TCP: Add comments to (near) all functions in tcp_output.c v3
While looking for something else I spent some time adding one liner comments to the tcp_output.c functions that didn't have any. That makes the comments more consistent. I hope I documented everything right. No code changes. v2: Incorporated feedback from Ilpo. v3: Change style of one liner comments, add a few more comments. Signed-off-by: Andi Kleen <ak@linux.intel.com> Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
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1 changed files with 44 additions and 14 deletions
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@ -59,6 +59,7 @@ int sysctl_tcp_base_mss __read_mostly = 512;
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/* By default, RFC2861 behavior. */
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int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
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/* Account for new data that has been sent to the network. */
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static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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@ -142,6 +143,7 @@ static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst)
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tp->snd_cwnd_used = 0;
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}
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/* Congestion state accounting after a packet has been sent. */
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static void tcp_event_data_sent(struct tcp_sock *tp,
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struct sk_buff *skb, struct sock *sk)
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{
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@ -161,6 +163,7 @@ static void tcp_event_data_sent(struct tcp_sock *tp,
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icsk->icsk_ack.pingpong = 1;
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}
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/* Account for an ACK we sent. */
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static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
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{
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tcp_dec_quickack_mode(sk, pkts);
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@ -276,6 +279,7 @@ static u16 tcp_select_window(struct sock *sk)
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return new_win;
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}
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/* Packet ECN state for a SYN-ACK */
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static inline void TCP_ECN_send_synack(struct tcp_sock *tp, struct sk_buff *skb)
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{
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TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_CWR;
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@ -283,6 +287,7 @@ static inline void TCP_ECN_send_synack(struct tcp_sock *tp, struct sk_buff *skb)
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TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_ECE;
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}
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/* Packet ECN state for a SYN. */
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static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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@ -301,6 +306,9 @@ TCP_ECN_make_synack(struct request_sock *req, struct tcphdr *th)
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th->ece = 1;
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}
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/* Set up ECN state for a packet on a ESTABLISHED socket that is about to
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* be sent.
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*/
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static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
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int tcp_header_len)
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{
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@ -362,7 +370,9 @@ struct tcp_out_options {
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__u32 tsval, tsecr; /* need to include OPTION_TS */
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};
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/* Beware: Something in the Internet is very sensitive to the ordering of
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/* Write previously computed TCP options to the packet.
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*
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* Beware: Something in the Internet is very sensitive to the ordering of
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* TCP options, we learned this through the hard way, so be careful here.
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* Luckily we can at least blame others for their non-compliance but from
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* inter-operatibility perspective it seems that we're somewhat stuck with
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@ -445,6 +455,9 @@ static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
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}
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}
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/* Compute TCP options for SYN packets. This is not the final
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* network wire format yet.
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*/
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static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
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struct tcp_out_options *opts,
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struct tcp_md5sig_key **md5) {
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@ -493,6 +506,7 @@ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
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return size;
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}
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/* Set up TCP options for SYN-ACKs. */
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static unsigned tcp_synack_options(struct sock *sk,
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struct request_sock *req,
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unsigned mss, struct sk_buff *skb,
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@ -541,6 +555,9 @@ static unsigned tcp_synack_options(struct sock *sk,
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return size;
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}
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/* Compute TCP options for ESTABLISHED sockets. This is not the
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* final wire format yet.
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*/
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static unsigned tcp_established_options(struct sock *sk, struct sk_buff *skb,
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struct tcp_out_options *opts,
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struct tcp_md5sig_key **md5) {
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@ -705,7 +722,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
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return net_xmit_eval(err);
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}
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/* This routine just queue's the buffer
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/* This routine just queues the buffer for sending.
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*
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* NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
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* otherwise socket can stall.
