Merge tag 'pwm/for-5.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/thierry...

[linux-2.6-microblaze.git] / net / batman-adv / tp_meter.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright (C) 2012-2020  B.A.T.M.A.N. contributors:
 *
 * Edo Monticelli, Antonio Quartulli
 */

#include "tp_meter.h"
#include "main.h"

#include <linux/atomic.h>
#include <linux/build_bug.h>
#include <linux/byteorder/generic.h>
#include <linux/cache.h>
#include <linux/compiler.h>
#include <linux/err.h>
#include <linux/etherdevice.h>
#include <linux/gfp.h>
#include <linux/if_ether.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/kref.h>
#include <linux/kthread.h>
#include <linux/limits.h>
#include <linux/list.h>
#include <linux/minmax.h>
#include <linux/netdevice.h>
#include <linux/param.h>
#include <linux/printk.h>
#include <linux/random.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stddef.h>
#include <linux/string.h>
#include <linux/timer.h>
#include <linux/wait.h>
#include <linux/workqueue.h>
#include <uapi/linux/batadv_packet.h>
#include <uapi/linux/batman_adv.h>

#include "hard-interface.h"
#include "log.h"
#include "netlink.h"
#include "originator.h"
#include "send.h"

/**
 * BATADV_TP_DEF_TEST_LENGTH - Default test length if not specified by the user
 *  in milliseconds
 */
#define BATADV_TP_DEF_TEST_LENGTH 10000

/**
 * BATADV_TP_AWND - Advertised window by the receiver (in bytes)
 */
#define BATADV_TP_AWND 0x20000000

/**
 * BATADV_TP_RECV_TIMEOUT - Receiver activity timeout. If the receiver does not
 *  get anything for such amount of milliseconds, the connection is killed
 */
#define BATADV_TP_RECV_TIMEOUT 1000

/**
 * BATADV_TP_MAX_RTO - Maximum sender timeout. If the sender RTO gets beyond
 * such amount of milliseconds, the receiver is considered unreachable and the
 * connection is killed
 */
#define BATADV_TP_MAX_RTO 30000

/**
 * BATADV_TP_FIRST_SEQ - First seqno of each session. The number is rather high
 *  in order to immediately trigger a wrap around (test purposes)
 */
#define BATADV_TP_FIRST_SEQ ((u32)-1 - 2000)

/**
 * BATADV_TP_PLEN - length of the payload (data after the batadv_unicast header)
 *  to simulate
 */
#define BATADV_TP_PLEN (BATADV_TP_PACKET_LEN - ETH_HLEN - \
                        sizeof(struct batadv_unicast_packet))

static u8 batadv_tp_prerandom[4096] __read_mostly;

/**
 * batadv_tp_session_cookie() - generate session cookie based on session ids
 * @session: TP session identifier
 * @icmp_uid: icmp pseudo uid of the tp session
 *
 * Return: 32 bit tp_meter session cookie
 */
static u32 batadv_tp_session_cookie(const u8 session[2], u8 icmp_uid)
{
        u32 cookie;

        cookie = icmp_uid << 16;
        cookie |= session[0] << 8;
        cookie |= session[1];

        return cookie;
}

/**
 * batadv_tp_cwnd() - compute the new cwnd size
 * @base: base cwnd size value
 * @increment: the value to add to base to get the new size
 * @min: minimum cwnd value (usually MSS)
 *
 * Return the new cwnd size and ensure it does not exceed the Advertised
 * Receiver Window size. It is wrapped around safely.
 * For details refer to Section 3.1 of RFC5681
 *
 * Return: new congestion window size in bytes
 */
static u32 batadv_tp_cwnd(u32 base, u32 increment, u32 min)
{
        u32 new_size = base + increment;

        /* check for wrap-around */
        if (new_size < base)
                new_size = (u32)ULONG_MAX;

        new_size = min_t(u32, new_size, BATADV_TP_AWND);

        return max_t(u32, new_size, min);
}

/**
 * batadv_tp_updated_cwnd() - update the Congestion Windows
 * @tp_vars: the private data of the current TP meter session
 * @mss: maximum segment size of transmission
 *
 * 1) if the session is in Slow Start, the CWND has to be increased by 1
 * MSS every unique received ACK
 * 2) if the session is in Congestion Avoidance, the CWND has to be
 * increased by MSS * MSS / CWND for every unique received ACK
 */
static void batadv_tp_update_cwnd(struct batadv_tp_vars *tp_vars, u32 mss)
{
        spin_lock_bh(&tp_vars->cwnd_lock);

