text: // SPDX-License-Identifier: GPL-2.0
  #include <linux/rcupdate.h>
  #include <linux/spinlock.h>
  #include <linux/jiffies.h>
  #include <linux/module.h>
  #include <linux/cache.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/tcp.h>
  #include <linux/hash.h>
  #include <linux/tcp_metrics.h>
  #include <linux/vmalloc.h>
  
  #include <net/inet_connection_sock.h>
  #include <net/net_namespace.h>
  #include <net/request_sock.h>
  #include <net/inetpeer.h>
  #include <net/sock.h>
  #include <net/ipv6.h>
  #include <net/dst.h>
  #include <net/tcp.h>
  #include <net/genetlink.h>
  
  int sysctl_tcp_nometrics_save __read_mostly;
  
  static struct tcp_metrics_block *__tcp_get_metrics(const struct inetpeer_addr *saddr,
  						   const struct inetpeer_addr *daddr,
  						   struct net *net, unsigned int hash);
  
  struct tcp_fastopen_metrics {
  	u16	mss;
  	u16	syn_loss:10,		/* Recurring Fast Open SYN losses */
  		try_exp:2;		/* Request w/ exp. option (once) */
  	unsigned long	last_syn_loss;	/* Last Fast Open SYN loss */
  	struct	tcp_fastopen_cookie	cookie;
  };
  
  /* TCP_METRIC_MAX includes 2 extra fields for userspace compatibility
   * Kernel only stores RTT and RTTVAR in usec resolution
   */
  #define TCP_METRIC_MAX_KERNEL (TCP_METRIC_MAX - 2)
  
  struct tcp_metrics_block {
  	struct tcp_metrics_block __rcu	*tcpm_next;
  	possible_net_t			tcpm_net;
  	struct inetpeer_addr		tcpm_saddr;
  	struct inetpeer_addr		tcpm_daddr;
  	unsigned long			tcpm_stamp;
  	u32				tcpm_lock;
  	u32				tcpm_vals[TCP_METRIC_MAX_KERNEL + 1];
  	struct tcp_fastopen_metrics	tcpm_fastopen;
  
  	struct rcu_head			rcu_head;
  };
  
  static inline struct net *tm_net(struct tcp_metrics_block *tm)
  {
  	return read_pnet(&tm->tcpm_net);
  }
  
  static bool tcp_metric_locked(struct tcp_metrics_block *tm,
  			      enum tcp_metric_index idx)
  {
  	return tm->tcpm_lock & (1 << idx);
  }
  
  static u32 tcp_metric_get(struct tcp_metrics_block *tm,
  			  enum tcp_metric_index idx)
  {
  	return tm->tcpm_vals[idx];
  }
  
  static void tcp_metric_set(struct tcp_metrics_block *tm,
  			   enum tcp_metric_index idx,
  			   u32 val)
  {
  	tm->tcpm_vals[idx] = val;
  }
  
  static bool addr_same(const struct inetpeer_addr *a,
  		      const struct inetpeer_addr *b)
  {
  	return inetpeer_addr_cmp(a, b) == 0;
  }
  
  struct tcpm_hash_bucket {
  	struct tcp_metrics_block __rcu	*chain;
  };
  
  static struct tcpm_hash_bucket	*tcp_metrics_hash __read_mostly;
  static unsigned int		tcp_metrics_hash_log __read_mostly;
  
  static DEFINE_SPINLOCK(tcp_metrics_lock);
  
  static void tcpm_suck_dst(struct tcp_metrics_block *tm,
  			  const struct dst_entry *dst,
  			  bool fastopen_clear)
  {
  	u32 msval;
  	u32 val;
  
  	tm->tcpm_stamp = jiffies;
  
  	val = 0;
  	if (dst_metric_locked(dst, RTAX_RTT))
  		val |= 1 << TCP_METRIC_RTT;
  	if (dst_metric_locked(dst, RTAX_RTTVAR))
  		val |= 1 << TCP_METRIC_RTTVAR;
  	if (dst_metric_locked(dst, RTAX_SSTHRESH))
  		val |= 1 << TCP_METRIC_SSTHRESH;
  	if (dst_metric_locked(dst, RTAX_CWND))
  		val |= 1 << TCP_METRIC_CWND;
  	if (dst_metric_locked(dst, RTAX_REORDERING))
  		val |= 1 << TCP_METRIC_REORDERING;
  	tm->tcpm_lock = val;
  
  	msval = dst_metric_raw(dst, RTAX_RTT);
  	tm->tcpm_vals[TCP_METRIC_RTT] = msval * USEC_PER_MSEC;
  
  	msval = dst_metric_raw(dst, RTAX_RTTVAR);
  	tm->tcpm_vals[TCP_METRIC_RTTVAR] = msval * USEC_PER_MSEC;
  	tm->tcpm_vals[TCP_METRIC_SSTHRESH] = dst_metric_raw(dst, RTAX_SSTHRESH);
  	tm->tcpm_vals[TCP_METRIC_CWND] = dst_metric_raw(dst, RTAX_CWND);
  	tm->tcpm_vals[TCP_METRIC_REORDERING] = dst_metric_raw(dst, RTAX_REORDERING);
  	if (fastopen_clear) {
  		tm->tcpm_fastopen.mss = 0;
  		tm->tcpm_fastopen.syn_loss = 0;
  		tm->tcpm_fastopen.try_exp = 0;
  		tm->tcpm_fastopen.cookie.exp = false;
  		tm->tcpm_fastopen.cookie.len = 0;
  	}
  }
  
