include/linux/tcp.h

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2 /*
   3  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   4  *              operating system.  INET is implemented using the  BSD Socket
   5  *              interface as the means of communication with the user level.
   6  *
   7  *              Definitions for the TCP protocol.
   8  *
   9  * Version:     @(#)tcp.h       1.0.2   04/28/93
  10  *
  11  * Author:      Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  12  */
  13 #ifndef _LINUX_TCP_H
  14 #define _LINUX_TCP_H
  15
  16
  17 #include <linux/skbuff.h>
  18 #include <linux/win_minmax.h>
  19 #include <net/sock.h>
  20 #include <net/inet_connection_sock.h>
  21 #include <net/inet_timewait_sock.h>
  22 #include <uapi/linux/tcp.h>
  23
  24 static inline struct tcphdr *tcp_hdr(const struct sk_buff *skb)
  25 {
  26         return (struct tcphdr *)skb_transport_header(skb);
  27 }
  28
  29 static inline unsigned int __tcp_hdrlen(const struct tcphdr *th)
  30 {
  31         return th->doff * 4;
  32 }
  33
  34 static inline unsigned int tcp_hdrlen(const struct sk_buff *skb)
  35 {
  36         return __tcp_hdrlen(tcp_hdr(skb));
  37 }
  38
  39 static inline struct tcphdr *inner_tcp_hdr(const struct sk_buff *skb)
  40 {
  41         return (struct tcphdr *)skb_inner_transport_header(skb);
  42 }
  43
  44 static inline unsigned int inner_tcp_hdrlen(const struct sk_buff *skb)
  45 {
  46         return inner_tcp_hdr(skb)->doff * 4;
  47 }
  48
  49 static inline unsigned int tcp_optlen(const struct sk_buff *skb)
  50 {
  51         return (tcp_hdr(skb)->doff - 5) * 4;
  52 }
  53
  54 /* TCP Fast Open */
  55 #define TCP_FASTOPEN_COOKIE_MIN 4       /* Min Fast Open Cookie size in bytes */
  56 #define TCP_FASTOPEN_COOKIE_MAX 16      /* Max Fast Open Cookie size in bytes */
  57 #define TCP_FASTOPEN_COOKIE_SIZE 8      /* the size employed by this impl. */
  58
  59 /* TCP Fast Open Cookie as stored in memory */
  60 struct tcp_fastopen_cookie {
  61         __le64  val[DIV_ROUND_UP(TCP_FASTOPEN_COOKIE_MAX, sizeof(u64))];
  62         s8      len;
  63         bool    exp;    /* In RFC6994 experimental option format */
  64 };
  65
  66 /* This defines a selective acknowledgement block. */
  67 struct tcp_sack_block_wire {
  68         __be32  start_seq;
  69         __be32  end_seq;
  70 };
  71
  72 struct tcp_sack_block {
  73         u32     start_seq;
  74         u32     end_seq;
  75 };
  76
  77 /*These are used to set the sack_ok field in struct tcp_options_received */
  78 #define TCP_SACK_SEEN     (1 << 0)   /*1 = peer is SACK capable, */
  79 #define TCP_DSACK_SEEN    (1 << 2)   /*1 = DSACK was received from peer*/
  80
  81 #if IS_ENABLED(CONFIG_MPTCP)
  82 struct mptcp_options_received {
  83         u64     sndr_key;
  84         u64     rcvr_key;
  85         u64     data_ack;
  86         u64     data_seq;
  87         u32     subflow_seq;
  88         u16     data_len;
  89         u16     mp_capable : 1,
  90                 mp_join : 1,
  91                 dss : 1,
  92                 add_addr : 1,
  93                 rm_addr : 1,
  94                 family : 4,
  95                 echo : 1,
  96                 backup : 1;
  97         u32     token;
  98         u32     nonce;
  99         u64     thmac;
 100         u8      hmac[20];
 101         u8      join_id;
 102         u8      use_map:1,
 103                 dsn64:1,
 104                 data_fin:1,
 105                 use_ack:1,
 106                 ack64:1,
 107                 mpc_map:1,
 108                 __unused:2;
 109         u8      addr_id;
 110         u8      rm_id;
 111         union {
 112                 struct in_addr  addr;
 113 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 114                 struct in6_addr addr6;
 115 #endif
 116         };
 117         u64     ahmac;
 118         u16     port;
 119 };
 120 #endif
 121
 122 struct tcp_options_received {
