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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
@ -397,6 +397,8 @@ enum
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NET_TCP_CONG_CONTROL=110,
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NET_TCP_ABC=111,
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NET_IPV4_IPFRAG_MAX_DIST=112,
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NET_TCP_MTU_PROBING=113,
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NET_TCP_BASE_MSS=114,
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};
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enum {
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@ -72,6 +72,7 @@ struct inet_connection_sock_af_ops {
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* @icsk_probes_out: unanswered 0 window probes
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* @icsk_ext_hdr_len: Network protocol overhead (IP/IPv6 options)
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* @icsk_ack: Delayed ACK control data
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* @icsk_mtup; MTU probing control data
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*/
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struct inet_connection_sock {
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/* inet_sock has to be the first member! */
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@ -104,6 +105,18 @@ struct inet_connection_sock {
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__u16 last_seg_size; /* Size of last incoming segment */
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__u16 rcv_mss; /* MSS used for delayed ACK decisions */
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} icsk_ack;
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struct {
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int enabled;
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/* Range of MTUs to search */
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int search_high;
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int search_low;
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/* Information on the current probe. */
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int probe_size;
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__u32 probe_seq_start;
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__u32 probe_seq_end;
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} icsk_mtup;
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u32 icsk_ca_priv[16];
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#define ICSK_CA_PRIV_SIZE (16 * sizeof(u32))
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};
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@ -60,6 +60,9 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
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/* Minimal RCV_MSS. */
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#define TCP_MIN_RCVMSS 536U
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/* The least MTU to use for probing */
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#define TCP_BASE_MSS 512
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/* After receiving this amount of duplicate ACKs fast retransmit starts. */
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#define TCP_FASTRETRANS_THRESH 3
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@ -219,6 +222,8 @@ extern int sysctl_tcp_nometrics_save;
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extern int sysctl_tcp_moderate_rcvbuf;
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extern int sysctl_tcp_tso_win_divisor;
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extern int sysctl_tcp_abc;
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extern int sysctl_tcp_mtu_probing;
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extern int sysctl_tcp_base_mss;
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extern atomic_t tcp_memory_allocated;
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extern atomic_t tcp_sockets_allocated;
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@ -447,6 +452,10 @@ extern int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
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extern void tcp_initialize_rcv_mss(struct sock *sk);
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extern int tcp_mtu_to_mss(struct sock *sk, int pmtu);
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extern int tcp_mss_to_mtu(struct sock *sk, int mss);
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extern void tcp_mtup_init(struct sock *sk);
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static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
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{
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tp->pred_flags = htonl((tp->tcp_header_len << 26) |
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@ -664,6 +664,22 @@ ctl_table ipv4_table[] = {
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.mode = 0644,
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.proc_handler = &proc_dointvec,
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},
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{
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.ctl_name = NET_TCP_MTU_PROBING,
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.procname = "tcp_mtu_probing",
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.data = &sysctl_tcp_mtu_probing,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = &proc_dointvec,
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},
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{
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.ctl_name = NET_TCP_BASE_MSS,
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.procname = "tcp_base_mss",
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.data = &sysctl_tcp_base_mss,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = &proc_dointvec,
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},
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{ .ctl_name = 0 }
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};
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@ -1891,6 +1891,34 @@ static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
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}
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}
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static void tcp_mtup_probe_failed(struct sock *sk)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
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icsk->icsk_mtup.probe_size = 0;
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}
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static void tcp_mtup_probe_success(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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/* FIXME: breaks with very large cwnd */
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tp->prior_ssthresh = tcp_current_ssthresh(sk);
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tp->snd_cwnd = tp->snd_cwnd *
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tcp_mss_to_mtu(sk, tp->mss_cache) /
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icsk->icsk_mtup.probe_size;
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tp->snd_cwnd_cnt = 0;
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tp->snd_cwnd_stamp = tcp_time_stamp;
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tp->rcv_ssthresh = tcp_current_ssthresh(sk);
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icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
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icsk->icsk_mtup.probe_size = 0;
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tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
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}
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/* Process an event, which can update packets-in-flight not trivially.
