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[TCP]: MTU probing
Implementation of packetization layer path mtu discovery for TCP, based on the internet-draft currently found at <http://www.ietf.org/internet-drafts/draft-ietf-pmtud-method-05.txt>. Signed-off-by: John Heffner <jheffner@psc.edu> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
John Heffner
David S. Miller
parent
1d60290f27
commit
5d424d5a67
9 changed files with 326 additions and 37 deletions
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@ -51,6 +51,12 @@ int sysctl_tcp_retrans_collapse = 1;
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*/
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int sysctl_tcp_tso_win_divisor = 3;
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int sysctl_tcp_mtu_probing = 0;
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int sysctl_tcp_base_mss = 512;
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EXPORT_SYMBOL(sysctl_tcp_mtu_probing);
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EXPORT_SYMBOL(sysctl_tcp_base_mss);
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static void update_send_head(struct sock *sk, struct tcp_sock *tp,
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struct sk_buff *skb)
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{
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@ -681,6 +687,62 @@ 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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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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struct inet_connection_sock *icsk = inet_csk(sk);
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int mss_now;
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/* Calculate base mss without TCP options:
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It is MMS_S - sizeof(tcphdr) of rfc1122
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*/
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mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
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/* Clamp it (mss_clamp does not include tcp options) */
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if (mss_now > tp->rx_opt.mss_clamp)
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mss_now = tp->rx_opt.mss_clamp;
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/* Now subtract optional transport overhead */
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mss_now -= icsk->icsk_ext_hdr_len;
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/* Then reserve room for full set of TCP options and 8 bytes of data */
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if (mss_now < 48)
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mss_now = 48;
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/* Now subtract TCP options size, not including SACKs */
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mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
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return mss_now;
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}
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/* Inverse of above */
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int tcp_mss_to_mtu(struct sock *sk, int mss)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct inet_connection_sock *icsk = inet_csk(sk);
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int mtu;
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mtu = mss +
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tp->tcp_header_len +
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icsk->icsk_ext_hdr_len +
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icsk->icsk_af_ops->net_header_len;
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return mtu;
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}
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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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struct inet_connection_sock *icsk = inet_csk(sk);
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icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
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icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
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icsk->icsk_af_ops->net_header_len;
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icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
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icsk->icsk_mtup.probe_size = 0;
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}
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/* This function synchronize snd mss to current pmtu/exthdr set.
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tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
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@ -708,25 +770,12 @@ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct inet_connection_sock *icsk = inet_csk(sk);
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/* Calculate base mss without TCP options:
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It is MMS_S - sizeof(tcphdr) of rfc1122
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*/
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int mss_now = (pmtu - icsk->icsk_af_ops->net_header_len -
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sizeof(struct tcphdr));
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int mss_now;
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/* Clamp it (mss_clamp does not include tcp options) */
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if (mss_now > tp->rx_opt.mss_clamp)
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mss_now = tp->rx_opt.mss_clamp;
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if (icsk->icsk_mtup.search_high > pmtu)
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icsk->icsk_mtup.search_high = pmtu;
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/* Now subtract optional transport overhead */
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mss_now -= icsk->icsk_ext_hdr_len;
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/* Then reserve room for full set of TCP options and 8 bytes of data */
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if (mss_now < 48)
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mss_now = 48;
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/* Now subtract TCP options size, not including SACKs */
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mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
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mss_now = tcp_mtu_to_mss(sk, pmtu);
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/* Bound mss with half of window */
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if (tp->max_window && mss_now > (tp->max_window>>1))
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@ -734,6 +783,8 @@ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
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/* And store cached results */
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icsk->icsk_pmtu_cookie = pmtu;
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if (icsk->icsk_mtup.enabled)
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mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
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tp->mss_cache = mss_now;
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return mss_now;
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@ -1063,6 +1114,140 @@ static int tcp_tso_should_defer(struct sock *sk, struct tcp_sock *tp, struct sk_
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return 1;
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}
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/* Create a new MTU probe if we are ready.
