_async_wait_queue);
                                  kfree_skb(skb);
                          }
                  }
          } while (wait);
  }
  #endif
  
  static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
  {
          struct sk_buff *skb;
          u32 offset;
  
          while ((skb = skb_peek(&sk->sk_receive_queue)) != NULL) {
                  offset = seq - TCP_SKB_CB(skb)->seq;
                  if (tcp_hdr(skb)->syn)
                          offset--;
                  if (offset < skb->len || tcp_hdr(skb)->fin) {
                          *off = offset;
                          return skb;
                  }
                  /* This looks weird, but this can happen if TCP collapsing
                   * splitted a fat GRO packet, while we released socket lock
                   * in skb_splice_bits()
                   */
                  sk_eat_skb(sk, skb, false);
          }
          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_sock *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) {
                          int used;
                          size_t 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 <= 0) {
                                  if (!copied)
                                          copied = used;
                                  break;
                          } else if (used <= len) {
                                  seq += used;
                                  copied += used;
                                  offset += used;
                          }
                          /* If recv_actor drops the lock (e.g. TCP splice
                           * receive) the skb pointer might be invalid when
                           * getting here: tcp_collapse might have deleted it
                           * while aggregating skbs from the socket queue.
                           */
                          skb = tcp_recv_skb(sk, seq - 1, &offset);
                          if (!skb)
                                  break;
                          /* TCP coalescing might have appended data to the skb.
                           * Try to splice more frags
                           */
                          if (offset + 1 != skb->len)
                                  continue;
                  }
                  if (tcp_hdr(skb)->fin) {
                          sk_eat_skb(sk, skb, false);
                          ++seq;
                          break;
                  }
                  sk_eat_skb(sk, skb, false);
                  if (!desc->count)
                          break;
                  tp->copied_seq = seq;
          }
          tp->copied_seq = seq;
  
          tcp_rcv_space_adjust(sk);
  
          /* Clean up data we have read: This will do ACK frames. */
          if (copied > 0) {
                  tcp_recv_skb(sk, seq, &offset);
                  tcp_cleanup_rbuf(sk, copied);
          }
          return copied;
  }
  EXPORT_SYMBOL(tcp_read_sock);
  
  /*
   *      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_sock *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;
          bool copied_early = false;
          struct sk_buff *skb;
          u32 urg_hole = 0;
  
          lock_sock(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;
  
          if (unlikely(tp->repair)) {
                  err = -EPERM;
                  if (!(flags & MSG_PEEK))
                          goto out;
  
                  if (tp->repair_queue == TCP_SEND_QUEUE)
                          goto recv_sndq;
  
                  err = -EINVAL;
                  if (tp->repair_queue == TCP_NO_QUEUE)
                          goto out;
  
                  /* 'common' recv queue MSG_PEEK-ing */
          }
  
          seq = &tp->copied_seq;
          if (flags & MSG_PEEK) {
                  peek_seq = tp->copied_seq;
                  seq = &peek_seq;
          }
  
          target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);
  
  #ifdef CONFIG_NET_DMA
          tp->ucopy.dma_chan = NULL;
          preempt_disable();
          skb = skb_peek_tail(&sk->sk_receive_queue);
          {
                  int available = 0;
  
                  if (skb)
                          available = TCP_SKB_CB(skb)->seq + skb->len - (*seq);
                  if ((available < target) &&
                      (len > sysctl_tcp_dma_copybreak) && !(flags & MSG_PEEK) &&
                      !sysctl_tcp_low_latency &&
                      net_dma_find_channel()) {
                          preempt_enable_no_resched();
                          tp->ucopy.pinned_list =
                                          dma_pin_iovec_pages(msg->msg_iov, len);
                  } else {
                          preempt_enable_no_resched();
                  }
          }
  #endif
  
          do {
                  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_queue_walk(&sk->sk_receive_queue, skb) {
                          /* Now that we have two receive queues this
                           * shouldn't happen.
                           */
                          if (WARN(before(*seq, TCP_SKB_CB(skb)->seq),
                                   "recvmsg bug: copied %X seq %X rcvnxt %X fl %X\n",
                                   *seq, TCP_SKB_CB(skb)->seq, tp->rcv_nxt,
                                   flags))
                                  break;
  
                          offset = *seq - TCP_SKB_CB(skb)->seq;
                          if (tcp_hdr(skb)->syn)
                                  offset--;
                          if (offset < skb->len)
                                  goto found_ok_skb;
                          if (tcp_hdr(skb)->fin)
                                  goto found_fin_ok;
                          WARN(!(flags & MSG_PEEK),
                               "recvmsg bug 2: copied %X seq %X rcvnxt %X fl %X\n",
                               *seq, TCP_SKB_CB(skb)->seq, tp->rcv_nxt, flags);
                  }
  
                  /* 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))
                                  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;
                          }
                  }
  
                  tcp_cleanup_rbuf(sk, copied);
  
                  if (!sysctl_tcp_low_latency && 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;
  
                          WARN_ON(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_empty(&tp->ucopy.prequeue))
                                  goto do_prequeue;
  
                          /* __ Set realtime policy in scheduler __ */
                  }
  
  #ifdef CONFIG_NET_DMA
                  if (tp->ucopy.dma_chan) {
                          if (tp->rcv_wnd == 0 &&
                              !skb_queue_empty(&sk->sk_async_wait_queue)) {
                                  tcp_service_net_dma(sk, true);
                                  tcp_cleanup_rbuf(sk, copied);
                          } else
                                  dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);
                  }
  #endif
                  if (copied >= target) {
                          /* Do not sleep, just process backlog. */
                          release_sock(sk);
                          lock_sock(sk);
                  } else
                          sk_wait_data(sk, &timeo);
  
  #ifdef CONFIG_NET_DMA
                  tcp_service_net_dma(sk, false);  /* Don't block */
                  tp->ucopy.wakeup = 0;
  #endif
  
                  if (user_recv) {
                          int chunk;
  
                          /* __ Restore normal policy in scheduler __ */
  
                          if ((chunk = len - tp->ucopy.len) != 0) {
                                  NET_ADD_STATS_USER(sock_net(sk), LINUX_MIB_TCPDIRECTCOPYFROMBACKLOG, chunk);
                                  len -= chunk;
                                  copied += chunk;
                          }
  
                          if (tp->rcv_nxt == tp->copied_seq &&
                              !skb_queue_empty(&tp->ucopy.prequeue)) {
  do_prequeue:
                                  tcp_prequeue_process(sk);
  
                                  if ((chunk = len - tp->ucopy.len) != 0) {
                                          NET_ADD_STATS_USER(sock_net(sk), LINUX_MIB_TCPDIRECTCOPYFROMPREQUEUE, chunk);
                                          len -= chunk;
                                          copied += chunk;
                                  }
                          }
                  }
                  if ((flags & MSG_PEEK) &&
                      (peek_seq - copied - urg_hole != tp->copied_seq)) {
                          net_dbg_ratelimited("TCP(%s:%d): Application bug, race in MSG_PEEK\n",
                                              current->comm,
                                              task_pid_nr(current));
                          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;
                                                  urg_hole++;
                                                  offset++;
                                                  used--;
                                                  if (!used)
                                                          goto skip_copy;
                                          }
                                  } else
                                          used = urg_offset;
                          }
                  }
  
                  if (!(flags & MSG_TRUNC)) {
  #ifdef CONFIG_NET_DMA
                          if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
                                  tp->ucopy.dma_chan = net_dma_find_channel();
  
                          if (tp->ucopy.dma_chan) {
                                  tp->ucopy.dma_cookie = dma_skb_copy_datagram_iovec(
                                          tp->ucopy.dma_chan, skb, offset,
                                          msg->msg_iov, used,
                                          tp->ucopy.pinned_list);
  