 123 /*      PAWS/RTTM data  */
 124         int     ts_recent_stamp;/* Time we stored ts_recent (for aging) */
 125         u32     ts_recent;      /* Time stamp to echo next              */
 126         u32     rcv_tsval;      /* Time stamp value                     */
 127         u32     rcv_tsecr;      /* Time stamp echo reply                */
 128         u16     saw_tstamp : 1, /* Saw TIMESTAMP on last packet         */
 129                 tstamp_ok : 1,  /* TIMESTAMP seen on SYN packet         */
 130                 dsack : 1,      /* D-SACK is scheduled                  */
 131                 wscale_ok : 1,  /* Wscale seen on SYN packet            */
 132                 sack_ok : 3,    /* SACK seen on SYN packet              */
 133                 smc_ok : 1,     /* SMC seen on SYN packet               */
 134                 snd_wscale : 4, /* Window scaling received from sender  */
 135                 rcv_wscale : 4; /* Window scaling to send to receiver   */
 136         u8      num_sacks;      /* Number of SACK blocks                */
 137         u16     user_mss;       /* mss requested by user in ioctl       */
 138         u16     mss_clamp;      /* Maximal mss, negotiated at connection setup */
 139 #if IS_ENABLED(CONFIG_MPTCP)
 140         struct mptcp_options_received   mptcp;
 141 #endif
 142 };
 143
 144 static inline void tcp_clear_options(struct tcp_options_received *rx_opt)
 145 {
 146         rx_opt->tstamp_ok = rx_opt->sack_ok = 0;
 147         rx_opt->wscale_ok = rx_opt->snd_wscale = 0;
 148 #if IS_ENABLED(CONFIG_SMC)
 149         rx_opt->smc_ok = 0;
 150 #endif
 151 #if IS_ENABLED(CONFIG_MPTCP)
 152         rx_opt->mptcp.mp_capable = 0;
 153         rx_opt->mptcp.mp_join = 0;
 154         rx_opt->mptcp.add_addr = 0;
 155         rx_opt->mptcp.rm_addr = 0;
 156         rx_opt->mptcp.dss = 0;
 157 #endif
 158 }
 159
 160 /* This is the max number of SACKS that we'll generate and process. It's safe
 161  * to increase this, although since:
 162  *   size = TCPOLEN_SACK_BASE_ALIGNED (4) + n * TCPOLEN_SACK_PERBLOCK (8)
 163  * only four options will fit in a standard TCP header */
 164 #define TCP_NUM_SACKS 4
 165
 166 struct tcp_request_sock_ops;
 167
 168 struct tcp_request_sock {
 169         struct inet_request_sock        req;
 170         const struct tcp_request_sock_ops *af_specific;
 171         u64                             snt_synack; /* first SYNACK sent time */
 172         bool                            tfo_listener;
 173         bool                            is_mptcp;
 174         u32                             txhash;
 175         u32                             rcv_isn;
 176         u32                             snt_isn;
 177         u32                             ts_off;
 178         u32                             last_oow_ack_time; /* last SYNACK */
 179         u32                             rcv_nxt; /* the ack # by SYNACK. For
 180                                                   * FastOpen it's the seq#
 181                                                   * after data-in-SYN.
 182                                                   */
 183 };
 184
 185 static inline struct tcp_request_sock *tcp_rsk(const struct request_sock *req)
 186 {
 187         return (struct tcp_request_sock *)req;
 188 }
 189
 190 struct tcp_sock {
 191         /* inet_connection_sock has to be the first member of tcp_sock */
 192         struct inet_connection_sock     inet_conn;
 193         u16     tcp_header_len; /* Bytes of tcp header to send          */
 194         u16     gso_segs;       /* Max number of segs per GSO packet    */
 195
 196 /*
 197  *      Header prediction flags
 198  *      0x5?10 << 16 + snd_wnd in net byte order
 199  */
 200         __be32  pred_flags;
 201
 202 /*
 203  *      RFC793 variables by their proper names. This means you can
 204  *      read the code and the spec side by side (and laugh ...)
 205  *      See RFC793 and RFC1122. The RFC writes these in capitals.