  #define TCP_METRICS_TIMEOUT		(60 * 60 * HZ)
  
  static void tcpm_check_stamp(struct tcp_metrics_block *tm, struct dst_entry *dst)
  {
  	if (tm && unlikely(time_after(jiffies, tm->tcpm_stamp + TCP_METRICS_TIMEOUT)))
  		tcpm_suck_dst(tm, dst, false);
  }
  
  #define TCP_METRICS_RECLAIM_DEPTH	5
  #define TCP_METRICS_RECLAIM_PTR		(struct tcp_metrics_block *) 0x1UL
  
  #define deref_locked(p)	\
  	rcu_dereference_protected(p, lockdep_is_held(&tcp_metrics_lock))
  
  static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst,
  					  struct inetpeer_addr *saddr,
  					  struct inetpeer_addr *daddr,
  					  unsigned int hash)
  {
  	struct tcp_metrics_block *tm;
  	struct net *net;
  	bool reclaim = false;
  
  	spin_lock_bh(&tcp_metrics_lock);
  	net = dev_net(dst->dev);
  
  	/* While waiting for the spin-lock the cache might have been populated
  	 * with this entry and so we have to check again.
  	 */
  	tm = __tcp_get_metrics(saddr, daddr, net, hash);
  	if (tm == TCP_METRICS_RECLAIM_PTR) {
  		reclaim = true;
  		tm = NULL;
  	}
  	if (tm) {
  		tcpm_check_stamp(tm, dst);
  		goto out_unlock;
  	}
  
  	if (unlikely(reclaim)) {
  		struct tcp_metrics_block *oldest;
  
  		oldest = deref_locked(tcp_metrics_hash[hash].chain);
  		for (tm = deref_locked(oldest->tcpm_next); tm;
  		     tm = deref_locked(tm->tcpm_next)) {
  			if (time_before(tm->tcpm_stamp, oldest->tcpm_stamp))
  				oldest = tm;
  		}
  		tm = oldest;
  	} else {
  		tm = kmalloc(sizeof(*tm), GFP_ATOMIC);
  		if (!tm)
  			goto out_unlock;
  	}
  	write_pnet(&tm->tcpm_net, net);
  	tm->tcpm_saddr = *saddr;
  	tm->tcpm_daddr = *daddr;
  
  	tcpm_suck_dst(tm, dst, true);
  
  	if (likely(!reclaim)) {
  		tm->tcpm_next = tcp_metrics_hash[hash].chain;
  		rcu_assign_pointer(tcp_metrics_hash[hash].chain, tm);
  	}
  
  out_unlock:
  	spin_unlock_bh(&tcp_metrics_lock);
  	return tm;
  }
  
  static struct tcp_metrics_block *tcp_get_encode(struct tcp_metrics_block *tm, int depth)
  {
  	if (tm)
  		return tm;
  	if (depth > TCP_METRICS_RECLAIM_DEPTH)
  		return TCP_METRICS_RECLAIM_PTR;
  	return NULL;
  }
  
  static struct tcp_metrics_block *__tcp_get_metrics(const struct inetpeer_addr *saddr,
  						   const struct inetpeer_addr *daddr,
  						   struct net *net, unsigned int hash)
  {
  	struct tcp_metrics_block *tm;
  	int depth = 0;
  
  	for (tm = rcu_dereference(tcp_metrics_hash[hash].chain); tm;
  	     tm = rcu_dereference(tm->tcpm_next)) {
  		if (addr_same(&tm->tcpm_saddr, saddr) &&
  		    addr_same(&tm->tcpm_daddr, daddr) &&
  		    net_eq(tm_net(tm), net))
  			break;
  		depth++;
  	}
  	return tcp_get_encode(tm, depth);
  }
  
  static struct tcp_metrics_block *__tcp_get_metrics_req(struct request_sock *req,
  						       struct dst_entry *dst)
  {
  	struct tcp_metrics_block *tm;
  	struct inetpeer_addr saddr, daddr;
  	unsigned int hash;
  	struct net *net;
  
  	saddr.family = req->rsk_ops->family;
  	daddr.family = req->rsk_ops->family;
  	switch (daddr.family) {
  	case AF_INET:
  		inetpeer_set_addr_v4(&saddr, inet_rsk(req)->ir_loc_addr);
  		inetpeer_set_addr_v4(&daddr, inet_rsk(req)->ir_rmt_addr);
  		hash = ipv4_addr_hash(inet_rsk(req)->ir_rmt_addr);
  		break;
  #if IS_ENABLED(CONFIG_IPV6)
  	case AF_INET6:
  		inetpeer_set_addr_v6(&saddr, &inet_rsk(req)->ir_v6_loc_addr);
  		inetpeer_set_addr_v6(&daddr, &inet_rsk(req)->ir_v6_rmt_addr);
  		hash = ipv6_addr_hash(&inet_rsk(req)->ir_v6_rmt_addr);
  		break;
  #endif
  	default:
  		return NULL;
  	}
  
