tcp_metrics.c

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#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;

struct tcp_fastopen_metrics {
    u16 mss;
    u16 syn_loss:10;        /* Recurring Fast Open SYN losses */
    unsigned long   last_syn_loss;  /* Last Fast Open SYN loss */
    struct  tcp_fastopen_cookie cookie;
};

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 + 1];
    struct tcp_fastopen_metrics tcpm_fastopen;

    struct rcu_head         rcu_head;
};

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;

    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;

    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;
    tm->tcpm_fastopen.mss = 0;
    tm->tcpm_fastopen.syn_loss = 0;
    tm->tcpm_fastopen.cookie.len = 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;

    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 = ipv6_addr_hash(&inet6_rsk(req)->rmt_addr);
        break;
    default:
        return NULL;
    }

    net = dev_net(dst->dev);
    hash = hash_32(hash, net->ipv4.tcp_metrics_hash_log);

    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 = ipv6_addr_hash(&tw6->tw_v6_daddr);
        break;
    default:
        return NULL;
    }

    net = twsk_net(tw);
    hash = hash_32(hash, net->ipv4.tcp_metrics_hash_log);

    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 = ipv6_addr_hash(&inet6_sk(sk)->daddr);
        break;
    default:
        return NULL;
    }

    net = dev_net(dst->dev);
    hash = hash_32(hash, net->ipv4.tcp_metrics_hash_log);

    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 (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;
            *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)
{
    struct tcp_metrics_block *tm;

    rcu_read_lock();
    tm = tcp_get_metrics(sk, __sk_dst_get(sk), true);
    if (tm) {
        struct tcp_fastopen_metrics *tfom = &tm->tcpm_fastopen;

        write_seqlock_bh(&fastopen_seqlock);
        tfom->mss = mss;
        if (cookie->len > 0)
            tfom->cookie = *cookie;
        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 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_addr.family) {
    case AF_INET:
        if (nla_put_be32(msg, TCP_METRICS_ATTR_ADDR_IPV4,
                tm->tcpm_addr.addr.a4) < 0)
            goto nla_put_failure;
        break;
    case AF_INET6:
        if (nla_put(msg, TCP_METRICS_ATTR_ADDR_IPV6, 16,
                tm->tcpm_addr.addr.a6) < 0)
            goto nla_put_failure;
        break;
    default:
        return -EAFNOSUPPORT;
    }

    if (nla_put_msecs(msg, TCP_METRICS_ATTR_AGE,
              jiffies - tm->tcpm_stamp) < 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 + 1; i++) {
            if (!tm->tcpm_vals[i])
                continue;
            if (nla_put_u32(msg, i + 1, tm->tcpm_vals[i]) < 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) < 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;

    return genlmsg_end(skb, hdr);

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 << net->ipv4.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 = net->ipv4.tcp_metrics_hash + row;

        rcu_read_lock();
        for (col = 0, tm = rcu_dereference(hb->chain); tm;
             tm = rcu_dereference(tm->tcpm_next), col++) {
            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)
{
    struct nlattr *a;

    a = info->attrs[TCP_METRICS_ATTR_ADDR_IPV4];
    if (a) {
        addr->family = AF_INET;
        addr->addr.a4 = nla_get_be32(a);
        *hash = (__force unsigned int) addr->addr.a4;
        return 0;
    }
    a = info->attrs[TCP_METRICS_ATTR_ADDR_IPV6];
    if (a) {
        if (nla_len(a) != sizeof(struct in6_addr))
            return -EINVAL;
        addr->family = AF_INET6;
        memcpy(addr->addr.a6, nla_data(a), sizeof(addr->addr.a6));
        *hash = ipv6_addr_hash((struct in6_addr *) addr->addr.a6);
        return 0;
    }
    return optional ? 1 : -EAFNOSUPPORT;
}

static int tcp_metrics_nl_cmd_get(struct sk_buff *skb, struct genl_info *info)
{
    struct tcp_metrics_block *tm;
    struct inetpeer_addr addr;
    unsigned int hash;
    struct sk_buff *msg;
    struct net *net = genl_info_net(info);
    void *reply;
    int ret;

    ret = parse_nl_addr(info, &addr, &hash, 0);
    if (ret < 0)
        return ret;