        /* slow start... */
        if (tp_vars->cwnd <= tp_vars->ss_threshold) {
                tp_vars->dec_cwnd = 0;
                tp_vars->cwnd = batadv_tp_cwnd(tp_vars->cwnd, mss, mss);
                spin_unlock_bh(&tp_vars->cwnd_lock);
                return;
        }

        /* increment CWND at least of 1 (section 3.1 of RFC5681) */
        tp_vars->dec_cwnd += max_t(u32, 1U << 3,
                                   ((mss * mss) << 6) / (tp_vars->cwnd << 3));
        if (tp_vars->dec_cwnd < (mss << 3)) {
                spin_unlock_bh(&tp_vars->cwnd_lock);
                return;
        }

        tp_vars->cwnd = batadv_tp_cwnd(tp_vars->cwnd, mss, mss);
        tp_vars->dec_cwnd = 0;

        spin_unlock_bh(&tp_vars->cwnd_lock);
}

/**
 * batadv_tp_update_rto() - calculate new retransmission timeout
 * @tp_vars: the private data of the current TP meter session
 * @new_rtt: new roundtrip time in msec
 */
static void batadv_tp_update_rto(struct batadv_tp_vars *tp_vars,
                                 u32 new_rtt)
{
        long m = new_rtt;

        /* RTT update
         * Details in Section 2.2 and 2.3 of RFC6298
         *
         * It's tricky to understand. Don't lose hair please.
         * Inspired by tcp_rtt_estimator() tcp_input.c
         */
        if (tp_vars->srtt != 0) {
                m -= (tp_vars->srtt >> 3); /* m is now error in rtt est */
                tp_vars->srtt += m; /* rtt = 7/8 srtt + 1/8 new */
                if (m < 0)
                        m = -m;

                m -= (tp_vars->rttvar >> 2);
                tp_vars->rttvar += m; /* mdev ~= 3/4 rttvar + 1/4 new */
        } else {
                /* first measure getting in */
                tp_vars->srtt = m << 3; /* take the measured time to be srtt */
                tp_vars->rttvar = m << 1; /* new_rtt / 2 */
        }

        /* rto = srtt + 4 * rttvar.
         * rttvar is scaled by 4, therefore doesn't need to be multiplied
         */
        tp_vars->rto = (tp_vars->srtt >> 3) + tp_vars->rttvar;
}

/**
 * batadv_tp_batctl_notify() - send client status result to client
 * @reason: reason for tp meter session stop
 * @dst: destination of tp_meter session
 * @bat_priv: the bat priv with all the soft interface information
 * @start_time: start of transmission in jiffies
 * @total_sent: bytes acked to the receiver
 * @cookie: cookie of tp_meter session
 */
static void batadv_tp_batctl_notify(enum batadv_tp_meter_reason reason,
                                    const u8 *dst, struct batadv_priv *bat_priv,
                                    unsigned long start_time, u64 total_sent,
                                    u32 cookie)
{
        u32 test_time;
        u8 result;
        u32 total_bytes;

        if (!batadv_tp_is_error(reason)) {
                result = BATADV_TP_REASON_COMPLETE;
                test_time = jiffies_to_msecs(jiffies - start_time);
                total_bytes = total_sent;
        } else {
                result = reason;
                test_time = 0;
                total_bytes = 0;
        }

        batadv_netlink_tpmeter_notify(bat_priv, dst, result, test_time,
                                      total_bytes, cookie);
}

/**
 * batadv_tp_batctl_error_notify() - send client error result to client
 * @reason: reason for tp meter session stop
 * @dst: destination of tp_meter session
 * @bat_priv: the bat priv with all the soft interface information
 * @cookie: cookie of tp_meter session
 */
static void batadv_tp_batctl_error_notify(enum batadv_tp_meter_reason reason,
                                          const u8 *dst,
                                          struct batadv_priv *bat_priv,
                                          u32 cookie)
{
        batadv_tp_batctl_notify(reason, dst, bat_priv, 0, 0, cookie);
}