  	net = dev_net(dst->dev);
  	hash ^= net_hash_mix(net);
  	hash = hash_32(hash, tcp_metrics_hash_log);
  
  	for (tm = rcu_dereference(tcp_metrics_hash[hash].chain); tm;
  	     tm = rcu_dereference(tm->tcpm_next)) {
  		if (addr_same(&tm->tcpm_saddr, &saddr) &&
  		    addr_same(&tm->tcpm_daddr, &daddr) &&
  		    net_eq(tm_net(tm), net))
  			break;
  	}
  	tcpm_check_stamp(tm, dst);
  	return tm;
  }
  
  static struct tcp_metrics_block *tcp_get_metrics(struct sock *sk,
  						 struct dst_entry *dst,
  						 bool create)
  {
  	struct tcp_metrics_block *tm;
  	struct inetpeer_addr saddr, daddr;
  	unsigned int hash;
  	struct net *net;
  
  	if (sk->sk_family == AF_INET) {
  		inetpeer_set_addr_v4(&saddr, inet_sk(sk)->inet_saddr);
  		inetpeer_set_addr_v4(&daddr, inet_sk(sk)->inet_daddr);
  		hash = ipv4_addr_hash(inet_sk(sk)->inet_daddr);
  	}
  #if IS_ENABLED(CONFIG_IPV6)
  	else if (sk->sk_family == AF_INET6) {
  		if (ipv6_addr_v4mapped(&sk->sk_v6_daddr)) {
  			inetpeer_set_addr_v4(&saddr, inet_sk(sk)->inet_saddr);
  			inetpeer_set_addr_v4(&daddr, inet_sk(sk)->inet_daddr);
  			hash = ipv4_addr_hash(inet_sk(sk)->inet_daddr);
  		} else {
  			inetpeer_set_addr_v6(&saddr, &sk->sk_v6_rcv_saddr);
  			inetpeer_set_addr_v6(&daddr, &sk->sk_v6_daddr);
  			hash = ipv6_addr_hash(&sk->sk_v6_daddr);
  		}
  	}
  #endif
  	else
  		return NULL;
  
  	net = dev_net(dst->dev);
  	hash ^= net_hash_mix(net);
  	hash = hash_32(hash, tcp_metrics_hash_log);
  
  	tm = __tcp_get_metrics(&saddr, &daddr, net, hash);
  	if (tm == TCP_METRICS_RECLAIM_PTR)
  		tm = NULL;
  	if (!tm && create)
  		tm = tcpm_new(dst, &saddr, &daddr, hash);
  	else
  		tcpm_check_stamp(tm, dst);
  
  	return tm;
  }
  
  /* Save metrics learned by this TCP session.  This function is called
   * only, when TCP finishes successfully i.e. when it enters TIME-WAIT
   * or goes from LAST-ACK to CLOSE.
   */
  void tcp_update_metrics(struct sock *sk)
  {
  	const struct inet_connection_sock *icsk = inet_csk(sk);
  	struct dst_entry *dst = __sk_dst_get(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct net *net = sock_net(sk);
  	struct tcp_metrics_block *tm;
  	unsigned long rtt;
  	u32 val;
  	int m;
  
  	sk_dst_confirm(sk);
  	if (sysctl_tcp_nometrics_save || !dst)
  		return;
  
  	rcu_read_lock();
  	if (icsk->icsk_backoff || !tp->srtt_us) {
  		/* This session failed to estimate rtt. Why?
  		 * Probably, no packets returned in time.  Reset our
  		 * results.
  		 */
  		tm = tcp_get_metrics(sk, dst, false);
  		if (tm && !tcp_metric_locked(tm, TCP_METRIC_RTT))
  			tcp_metric_set(tm, TCP_METRIC_RTT, 0);
  		goto out_unlock;
  	} else
  		tm = tcp_get_metrics(sk, dst, true);
  
  	if (!tm)
  		goto out_unlock;
  
  	rtt = tcp_metric_get(tm, TCP_METRIC_RTT);
  	m = rtt - tp->srtt_us;
  
  	/* If newly calculated rtt larger than stored one, store new
  	 * one. Otherwise, use EWMA. Remember, rtt overestimation is
  	 * always better than underestimation.
  	 */
  	if (!tcp_metric_locked(tm, TCP_METRIC_RTT)) {
  		if (m <= 0)
  			rtt = tp->srtt_us;
  		else
  			rtt -= (m >> 3);
  		tcp_metric_set(tm, TCP_METRIC_RTT, rtt);
  	}
  
  	if (!tcp_metric_locked(tm, TCP_METRIC_RTTVAR)) {
  		unsigned long var;
  
  		if (m < 0)
  			m = -m;
  