                                  if (tp->ucopy.dma_cookie < 0) {
  
                                          pr_alert("%s: dma_cookie < 0\n",
                                                   __func__);
  
                                          /* Exception. Bailout! */
                                          if (!copied)
                                                  copied = -EFAULT;
                                          break;
                                  }
  
                                  dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);
  
                                  if ((offset + used) == skb->len)
                                          copied_early = true;
  
                          } else
  #endif
                          {
                                  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);
                  }
                  if (used + offset < skb->len)
                          continue;
  
                  if (tcp_hdr(skb)->fin)
                          goto found_fin_ok;
                  if (!(flags & MSG_PEEK)) {
                          sk_eat_skb(sk, skb, copied_early);
                          copied_early = false;
                  }
                  continue;
  
          found_fin_ok:
                  /* Process the FIN. */
                  ++*seq;
                  if (!(flags & MSG_PEEK)) {
                          sk_eat_skb(sk, skb, copied_early);
                          copied_early = false;
                  }
                  break;
          } while (len > 0);
  
          if (user_recv) {
                  if (!skb_queue_empty(&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(sock_net(sk), LINUX_MIB_TCPDIRECTCOPYFROMPREQUEUE, chunk);
                                  len -= chunk;
                                  copied += chunk;
                          }
                  }
  
                  tp->ucopy.task = NULL;
                  tp->ucopy.len = 0;
          }
  
  #ifdef CONFIG_NET_DMA
          tcp_service_net_dma(sk, true);  /* Wait for queue to drain */
          tp->ucopy.dma_chan = NULL;
  
          if (tp->ucopy.pinned_list) {
                  dma_unpin_iovec_pages(tp->ucopy.pinned_list);
                  tp->ucopy.pinned_list = NULL;
          }
  #endif
  
          /* 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. */
          tcp_cleanup_rbuf(sk, copied);
  
          release_sock(sk);
          return copied;
  
  out:
          release_sock(sk);
          return err;
  
  recv_urg:
          err = tcp_recv_urg(sk, msg, len, flags);
          goto out;
  
  recv_sndq:
          err = tcp_peek_sndq(sk, msg, len);
          goto out;
  }
  EXPORT_SYMBOL(tcp_recvmsg);
  
  void tcp_set_state(struct sock *sk, int state)
  {
          int oldstate = sk->sk_state;
  
          switch (state) {
          case TCP_ESTABLISHED:
                  if (oldstate != TCP_ESTABLISHED)
                          TCP_INC_STATS(sock_net(sk), TCP_MIB_CURRESTAB);
                  break;
  
          case TCP_CLOSE:
                  if (oldstate == TCP_CLOSE_WAIT || oldstate == TCP_ESTABLISHED)
                          TCP_INC_STATS(sock_net(sk), TCP_MIB_ESTABRESETS);
  
                  sk->sk_prot->unhash(sk);
                  if (inet_csk(sk)->icsk_bind_hash &&
                      !(sk->sk_userlocks & SOCK_BINDPORT_LOCK))
                          inet_put_port(sk);
                  /* fall through */
          default:
                  if (oldstate == TCP_ESTABLISHED)
                          TCP_DEC_STATS(sock_net(sk), TCP_MIB_CURRESTAB);
          }
  
          /* Change state AFTER socket is unhashed to avoid closed
           * socket sitting in hash tables.
           */
          sk->sk_state = state;
  
  #ifdef STATE_TRACE
          SOCK_DEBUG(sk, "TCP sk=%p, State %s -> %s\n", sk, statename[oldstate], statename[state]);
  #endif
  }
  EXPORT_SYMBOL_GPL(tcp_set_state);
  
  /*
   *      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 const 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 sock_set_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);
          }
  }
  EXPORT_SYMBOL(tcp_shutdown);
  
  bool tcp_check_oom(struct sock *sk, int shift)
  {
          bool too_many_orphans, out_of_socket_memory;
  
          too_many_orphans = tcp_too_many_orphans(sk, shift);
          out_of_socket_memory = tcp_out_of_memory(sk);
  
          if (too_many_orphans)
                  net_info_ratelimited("too many orphaned sockets\n");
          if (out_of_socket_memory)
                  net_info_ratelimited("out of memory -- consider tuning tcp_mem\n");
          return too_many_orphans || out_of_socket_memory;
  }
  
  void tcp_close(struct sock *sk, long timeout)
  {
          struct sk_buff *skb;
          int data_was_unread = 0;
          int state;
  
          lock_sock(sk);
          sk->sk_shutdown = SHUTDOWN_MASK;
  
          if (sk->sk_state == TCP_LISTEN) {
                  tcp_set_state(sk, TCP_CLOSE);
  
                  /* Special case. */
                  inet_csk_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 -
                            tcp_hdr(skb)->fin;
                  data_was_unread += len;
                  __kfree_skb(skb);
          }
  
          sk_mem_reclaim(sk);
  
          /* If socket has been already reset (e.g. in tcp_reset()) - kill it. */
          if (sk->sk_state == TCP_CLOSE)
                  goto adjudge_to_death;
  
          /* As outlined in RFC 2525, section 2.17, 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 (unlikely(tcp_sk(sk)->repair)) {
                  sk->sk_prot->disconnect(sk, 0);
          } else if (data_was_unread) {
                  /* Unread data was tossed, zap the connection. */
                  NET_INC_STATS_USER(sock_net(sk), LINUX_MIB_TCPABORTONCLOSE);
                  tcp_set_state(sk, TCP_CLOSE);
                  tcp_send_active_reset(sk, sk->sk_allocation);
          } 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(sock_net(sk), LINUX_MIB_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
                   * XXX (TFO) - To start off we don't support SYN+ACK+FIN
                   * in a single packet! (May consider it later but will
                   * probably need API support or TCP_CORK SYN-ACK until
                   * data is written and socket is closed.)
                   */
                  tcp_send_fin(sk);
          }
  
          sk_stream_wait_close(sk, timeout);
  
  adjudge_to_death:
          state = sk->sk_state;
          sock_hold(sk);
          sock_orphan(sk);
  
          /* 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);
          WARN_ON(sock_owned_by_user(sk));
  
          percpu_counter_inc(sk->sk_prot->orphan_count);
  
          /* Have we already been destroyed by a softirq or backlog? */
          if (state != TCP_CLOSE && sk->sk_state == TCP_CLOSE)
                  goto out;
  
          /*      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_sock *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(sock_net(sk),
                                          LINUX_MIB_TCPABORTONLINGER);
                  } else {
                          const int tmo = tcp_fin_time(sk);
  
                          if (tmo > TCP_TIMEWAIT_LEN) {
                                  inet_csk_reset_keepalive_timer(sk,
                                                  tmo - TCP_TIMEWAIT_LEN);
                          } else {
                                  tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
                                  goto out;
                          }
                  }
          }
          if (sk->sk_state != TCP_CLOSE) {
                  sk_mem_reclaim(sk);
                  if (tcp_check_oom(sk, 0)) {
                          tcp_set_state(sk, TCP_CLOSE);
                          tcp_send_active_reset(sk, GFP_ATOMIC);
                          NET_INC_STATS_BH(sock_net(sk),
                                          LINUX_MIB_TCPABORTONMEMORY);
                  }
          }
  
          if (sk->sk_state == TCP_CLOSE) {
                  struct request_sock *req = tcp_sk(sk)->fastopen_rsk;
                  /* We could get here with a non-NULL req if the socket is
                   * aborted (e.g., closed with unread data) before 3WHS
                   * finishes.
                   */
                  if (req != NULL)
                          reqsk_fastopen_remove(sk, req, false);
                  inet_csk_destroy_sock(sk);
          }
          /* Otherwise, socket is reprieved until protocol close. */
  
  out:
          bh_unlock_sock(sk);
          local_bh_enable();
          sock_put(sk);
  }
  EXPORT_SYMBOL(tcp_close);
  