/**
 * batadv_tp_list_find() - find a tp_vars object in the global list
 * @bat_priv: the bat priv with all the soft interface information
 * @dst: the other endpoint MAC address to look for
 *
 * Look for a tp_vars object matching dst as end_point and return it after
 * having increment the refcounter. Return NULL is not found
 *
 * Return: matching tp_vars or NULL when no tp_vars with @dst was found
 */
static struct batadv_tp_vars *batadv_tp_list_find(struct batadv_priv *bat_priv,
                                                  const u8 *dst)
{
        struct batadv_tp_vars *pos, *tp_vars = NULL;

        rcu_read_lock();
        hlist_for_each_entry_rcu(pos, &bat_priv->tp_list, list) {
                if (!batadv_compare_eth(pos->other_end, dst))
                        continue;

                /* most of the time this function is invoked during the normal
                 * process..it makes sens to pay more when the session is
                 * finished and to speed the process up during the measurement
                 */
                if (unlikely(!kref_get_unless_zero(&pos->refcount)))
                        continue;

                tp_vars = pos;
                break;
        }
        rcu_read_unlock();

        return tp_vars;
}

/**
 * batadv_tp_list_find_session() - find tp_vars session object in the global
 *  list
 * @bat_priv: the bat priv with all the soft interface information
 * @dst: the other endpoint MAC address to look for
 * @session: session identifier
 *
 * Look for a tp_vars object matching dst as end_point, session as tp meter
 * session and return it after having increment the refcounter. Return NULL
 * is not found
 *
 * Return: matching tp_vars or NULL when no tp_vars was found
 */
static struct batadv_tp_vars *
batadv_tp_list_find_session(struct batadv_priv *bat_priv, const u8 *dst,
                            const u8 *session)
{
        struct batadv_tp_vars *pos, *tp_vars = NULL;

        rcu_read_lock();
        hlist_for_each_entry_rcu(pos, &bat_priv->tp_list, list) {
                if (!batadv_compare_eth(pos->other_end, dst))
                        continue;

                if (memcmp(pos->session, session, sizeof(pos->session)) != 0)
                        continue;

                /* most of the time this function is invoked during the normal
                 * process..it makes sense to pay more when the session is
                 * finished and to speed the process up during the measurement
                 */
                if (unlikely(!kref_get_unless_zero(&pos->refcount)))
                        continue;

                tp_vars = pos;
                break;
        }
        rcu_read_unlock();

        return tp_vars;
}

/**
 * batadv_tp_vars_release() - release batadv_tp_vars from lists and queue for
 *  free after rcu grace period
 * @ref: kref pointer of the batadv_tp_vars
 */
static void batadv_tp_vars_release(struct kref *ref)
{
        struct batadv_tp_vars *tp_vars;
        struct batadv_tp_unacked *un, *safe;

        tp_vars = container_of(ref, struct batadv_tp_vars, refcount);

        /* lock should not be needed because this object is now out of any
         * context!
         */
        spin_lock_bh(&tp_vars->unacked_lock);
        list_for_each_entry_safe(un, safe, &tp_vars->unacked_list, list) {
                list_del(&un->list);
                kfree(un);
        }
        spin_unlock_bh(&tp_vars->unacked_lock);

        kfree_rcu(tp_vars, rcu);
}

/**
 * batadv_tp_vars_put() - decrement the batadv_tp_vars refcounter and possibly
 *  release it
 * @tp_vars: the private data of the current TP meter session to be free'd
 */
static void batadv_tp_vars_put(struct batadv_tp_vars *tp_vars)
{
        kref_put(&tp_vars->refcount, batadv_tp_vars_release);
}

/**
 * batadv_tp_sender_cleanup() - cleanup sender data and drop and timer
 * @bat_priv: the bat priv with all the soft interface information
 * @tp_vars: the private data of the current TP meter session to cleanup
 */
static void batadv_tp_sender_cleanup(struct batadv_priv *bat_priv,
                                     struct batadv_tp_vars *tp_vars)
{
        cancel_delayed_work(&tp_vars->finish_work);

        spin_lock_bh(&tp_vars->bat_priv->tp_list_lock);
        hlist_del_rcu(&tp_vars->list);
        spin_unlock_bh(&tp_vars->bat_priv->tp_list_lock);