  		/* Scale deviation to rttvar fixed point */
  		m >>= 1;
  		if (m < tp->mdev_us)
  			m = tp->mdev_us;
  
  		var = tcp_metric_get(tm, TCP_METRIC_RTTVAR);
  		if (m >= var)
  			var = m;
  		else
  			var -= (var - m) >> 2;
  
  		tcp_metric_set(tm, TCP_METRIC_RTTVAR, var);
  	}
  
  	if (tcp_in_initial_slowstart(tp)) {
  		/* Slow start still did not finish. */
  		if (!tcp_metric_locked(tm, TCP_METRIC_SSTHRESH)) {
  			val = tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
  			if (val && (tp->snd_cwnd >> 1) > val)
  				tcp_metric_set(tm, TCP_METRIC_SSTHRESH,
  					       tp->snd_cwnd >> 1);
  		}
  		if (!tcp_metric_locked(tm, TCP_METRIC_CWND)) {
  			val = tcp_metric_get(tm, TCP_METRIC_CWND);
  			if (tp->snd_cwnd > val)
  				tcp_metric_set(tm, TCP_METRIC_CWND,
  					       tp->snd_cwnd);
  		}
  	} else if (!tcp_in_slow_start(tp) &&
  		   icsk->icsk_ca_state == TCP_CA_Open) {
  		/* Cong. avoidance phase, cwnd is reliable. */
  		if (!tcp_metric_locked(tm, TCP_METRIC_SSTHRESH))
  			tcp_metric_set(tm, TCP_METRIC_SSTHRESH,
  				       max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
  		if (!tcp_metric_locked(tm, TCP_METRIC_CWND)) {
  			val = tcp_metric_get(tm, TCP_METRIC_CWND);
  			tcp_metric_set(tm, TCP_METRIC_CWND, (val + tp->snd_cwnd) >> 1);
  		}
  	} else {
  		/* Else slow start did not finish, cwnd is non-sense,
  		 * ssthresh may be also invalid.
  		 */
  		if (!tcp_metric_locked(tm, TCP_METRIC_CWND)) {
  			val = tcp_metric_get(tm, TCP_METRIC_CWND);
  			tcp_metric_set(tm, TCP_METRIC_CWND,
  				       (val + tp->snd_ssthresh) >> 1);
  		}
  		if (!tcp_metric_locked(tm, TCP_METRIC_SSTHRESH)) {
  			val = tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
  			if (val && tp->snd_ssthresh > val)
  				tcp_metric_set(tm, TCP_METRIC_SSTHRESH,
  					       tp->snd_ssthresh);
  		}
  		if (!tcp_metric_locked(tm, TCP_METRIC_REORDERING)) {
  			val = tcp_metric_get(tm, TCP_METRIC_REORDERING);
  			if (val < tp->reordering &&
  			    tp->reordering != net->ipv4.sysctl_tcp_reordering)
  				tcp_metric_set(tm, TCP_METRIC_REORDERING,
  					       tp->reordering);
  		}
  	}
  	tm->tcpm_stamp = jiffies;
  out_unlock:
  	rcu_read_unlock();
  }
  
  /* Initialize metrics on socket. */
  
  void tcp_init_metrics(struct sock *sk)
  {
  	struct dst_entry *dst = __sk_dst_get(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct tcp_metrics_block *tm;
  	u32 val, crtt = 0; /* cached RTT scaled by 8 */
  
  	sk_dst_confirm(sk);
  	if (!dst)
  		goto reset;
  
  	rcu_read_lock();
  	tm = tcp_get_metrics(sk, dst, true);
  	if (!tm) {
  		rcu_read_unlock();
  		goto reset;
  	}
  
  	if (tcp_metric_locked(tm, TCP_METRIC_CWND))
  		tp->snd_cwnd_clamp = tcp_metric_get(tm, TCP_METRIC_CWND);
  
  	val = tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
  	if (val) {
  		tp->snd_ssthresh = val;
  		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
  			tp->snd_ssthresh = tp->snd_cwnd_clamp;
  	} else {
  		/* ssthresh may have been reduced unnecessarily during.
  		 * 3WHS. Restore it back to its initial default.
  		 */
  		tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
  	}
  	val = tcp_metric_get(tm, TCP_METRIC_REORDERING);
  	if (val && tp->reordering != val) {
  		tcp_disable_fack(tp);
  		tp->reordering = val;
  	}
  
  	crtt = tcp_metric_get(tm, TCP_METRIC_RTT);
  	rcu_read_unlock();
  reset:
  	/* The initial RTT measurement from the SYN/SYN-ACK is not ideal
  	 * to seed the RTO for later data packets because SYN packets are
  	 * small. Use the per-dst cached values to seed the RTO but keep
  	 * the RTT estimator variables intact (e.g., srtt, mdev, rttvar).
  	 * Later the RTO will be updated immediately upon obtaining the first
  	 * data RTT sample (tcp_rtt_estimator()). Hence the cached RTT only
  	 * influences the first RTO but not later RTT estimation.
  	 *
  	 * But if RTT is not available from the SYN (due to retransmits or
  	 * syn cookies) or the cache, force a conservative 3secs timeout.
  	 *
  	 * A bit of theory. RTT is time passed after "normal" sized packet
  	 * is sent until it is ACKed. In normal circumstances sending small
  	 * packets force peer to delay ACKs and calculation is correct too.
  	 * The algorithm is adaptive and, provided we follow specs, it
  	 * NEVER underestimate RTT. BUT! If peer tries to make some clever
  	 * tricks sort of "quick acks" for time long enough to decrease RTT
  	 * to low value, and then abruptly stops to do it and starts to delay
  	 * ACKs, wait for troubles.
  	 */
  	if (crtt > tp->srtt_us) {
  		/* Set RTO like tcp_rtt_estimator(), but from cached RTT. */
  		crtt /= 8 * USEC_PER_SEC / HZ;
  		inet_csk(sk)->icsk_rto = crtt + max(2 * crtt, tcp_rto_min(sk));
  	} else if (tp->srtt_us == 0) {
  		/* RFC6298: 5.7 We've failed to get a valid RTT sample from
  		 * 3WHS. This is most likely due to retransmission,
  		 * including spurious one. Reset the RTO back to 3secs
  		 * from the more aggressive 1sec to avoid more spurious
  		 * retransmission.
  		 */
  		tp->rttvar_us = jiffies_to_usecs(TCP_TIMEOUT_FALLBACK);
  		tp->mdev_us = tp->mdev_max_us = tp->rttvar_us;
  