 206  */
 207         u64     bytes_received; /* RFC4898 tcpEStatsAppHCThruOctetsReceived
 208                                  * sum(delta(rcv_nxt)), or how many bytes
 209                                  * were acked.
 210                                  */
 211         u32     segs_in;        /* RFC4898 tcpEStatsPerfSegsIn
 212                                  * total number of segments in.
 213                                  */
 214         u32     data_segs_in;   /* RFC4898 tcpEStatsPerfDataSegsIn
 215                                  * total number of data segments in.
 216                                  */
 217         u32     rcv_nxt;        /* What we want to receive next         */
 218         u32     copied_seq;     /* Head of yet unread data              */
 219         u32     rcv_wup;        /* rcv_nxt on last window update sent   */
 220         u32     snd_nxt;        /* Next sequence we send                */
 221         u32     segs_out;       /* RFC4898 tcpEStatsPerfSegsOut
 222                                  * The total number of segments sent.
 223                                  */
 224         u32     data_segs_out;  /* RFC4898 tcpEStatsPerfDataSegsOut
 225                                  * total number of data segments sent.
 226                                  */
 227         u64     bytes_sent;     /* RFC4898 tcpEStatsPerfHCDataOctetsOut
 228                                  * total number of data bytes sent.
 229                                  */
 230         u64     bytes_acked;    /* RFC4898 tcpEStatsAppHCThruOctetsAcked
 231                                  * sum(delta(snd_una)), or how many bytes
 232                                  * were acked.
 233                                  */
 234         u32     dsack_dups;     /* RFC4898 tcpEStatsStackDSACKDups
 235                                  * total number of DSACK blocks received
 236                                  */
 237         u32     snd_una;        /* First byte we want an ack for        */
 238         u32     snd_sml;        /* Last byte of the most recently transmitted small packet */
 239         u32     rcv_tstamp;     /* timestamp of last received ACK (for keepalives) */
 240         u32     lsndtime;       /* timestamp of last sent data packet (for restart window) */
 241         u32     last_oow_ack_time;  /* timestamp of last out-of-window ACK */
 242         u32     compressed_ack_rcv_nxt;
 243
 244         u32     tsoffset;       /* timestamp offset */
 245
 246         struct list_head tsq_node; /* anchor in tsq_tasklet.head list */
 247         struct list_head tsorted_sent_queue; /* time-sorted sent but un-SACKed skbs */
 248
 249         u32     snd_wl1;        /* Sequence for window update           */
 250         u32     snd_wnd;        /* The window we expect to receive      */
 251         u32     max_window;     /* Maximal window ever seen from peer   */
 252         u32     mss_cache;      /* Cached effective mss, not including SACKS */
 253
 254         u32     window_clamp;   /* Maximal window to advertise          */
 255         u32     rcv_ssthresh;   /* Current window clamp                 */
 256
 257         /* Information of the most recently (s)acked skb */
 258         struct tcp_rack {
 259                 u64 mstamp; /* (Re)sent time of the skb */
 260                 u32 rtt_us;  /* Associated RTT */
 261                 u32 end_seq; /* Ending TCP sequence of the skb */
 262                 u32 last_delivered; /* tp->delivered at last reo_wnd adj */
 263                 u8 reo_wnd_steps;   /* Allowed reordering window */
 264 #define TCP_RACK_RECOVERY_THRESH 16
 265                 u8 reo_wnd_persist:5, /* No. of recovery since last adj */
 266                    dsack_seen:1, /* Whether DSACK seen after last adj */
 267                    advanced:1;   /* mstamp advanced since last lost marking */
 268         } rack;
 269         u16     advmss;         /* Advertised MSS                       */
 270         u8      compressed_ack;
 271         u32     chrono_start;   /* Start time in jiffies of a TCP chrono */
 272         u32     chrono_stat[3]; /* Time in jiffies for chrono_stat stats */
 273         u8      chrono_type:2,  /* current chronograph type */
 274                 rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
 275                 fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */
 276                 fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */
 277                 is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
