tcp_metrics.c

#include <linux/rcupdate.h>
#include <linux/spinlock.h>
#include <linux/jiffies.h>
#include <linux/bootmem.h>
#include <linux/module.h>
#include <linux/cache.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/tcp.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>

int sysctl_tcp_nometrics_save __read_mostly;

enum tcp_metric_index {
	TCP_METRIC_RTT,
	TCP_METRIC_RTTVAR,
	TCP_METRIC_SSTHRESH,
	TCP_METRIC_CWND,
	TCP_METRIC_REORDERING,

	/* Always last.  */
	TCP_METRIC_MAX,
};

struct tcp_metrics_block {
	struct tcp_metrics_block __rcu	*tcpm_next;
	struct inetpeer_addr		tcpm_addr;
	unsigned long			tcpm_stamp;
	u32				tcpm_ts;
	u32				tcpm_ts_stamp;
	u32				tcpm_lock;
	u32				tcpm_vals[TCP_METRIC_MAX];
};

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 u32 tcp_metric_get_jiffies(struct tcp_metrics_block *tm,
				  enum tcp_metric_index idx)
{
	return msecs_to_jiffies(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 void tcp_metric_set_msecs(struct tcp_metrics_block *tm,
				 enum tcp_metric_index idx,
				 u32 val)
{
	tm->tcpm_vals[idx] = jiffies_to_msecs(val);
}

static bool addr_same(const struct inetpeer_addr *a,
		      const struct inetpeer_addr *b)
{
	const struct in6_addr *a6, *b6;

	if (a->family != b->family)
		return false;
	if (a->family == AF_INET)
		return a->addr.a4 == b->addr.a4;

	a6 = (const struct in6_addr *) &a->addr.a6[0];
	b6 = (const struct in6_addr *) &b->addr.a6[0];

	return ipv6_addr_equal(a6, b6);
}

struct tcpm_hash_bucket {
	struct tcp_metrics_block __rcu	*chain;
};

static DEFINE_SPINLOCK(tcp_metrics_lock);

static void tcpm_suck_dst(struct tcp_metrics_block *tm, struct dst_entry *dst)
{
	u32 val;

	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;

	tm->tcpm_vals[TCP_METRIC_RTT] = dst_metric_raw(dst, RTAX_RTT);
	tm->tcpm_vals[TCP_METRIC_RTTVAR] = dst_metric_raw(dst, RTAX_RTTVAR);
	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);
	tm->tcpm_ts = 0;
	tm->tcpm_ts_stamp = 0;
}

static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst,
					  struct inetpeer_addr *addr,
					  unsigned int hash,
					  bool reclaim)
{
	struct tcp_metrics_block *tm;
	struct net *net;

	spin_lock_bh(&tcp_metrics_lock);
	net = dev_net(dst->dev);
	if (unlikely(reclaim)) {
		struct tcp_metrics_block *oldest;

		oldest = rcu_dereference(net->ipv4.tcp_metrics_hash[hash].chain);
		for (tm = rcu_dereference(oldest->tcpm_next); tm;
		     tm = rcu_dereference(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;
	}
	tm->tcpm_addr = *addr;
	tm->tcpm_stamp = jiffies;

	tcpm_suck_dst(tm, dst);

	if (likely(!reclaim)) {
		tm->tcpm_next = net->ipv4.tcp_metrics_hash[hash].chain;
		rcu_assign_pointer(net->ipv4.tcp_metrics_hash[hash].chain, tm);
	}

out_unlock:
	spin_unlock_bh(&tcp_metrics_lock);
	return tm;
}

#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);
}

#define TCP_METRICS_RECLAIM_DEPTH	5
#define TCP_METRICS_RECLAIM_PTR		(struct tcp_metrics_block *) 0x1UL

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 *addr,
						   struct net *net, unsigned int hash)
{
	struct tcp_metrics_block *tm;
	int depth = 0;

	for (tm = rcu_dereference(net->ipv4.tcp_metrics_hash[hash].chain); tm;
	     tm = rcu_dereference(tm->tcpm_next)) {
		if (addr_same(&tm->tcpm_addr, addr))
			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 addr;
	unsigned int hash;
	struct net *net;

	addr.family = req->rsk_ops->family;
	switch (addr.family) {
	case AF_INET:
		addr.addr.a4 = inet_rsk(req)->rmt_addr;
		hash = (__force unsigned int) addr.addr.a4;
		break;
	case AF_INET6:
		*(struct in6_addr *)addr.addr.a6 = inet6_rsk(req)->rmt_addr;
		hash = ((__force unsigned int) addr.addr.a6[0] ^
			(__force unsigned int) addr.addr.a6[1] ^
			(__force unsigned int) addr.addr.a6[2] ^
			(__force unsigned int) addr.addr.a6[3]);
		break;
	default:
		return NULL;
	}