  		inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
  	}
  	/* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
  	 * retransmitted. In light of RFC6298 more aggressive 1sec
  	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
  	 * retransmission has occurred.
  	 */
  	if (tp->total_retrans > 1)
  		tp->snd_cwnd = 1;
  	else
  		tp->snd_cwnd = tcp_init_cwnd(tp, dst);
  	tp->snd_cwnd_stamp = tcp_jiffies32;
  }
  
  bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst)
  {
  	struct tcp_metrics_block *tm;
  	bool ret;
  
  	if (!dst)
  		return false;
  
  	rcu_read_lock();
  	tm = __tcp_get_metrics_req(req, dst);
  	if (tm && tcp_metric_get(tm, TCP_METRIC_RTT))
  		ret = true;
  	else
  		ret = false;
  	rcu_read_unlock();
  
  	return ret;
  }
  
  static DEFINE_SEQLOCK(fastopen_seqlock);
  
  void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
  			    struct tcp_fastopen_cookie *cookie,
  			    int *syn_loss, unsigned long *last_syn_loss)
  {
  	struct tcp_metrics_block *tm;
  
  	rcu_read_lock();
  	tm = tcp_get_metrics(sk, __sk_dst_get(sk), false);
  	if (tm) {
  		struct tcp_fastopen_metrics *tfom = &tm->tcpm_fastopen;
  		unsigned int seq;
  
  		do {
  			seq = read_seqbegin(&fastopen_seqlock);
  			if (tfom->mss)
  				*mss = tfom->mss;
  			*cookie = tfom->cookie;
  			if (cookie->len <= 0 && tfom->try_exp == 1)
  				cookie->exp = true;
  			*syn_loss = tfom->syn_loss;
  			*last_syn_loss = *syn_loss ? tfom->last_syn_loss : 0;
  		} while (read_seqretry(&fastopen_seqlock, seq));
  	}
  	rcu_read_unlock();
  }
  
  void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
  			    struct tcp_fastopen_cookie *cookie, bool syn_lost,
  			    u16 try_exp)
  {
  	struct dst_entry *dst = __sk_dst_get(sk);
  	struct tcp_metrics_block *tm;
  
  	if (!dst)
  		return;
  	rcu_read_lock();
  	tm = tcp_get_metrics(sk, dst, true);
  	if (tm) {
  		struct tcp_fastopen_metrics *tfom = &tm->tcpm_fastopen;
  
  		write_seqlock_bh(&fastopen_seqlock);
  		if (mss)
  			tfom->mss = mss;
  		if (cookie && cookie->len > 0)
  			tfom->cookie = *cookie;
  		else if (try_exp > tfom->try_exp &&
  			 tfom->cookie.len <= 0 && !tfom->cookie.exp)
  			tfom->try_exp = try_exp;
  		if (syn_lost) {
  			++tfom->syn_loss;
  			tfom->last_syn_loss = jiffies;
  		} else
  			tfom->syn_loss = 0;
  		write_sequnlock_bh(&fastopen_seqlock);
  	}
  	rcu_read_unlock();
  }
  
  static struct genl_family tcp_metrics_nl_family;
  
  static const struct nla_policy tcp_metrics_nl_policy[TCP_METRICS_ATTR_MAX + 1] = {
  	[TCP_METRICS_ATTR_ADDR_IPV4]	= { .type = NLA_U32, },
  	[TCP_METRICS_ATTR_ADDR_IPV6]	= { .type = NLA_BINARY,
  					    .len = sizeof(struct in6_addr), },
  	/* Following attributes are not received for GET/DEL,
  	 * we keep them for reference
  	 */
  #if 0
  	[TCP_METRICS_ATTR_AGE]		= { .type = NLA_MSECS, },
  	[TCP_METRICS_ATTR_TW_TSVAL]	= { .type = NLA_U32, },
  	[TCP_METRICS_ATTR_TW_TS_STAMP]	= { .type = NLA_S32, },
  	[TCP_METRICS_ATTR_VALS]		= { .type = NLA_NESTED, },
  	[TCP_METRICS_ATTR_FOPEN_MSS]	= { .type = NLA_U16, },
  	[TCP_METRICS_ATTR_FOPEN_SYN_DROPS]	= { .type = NLA_U16, },
  	[TCP_METRICS_ATTR_FOPEN_SYN_DROP_TS]	= { .type = NLA_MSECS, },
  	[TCP_METRICS_ATTR_FOPEN_COOKIE]	= { .type = NLA_BINARY,
  					    .len = TCP_FASTOPEN_COOKIE_MAX, },
  #endif
  };
  