  /* These states need RST on ABORT according to RFC793 */
  
  static inline bool 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_sock *inet = inet_sk(sk);
          struct inet_connection_sock *icsk = inet_csk(sk);
          struct tcp_sock *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) {
                  inet_csk_listen_stop(sk);
          } else if (unlikely(tp->repair)) {
                  sk->sk_err = ECONNABORTED;
          } 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 discrepancy 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_write_queue_purge(sk);
          __skb_queue_purge(&tp->out_of_order_queue);
  #ifdef CONFIG_NET_DMA
          __skb_queue_purge(&sk->sk_async_wait_queue);
  #endif
  
          inet->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;
          icsk->icsk_backoff = 0;
          tp->snd_cwnd = 2;
          icsk->icsk_probes_out = 0;
          tp->packets_out = 0;
          tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
          tp->snd_cwnd_cnt = 0;
          tp->bytes_acked = 0;
          tp->window_clamp = 0;
          tcp_set_ca_state(sk, TCP_CA_Open);
          tcp_clear_retrans(tp);
          inet_csk_delack_init(sk);
          tcp_init_send_head(sk);
          memset(&tp->rx_opt, 0, sizeof(tp->rx_opt));
          __sk_dst_reset(sk);
  
          WARN_ON(inet->inet_num && !icsk->icsk_bind_hash);
  
          sk->sk_error_report(sk);
          return err;
  }
  EXPORT_SYMBOL(tcp_disconnect);
  
  void tcp_sock_destruct(struct sock *sk)
  {
          inet_sock_destruct(sk);
  
          kfree(inet_csk(sk)->icsk_accept_queue.fastopenq);
  }
  
  static inline bool tcp_can_repair_sock(const struct sock *sk)
  {
          return ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN) &&
                  ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_ESTABLISHED));
  }
  
  static int tcp_repair_options_est(struct tcp_sock *tp,
                  struct tcp_repair_opt __user *optbuf, unsigned int len)
  {
          struct tcp_repair_opt opt;
  
          while (len >= sizeof(opt)) {
                  if (copy_from_user(&opt, optbuf, sizeof(opt)))
                          return -EFAULT;
  
                  optbuf++;
                  len -= sizeof(opt);
  
                  switch (opt.opt_code) {
                  case TCPOPT_MSS:
                          tp->rx_opt.mss_clamp = opt.opt_val;
                          break;
                  case TCPOPT_WINDOW:
                          {
                                  u16 snd_wscale = opt.opt_val & 0xFFFF;
                                  u16 rcv_wscale = opt.opt_val >> 16;
  
                                  if (snd_wscale > 14 || rcv_wscale > 14)
                                          return -EFBIG;
  
                                  tp->rx_opt.snd_wscale = snd_wscale;
                                  tp->rx_opt.rcv_wscale = rcv_wscale;
                                  tp->rx_opt.wscale_ok = 1;
                          }
                          break;
                  case TCPOPT_SACK_PERM:
                          if (opt.opt_val != 0)
                                  return -EINVAL;
  
                          tp->rx_opt.sack_ok |= TCP_SACK_SEEN;
                          if (sysctl_tcp_fack)
                                  tcp_enable_fack(tp);
                          break;
                  case TCPOPT_TIMESTAMP:
                          if (opt.opt_val != 0)
                                  return -EINVAL;
  
                          tp->rx_opt.tstamp_ok = 1;
                          break;
                  }
          }
  
          return 0;
  }
  
  /*
   *      Socket option code for TCP.
   */
  static int do_tcp_setsockopt(struct sock *sk, int level,
                  int optname, char __user *optval, unsigned int optlen)
  {
          struct tcp_sock *tp = tcp_sk(sk);
          struct inet_connection_sock *icsk = inet_csk(sk);
          int val;
          int err = 0;
  
          /* These are data/string values, all the others are ints */
          switch (optname) {
          case TCP_CONGESTION: {
                  char name[TCP_CA_NAME_MAX];
  
                  if (optlen < 1)
                          return -EINVAL;
  
                  val = strncpy_from_user(name, optval,
                                          min_t(long, TCP_CA_NAME_MAX-1, optlen));
                  if (val < 0)
                          return -EFAULT;
                  name[val] = 0;
  
                  lock_sock(sk);
                  err = tcp_set_congestion_control(sk, name);
                  release_sock(sk);
                  return err;
          }
          case TCP_COOKIE_TRANSACTIONS: {
                  struct tcp_cookie_transactions ctd;
                  struct tcp_cookie_values *cvp = NULL;
  
                  if (sizeof(ctd) > optlen)
                          return -EINVAL;
                  if (copy_from_user(&ctd, optval, sizeof(ctd)))
                          return -EFAULT;
  
                  if (ctd.tcpct_used > sizeof(ctd.tcpct_value) ||
                      ctd.tcpct_s_data_desired > TCP_MSS_DESIRED)
                          return -EINVAL;
  
                  if (ctd.tcpct_cookie_desired == 0) {
                          /* default to global value */
                  } else if ((0x1 & ctd.tcpct_cookie_desired) ||
                             ctd.tcpct_cookie_desired > TCP_COOKIE_MAX ||
                             ctd.tcpct_cookie_desired < TCP_COOKIE_MIN) {
                          return -EINVAL;
                  }
  
                  if (TCP_COOKIE_OUT_NEVER & ctd.tcpct_flags) {
                          /* Supercedes all other values */
                          lock_sock(sk);
                          if (tp->cookie_values != NULL) {
                                  kref_put(&tp->cookie_values->kref,
                                           tcp_cookie_values_release);
                                  tp->cookie_values = NULL;
                          }
                          tp->rx_opt.cookie_in_always = 0; /* false */
                          tp->rx_opt.cookie_out_never = 1; /* true */
                          release_sock(sk);
                          return err;
                  }
  
                  /* Allocate ancillary memory before locking.
                   */
                  if (ctd.tcpct_used > 0 ||
                      (tp->cookie_values == NULL &&
                       (sysctl_tcp_cookie_size > 0 ||
                        ctd.tcpct_cookie_desired > 0 ||
                        ctd.tcpct_s_data_desired > 0))) {
                          cvp = kzalloc(sizeof(*cvp) + ctd.tcpct_used,
                                        GFP_KERNEL);
                          if (cvp == NULL)
                                  return -ENOMEM;
  
                          kref_init(&cvp->kref);
                  }
                  lock_sock(sk);
                  tp->rx_opt.cookie_in_always =
                          (TCP_COOKIE_IN_ALWAYS & ctd.tcpct_flags);
                  tp->rx_opt.cookie_out_never = 0; /* false */
  
                  if (tp->cookie_values != NULL) {
                          if (cvp != NULL) {
                                  /* Changed values are recorded by a changed
                                   * pointer, ensuring the cookie will differ,
                                   * without separately hashing each value later.
                                   */
                                  kref_put(&tp->cookie_values->kref,
                                           tcp_cookie_values_release);
                          } else {
                                  cvp = tp->cookie_values;
                          }
                  }
  
                  if (cvp != NULL) {
                          cvp->cookie_desired = ctd.tcpct_cookie_desired;
  