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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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static int tcp_mtu_probe(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct inet_connection_sock *icsk = inet_csk(sk);
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struct sk_buff *skb, *nskb, *next;
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int len;
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int probe_size;
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unsigned int pif;
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int copy;
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int mss_now;
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/* Not currently probing/verifying,
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* not in recovery,
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* have enough cwnd, and
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* not SACKing (the variable headers throw things off) */
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if (!icsk->icsk_mtup.enabled ||
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icsk->icsk_mtup.probe_size ||
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inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
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tp->snd_cwnd < 11 ||
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tp->rx_opt.eff_sacks)
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return -1;
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/* Very simple search strategy: just double the MSS. */
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mss_now = tcp_current_mss(sk, 0);
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probe_size = 2*tp->mss_cache;
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if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
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/* TODO: set timer for probe_converge_event */
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return -1;
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}
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/* Have enough data in the send queue to probe? */
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len = 0;
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if ((skb = sk->sk_send_head) == NULL)
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return -1;
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while ((len += skb->len) < probe_size && !tcp_skb_is_last(sk, skb))
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skb = skb->next;
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if (len < probe_size)
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return -1;
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/* Receive window check. */
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if (after(TCP_SKB_CB(skb)->seq + probe_size, tp->snd_una + tp->snd_wnd)) {
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if (tp->snd_wnd < probe_size)
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return -1;
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else
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return 0;
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}
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/* Do we need to wait to drain cwnd? */
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pif = tcp_packets_in_flight(tp);
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if (pif + 2 > tp->snd_cwnd) {
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/* With no packets in flight, don't stall. */
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if (pif == 0)
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return -1;
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else
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return 0;
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}
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/* We're allowed to probe. Build it now. */
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if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
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return -1;
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sk_charge_skb(sk, nskb);
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skb = sk->sk_send_head;
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__skb_insert(nskb, skb->prev, skb, &sk->sk_write_queue);
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sk->sk_send_head = nskb;
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TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
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TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
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TCP_SKB_CB(nskb)->flags = TCPCB_FLAG_ACK;
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TCP_SKB_CB(nskb)->sacked = 0;
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nskb->csum = 0;
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if (skb->ip_summed == CHECKSUM_HW)
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nskb->ip_summed = CHECKSUM_HW;
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len = 0;
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while (len < probe_size) {
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next = skb->next;
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copy = min_t(int, skb->len, probe_size - len);
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if (nskb->ip_summed)
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skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
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else
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nskb->csum = skb_copy_and_csum_bits(skb, 0,
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skb_put(nskb, copy), copy, nskb->csum);
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if (skb->len <= copy) {
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/* We've eaten all the data from this skb.
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* Throw it away. */
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TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags;
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__skb_unlink(skb, &sk->sk_write_queue);
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sk_stream_free_skb(sk, skb);
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} else {
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TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
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~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
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if (!skb_shinfo(skb)->nr_frags) {
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skb_pull(skb, copy);
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if (skb->ip_summed != CHECKSUM_HW)
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skb->csum = csum_partial(skb->data, skb->len, 0);
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} else {
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__pskb_trim_head(skb, copy);
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tcp_set_skb_tso_segs(sk, skb, mss_now);
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}
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TCP_SKB_CB(skb)->seq += copy;
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}
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len += copy;
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skb = next;
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}
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tcp_init_tso_segs(sk, nskb, nskb->len);
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/* We're ready to send. If this fails, the probe will
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* be resegmented into mss-sized pieces by tcp_write_xmit(). */
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TCP_SKB_CB(nskb)->when = tcp_time_stamp;
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if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
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/* Decrement cwnd here because we are sending
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* effectively two packets. */
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tp->snd_cwnd--;
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update_send_head(sk, tp, nskb);
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icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
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icsk->icsk_mtup.probe_seq_start = TCP_SKB_CB(nskb)->seq;
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icsk->icsk_mtup.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
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return 1;
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}
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return -1;
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}
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/* This routine writes packets to the network. It advances the
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* send_head. This happens as incoming acks open up the remote
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* window for us.
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@ -1076,6 +1261,7 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
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struct sk_buff *skb;
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unsigned int tso_segs, sent_pkts;
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int cwnd_quota;
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int result;
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/* If we are closed, the bytes will have to remain here.
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* In time closedown will finish, we empty the write queue and all
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@ -1085,6 +1271,14 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
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return 0;
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sent_pkts = 0;
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/* Do MTU probing. */
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if ((result = tcp_mtu_probe(sk)) == 0) {
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return 0;
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} else if (result > 0) {
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sent_pkts = 1;
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}
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while ((skb = sk->sk_send_head)) {
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unsigned int limit;
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@ -1455,9 +1649,15 @@ void tcp_simple_retransmit(struct sock *sk)
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int tcp_retransmit_skb(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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struct inet_connection_sock *icsk = inet_csk(sk);
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unsigned int cur_mss = tcp_current_mss(sk, 0);
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int err;
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/* Inconslusive MTU probe */
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if (icsk->icsk_mtup.probe_size) {
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icsk->icsk_mtup.probe_size = 0;
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}
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/* Do not sent more than we queued. 1/4 is reserved for possible
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* copying overhead: fragmentation, tunneling, mangling etc.
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*/
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@ -1883,6 +2083,7 @@ static void tcp_connect_init(struct sock *sk)
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if (tp->rx_opt.user_mss)
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tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
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tp->max_window = 0;
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tcp_mtup_init(sk);
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tcp_sync_mss(sk, dst_mtu(dst));
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if (!tp->window_clamp)
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@ -2180,3 +2381,4 @@ EXPORT_SYMBOL(tcp_make_synack);
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EXPORT_SYMBOL(tcp_simple_retransmit);
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EXPORT_SYMBOL(tcp_sync_mss);
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EXPORT_SYMBOL(sysctl_tcp_tso_win_divisor);
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EXPORT_SYMBOL(tcp_mtup_init);
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