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* Main goal of this function is to calculate new estimate for left_out,
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* taking into account both packets sitting in receiver's buffer and
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@ -2023,6 +2051,17 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
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return;
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}
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/* MTU probe failure: don't reduce cwnd */
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if (icsk->icsk_ca_state < TCP_CA_CWR &&
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icsk->icsk_mtup.probe_size &&
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tp->snd_una == icsk->icsk_mtup.probe_seq_start) {
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tcp_mtup_probe_failed(sk);
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/* Restores the reduction we did in tcp_mtup_probe() */
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tp->snd_cwnd++;
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tcp_simple_retransmit(sk);
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return;
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}
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/* Otherwise enter Recovery state */
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if (IsReno(tp))
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@ -2243,6 +2282,13 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
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tp->retrans_stamp = 0;
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}
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/* MTU probing checks */
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if (icsk->icsk_mtup.probe_size) {
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if (!after(icsk->icsk_mtup.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {
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tcp_mtup_probe_success(sk, skb);
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}
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}
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if (sacked) {
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if (sacked & TCPCB_RETRANS) {
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if(sacked & TCPCB_SACKED_RETRANS)
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@ -4101,6 +4147,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
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if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
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tp->rx_opt.sack_ok |= 2;
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tcp_mtup_init(sk);
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tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
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tcp_initialize_rcv_mss(sk);
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@ -4211,6 +4258,7 @@ discard:
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if (tp->ecn_flags&TCP_ECN_OK)
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sock_set_flag(sk, SOCK_NO_LARGESEND);
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tcp_mtup_init(sk);
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tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
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tcp_initialize_rcv_mss(sk);
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@ -4399,6 +4447,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
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*/
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tp->lsndtime = tcp_time_stamp;
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tcp_mtup_init(sk);
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tcp_initialize_rcv_mss(sk);
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tcp_init_buffer_space(sk);
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tcp_fast_path_on(tp);
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@ -900,6 +900,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
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inet_csk(newsk)->icsk_ext_hdr_len = newinet->opt->optlen;
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newinet->id = newtp->write_seq ^ jiffies;
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tcp_mtup_init(newsk);
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tcp_sync_mss(newsk, dst_mtu(dst));
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newtp->advmss = dst_metric(dst, RTAX_ADVMSS);
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tcp_initialize_rcv_mss(newsk);
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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);
|
||||
} else {
|
||||
__pskb_trim_head(skb, copy);
|
||||
tcp_set_skb_tso_segs(sk, skb, mss_now);
|
||||
}
|
||||
TCP_SKB_CB(skb)->seq += copy;
|
||||
}
|
||||
|
||||
len += copy;
|
||||
skb = next;
|
||||
}
|
||||
tcp_init_tso_segs(sk, nskb, nskb->len);
|
||||
|
||||
/* We're ready to send. If this fails, the probe will
|
||||
* be resegmented into mss-sized pieces by tcp_write_xmit(). */
|
||||
TCP_SKB_CB(nskb)->when = tcp_time_stamp;
|
||||
if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
|
||||
/* Decrement cwnd here because we are sending
|
||||
* effectively two packets. */
|
||||
tp->snd_cwnd--;
|
||||
update_send_head(sk, tp, nskb);
|
||||
|
||||
icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
|
||||
icsk->icsk_mtup.probe_seq_start = TCP_SKB_CB(nskb)->seq;
|
||||
icsk->icsk_mtup.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
|
||||
|
||||
return 1;
|
||||
}
|
||||
|
||||
return -1;
|
||||
}
|
||||
|
||||
|
||||
/* This routine writes packets to the network. It advances the
|
||||
* send_head. This happens as incoming acks open up the remote
|
||||
* window for us.
|
||||
@ -1076,6 +1261,7 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
|
||||
struct sk_buff *skb;
|
||||
unsigned int tso_segs, sent_pkts;
|
||||
int cwnd_quota;
|
||||
int result;
|
||||
|
||||
/* If we are closed, the bytes will have to remain here.
|
||||
* In time closedown will finish, we empty the write queue and all
|
||||
@ -1085,6 +1271,14 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
|
||||
return 0;
|
||||
|
||||
sent_pkts = 0;
|
||||
|
||||
/* Do MTU probing. */
|
||||
if ((result = tcp_mtu_probe(sk)) == 0) {
|
||||
return 0;
|
||||
} else if (result > 0) {
|
||||
sent_pkts = 1;
|
||||
}
|
||||
|
||||
while ((skb = sk->sk_send_head)) {
|
||||
unsigned int limit;
|
||||
|
||||
@ -1455,9 +1649,15 @@ void tcp_simple_retransmit(struct sock *sk)
|
||||
int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
|
||||
{
|
||||
struct tcp_sock *tp = tcp_sk(sk);
|
||||
struct inet_connection_sock *icsk = inet_csk(sk);
|
||||
unsigned int cur_mss = tcp_current_mss(sk, 0);
|
||||
int err;
|
||||
|
||||
/* Inconslusive MTU probe */
|
||||
if (icsk->icsk_mtup.probe_size) {
|
||||
icsk->icsk_mtup.probe_size = 0;
|
||||
}
|
||||
|
||||
/* Do not sent more than we queued. 1/4 is reserved for possible
|
||||
* copying overhead: fragmentation, tunneling, mangling etc.