                          if (ctd.tcpct_used > 0) {
                                  memcpy(cvp->s_data_payload, ctd.tcpct_value,
                                         ctd.tcpct_used);
                                  cvp->s_data_desired = ctd.tcpct_used;
                                  cvp->s_data_constant = 1; /* true */
                          } else {
                                  /* No constant payload data. */
                                  cvp->s_data_desired = ctd.tcpct_s_data_desired;
                                  cvp->s_data_constant = 0; /* false */
                          }
  
                          tp->cookie_values = cvp;
                  }
                  release_sock(sk);
                  return err;
          }
          default:
                  /* fallthru */
                  break;
          }
  
          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 < TCP_MIN_MSS || val > MAX_TCP_WINDOW) {
                          err = -EINVAL;
                          break;
                  }
                  tp->rx_opt.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);
                  } else {
                          tp->nonagle &= ~TCP_NAGLE_OFF;
                  }
                  break;
  
          case TCP_THIN_LINEAR_TIMEOUTS:
                  if (val < 0 || val > 1)
                          err = -EINVAL;
                  else
                          tp->thin_lto = val;
                  break;
  
          case TCP_THIN_DUPACK:
                  if (val < 0 || val > 1)
                          err = -EINVAL;
                  else
                          tp->thin_dupack = val;
                          if (tp->thin_dupack)
                                  tcp_disable_early_retrans(tp);
                  break;
  
          case TCP_REPAIR:
                  if (!tcp_can_repair_sock(sk))
                          err = -EPERM;
                  else if (val == 1) {
                          tp->repair = 1;
                          sk->sk_reuse = SK_FORCE_REUSE;
                          tp->repair_queue = TCP_NO_QUEUE;
                  } else if (val == 0) {
                          tp->repair = 0;
                          sk->sk_reuse = SK_NO_REUSE;
                          tcp_send_window_probe(sk);
                  } else
                          err = -EINVAL;
  
                  break;
  
          case TCP_REPAIR_QUEUE:
                  if (!tp->repair)
                          err = -EPERM;
                  else if (val < TCP_QUEUES_NR)
                          tp->repair_queue = val;
                  else
                          err = -EINVAL;
                  break;
  
          case TCP_QUEUE_SEQ:
                  if (sk->sk_state != TCP_CLOSE)
                          err = -EPERM;
                  else if (tp->repair_queue == TCP_SEND_QUEUE)
                          tp->write_seq = val;
                  else if (tp->repair_queue == TCP_RECV_QUEUE)
                          tp->rcv_nxt = val;
                  else
                          err = -EINVAL;
                  break;
  
          case TCP_REPAIR_OPTIONS:
                  if (!tp->repair)
                          err = -EINVAL;
                  else if (sk->sk_state == TCP_ESTABLISHED)
                          err = tcp_repair_options_est(tp,
                                          (struct tcp_repair_opt __user *)optval,
                                          optlen);
                  else
                          err = -EPERM;
                  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);
                  }
                  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 = keepalive_time_elapsed(tp);
                                  if (tp->keepalive_time > elapsed)
                                          elapsed = tp->keepalive_time - elapsed;
                                  else
                                          elapsed = 0;
                                  inet_csk_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
                          icsk->icsk_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:
                  /* Translate value in seconds to number of retransmits */
                  icsk->icsk_accept_queue.rskq_defer_accept =
                          secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
                                          TCP_RTO_MAX / HZ);
                  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) {
                          icsk->icsk_ack.pingpong = 1;
                  } else {
                          icsk->icsk_ack.pingpong = 0;
                          if ((1 << sk->sk_state) &
                              (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT) &&
                              inet_csk_ack_scheduled(sk)) {
                                  icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
                                  tcp_cleanup_rbuf(sk, 1);
                                  if (!(val & 1))
                                          icsk->icsk_ack.pingpong = 1;
                          }
                  }
                  break;
  
  #ifdef CONFIG_TCP_MD5SIG
          case TCP_MD5SIG:
                  /* Read the IP->Key mappings from userspace */
                  err = tp->af_specific->md5_parse(sk, optval, optlen);
                  break;
  #endif
          case TCP_USER_TIMEOUT:
                  /* Cap the max timeout in ms TCP will retry/retrans
                   * before giving up and aborting (ETIMEDOUT) a connection.
                   */
                  if (val < 0)
                          err = -EINVAL;
                  else
                          icsk->icsk_user_timeout = msecs_to_jiffies(val);
                  break;
  
          case TCP_FASTOPEN:
                  if (val >= 0 && ((1 << sk->sk_state) & (TCPF_CLOSE |
                      TCPF_LISTEN)))
                          err = fastopen_init_queue(sk, val);
                  else
                          err = -EINVAL;
                  break;
          default:
                  err = -ENOPROTOOPT;
                  break;
          }
  
          release_sock(sk);
          return err;
  }
  
  int tcp_setsockopt(struct sock *sk, int level, int optname, char __user *optval,
                     unsigned int optlen)
  {
          const struct inet_connection_sock *icsk = inet_csk(sk);
  
          if (level != SOL_TCP)
                  return icsk->icsk_af_ops->setsockopt(sk, level, optname,
                                                       optval, optlen);
          return do_tcp_setsockopt(sk, level, optname, optval, optlen);
  }
  EXPORT_SYMBOL(tcp_setsockopt);
  
  #ifdef CONFIG_COMPAT
  int compat_tcp_setsockopt(struct sock *sk, int level, int optname,
                            char __user *optval, unsigned int optlen)
  {
          if (level != SOL_TCP)
                  return inet_csk_compat_setsockopt(sk, level, optname,
                                                    optval, optlen);
          return do_tcp_setsockopt(sk, level, optname, optval, optlen);
  }
  EXPORT_SYMBOL(compat_tcp_setsockopt);
  #endif
  
  /* Return information about state of tcp endpoint in API format. */
  void tcp_get_info(const struct sock *sk, struct tcp_info *info)
  {
          const struct tcp_sock *tp = tcp_sk(sk);
          const struct inet_connection_sock *icsk = inet_csk(sk);
          u32 now = tcp_time_stamp;
  
          memset(info, 0, sizeof(*info));
  
          info->tcpi_state = sk->sk_state;
          info->tcpi_ca_state = icsk->icsk_ca_state;
          info->tcpi_retransmits = icsk->icsk_retransmits;
          info->tcpi_probes = icsk->icsk_probes_out;
          info->tcpi_backoff = icsk->icsk_backoff;
  
          if (tp->rx_opt.tstamp_ok)
                  info->tcpi_options |= TCPI_OPT_TIMESTAMPS;
          if (tcp_is_sack(tp))
                  info->tcpi_options |= TCPI_OPT_SACK;
          if (tp->rx_opt.wscale_ok) {
                  info->tcpi_options |= TCPI_OPT_WSCALE;
                  info->tcpi_snd_wscale = tp->rx_opt.snd_wscale;
                  info->tcpi_rcv_wscale = tp->rx_opt.rcv_wscale;
          }
  
          if (tp->ecn_flags & TCP_ECN_OK)
                  info->tcpi_options |= TCPI_OPT_ECN;
          if (tp->ecn_flags & TCP_ECN_SEEN)
                  info->tcpi_options |= TCPI_OPT_ECN_SEEN;
          if (tp->syn_data_acked)
                  info->tcpi_options |= TCPI_OPT_SYN_DATA;
  
          info->tcpi_rto = jiffies_to_usecs(icsk->icsk_rto);
          info->tcpi_ato = jiffies_to_usecs(icsk->icsk_ack.ato);
          info->tcpi_snd_mss = tp->mss_cache;
          info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss;
  