 278                 fastopen_client_fail:2; /* reason why fastopen failed */
 279         u8      nonagle     : 4,/* Disable Nagle algorithm?             */
 280                 thin_lto    : 1,/* Use linear timeouts for thin streams */
 281                 recvmsg_inq : 1,/* Indicate # of bytes in queue upon recvmsg */
 282                 repair      : 1,
 283                 frto        : 1;/* F-RTO (RFC5682) activated in CA_Loss */
 284         u8      repair_queue;
 285         u8      syn_data:1,     /* SYN includes data */
 286                 syn_fastopen:1, /* SYN includes Fast Open option */
 287                 syn_fastopen_exp:1,/* SYN includes Fast Open exp. option */
 288                 syn_fastopen_ch:1, /* Active TFO re-enabling probe */
 289                 syn_data_acked:1,/* data in SYN is acked by SYN-ACK */
 290                 save_syn:1,     /* Save headers of SYN packet */
 291                 is_cwnd_limited:1,/* forward progress limited by snd_cwnd? */
 292                 syn_smc:1;      /* SYN includes SMC */
 293         u32     tlp_high_seq;   /* snd_nxt at the time of TLP retransmit. */
 294
 295         u32     tcp_tx_delay;   /* delay (in usec) added to TX packets */
 296         u64     tcp_wstamp_ns;  /* departure time for next sent data packet */
 297         u64     tcp_clock_cache; /* cache last tcp_clock_ns() (see tcp_mstamp_refresh()) */
 298
 299 /* RTT measurement */
 300         u64     tcp_mstamp;     /* most recent packet received/sent */
 301         u32     srtt_us;        /* smoothed round trip time << 3 in usecs */
 302         u32     mdev_us;        /* medium deviation                     */
 303         u32     mdev_max_us;    /* maximal mdev for the last rtt period */
 304         u32     rttvar_us;      /* smoothed mdev_max                    */
 305         u32     rtt_seq;        /* sequence number to update rttvar     */
 306         struct  minmax rtt_min;
 307
 308         u32     packets_out;    /* Packets which are "in flight"        */
 309         u32     retrans_out;    /* Retransmitted packets out            */
 310         u32     max_packets_out;  /* max packets_out in last window */
 311         u32     max_packets_seq;  /* right edge of max_packets_out flight */
 312
 313         u16     urg_data;       /* Saved octet of OOB data and control flags */
 314         u8      ecn_flags;      /* ECN status bits.                     */
 315         u8      keepalive_probes; /* num of allowed keep alive probes   */
 316         u32     reordering;     /* Packet reordering metric.            */
 317         u32     reord_seen;     /* number of data packet reordering events */
 318         u32     snd_up;         /* Urgent pointer               */
 319
 320 /*
 321  *      Options received (usually on last packet, some only on SYN packets).
 322  */
 323         struct tcp_options_received rx_opt;
 324
 325 /*
 326  *      Slow start and congestion control (see also Nagle, and Karn & Partridge)
 327  */
 328         u32     snd_ssthresh;   /* Slow start size threshold            */
 329         u32     snd_cwnd;       /* Sending congestion window            */
 330         u32     snd_cwnd_cnt;   /* Linear increase counter              */
 331         u32     snd_cwnd_clamp; /* Do not allow snd_cwnd to grow above this */
 332         u32     snd_cwnd_used;
 333         u32     snd_cwnd_stamp;
 334         u32     prior_cwnd;     /* cwnd right before starting loss recovery */
 335         u32     prr_delivered;  /* Number of newly delivered packets to
 336                                  * receiver in Recovery. */
 337         u32     prr_out;        /* Total number of pkts sent during Recovery. */
 338         u32     delivered;      /* Total data packets delivered incl. rexmits */
 339         u32     delivered_ce;   /* Like the above but only ECE marked packets */
 340         u32     lost;           /* Total data packets lost incl. rexmits */
 341         u32     app_limited;    /* limited until "delivered" reaches this val */
 342         u64     first_tx_mstamp;  /* start of window send phase */
 343         u64     delivered_mstamp; /* time we reached "delivered" */
 344         u32     rate_delivered;    /* saved rate sample: packets delivered */
 345         u32     rate_interval_us;  /* saved rate sample: time elapsed */
 346
 347         u32     rcv_wnd;        /* Current receiver window              */
 348         u32     write_seq;      /* Tail(+1) of data held in tcp send buffer */
 349         u32     notsent_lowat;  /* TCP_NOTSENT_LOWAT */
