#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_ts;
        u32                             tcpm_ts_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);
        tm->tcpm_ts = 0;
        tm->tcpm_ts_stamp = 0;
        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_tw(struct inet_timewait_sock *tw)
{
        struct tcp_metrics_block *tm;
        struct inetpeer_addr saddr, daddr;
        unsigned int hash;
        struct net *net;

        if (tw->tw_family == AF_INET) {
                inetpeer_set_addr_v4(&saddr, tw->tw_rcv_saddr);
                inetpeer_set_addr_v4(&daddr, tw->tw_daddr);
                hash = ipv4_addr_hash(tw->tw_daddr);
        }
#if IS_ENABLED(CONFIG_IPV6)
        else if (tw->tw_family == AF_INET6) {
                if (ipv6_addr_v4mapped(&tw->tw_v6_daddr)) {
                        inetpeer_set_addr_v4(&saddr, tw->tw_rcv_saddr);
                        inetpeer_set_addr_v4(&daddr, tw->tw_daddr);
                        hash = ipv4_addr_hash(tw->tw_daddr);
                } else {
                        inetpeer_set_addr_v6(&saddr, &tw->tw_v6_rcv_saddr);
                        inetpeer_set_addr_v6(&daddr, &tw->tw_v6_daddr);
                        hash = ipv6_addr_hash(&tw->tw_v6_daddr);
                }
        }
#endif
        else
                return NULL;

        net = twsk_net(tw);
        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;
        }
        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;

        if (sysctl_tcp_nometrics_save || !dst)
                return;

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

        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 */

        if (!dst)
                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;
        }

        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_time_stamp;
}

bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
                        bool paws_check, bool timestamps)
{
        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 ||
                     !timestamps))
                        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 (tm) {
                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 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 = {
        .id             = GENL_ID_GENERATE,
        .hdrsize        = 0,
        .name           = TCP_METRICS_GENL_NAME,
        .version        = TCP_METRICS_GENL_VERSION,
        .maxattr        = TCP_METRICS_ATTR_MAX,
        .netnsok        = true,
};

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;
        if (tm->tcpm_ts_stamp) {
                if (nla_put_s32(msg, TCP_METRICS_ATTR_TW_TS_STAMP,
                                (s32) (get_seconds() - tm->tcpm_ts_stamp)) < 0)
                        goto nla_put_failure;
                if (nla_put_u32(msg, TCP_METRICS_ATTR_TW_TSVAL,
                                tm->tcpm_ts) < 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 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 = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
        if (!tcp_metrics_hash)
                tcp_metrics_hash = vzalloc(size);

        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_with_ops(&tcp_metrics_nl_family,
                                            tcp_metrics_nl_ops);
        if (ret < 0)
                panic("Could not register tcp_metrics generic netlink\n");
}