          if (sk->sk_state == TCP_LISTEN) {
                  info->tcpi_unacked = sk->sk_ack_backlog;
                  info->tcpi_sacked = sk->sk_max_ack_backlog;
          } else {
                  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 = jiffies_to_msecs(now - tp->lsndtime);
          info->tcpi_last_data_recv = jiffies_to_msecs(now - icsk->icsk_ack.lrcvtime);
          info->tcpi_last_ack_recv = jiffies_to_msecs(now - tp->rcv_tstamp);
  
          info->tcpi_pmtu = icsk->icsk_pmtu_cookie;
          info->tcpi_rcv_ssthresh = tp->rcv_ssthresh;
          info->tcpi_rtt = jiffies_to_usecs(tp->srtt)>>3;
          info->tcpi_rttvar = jiffies_to_usecs(tp->mdev)>>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;
  
          info->tcpi_rcv_rtt = jiffies_to_usecs(tp->rcv_rtt_est.rtt)>>3;
          info->tcpi_rcv_space = tp->rcvq_space.space;
  
          info->tcpi_total_retrans = tp->total_retrans;
  }
  EXPORT_SYMBOL_GPL(tcp_get_info);
  
  static int do_tcp_getsockopt(struct sock *sk, int level,
                  int optname, char __user *optval, int __user *optlen)
  {
          struct inet_connection_sock *icsk = inet_csk(sk);
          struct tcp_sock *tp = tcp_sk(sk);
          int val, len;
  
          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;
                  if (!val && ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
                          val = tp->rx_opt.user_mss;
                  if (tp->repair)
                          val = tp->rx_opt.mss_clamp;
                  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 = keepalive_time_when(tp) / HZ;
                  break;
          case TCP_KEEPINTVL:
                  val = keepalive_intvl_when(tp) / HZ;
                  break;
          case TCP_KEEPCNT:
                  val = keepalive_probes(tp);
                  break;
          case TCP_SYNCNT:
                  val = icsk->icsk_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 = retrans_to_secs(icsk->icsk_accept_queue.rskq_defer_accept,
                                        TCP_TIMEOUT_INIT / HZ, TCP_RTO_MAX / HZ);
                  break;
          case TCP_WINDOW_CLAMP:
                  val = tp->window_clamp;
                  break;
          case TCP_INFO: {
                  struct tcp_info info;
  
                  if (get_user(len, optlen))
                          return -EFAULT;
  
                  tcp_get_info(sk, &info);
  
                  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 = !icsk->icsk_ack.pingpong;
                  break;
  
          case TCP_CONGESTION:
                  if (get_user(len, optlen))
                          return -EFAULT;
                  len = min_t(unsigned int, len, TCP_CA_NAME_MAX);
                  if (put_user(len, optlen))
                          return -EFAULT;
                  if (copy_to_user(optval, icsk->icsk_ca_ops->name, len))
                          return -EFAULT;
                  return 0;
  
          case TCP_COOKIE_TRANSACTIONS: {
                  struct tcp_cookie_transactions ctd;
                  struct tcp_cookie_values *cvp = tp->cookie_values;
  
                  if (get_user(len, optlen))
                          return -EFAULT;
                  if (len < sizeof(ctd))
                          return -EINVAL;
  
                  memset(&ctd, 0, sizeof(ctd));
                  ctd.tcpct_flags = (tp->rx_opt.cookie_in_always ?
                                     TCP_COOKIE_IN_ALWAYS : 0)
                                  | (tp->rx_opt.cookie_out_never ?
                                     TCP_COOKIE_OUT_NEVER : 0);
  
                  if (cvp != NULL) {
                          ctd.tcpct_flags |= (cvp->s_data_in ?
                                              TCP_S_DATA_IN : 0)
                                           | (cvp->s_data_out ?
                                              TCP_S_DATA_OUT : 0);
  
                          ctd.tcpct_cookie_desired = cvp->cookie_desired;
                          ctd.tcpct_s_data_desired = cvp->s_data_desired;
  
                          memcpy(&ctd.tcpct_value[0], &cvp->cookie_pair[0],
                                 cvp->cookie_pair_size);
                          ctd.tcpct_used = cvp->cookie_pair_size;
                  }
  
                  if (put_user(sizeof(ctd), optlen))
                          return -EFAULT;
                  if (copy_to_user(optval, &ctd, sizeof(ctd)))
                          return -EFAULT;
                  return 0;
          }
          case TCP_THIN_LINEAR_TIMEOUTS:
                  val = tp->thin_lto;
                  break;
          case TCP_THIN_DUPACK:
                  val = tp->thin_dupack;
                  break;
  
          case TCP_REPAIR:
                  val = tp->repair;
                  break;
  
          case TCP_REPAIR_QUEUE:
                  if (tp->repair)
                          val = tp->repair_queue;
                  else
                          return -EINVAL;
                  break;
  
          case TCP_QUEUE_SEQ:
                  if (tp->repair_queue == TCP_SEND_QUEUE)
                          val = tp->write_seq;
                  else if (tp->repair_queue == TCP_RECV_QUEUE)
                          val = tp->rcv_nxt;
                  else
                          return -EINVAL;
                  break;
  
          case TCP_USER_TIMEOUT:
                  val = jiffies_to_msecs(icsk->icsk_user_timeout);
                  break;
          default:
                  return -ENOPROTOOPT;
          }
  
          if (put_user(len, optlen))
                  return -EFAULT;
          if (copy_to_user(optval, &val, len))
                  return -EFAULT;
          return 0;
  }
  
  int tcp_getsockopt(struct sock *sk, int level, int optname, char __user *optval,
                     int __user *optlen)
  {
          struct inet_connection_sock *icsk = inet_csk(sk);
  
          if (level != SOL_TCP)
                  return icsk->icsk_af_ops->getsockopt(sk, level, optname,
                                                       optval, optlen);
          return do_tcp_getsockopt(sk, level, optname, optval, optlen);
  }
  EXPORT_SYMBOL(tcp_getsockopt);
  
  #ifdef CONFIG_COMPAT
  int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
                            char __user *optval, int __user *optlen)
  {
          if (level != SOL_TCP)
                  return inet_csk_compat_getsockopt(sk, level, optname,
                                                    optval, optlen);
          return do_tcp_getsockopt(sk, level, optname, optval, optlen);
  }
  EXPORT_SYMBOL(compat_tcp_getsockopt);
  #endif
  
  struct sk_buff *tcp_tso_segment(struct sk_buff *skb,
          netdev_features_t features)
  {
          struct sk_buff *segs = ERR_PTR(-EINVAL);
          struct tcphdr *th;
          unsigned int thlen;
          unsigned int seq;
          __be32 delta;
          unsigned int oldlen;
          unsigned int mss;
  
          if (!pskb_may_pull(skb, sizeof(*th)))
                  goto out;
  
          th = tcp_hdr(skb);
          thlen = th->doff * 4;
          if (thlen < sizeof(*th))
                  goto out;
  
          if (!pskb_may_pull(skb, thlen))
                  goto out;
  
          oldlen = (u16)~skb->len;
          __skb_pull(skb, thlen);
  
          mss = skb_shinfo(skb)->gso_size;
          if (unlikely(skb->len <= mss))
                  goto out;
  
          if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) {
                  /* Packet is from an untrusted source, reset gso_segs. */
                  int type = skb_shinfo(skb)->gso_type;
  
                  if (unlikely(type &
                               ~(SKB_GSO_TCPV4 |
                                 SKB_GSO_DODGY |
                                 SKB_GSO_TCP_ECN |
                                 SKB_GSO_TCPV6 |
                                 0) ||
                               !(type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))))
                          goto out;
  
                  skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss);
  
                  segs = NULL;
                  goto out;
          }
  
          segs = skb_segment(skb, features);
          if (IS_ERR(segs))
                  goto out;
  