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@ -722,6 +739,7 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
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sk_mem_charge(sk, skb->truesize);
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}
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/* Initialize TSO segments for a packet. */
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static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb,
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unsigned int mss_now)
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{
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@ -909,6 +927,7 @@ static void __pskb_trim_head(struct sk_buff *skb, int len)
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skb->len = skb->data_len;
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}
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/* Remove acked data from a packet in the transmit queue. */
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int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
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{
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if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
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@ -937,7 +956,7 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
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return 0;
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}
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/* Not accounting for SACKs here. */
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/* Calculate MSS. Not accounting for SACKs here. */
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int tcp_mtu_to_mss(struct sock *sk, int pmtu)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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@ -981,6 +1000,7 @@ int tcp_mss_to_mtu(struct sock *sk, int mss)
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return mtu;
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}
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/* MTU probing init per socket */
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void tcp_mtup_init(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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@ -1143,7 +1163,8 @@ static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp,
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return 0;
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}
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/* This must be invoked the first time we consider transmitting
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/* Intialize TSO state of a skb.
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* This must be invoked the first time we consider transmitting
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* SKB onto the wire.
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*/
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static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
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@ -1158,6 +1179,7 @@ static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
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return tso_segs;
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}
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/* Minshall's variant of the Nagle send check. */
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static inline int tcp_minshall_check(const struct tcp_sock *tp)
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{
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return after(tp->snd_sml, tp->snd_una) &&
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@ -1242,6 +1264,7 @@ static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb,
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return cwnd_quota;
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}
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/* Test if sending is allowed right now. */
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int tcp_may_send_now(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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@ -1378,6 +1401,10 @@ static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
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}
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/* Create a new MTU probe if we are ready.
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* MTU probe is regularly attempting to increase the path MTU by
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* deliberately sending larger packets. This discovers routing
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* changes resulting in larger path MTUs.
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*
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* Returns 0 if we should wait to probe (no cwnd available),
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* 1 if a probe was sent,
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* -1 otherwise
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@ -1790,6 +1817,7 @@ static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
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sk_wmem_free_skb(sk, next_skb);
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}
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/* Check if coalescing SKBs is legal. */
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static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb)
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{
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if (tcp_skb_pcount(skb) > 1)
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@ -1808,6 +1836,9 @@ static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb)
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return 1;
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}
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/* Collapse packets in the retransmit queue to make to create
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* less packets on the wire. This is only done on retransmission.
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*/
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static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
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int space)
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{
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@ -1957,6 +1988,9 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
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return err;
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}
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/* Check if we forward retransmits are possible in the current
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* window/congestion state.
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*/
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static int tcp_can_forward_retransmit(struct sock *sk)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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@ -2145,7 +2179,8 @@ void tcp_send_active_reset(struct sock *sk, gfp_t priority)
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TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
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}
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/* WARNING: This routine must only be called when we have already sent
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/* Send a crossed SYN-ACK during socket establishment.
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* WARNING: This routine must only be called when we have already sent
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* a SYN packet that crossed the incoming SYN that caused this routine
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* to get called. If this assumption fails then the initial rcv_wnd
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* and rcv_wscale values will not be correct.
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@ -2180,9 +2215,7 @@ int tcp_send_synack(struct sock *sk)
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return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
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}
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/*
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* Prepare a SYN-ACK.
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*/
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/* Prepare a SYN-ACK. */
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struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
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struct request_sock *req)
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{
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@ -2269,9 +2302,7 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
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return skb;
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}
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/*
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* Do all connect socket setups that can be done AF independent.
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*/
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/* Do all connect socket setups that can be done AF independent. */
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static void tcp_connect_init(struct sock *sk)
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{
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struct dst_entry *dst = __sk_dst_get(sk);
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@ -2330,9 +2361,7 @@ static void tcp_connect_init(struct sock *sk)
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tcp_clear_retrans(tp);
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}
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/*
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* Build a SYN and send it off.
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*/
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/* Build a SYN and send it off. */
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int tcp_connect(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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@ -2493,6 +2522,7 @@ static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
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return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
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}
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/* Initiate keepalive or window probe from timer. */
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int tcp_write_wakeup(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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