	hash ^= (hash >> 24) ^ (hash >> 16) ^ (hash >> 8);

	net = dev_net(dst->dev);
	hash &= net->ipv4.tcp_metrics_hash_mask;

	for (tm = rcu_dereference(net->ipv4.tcp_metrics_hash[hash].chain); tm;
	     tm = rcu_dereference(tm->tcpm_next)) {
		if (addr_same(&tm->tcpm_addr, &addr))
			break;
	}
	tcpm_check_stamp(tm, dst);
	return tm;
}

static struct tcp_metrics_block *__tcp_get_metrics_tw(struct inet_timewait_sock *tw)
{
	struct inet6_timewait_sock *tw6;
	struct tcp_metrics_block *tm;
	struct inetpeer_addr addr;
	unsigned int hash;
	struct net *net;

	addr.family = tw->tw_family;
	switch (addr.family) {
	case AF_INET:
		addr.addr.a4 = tw->tw_daddr;
		hash = (__force unsigned int) addr.addr.a4;
		break;
	case AF_INET6:
		tw6 = inet6_twsk((struct sock *)tw);
		*(struct in6_addr *)addr.addr.a6 = tw6->tw_v6_daddr;
		hash = ((__force unsigned int) addr.addr.a6[0] ^
			(__force unsigned int) addr.addr.a6[1] ^
			(__force unsigned int) addr.addr.a6[2] ^
			(__force unsigned int) addr.addr.a6[3]);
		break;
	default:
		return NULL;
	}

	hash ^= (hash >> 24) ^ (hash >> 16) ^ (hash >> 8);

	net = twsk_net(tw);
	hash &= net->ipv4.tcp_metrics_hash_mask;

	for (tm = rcu_dereference(net->ipv4.tcp_metrics_hash[hash].chain); tm;
	     tm = rcu_dereference(tm->tcpm_next)) {
		if (addr_same(&tm->tcpm_addr, &addr))
			break;
	}
	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 addr;
	unsigned int hash;
	struct net *net;
	bool reclaim;

	addr.family = sk->sk_family;
	switch (addr.family) {
	case AF_INET:
		addr.addr.a4 = inet_sk(sk)->inet_daddr;
		hash = (__force unsigned int) addr.addr.a4;
		break;
	case AF_INET6:
		*(struct in6_addr *)addr.addr.a6 = inet6_sk(sk)->daddr;
		hash = ((__force unsigned int) addr.addr.a6[0] ^
			(__force unsigned int) addr.addr.a6[1] ^
			(__force unsigned int) addr.addr.a6[2] ^
			(__force unsigned int) addr.addr.a6[3]);
		break;
	default:
		return NULL;
	}

	hash ^= (hash >> 24) ^ (hash >> 16) ^ (hash >> 8);

	net = dev_net(dst->dev);
	hash &= net->ipv4.tcp_metrics_hash_mask;

	tm = __tcp_get_metrics(&addr, net, hash);
	reclaim = false;
	if (tm == TCP_METRICS_RECLAIM_PTR) {
		reclaim = true;
		tm = NULL;
	}
	if (!tm && create)
		tm = tcpm_new(dst, &addr, hash, reclaim);
	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 tcp_metrics_block *tm;
	unsigned long rtt;
	u32 val;
	int m;

	if (sysctl_tcp_nometrics_save || !dst)
		return;

	if (dst->flags & DST_HOST)
		dst_confirm(dst);

	rcu_read_lock();
	if (icsk->icsk_backoff || !tp->srtt) {
		/* 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_jiffies(tm, TCP_METRIC_RTT);
	m = rtt - tp->srtt;

	/* 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;
		else
			rtt -= (m >> 3);
		tcp_metric_set_msecs(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)
			m = tp->mdev;

		var = tcp_metric_get_jiffies(tm, TCP_METRIC_RTTVAR);
		if (m >= var)
			var = m;
		else
			var -= (var - m) >> 2;

		tcp_metric_set_msecs(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 (tp->snd_cwnd > tp->snd_ssthresh &&
		   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 != 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;

	if (dst == NULL)
		goto reset;

	dst_confirm(dst);