          delta = htonl(oldlen + (thlen + mss));
  
          skb = segs;
          th = tcp_hdr(skb);
          seq = ntohl(th->seq);
  
          do {
                  th->fin = th->psh = 0;
  
                  th->check = ~csum_fold((__force __wsum)((__force u32)th->check +
                                         (__force u32)delta));
                  if (skb->ip_summed != CHECKSUM_PARTIAL)
                          th->check =
                               csum_fold(csum_partial(skb_transport_header(skb),
                                                      thlen, skb->csum));
  
                  seq += mss;
                  skb = skb->next;
                  th = tcp_hdr(skb);
  
                  th->seq = htonl(seq);
                  th->cwr = 0;
          } while (skb->next);
  
          delta = htonl(oldlen + (skb->tail - skb->transport_header) +
                        skb->data_len);
          th->check = ~csum_fold((__force __wsum)((__force u32)th->check +
                                  (__force u32)delta));
          if (skb->ip_summed != CHECKSUM_PARTIAL)
                  th->check = csum_fold(csum_partial(skb_transport_header(skb),
                                                     thlen, skb->csum));
  
  out:
          return segs;
  }
  EXPORT_SYMBOL(tcp_tso_segment);
  
  struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb)
  {
          struct sk_buff **pp = NULL;
          struct sk_buff *p;
          struct tcphdr *th;
          struct tcphdr *th2;
          unsigned int len;
          unsigned int thlen;
          __be32 flags;
          unsigned int mss = 1;
          unsigned int hlen;
          unsigned int off;
          int flush = 1;
          int i;
  
          off = skb_gro_offset(skb);
          hlen = off + sizeof(*th);
          th = skb_gro_header_fast(skb, off);
          if (skb_gro_header_hard(skb, hlen)) {
                  th = skb_gro_header_slow(skb, hlen, off);
                  if (unlikely(!th))
                          goto out;
          }
  
          thlen = th->doff * 4;
          if (thlen < sizeof(*th))
                  goto out;
  
          hlen = off + thlen;
          if (skb_gro_header_hard(skb, hlen)) {
                  th = skb_gro_header_slow(skb, hlen, off);
                  if (unlikely(!th))
                          goto out;
          }
  
          skb_gro_pull(skb, thlen);
  
          len = skb_gro_len(skb);
          flags = tcp_flag_word(th);
  
          for (; (p = *head); head = &p->next) {
                  if (!NAPI_GRO_CB(p)->same_flow)
                          continue;
  
                  th2 = tcp_hdr(p);
  
                  if (*(u32 *)&th->source ^ *(u32 *)&th2->source) {
                          NAPI_GRO_CB(p)->same_flow = 0;
                          continue;
                  }
  
                  goto found;
          }
  
          goto out_check_final;
  
  found:
          flush = NAPI_GRO_CB(p)->flush;
          flush |= (__force int)(flags & TCP_FLAG_CWR);
          flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
                    ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));
          flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
          for (i = sizeof(*th); i < thlen; i += 4)
                  flush |= *(u32 *)((u8 *)th + i) ^
                           *(u32 *)((u8 *)th2 + i);
  
          mss = skb_shinfo(p)->gso_size;
  
          flush |= (len - 1) >= mss;
          flush |= (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq);
  
          if (flush || skb_gro_receive(head, skb)) {
                  mss = 1;
                  goto out_check_final;
          }
  
          p = *head;
          th2 = tcp_hdr(p);
          tcp_flag_word(th2) |= flags & (TCP_FLAG_FIN | TCP_FLAG_PSH);
  
  out_check_final:
          flush = len < mss;
          flush |= (__force int)(flags & (TCP_FLAG_URG | TCP_FLAG_PSH |
                                          TCP_FLAG_RST | TCP_FLAG_SYN |
                                          TCP_FLAG_FIN));
  
          if (p && (!NAPI_GRO_CB(skb)->same_flow || flush))
                  pp = head;
  
  out:
          NAPI_GRO_CB(skb)->flush |= flush;
  
          return pp;
  }
  EXPORT_SYMBOL(tcp_gro_receive);
  
  int tcp_gro_complete(struct sk_buff *skb)
  {
          struct tcphdr *th = tcp_hdr(skb);
  
          skb->csum_start = skb_transport_header(skb) - skb->head;
          skb->csum_offset = offsetof(struct tcphdr, check);
          skb->ip_summed = CHECKSUM_PARTIAL;
  
          skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
  
          if (th->cwr)
                  skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
  
          return 0;
  }
  EXPORT_SYMBOL(tcp_gro_complete);
  
  #ifdef CONFIG_TCP_MD5SIG
  static unsigned long tcp_md5sig_users;
  static struct tcp_md5sig_pool __percpu *tcp_md5sig_pool;
  static DEFINE_SPINLOCK(tcp_md5sig_pool_lock);
  
  static void __tcp_free_md5sig_pool(struct tcp_md5sig_pool __percpu *pool)
  {
          int cpu;
  
          for_each_possible_cpu(cpu) {
                  struct tcp_md5sig_pool *p = per_cpu_ptr(pool, cpu);
  
                  if (p->md5_desc.tfm)
                          crypto_free_hash(p->md5_desc.tfm);
          }
          free_percpu(pool);
  }
  
  void tcp_free_md5sig_pool(void)
  {
          struct tcp_md5sig_pool __percpu *pool = NULL;
  
          spin_lock_bh(&tcp_md5sig_pool_lock);
          if (--tcp_md5sig_users == 0) {
                  pool = tcp_md5sig_pool;
                  tcp_md5sig_pool = NULL;
          }
          spin_unlock_bh(&tcp_md5sig_pool_lock);
          if (pool)
                  __tcp_free_md5sig_pool(pool);
  }
  EXPORT_SYMBOL(tcp_free_md5sig_pool);
  
  static struct tcp_md5sig_pool __percpu *
  __tcp_alloc_md5sig_pool(struct sock *sk)
  {
          int cpu;
          struct tcp_md5sig_pool __percpu *pool;
  
          pool = alloc_percpu(struct tcp_md5sig_pool);
          if (!pool)
                  return NULL;
  
          for_each_possible_cpu(cpu) {
                  struct crypto_hash *hash;
  
                  hash = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC);
                  if (!hash || IS_ERR(hash))
                          goto out_free;
  
                  per_cpu_ptr(pool, cpu)->md5_desc.tfm = hash;
          }
          return pool;
  out_free:
          __tcp_free_md5sig_pool(pool);
          return NULL;
  }
  
  struct tcp_md5sig_pool __percpu *tcp_alloc_md5sig_pool(struct sock *sk)
  {
          struct tcp_md5sig_pool __percpu *pool;
          bool alloc = false;
  
  retry:
          spin_lock_bh(&tcp_md5sig_pool_lock);
          pool = tcp_md5sig_pool;
          if (tcp_md5sig_users++ == 0) {
                  alloc = true;
                  spin_unlock_bh(&tcp_md5sig_pool_lock);
          } else if (!pool) {
                  tcp_md5sig_users--;
                  spin_unlock_bh(&tcp_md5sig_pool_lock);
                  cpu_relax();
                  goto retry;
          } else
                  spin_unlock_bh(&tcp_md5sig_pool_lock);
  
          if (alloc) {
                  /* we cannot hold spinlock here because this may sleep. */
                  struct tcp_md5sig_pool __percpu *p;
  
                  p = __tcp_alloc_md5sig_pool(sk);
                  spin_lock_bh(&tcp_md5sig_pool_lock);
                  if (!p) {
                          tcp_md5sig_users--;
                          spin_unlock_bh(&tcp_md5sig_pool_lock);
                          return NULL;
                  }
                  pool = tcp_md5sig_pool;
                  if (pool) {
                          /* oops, it has already been assigned. */
                          spin_unlock_bh(&tcp_md5sig_pool_lock);
                          __tcp_free_md5sig_pool(p);
                  } else {
                          tcp_md5sig_pool = pool = p;
                          spin_unlock_bh(&tcp_md5sig_pool_lock);
                  }
          }
          return pool;
  }
  EXPORT_SYMBOL(tcp_alloc_md5sig_pool);
  