 350         u32     pushed_seq;     /* Last pushed seq, required to talk to windows */
 351         u32     lost_out;       /* Lost packets                 */
 352         u32     sacked_out;     /* SACK'd packets                       */
 353
 354         struct hrtimer  pacing_timer;
 355         struct hrtimer  compressed_ack_timer;
 356
 357         /* from STCP, retrans queue hinting */
 358         struct sk_buff* lost_skb_hint;
 359         struct sk_buff *retransmit_skb_hint;
 360
 361         /* OOO segments go in this rbtree. Socket lock must be held. */
 362         struct rb_root  out_of_order_queue;
 363         struct sk_buff  *ooo_last_skb; /* cache rb_last(out_of_order_queue) */
 364
 365         /* SACKs data, these 2 need to be together (see tcp_options_write) */
 366         struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */
 367         struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/
 368
 369         struct tcp_sack_block recv_sack_cache[4];
 370
 371         struct sk_buff *highest_sack;   /* skb just after the highest
 372                                          * skb with SACKed bit set
 373                                          * (validity guaranteed only if
 374                                          * sacked_out > 0)
 375                                          */
 376
 377         int     lost_cnt_hint;
 378
 379         u32     prior_ssthresh; /* ssthresh saved at recovery start     */
 380         u32     high_seq;       /* snd_nxt at onset of congestion       */
 381
 382         u32     retrans_stamp;  /* Timestamp of the last retransmit,
 383                                  * also used in SYN-SENT to remember stamp of
 384                                  * the first SYN. */
 385         u32     undo_marker;    /* snd_una upon a new recovery episode. */
 386         int     undo_retrans;   /* number of undoable retransmissions. */
 387         u64     bytes_retrans;  /* RFC4898 tcpEStatsPerfOctetsRetrans
 388                                  * Total data bytes retransmitted
 389                                  */
 390         u32     total_retrans;  /* Total retransmits for entire connection */
 391
 392         u32     urg_seq;        /* Seq of received urgent pointer */
 393         unsigned int            keepalive_time;   /* time before keep alive takes place */
 394         unsigned int            keepalive_intvl;  /* time interval between keep alive probes */
 395
 396         int                     linger2;
 397
 398
 399 /* Sock_ops bpf program related variables */
 400 #ifdef CONFIG_BPF
 401         u8      bpf_sock_ops_cb_flags;  /* Control calling BPF programs
 402                                          * values defined in uapi/linux/tcp.h
 403                                          */
 404 #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) (TP->bpf_sock_ops_cb_flags & ARG)
 405 #else
 406 #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0
 407 #endif
 408
 409         u16 timeout_rehash;     /* Timeout-triggered rehash attempts */
 410
 411         u32 rcv_ooopack; /* Received out-of-order packets, for tcpinfo */
 412
 413 /* Receiver side RTT estimation */
 414         u32 rcv_rtt_last_tsecr;
 415         struct {
 416                 u32     rtt_us;
 417                 u32     seq;
 418                 u64     time;
 419         } rcv_rtt_est;
 420
 421 /* Receiver queue space */
 422         struct {
 423                 u32     space;
 424                 u32     seq;
 425                 u64     time;
 426         } rcvq_space;
 427
 428 /* TCP-specific MTU probe information. */
 429         struct {
 430                 u32               probe_seq_start;
 431                 u32               probe_seq_end;
 432         } mtu_probe;
 433         u32     mtu_info; /* We received an ICMP_FRAG_NEEDED / ICMPV6_PKT_TOOBIG
 434                            * while socket was owned by user.
 435                            */
 436 #if IS_ENABLED(CONFIG_MPTCP)
 437         bool    is_mptcp;
 438 #endif
 439
 440 #ifdef CONFIG_TCP_MD5SIG
 441 /* TCP AF-Specific parts; only used by MD5 Signature support so far */
 442         const struct tcp_sock_af_ops    *af_specific;
 443
 444 /* TCP MD5 Signature Option information */
 445         struct tcp_md5sig_info  __rcu *md5sig_info;
 446 #endif
 447
 448 /* TCP fastopen related information */
 449         struct tcp_fastopen_request *fastopen_req;
 450         /* fastopen_rsk points to request_sock that resulted in this big
 451          * socket. Used to retransmit SYNACKs etc.