  /* Add attributes, caller cancels its header on failure */
  static int tcp_metrics_fill_info(struct sk_buff *msg,
  				 struct tcp_metrics_block *tm)
  {
  	struct nlattr *nest;
  	int i;
  
  	switch (tm->tcpm_daddr.family) {
  	case AF_INET:
  		if (nla_put_in_addr(msg, TCP_METRICS_ATTR_ADDR_IPV4,
  				    inetpeer_get_addr_v4(&tm->tcpm_daddr)) < 0)
  			goto nla_put_failure;
  		if (nla_put_in_addr(msg, TCP_METRICS_ATTR_SADDR_IPV4,
  				    inetpeer_get_addr_v4(&tm->tcpm_saddr)) < 0)
  			goto nla_put_failure;
  		break;
  	case AF_INET6:
  		if (nla_put_in6_addr(msg, TCP_METRICS_ATTR_ADDR_IPV6,
  				     inetpeer_get_addr_v6(&tm->tcpm_daddr)) < 0)
  			goto nla_put_failure;
  		if (nla_put_in6_addr(msg, TCP_METRICS_ATTR_SADDR_IPV6,
  				     inetpeer_get_addr_v6(&tm->tcpm_saddr)) < 0)
  			goto nla_put_failure;
  		break;
  	default:
  		return -EAFNOSUPPORT;
  	}
  
  	if (nla_put_msecs(msg, TCP_METRICS_ATTR_AGE,
  			  jiffies - tm->tcpm_stamp,
  			  TCP_METRICS_ATTR_PAD) < 0)
  		goto nla_put_failure;
  
  	{
  		int n = 0;
  
  		nest = nla_nest_start(msg, TCP_METRICS_ATTR_VALS);
  		if (!nest)
  			goto nla_put_failure;
  		for (i = 0; i < TCP_METRIC_MAX_KERNEL + 1; i++) {
  			u32 val = tm->tcpm_vals[i];
  
  			if (!val)
  				continue;
  			if (i == TCP_METRIC_RTT) {
  				if (nla_put_u32(msg, TCP_METRIC_RTT_US + 1,
  						val) < 0)
  					goto nla_put_failure;
  				n++;
  				val = max(val / 1000, 1U);
  			}
  			if (i == TCP_METRIC_RTTVAR) {
  				if (nla_put_u32(msg, TCP_METRIC_RTTVAR_US + 1,
  						val) < 0)
  					goto nla_put_failure;
  				n++;
  				val = max(val / 1000, 1U);
  			}
  			if (nla_put_u32(msg, i + 1, val) < 0)
  				goto nla_put_failure;
  			n++;
  		}
  		if (n)
  			nla_nest_end(msg, nest);
  		else
  			nla_nest_cancel(msg, nest);
  	}
  
  	{
  		struct tcp_fastopen_metrics tfom_copy[1], *tfom;
  		unsigned int seq;
  
  		do {
  			seq = read_seqbegin(&fastopen_seqlock);
  			tfom_copy[0] = tm->tcpm_fastopen;
  		} while (read_seqretry(&fastopen_seqlock, seq));
  
  		tfom = tfom_copy;
  		if (tfom->mss &&
  		    nla_put_u16(msg, TCP_METRICS_ATTR_FOPEN_MSS,
  				tfom->mss) < 0)
  			goto nla_put_failure;
  		if (tfom->syn_loss &&
  		    (nla_put_u16(msg, TCP_METRICS_ATTR_FOPEN_SYN_DROPS,
  				tfom->syn_loss) < 0 ||
  		     nla_put_msecs(msg, TCP_METRICS_ATTR_FOPEN_SYN_DROP_TS,
  				jiffies - tfom->last_syn_loss,
  				TCP_METRICS_ATTR_PAD) < 0))
  			goto nla_put_failure;
  		if (tfom->cookie.len > 0 &&
  		    nla_put(msg, TCP_METRICS_ATTR_FOPEN_COOKIE,
  			    tfom->cookie.len, tfom->cookie.val) < 0)
  			goto nla_put_failure;
  	}
  
  	return 0;
  
  nla_put_failure:
  	return -EMSGSIZE;
  }
  
  static int tcp_metrics_dump_info(struct sk_buff *skb,
  				 struct netlink_callback *cb,
  				 struct tcp_metrics_block *tm)
  {
  	void *hdr;
  
  	hdr = genlmsg_put(skb, NETLINK_CB(cb->skb).portid, cb->nlh->nlmsg_seq,
  			  &tcp_metrics_nl_family, NLM_F_MULTI,
  			  TCP_METRICS_CMD_GET);
  	if (!hdr)
  		return -EMSGSIZE;
  
  	if (tcp_metrics_fill_info(skb, tm) < 0)
  		goto nla_put_failure;
  
  	genlmsg_end(skb, hdr);
  	return 0;
  