	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);
		tcp_disable_early_retrans(tp);
		tp->reordering = val;
	}

	val = tcp_metric_get(tm, TCP_METRIC_RTT);
	if (val == 0 || tp->srtt == 0) {
		rcu_read_unlock();
		goto reset;
	}
	/* Initial rtt is determined from SYN,SYN-ACK.
	 * The segment is small and rtt may appear much
	 * less than real one. Use per-dst memory
	 * to make it more realistic.
	 *
	 * 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.
	 */
	val = msecs_to_jiffies(val);
	if (val > tp->srtt) {
		tp->srtt = val;
		tp->rtt_seq = tp->snd_nxt;
	}
	val = tcp_metric_get_jiffies(tm, TCP_METRIC_RTTVAR);
	if (val > tp->mdev) {
		tp->mdev = val;
		tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
	}
	rcu_read_unlock();

	tcp_set_rto(sk);
reset:
	if (tp->srtt == 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->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
		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_time_stamp;
}

bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst, bool paws_check)
{
	struct tcp_metrics_block *tm;
	bool ret;

	if (!dst)
		return false;

	rcu_read_lock();
	tm = __tcp_get_metrics_req(req, dst);
	if (paws_check) {
		if (tm &&
		    (u32)get_seconds() - tm->tcpm_ts_stamp < TCP_PAWS_MSL &&
		    (s32)(tm->tcpm_ts - req->ts_recent) > TCP_PAWS_WINDOW)
			ret = false;
		else
			ret = true;
	} else {
		if (tm && tcp_metric_get(tm, TCP_METRIC_RTT) && tm->tcpm_ts_stamp)
			ret = true;
		else
			ret = false;
	}
	rcu_read_unlock();

	return ret;
}
EXPORT_SYMBOL_GPL(tcp_peer_is_proven);

void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst)
{
	struct tcp_metrics_block *tm;

	rcu_read_lock();
	tm = tcp_get_metrics(sk, dst, true);
	if (tm) {
		struct tcp_sock *tp = tcp_sk(sk);

		if ((u32)get_seconds() - tm->tcpm_ts_stamp <= TCP_PAWS_MSL) {
			tp->rx_opt.ts_recent_stamp = tm->tcpm_ts_stamp;
			tp->rx_opt.ts_recent = tm->tcpm_ts;
		}
	}
	rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(tcp_fetch_timewait_stamp);

/* VJ's idea. Save last timestamp seen from this destination and hold
 * it at least for normal timewait interval to use for duplicate
 * segment detection in subsequent connections, before they enter
 * synchronized state.
 */
bool tcp_remember_stamp(struct sock *sk)
{
	struct dst_entry *dst = __sk_dst_get(sk);
	bool ret = false;

	if (dst) {
		struct tcp_metrics_block *tm;

		rcu_read_lock();
		tm = tcp_get_metrics(sk, dst, true);
		if (tm) {
			struct tcp_sock *tp = tcp_sk(sk);

			if ((s32)(tm->tcpm_ts - tp->rx_opt.ts_recent) <= 0 ||
			    ((u32)get_seconds() - tm->tcpm_ts_stamp > TCP_PAWS_MSL &&
			     tm->tcpm_ts_stamp <= (u32)tp->rx_opt.ts_recent_stamp)) {
				tm->tcpm_ts_stamp = (u32)tp->rx_opt.ts_recent_stamp;
				tm->tcpm_ts = tp->rx_opt.ts_recent;
			}
			ret = true;
		}
		rcu_read_unlock();
	}
	return ret;
}

bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw)
{
	struct tcp_metrics_block *tm;
	bool ret = false;

	rcu_read_lock();
	tm = __tcp_get_metrics_tw(tw);
	if (tw) {
		const struct tcp_timewait_sock *tcptw;
		struct sock *sk = (struct sock *) tw;

		tcptw = tcp_twsk(sk);
		if ((s32)(tm->tcpm_ts - tcptw->tw_ts_recent) <= 0 ||
		    ((u32)get_seconds() - tm->tcpm_ts_stamp > TCP_PAWS_MSL &&
		     tm->tcpm_ts_stamp <= (u32)tcptw->tw_ts_recent_stamp)) {
			tm->tcpm_ts_stamp = (u32)tcptw->tw_ts_recent_stamp;
			tm->tcpm_ts	   = tcptw->tw_ts_recent;
		}
		ret = true;
	}
	rcu_read_unlock();

	return ret;
}

static unsigned long tcpmhash_entries;
static int __init set_tcpmhash_entries(char *str)
{
	ssize_t ret;

	if (!str)
		return 0;

	ret = kstrtoul(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)
{
	int slots, size;

	slots = tcpmhash_entries;
	if (!slots) {
		if (totalram_pages >= 128 * 1024)
			slots = 16 * 1024;
		else
			slots = 8 * 1024;
	}

	size = slots * sizeof(struct tcpm_hash_bucket);

	net->ipv4.tcp_metrics_hash = kzalloc(size, GFP_KERNEL);
	if (!net->ipv4.tcp_metrics_hash)
		return -ENOMEM;

	net->ipv4.tcp_metrics_hash_mask = (slots - 1);

	return 0;
}

static void __net_exit tcp_net_metrics_exit(struct net *net)
{
	kfree(net->ipv4.tcp_metrics_hash);
}

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)
{
	register_pernet_subsys(&tcp_net_metrics_ops);
}