        /* drop list reference */
        batadv_tp_vars_put(tp_vars);

        atomic_dec(&tp_vars->bat_priv->tp_num);

        /* kill the timer and remove its reference */
        del_timer_sync(&tp_vars->timer);
        /* the worker might have rearmed itself therefore we kill it again. Note
         * that if the worker should run again before invoking the following
         * del_timer(), it would not re-arm itself once again because the status
         * is OFF now
         */
        del_timer(&tp_vars->timer);
        batadv_tp_vars_put(tp_vars);
}

/**
 * batadv_tp_sender_end() - print info about ended session and inform client
 * @bat_priv: the bat priv with all the soft interface information
 * @tp_vars: the private data of the current TP meter session
 */
static void batadv_tp_sender_end(struct batadv_priv *bat_priv,
                                 struct batadv_tp_vars *tp_vars)
{
        u32 session_cookie;

        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                   "Test towards %pM finished..shutting down (reason=%d)\n",
                   tp_vars->other_end, tp_vars->reason);

        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                   "Last timing stats: SRTT=%ums RTTVAR=%ums RTO=%ums\n",
                   tp_vars->srtt >> 3, tp_vars->rttvar >> 2, tp_vars->rto);

        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                   "Final values: cwnd=%u ss_threshold=%u\n",
                   tp_vars->cwnd, tp_vars->ss_threshold);

        session_cookie = batadv_tp_session_cookie(tp_vars->session,
                                                  tp_vars->icmp_uid);

        batadv_tp_batctl_notify(tp_vars->reason,
                                tp_vars->other_end,
                                bat_priv,
                                tp_vars->start_time,
                                atomic64_read(&tp_vars->tot_sent),
                                session_cookie);
}

/**
 * batadv_tp_sender_shutdown() - let sender thread/timer stop gracefully
 * @tp_vars: the private data of the current TP meter session
 * @reason: reason for tp meter session stop
 */
static void batadv_tp_sender_shutdown(struct batadv_tp_vars *tp_vars,
                                      enum batadv_tp_meter_reason reason)
{
        if (!atomic_dec_and_test(&tp_vars->sending))
                return;

        tp_vars->reason = reason;
}

/**
 * batadv_tp_sender_finish() - stop sender session after test_length was reached
 * @work: delayed work reference of the related tp_vars
 */
static void batadv_tp_sender_finish(struct work_struct *work)
{
        struct delayed_work *delayed_work;
        struct batadv_tp_vars *tp_vars;

        delayed_work = to_delayed_work(work);
        tp_vars = container_of(delayed_work, struct batadv_tp_vars,
                               finish_work);

        batadv_tp_sender_shutdown(tp_vars, BATADV_TP_REASON_COMPLETE);
}

/**
 * batadv_tp_reset_sender_timer() - reschedule the sender timer
 * @tp_vars: the private TP meter data for this session
 *
 * Reschedule the timer using tp_vars->rto as delay
 */
static void batadv_tp_reset_sender_timer(struct batadv_tp_vars *tp_vars)
{
        /* most of the time this function is invoked while normal packet
         * reception...
         */
        if (unlikely(atomic_read(&tp_vars->sending) == 0))
                /* timer ref will be dropped in batadv_tp_sender_cleanup */
                return;

        mod_timer(&tp_vars->timer, jiffies + msecs_to_jiffies(tp_vars->rto));
}

/**
 * batadv_tp_sender_timeout() - timer that fires in case of packet loss
 * @t: address to timer_list inside tp_vars
 *
 * If fired it means that there was packet loss.
 * Switch to Slow Start, set the ss_threshold to half of the current cwnd and
 * reset the cwnd to 3*MSS
 */
static void batadv_tp_sender_timeout(struct timer_list *t)
{
        struct batadv_tp_vars *tp_vars = from_timer(tp_vars, t, timer);
        struct batadv_priv *bat_priv = tp_vars->bat_priv;

        if (atomic_read(&tp_vars->sending) == 0)
                return;