 452          */
 453         struct request_sock __rcu *fastopen_rsk;
 454         u32     *saved_syn;
 455 };
 456
 457 enum tsq_enum {
 458         TSQ_THROTTLED,
 459         TSQ_QUEUED,
 460         TCP_TSQ_DEFERRED,          /* tcp_tasklet_func() found socket was owned */
 461         TCP_WRITE_TIMER_DEFERRED,  /* tcp_write_timer() found socket was owned */
 462         TCP_DELACK_TIMER_DEFERRED, /* tcp_delack_timer() found socket was owned */
 463         TCP_MTU_REDUCED_DEFERRED,  /* tcp_v{4|6}_err() could not call
 464                                     * tcp_v{4|6}_mtu_reduced()
 465                                     */
 466 };
 467
 468 enum tsq_flags {
 469         TSQF_THROTTLED                  = (1UL << TSQ_THROTTLED),
 470         TSQF_QUEUED                     = (1UL << TSQ_QUEUED),
 471         TCPF_TSQ_DEFERRED               = (1UL << TCP_TSQ_DEFERRED),
 472         TCPF_WRITE_TIMER_DEFERRED       = (1UL << TCP_WRITE_TIMER_DEFERRED),
 473         TCPF_DELACK_TIMER_DEFERRED      = (1UL << TCP_DELACK_TIMER_DEFERRED),
 474         TCPF_MTU_REDUCED_DEFERRED       = (1UL << TCP_MTU_REDUCED_DEFERRED),
 475 };
 476
 477 static inline struct tcp_sock *tcp_sk(const struct sock *sk)
 478 {
 479         return (struct tcp_sock *)sk;
 480 }
 481
 482 struct tcp_timewait_sock {
 483         struct inet_timewait_sock tw_sk;
 484 #define tw_rcv_nxt tw_sk.__tw_common.skc_tw_rcv_nxt
 485 #define tw_snd_nxt tw_sk.__tw_common.skc_tw_snd_nxt
 486         u32                       tw_rcv_wnd;
 487         u32                       tw_ts_offset;
 488         u32                       tw_ts_recent;
 489
 490         /* The time we sent the last out-of-window ACK: */
 491         u32                       tw_last_oow_ack_time;
 492
 493         int                       tw_ts_recent_stamp;
 494         u32                       tw_tx_delay;
 495 #ifdef CONFIG_TCP_MD5SIG
 496         struct tcp_md5sig_key     *tw_md5_key;
 497 #endif
 498 };
 499
 500 static inline struct tcp_timewait_sock *tcp_twsk(const struct sock *sk)
 501 {
 502         return (struct tcp_timewait_sock *)sk;
 503 }
 504
 505 static inline bool tcp_passive_fastopen(const struct sock *sk)
 506 {
 507         return sk->sk_state == TCP_SYN_RECV &&
 508                rcu_access_pointer(tcp_sk(sk)->fastopen_rsk) != NULL;
 509 }
 510
 511 static inline void fastopen_queue_tune(struct sock *sk, int backlog)
 512 {
 513         struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
 514         int somaxconn = READ_ONCE(sock_net(sk)->core.sysctl_somaxconn);
 515
 516         queue->fastopenq.max_qlen = min_t(unsigned int, backlog, somaxconn);
 517 }
 518
 519 static inline void tcp_move_syn(struct tcp_sock *tp,
 520                                 struct request_sock *req)
 521 {
 522         tp->saved_syn = req->saved_syn;
 523         req->saved_syn = NULL;
 524 }
 525
 526 static inline void tcp_saved_syn_free(struct tcp_sock *tp)
 527 {
 528         kfree(tp->saved_syn);
 529         tp->saved_syn = NULL;
 530 }
 531
 532 struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk);
 533
 534 static inline u16 tcp_mss_clamp(const struct tcp_sock *tp, u16 mss)
 535 {
 536         /* We use READ_ONCE() here because socket might not be locked.
 537          * This happens for listeners.
 538          */
 539         u16 user_mss = READ_ONCE(tp->rx_opt.user_mss);
 540
 541         return (user_mss && user_mss < mss) ? user_mss : mss;
 542 }
 543
 544 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, int pcount,
 545                   int shiftlen);
 546
 547 #endif  /* _LINUX_TCP_H */