  
  /**
   *      tcp_get_md5sig_pool - get md5sig_pool for this user
   *
   *      We use percpu structure, so if we succeed, we exit with preemption
   *      and BH disabled, to make sure another thread or softirq handling
   *      wont try to get same context.
   */
  struct tcp_md5sig_pool *tcp_get_md5sig_pool(void)
  {
          struct tcp_md5sig_pool __percpu *p;
  
          local_bh_disable();
  
          spin_lock(&tcp_md5sig_pool_lock);
          p = tcp_md5sig_pool;
          if (p)
                  tcp_md5sig_users++;
          spin_unlock(&tcp_md5sig_pool_lock);
  
          if (p)
                  return this_cpu_ptr(p);
  
          local_bh_enable();
          return NULL;
  }
  EXPORT_SYMBOL(tcp_get_md5sig_pool);
  
  void tcp_put_md5sig_pool(void)
  {
          local_bh_enable();
          tcp_free_md5sig_pool();
  }
  EXPORT_SYMBOL(tcp_put_md5sig_pool);
  
  int tcp_md5_hash_header(struct tcp_md5sig_pool *hp,
                          const struct tcphdr *th)
  {
          struct scatterlist sg;
          struct tcphdr hdr;
          int err;
  
          /* We are not allowed to change tcphdr, make a local copy */
          memcpy(&hdr, th, sizeof(hdr));
          hdr.check = 0;
  
          /* options aren't included in the hash */
          sg_init_one(&sg, &hdr, sizeof(hdr));
          err = crypto_hash_update(&hp->md5_desc, &sg, sizeof(hdr));
          return err;
  }
  EXPORT_SYMBOL(tcp_md5_hash_header);
  
  int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *hp,
                            const struct sk_buff *skb, unsigned int header_len)
  {
          struct scatterlist sg;
          const struct tcphdr *tp = tcp_hdr(skb);
          struct hash_desc *desc = &hp->md5_desc;
          unsigned int i;
          const unsigned int head_data_len = skb_headlen(skb) > header_len ?
                                             skb_headlen(skb) - header_len : 0;
          const struct skb_shared_info *shi = skb_shinfo(skb);
          struct sk_buff *frag_iter;
  
          sg_init_table(&sg, 1);
  
          sg_set_buf(&sg, ((u8 *) tp) + header_len, head_data_len);
          if (crypto_hash_update(desc, &sg, head_data_len))
                  return 1;
  
          for (i = 0; i < shi->nr_frags; ++i) {
                  const struct skb_frag_struct *f = &shi->frags[i];
                  struct page *page = skb_frag_page(f);
                  sg_set_page(&sg, page, skb_frag_size(f), f->page_offset);
                  if (crypto_hash_update(desc, &sg, skb_frag_size(f)))
                          return 1;
          }
  
          skb_walk_frags(skb, frag_iter)
                  if (tcp_md5_hash_skb_data(hp, frag_iter, 0))
                          return 1;
  
          return 0;
  }
  EXPORT_SYMBOL(tcp_md5_hash_skb_data);
  
  int tcp_md5_hash_key(struct tcp_md5sig_pool *hp, const struct tcp_md5sig_key *key)
  {
          struct scatterlist sg;
  
          sg_init_one(&sg, key->key, key->keylen);
          return crypto_hash_update(&hp->md5_desc, &sg, key->keylen);
  }
  EXPORT_SYMBOL(tcp_md5_hash_key);
  
  #endif
  
  /* Each Responder maintains up to two secret values concurrently for
   * efficient secret rollover.  Each secret value has 4 states:
   *
   * Generating.  (tcp_secret_generating != tcp_secret_primary)
   *    Generates new Responder-Cookies, but not yet used for primary
   *    verification.  This is a short-term state, typically lasting only
   *    one round trip time (RTT).
   *
   * Primary.  (tcp_secret_generating == tcp_secret_primary)
   *    Used both for generation and primary verification.
   *
   * Retiring.  (tcp_secret_retiring != tcp_secret_secondary)
   *    Used for verification, until the first failure that can be
   *    verified by the newer Generating secret.  At that time, this
   *    cookie's state is changed to Secondary, and the Generating
   *    cookie's state is changed to Primary.  This is a short-term state,
   *    typically lasting only one round trip time (RTT).
   *
   * Secondary.  (tcp_secret_retiring == tcp_secret_secondary)
   *    Used for secondary verification, after primary verification
   *    failures.  This state lasts no more than twice the Maximum Segment
   *    Lifetime (2MSL).  Then, the secret is discarded.
   */
  struct tcp_cookie_secret {
          /* The secret is divided into two parts.  The digest part is the
           * equivalent of previously hashing a secret and saving the state,
           * and serves as an initialization vector (IV).  The message part
           * serves as the trailing secret.
           */
          u32                             secrets[COOKIE_WORKSPACE_WORDS];
          unsigned long                   expires;
  };
  
  #define TCP_SECRET_1MSL (HZ * TCP_PAWS_MSL)
  #define TCP_SECRET_2MSL (HZ * TCP_PAWS_MSL * 2)
  #define TCP_SECRET_LIFE (HZ * 600)
  
  static struct tcp_cookie_secret tcp_secret_one;
  static struct tcp_cookie_secret tcp_secret_two;
  
  /* Essentially a circular list, without dynamic allocation. */
  static struct tcp_cookie_secret *tcp_secret_generating;
  static struct tcp_cookie_secret *tcp_secret_primary;
  static struct tcp_cookie_secret *tcp_secret_retiring;
  static struct tcp_cookie_secret *tcp_secret_secondary;
  
  static DEFINE_SPINLOCK(tcp_secret_locker);
  
  /* Select a pseudo-random word in the cookie workspace.
   */
  static inline u32 tcp_cookie_work(const u32 *ws, const int n)
  {
          return ws[COOKIE_DIGEST_WORDS + ((COOKIE_MESSAGE_WORDS-1) & ws[n])];
  }
  
  /* Fill bakery[COOKIE_WORKSPACE_WORDS] with generator, updating as needed.
   * Called in softirq context.
   * Returns: 0 for success.
   */
  int tcp_cookie_generator(u32 *bakery)
  {
          unsigned long jiffy = jiffies;
  
          if (unlikely(time_after_eq(jiffy, tcp_secret_generating->expires))) {
                  spin_lock_bh(&tcp_secret_locker);
                  if (!time_after_eq(jiffy, tcp_secret_generating->expires)) {
                          /* refreshed by another */
                          memcpy(bakery,
                                 &tcp_secret_generating->secrets[0],
                                 COOKIE_WORKSPACE_WORDS);
                  } else {
                          /* still needs refreshing */
                          get_random_bytes(bakery, COOKIE_WORKSPACE_WORDS);
  
                          /* The first time, paranoia assumes that the
                           * randomization function isn't as strong.  But,
                           * this secret initialization is delayed until
                           * the last possible moment (packet arrival).
                           * Although that time is observable, it is
                           * unpredictably variable.  Mash in the most
                           * volatile clock bits available, and expire the
                           * secret extra quickly.
                           */
                          if (unlikely(tcp_secret_primary->expires ==
                                       tcp_secret_secondary->expires)) {
                                  struct timespec tv;
  