    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 = hash_32(hash, net->ipv4.tcp_metrics_hash_log);
    ret = -ESRCH;
    rcu_read_lock();
    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)) {
            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;
}

#define deref_locked_genl(p)    \
    rcu_dereference_protected(p, lockdep_genl_is_held() && \
                     lockdep_is_held(&tcp_metrics_lock))

#define deref_genl(p)   rcu_dereference_protected(p, lockdep_genl_is_held())

static int tcp_metrics_flush_all(struct net *net)
{
    unsigned int max_rows = 1U << net->ipv4.tcp_metrics_hash_log;
    struct tcpm_hash_bucket *hb = net->ipv4.tcp_metrics_hash;
    struct tcp_metrics_block *tm;
    unsigned int row;

    for (row = 0; row < max_rows; row++, hb++) {
        spin_lock_bh(&tcp_metrics_lock);
        tm = deref_locked_genl(hb->chain);
        if (tm)
            hb->chain = NULL;
        spin_unlock_bh(&tcp_metrics_lock);
        while (tm) {
            struct tcp_metrics_block *next;

            next = deref_genl(tm->tcpm_next);
            kfree_rcu(tm, rcu_head);
            tm = next;
        }
    }
    return 0;
}

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 addr;
    unsigned int hash;
    struct net *net = genl_info_net(info);
    int ret;

    ret = parse_nl_addr(info, &addr, &hash, 1);
    if (ret < 0)
        return ret;
    if (ret > 0)
        return tcp_metrics_flush_all(net);

    hash = hash_32(hash, net->ipv4.tcp_metrics_hash_log);
    hb = net->ipv4.tcp_metrics_hash + hash;
    pp = &hb->chain;
    spin_lock_bh(&tcp_metrics_lock);
    for (tm = deref_locked_genl(*pp); tm;
         pp = &tm->tcpm_next, tm = deref_locked_genl(*pp)) {
        if (addr_same(&tm->tcpm_addr, &addr)) {
            *pp = tm->tcpm_next;
            break;
        }
    }
    spin_unlock_bh(&tcp_metrics_lock);
    if (!tm)
        return -ESRCH;
    kfree_rcu(tm, rcu_head);
    return 0;
}

static 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,
        .flags = GENL_ADMIN_PERM,
    },
    {
        .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;

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

    net->ipv4.tcp_metrics_hash_log = order_base_2(slots);
    size = sizeof(struct tcpm_hash_bucket) << net->ipv4.tcp_metrics_hash_log;

    net->ipv4.tcp_metrics_hash = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
    if (!net->ipv4.tcp_metrics_hash)
        net->ipv4.tcp_metrics_hash = vzalloc(size);

    if (!net->ipv4.tcp_metrics_hash)
        return -ENOMEM;

    return 0;
}

static void __net_exit tcp_net_metrics_exit(struct net *net)
{
    unsigned int i;

    for (i = 0; i < (1U << net->ipv4.tcp_metrics_hash_log) ; i++) {
        struct tcp_metrics_block *tm, *next;

        tm = rcu_dereference_protected(net->ipv4.tcp_metrics_hash[i].chain, 1);
        while (tm) {
            next = rcu_dereference_protected(tm->tcpm_next, 1);
            kfree(tm);
            tm = next;
        }
    }
    if (is_vmalloc_addr(net->ipv4.tcp_metrics_hash))
        vfree(net->ipv4.tcp_metrics_hash);
    else
        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)
{
    int ret;

    ret = register_pernet_subsys(&tcp_net_metrics_ops);
    if (ret < 0)
        goto cleanup;
    ret = genl_register_family_with_ops(&tcp_metrics_nl_family,
                        tcp_metrics_nl_ops,
                        ARRAY_SIZE(tcp_metrics_nl_ops));
    if (ret < 0)
        goto cleanup_subsys;
    return;

cleanup_subsys:
    unregister_pernet_subsys(&tcp_net_metrics_ops);

cleanup:
    return;
}