|
||||
*/
|
||||
@ -1883,6 +2083,7 @@ static void tcp_connect_init(struct sock *sk)
|
||||
if (tp->rx_opt.user_mss)
|
||||
tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
|
||||
tp->max_window = 0;
|
||||
tcp_mtup_init(sk);
|
||||
tcp_sync_mss(sk, dst_mtu(dst));
|
||||
|
||||
if (!tp->window_clamp)
|
||||
@ -2180,3 +2381,4 @@ EXPORT_SYMBOL(tcp_make_synack);
|
||||
EXPORT_SYMBOL(tcp_simple_retransmit);
|
||||
EXPORT_SYMBOL(tcp_sync_mss);
|
||||
EXPORT_SYMBOL(sysctl_tcp_tso_win_divisor);
|
||||
EXPORT_SYMBOL(tcp_mtup_init);
|
||||
|
||||
@ -119,8 +119,10 @@ static int tcp_orphan_retries(struct sock *sk, int alive)
|
||||
/* A write timeout has occurred. Process the after effects. */
|
||||
static int tcp_write_timeout(struct sock *sk)
|
||||
{
|
||||
const struct inet_connection_sock *icsk = inet_csk(sk);
|
||||
struct inet_connection_sock *icsk = inet_csk(sk);
|
||||
struct tcp_sock *tp = tcp_sk(sk);
|
||||
int retry_until;
|
||||
int mss;
|
||||
|
||||
if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
|
||||
if (icsk->icsk_retransmits)
|
||||
@ -128,25 +130,19 @@ static int tcp_write_timeout(struct sock *sk)
|
||||
retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
|
||||
} else {
|
||||
if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
|
||||
/* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu black
|
||||
hole detection. :-(
|
||||
|
||||
It is place to make it. It is not made. I do not want
|
||||
to make it. It is disgusting. It does not work in any
|
||||
case. Let me to cite the same draft, which requires for
|
||||
us to implement this:
|
||||
|
||||
"The one security concern raised by this memo is that ICMP black holes
|
||||
are often caused by over-zealous security administrators who block
|
||||
all ICMP messages. It is vitally important that those who design and
|
||||
deploy security systems understand the impact of strict filtering on
|
||||
upper-layer protocols. The safest web site in the world is worthless
|
||||
if most TCP implementations cannot transfer data from it. It would
|
||||
be far nicer to have all of the black holes fixed rather than fixing
|
||||
all of the TCP implementations."
|
||||
|
||||
Golden words :-).
|
||||
*/
|
||||
/* Black hole detection */
|
||||
if (sysctl_tcp_mtu_probing) {
|
||||
if (!icsk->icsk_mtup.enabled) {
|
||||
icsk->icsk_mtup.enabled = 1;
|
||||
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
|
||||
} else {
|
||||
mss = min(sysctl_tcp_base_mss,
|
||||
tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)/2);
|
||||
mss = max(mss, 68 - tp->tcp_header_len);
|
||||
icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
|
||||
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
|
||||
}
|
||||
}
|
||||
|
||||
dst_negative_advice(&sk->sk_dst_cache);
|
||||
}
|
||||
|
||||
@ -987,6 +987,7 @@ static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
|
||||
inet_csk(newsk)->icsk_ext_hdr_len = (newnp->opt->opt_nflen +
|
||||
newnp->opt->opt_flen);
|
||||
|
||||
tcp_mtup_init(newsk);
|
||||
tcp_sync_mss(newsk, dst_mtu(dst));
|
||||
newtp->advmss = dst_metric(dst, RTAX_ADVMSS);
|
||||
tcp_initialize_rcv_mss(newsk);
|
||||
|
||||
Loading…
Reference in New Issue
Block a user