  nla_put_failure:
  	genlmsg_cancel(skb, hdr);
  	return -EMSGSIZE;
  }
  
  static int tcp_metrics_nl_dump(struct sk_buff *skb,
  			       struct netlink_callback *cb)
  {
  	struct net *net = sock_net(skb->sk);
  	unsigned int max_rows = 1U << tcp_metrics_hash_log;
  	unsigned int row, s_row = cb->args[0];
  	int s_col = cb->args[1], col = s_col;
  
  	for (row = s_row; row < max_rows; row++, s_col = 0) {
  		struct tcp_metrics_block *tm;
  		struct tcpm_hash_bucket *hb = tcp_metrics_hash + row;
  
  		rcu_read_lock();
  		for (col = 0, tm = rcu_dereference(hb->chain); tm;
  		     tm = rcu_dereference(tm->tcpm_next), col++) {
  			if (!net_eq(tm_net(tm), net))
  				continue;
  			if (col < s_col)
  				continue;
  			if (tcp_metrics_dump_info(skb, cb, tm) < 0) {
  				rcu_read_unlock();
  				goto done;
  			}
  		}
  		rcu_read_unlock();
  	}
  
  done:
  	cb->args[0] = row;
  	cb->args[1] = col;
  	return skb->len;
  }
  
  static int __parse_nl_addr(struct genl_info *info, struct inetpeer_addr *addr,
  			   unsigned int *hash, int optional, int v4, int v6)
  {
  	struct nlattr *a;
  
  	a = info->attrs[v4];
  	if (a) {
  		inetpeer_set_addr_v4(addr, nla_get_in_addr(a));
  		if (hash)
  			*hash = ipv4_addr_hash(inetpeer_get_addr_v4(addr));
  		return 0;
  	}
  	a = info->attrs[v6];
  	if (a) {
  		struct in6_addr in6;
  
  		if (nla_len(a) != sizeof(struct in6_addr))
  			return -EINVAL;
  		in6 = nla_get_in6_addr(a);
  		inetpeer_set_addr_v6(addr, &in6);
  		if (hash)
  			*hash = ipv6_addr_hash(inetpeer_get_addr_v6(addr));
  		return 0;
  	}
  	return optional ? 1 : -EAFNOSUPPORT;
  }
  
  static int parse_nl_addr(struct genl_info *info, struct inetpeer_addr *addr,
  			 unsigned int *hash, int optional)
  {
  	return __parse_nl_addr(info, addr, hash, optional,
  			       TCP_METRICS_ATTR_ADDR_IPV4,
  			       TCP_METRICS_ATTR_ADDR_IPV6);
  }
  
  static int parse_nl_saddr(struct genl_info *info, struct inetpeer_addr *addr)
  {
  	return __parse_nl_addr(info, addr, NULL, 0,
  			       TCP_METRICS_ATTR_SADDR_IPV4,
  			       TCP_METRICS_ATTR_SADDR_IPV6);
  }
  
  static int tcp_metrics_nl_cmd_get(struct sk_buff *skb, struct genl_info *info)
  {
  	struct tcp_metrics_block *tm;
  	struct inetpeer_addr saddr, daddr;
  	unsigned int hash;
  	struct sk_buff *msg;
  	struct net *net = genl_info_net(info);
  	void *reply;
  	int ret;
  	bool src = true;
  
  	ret = parse_nl_addr(info, &daddr, &hash, 0);
  	if (ret < 0)
  		return ret;
  
  	ret = parse_nl_saddr(info, &saddr);
  	if (ret < 0)
  		src = false;
  
  	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
  	if (!msg)
  		return -ENOMEM;
  
  	reply = genlmsg_put_reply(msg, info, &tcp_metrics_nl_family, 0,
  				  info->genlhdr->cmd);
  	if (!reply)
  		goto nla_put_failure;
  
  	hash ^= net_hash_mix(net);
  	hash = hash_32(hash, tcp_metrics_hash_log);
  	ret = -ESRCH;
  	rcu_read_lock();
  	for (tm = rcu_dereference(tcp_metrics_hash[hash].chain); tm;
  	     tm = rcu_dereference(tm->tcpm_next)) {
  		if (addr_same(&tm->tcpm_daddr, &daddr) &&
  		    (!src || addr_same(&tm->tcpm_saddr, &saddr)) &&
  		    net_eq(tm_net(tm), net)) {
  			ret = tcp_metrics_fill_info(msg, tm);
  			break;
  		}
  	}
  	rcu_read_unlock();
  	if (ret < 0)
  		goto out_free;
  
  	genlmsg_end(msg, reply);
  	return genlmsg_reply(msg, info);
  
  nla_put_failure:
  	ret = -EMSGSIZE;
  
  out_free:
  	nlmsg_free(msg);
  	return ret;
  }
  
  static void tcp_metrics_flush_all(struct net *net)
  {
  	unsigned int max_rows = 1U << tcp_metrics_hash_log;
  	struct tcpm_hash_bucket *hb = tcp_metrics_hash;
  	struct tcp_metrics_block *tm;
  	unsigned int row;
  