                                  getnstimeofday(&tv);
                                  bakery[COOKIE_DIGEST_WORDS+0] ^=
                                          (u32)tv.tv_nsec;
  
                                  tcp_secret_secondary->expires = jiffy
                                          + TCP_SECRET_1MSL
                                          + (0x0f & tcp_cookie_work(bakery, 0));
                          } else {
                                  tcp_secret_secondary->expires = jiffy
                                          + TCP_SECRET_LIFE
                                          + (0xff & tcp_cookie_work(bakery, 1));
                                  tcp_secret_primary->expires = jiffy
                                          + TCP_SECRET_2MSL
                                          + (0x1f & tcp_cookie_work(bakery, 2));
                          }
                          memcpy(&tcp_secret_secondary->secrets[0],
                                 bakery, COOKIE_WORKSPACE_WORDS);
  
                          rcu_assign_pointer(tcp_secret_generating,
                                             tcp_secret_secondary);
                          rcu_assign_pointer(tcp_secret_retiring,
                                             tcp_secret_primary);
                          /*
                           * Neither call_rcu() nor synchronize_rcu() needed.
                           * Retiring data is not freed.  It is replaced after
                           * further (locked) pointer updates, and a quiet time
                           * (minimum 1MSL, maximum LIFE - 2MSL).
                           */
                  }
                  spin_unlock_bh(&tcp_secret_locker);
          } else {
                  rcu_read_lock_bh();
                  memcpy(bakery,
                         &rcu_dereference(tcp_secret_generating)->secrets[0],
                         COOKIE_WORKSPACE_WORDS);
                  rcu_read_unlock_bh();
          }
          return 0;
  }
  EXPORT_SYMBOL(tcp_cookie_generator);
  
  void tcp_done(struct sock *sk)
  {
          struct request_sock *req = tcp_sk(sk)->fastopen_rsk;
  
          if (sk->sk_state == TCP_SYN_SENT || sk->sk_state == TCP_SYN_RECV)
                  TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_ATTEMPTFAILS);
  
          tcp_set_state(sk, TCP_CLOSE);
          tcp_clear_xmit_timers(sk);
          if (req != NULL)
                  reqsk_fastopen_remove(sk, req, false);
  
          sk->sk_shutdown = SHUTDOWN_MASK;
  
          if (!sock_flag(sk, SOCK_DEAD))
                  sk->sk_state_change(sk);
          else
                  inet_csk_destroy_sock(sk);
  }
  EXPORT_SYMBOL_GPL(tcp_done);
  
  extern struct tcp_congestion_ops tcp_reno;
  
  static __initdata unsigned long thash_entries;
  static int __init set_thash_entries(char *str)
  {
          ssize_t ret;
  
          if (!str)
                  return 0;
  
          ret = kstrtoul(str, 0, &thash_entries);
          if (ret)
                  return 0;
  
          return 1;
  }
  __setup("thash_entries=", set_thash_entries);
  
  void tcp_init_mem(struct net *net)
  {
          unsigned long limit = nr_free_buffer_pages() / 8;
          limit = max(limit, 128UL);
          net->ipv4.sysctl_tcp_mem[0] = limit / 4 * 3;
          net->ipv4.sysctl_tcp_mem[1] = limit;
          net->ipv4.sysctl_tcp_mem[2] = net->ipv4.sysctl_tcp_mem[0] * 2;
  }
  
  void __init tcp_init(void)
  {
          struct sk_buff *skb = NULL;
          unsigned long limit;
          int max_rshare, max_wshare, cnt;
          unsigned int i;
          unsigned long jiffy = jiffies;
  
          BUILD_BUG_ON(sizeof(struct tcp_skb_cb) > sizeof(skb->cb));
  
          percpu_counter_init(&tcp_sockets_allocated, 0);
          percpu_counter_init(&tcp_orphan_count, 0);
          tcp_hashinfo.bind_bucket_cachep =
                  kmem_cache_create("tcp_bind_bucket",
                                    sizeof(struct inet_bind_bucket), 0,
                                    SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
  
          /* Size and allocate the main established and bind bucket
           * hash tables.
           *
           * The methodology is similar to that of the buffer cache.
           */
          tcp_hashinfo.ehash =
                  alloc_large_system_hash("TCP established",
                                          sizeof(struct inet_ehash_bucket),
                                          thash_entries,
                                          17, /* one slot per 128 KB of memory */
                                          0,
                                          NULL,
                                          &tcp_hashinfo.ehash_mask,
                                          0,
                                          thash_entries ? 0 : 512 * 1024);
          for (i = 0; i <= tcp_hashinfo.ehash_mask; i++) {
                  INIT_HLIST_NULLS_HEAD(&tcp_hashinfo.ehash[i].chain, i);
                  INIT_HLIST_NULLS_HEAD(&tcp_hashinfo.ehash[i].twchain, i);
          }
          if (inet_ehash_locks_alloc(&tcp_hashinfo))
                  panic("TCP: failed to alloc ehash_locks");
          tcp_hashinfo.bhash =
                  alloc_large_system_hash("TCP bind",
                                          sizeof(struct inet_bind_hashbucket),
                                          tcp_hashinfo.ehash_mask + 1,
                                          17, /* one slot per 128 KB of memory */
                                          0,
                                          &tcp_hashinfo.bhash_size,
                                          NULL,
                                          0,
                                          64 * 1024);
          tcp_hashinfo.bhash_size = 1U << tcp_hashinfo.bhash_size;
          for (i = 0; i < tcp_hashinfo.bhash_size; i++) {
                  spin_lock_init(&tcp_hashinfo.bhash[i].lock);
                  INIT_HLIST_HEAD(&tcp_hashinfo.bhash[i].chain);
          }
  
  
          cnt = tcp_hashinfo.ehash_mask + 1;
  
          tcp_death_row.sysctl_max_tw_buckets = cnt / 2;
          sysctl_tcp_max_orphans = cnt / 2;
          sysctl_max_syn_backlog = max(128, cnt / 256);
  
          tcp_init_mem(&init_net);
          /* Set per-socket limits to no more than 1/128 the pressure threshold */
          limit = nr_free_buffer_pages() << (PAGE_SHIFT - 7);
          max_wshare = min(4UL*1024*1024, limit);
          max_rshare = min(6UL*1024*1024, limit);
  
          sysctl_tcp_wmem[0] = SK_MEM_QUANTUM;
          sysctl_tcp_wmem[1] = 16*1024;
          sysctl_tcp_wmem[2] = max(64*1024, max_wshare);
  
          sysctl_tcp_rmem[0] = SK_MEM_QUANTUM;
          sysctl_tcp_rmem[1] = 87380;
          sysctl_tcp_rmem[2] = max(87380, max_rshare);
  
          pr_info("Hash tables configured (established %u bind %u)\n",
                  tcp_hashinfo.ehash_mask + 1, tcp_hashinfo.bhash_size);
  
          tcp_metrics_init();
  
          tcp_register_congestion_control(&tcp_reno);
  
          memset(&tcp_secret_one.secrets[0], 0, sizeof(tcp_secret_one.secrets));
          memset(&tcp_secret_two.secrets[0], 0, sizeof(tcp_secret_two.secrets));
          tcp_secret_one.expires = jiffy; /* past due */
          tcp_secret_two.expires = jiffy; /* past due */
          tcp_secret_generating = &tcp_secret_one;
          tcp_secret_primary = &tcp_secret_one;
          tcp_secret_retiring = &tcp_secret_two;
          tcp_secret_secondary = &tcp_secret_two;
          tcp_tasklet_init();
  }