  	for (row = 0; row < max_rows; row++, hb++) {
  		struct tcp_metrics_block __rcu **pp;
  		spin_lock_bh(&tcp_metrics_lock);
  		pp = &hb->chain;
  		for (tm = deref_locked(*pp); tm; tm = deref_locked(*pp)) {
  			if (net_eq(tm_net(tm), net)) {
  				*pp = tm->tcpm_next;
  				kfree_rcu(tm, rcu_head);
  			} else {
  				pp = &tm->tcpm_next;
  			}
  		}
  		spin_unlock_bh(&tcp_metrics_lock);
  	}
  }
  
  static int tcp_metrics_nl_cmd_del(struct sk_buff *skb, struct genl_info *info)
  {
  	struct tcpm_hash_bucket *hb;
  	struct tcp_metrics_block *tm;
  	struct tcp_metrics_block __rcu **pp;
  	struct inetpeer_addr saddr, daddr;
  	unsigned int hash;
  	struct net *net = genl_info_net(info);
  	int ret;
  	bool src = true, found = false;
  
  	ret = parse_nl_addr(info, &daddr, &hash, 1);
  	if (ret < 0)
  		return ret;
  	if (ret > 0) {
  		tcp_metrics_flush_all(net);
  		return 0;
  	}
  	ret = parse_nl_saddr(info, &saddr);
  	if (ret < 0)
  		src = false;
  
  	hash ^= net_hash_mix(net);
  	hash = hash_32(hash, tcp_metrics_hash_log);
  	hb = tcp_metrics_hash + hash;
  	pp = &hb->chain;
  	spin_lock_bh(&tcp_metrics_lock);
  	for (tm = deref_locked(*pp); tm; tm = deref_locked(*pp)) {
  		if (addr_same(&tm->tcpm_daddr, &daddr) &&
  		    (!src || addr_same(&tm->tcpm_saddr, &saddr)) &&
  		    net_eq(tm_net(tm), net)) {
  			*pp = tm->tcpm_next;
  			kfree_rcu(tm, rcu_head);
  			found = true;
  		} else {
  			pp = &tm->tcpm_next;
  		}
  	}
  	spin_unlock_bh(&tcp_metrics_lock);
  	if (!found)
  		return -ESRCH;
  	return 0;
  }
  
  static const struct genl_ops tcp_metrics_nl_ops[] = {
  	{
  		.cmd = TCP_METRICS_CMD_GET,
  		.doit = tcp_metrics_nl_cmd_get,
  		.dumpit = tcp_metrics_nl_dump,
  		.policy = tcp_metrics_nl_policy,
  	},
  	{
  		.cmd = TCP_METRICS_CMD_DEL,
  		.doit = tcp_metrics_nl_cmd_del,
  		.policy = tcp_metrics_nl_policy,
  		.flags = GENL_ADMIN_PERM,
  	},
  };
  
  static struct genl_family tcp_metrics_nl_family __ro_after_init = {
  	.hdrsize	= 0,
  	.name		= TCP_METRICS_GENL_NAME,
  	.version	= TCP_METRICS_GENL_VERSION,
  	.maxattr	= TCP_METRICS_ATTR_MAX,
  	.netnsok	= true,
  	.module		= THIS_MODULE,
  	.ops		= tcp_metrics_nl_ops,
  	.n_ops		= ARRAY_SIZE(tcp_metrics_nl_ops),
  };
  
  static unsigned int tcpmhash_entries;
  static int __init set_tcpmhash_entries(char *str)
  {
  	ssize_t ret;
  
  	if (!str)
  		return 0;
  
  	ret = kstrtouint(str, 0, &tcpmhash_entries);
  	if (ret)
  		return 0;
  
  	return 1;
  }
  __setup("tcpmhash_entries=", set_tcpmhash_entries);
  
  static int __net_init tcp_net_metrics_init(struct net *net)
  {
  	size_t size;
  	unsigned int slots;
  
  	if (!net_eq(net, &init_net))
  		return 0;
  
  	slots = tcpmhash_entries;
  	if (!slots) {
  		if (totalram_pages >= 128 * 1024)
  			slots = 16 * 1024;
  		else
  			slots = 8 * 1024;
  	}
  
  	tcp_metrics_hash_log = order_base_2(slots);
  	size = sizeof(struct tcpm_hash_bucket) << tcp_metrics_hash_log;
  
  	tcp_metrics_hash = kvzalloc(size, GFP_KERNEL);
  	if (!tcp_metrics_hash)
  		return -ENOMEM;
  
  	return 0;
  }
  
  static void __net_exit tcp_net_metrics_exit(struct net *net)
  {
  	tcp_metrics_flush_all(net);
  }
  
  static __net_initdata struct pernet_operations tcp_net_metrics_ops = {
  	.init	=	tcp_net_metrics_init,
  	.exit	=	tcp_net_metrics_exit,
  };
  
  void __init tcp_metrics_init(void)
  {
  	int ret;
  
  	ret = register_pernet_subsys(&tcp_net_metrics_ops);
  	if (ret < 0)
  		panic("Could not allocate the tcp_metrics hash table\n");
  
  	ret = genl_register_family(&tcp_metrics_nl_family);
  	if (ret < 0)
  		panic("Could not register tcp_metrics generic netlink\n");
  }
  