        /* if the user waited long enough...shutdown the test */
        if (unlikely(tp_vars->rto >= BATADV_TP_MAX_RTO)) {
                batadv_tp_sender_shutdown(tp_vars,
                                          BATADV_TP_REASON_DST_UNREACHABLE);
                return;
        }

        /* RTO exponential backoff
         * Details in Section 5.5 of RFC6298
         */
        tp_vars->rto <<= 1;

        spin_lock_bh(&tp_vars->cwnd_lock);

        tp_vars->ss_threshold = tp_vars->cwnd >> 1;
        if (tp_vars->ss_threshold < BATADV_TP_PLEN * 2)
                tp_vars->ss_threshold = BATADV_TP_PLEN * 2;

        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                   "Meter: RTO fired during test towards %pM! cwnd=%u new ss_thr=%u, resetting last_sent to %u\n",
                   tp_vars->other_end, tp_vars->cwnd, tp_vars->ss_threshold,
                   atomic_read(&tp_vars->last_acked));

        tp_vars->cwnd = BATADV_TP_PLEN * 3;

        spin_unlock_bh(&tp_vars->cwnd_lock);

        /* resend the non-ACKed packets.. */
        tp_vars->last_sent = atomic_read(&tp_vars->last_acked);
        wake_up(&tp_vars->more_bytes);

        batadv_tp_reset_sender_timer(tp_vars);
}

/**
 * batadv_tp_fill_prerandom() - Fill buffer with prefetched random bytes
 * @tp_vars: the private TP meter data for this session
 * @buf: Buffer to fill with bytes
 * @nbytes: amount of pseudorandom bytes
 */
static void batadv_tp_fill_prerandom(struct batadv_tp_vars *tp_vars,
                                     u8 *buf, size_t nbytes)
{
        u32 local_offset;
        size_t bytes_inbuf;
        size_t to_copy;
        size_t pos = 0;

        spin_lock_bh(&tp_vars->prerandom_lock);
        local_offset = tp_vars->prerandom_offset;
        tp_vars->prerandom_offset += nbytes;
        tp_vars->prerandom_offset %= sizeof(batadv_tp_prerandom);
        spin_unlock_bh(&tp_vars->prerandom_lock);

        while (nbytes) {
                local_offset %= sizeof(batadv_tp_prerandom);
                bytes_inbuf = sizeof(batadv_tp_prerandom) - local_offset;
                to_copy = min(nbytes, bytes_inbuf);

                memcpy(&buf[pos], &batadv_tp_prerandom[local_offset], to_copy);
                pos += to_copy;
                nbytes -= to_copy;
                local_offset = 0;
        }
}

/**
 * batadv_tp_send_msg() - send a single message
 * @tp_vars: the private TP meter data for this session
 * @src: source mac address
 * @orig_node: the originator of the destination
 * @seqno: sequence number of this packet
 * @len: length of the entire packet
 * @session: session identifier
 * @uid: local ICMP "socket" index
 * @timestamp: timestamp in jiffies which is replied in ack
 *
 * Create and send a single TP Meter message.
 *
 * Return: 0 on success, BATADV_TP_REASON_DST_UNREACHABLE if the destination is
 * not reachable, BATADV_TP_REASON_MEMORY_ERROR if the packet couldn't be
 * allocated
 */
static int batadv_tp_send_msg(struct batadv_tp_vars *tp_vars, const u8 *src,
                              struct batadv_orig_node *orig_node,
                              u32 seqno, size_t len, const u8 *session,
                              int uid, u32 timestamp)
{
        struct batadv_icmp_tp_packet *icmp;
        struct sk_buff *skb;
        int r;
        u8 *data;
        size_t data_len;

        skb = netdev_alloc_skb_ip_align(NULL, len + ETH_HLEN);
        if (unlikely(!skb))
                return BATADV_TP_REASON_MEMORY_ERROR;

        skb_reserve(skb, ETH_HLEN);
        icmp = skb_put(skb, sizeof(*icmp));

        /* fill the icmp header */
        ether_addr_copy(icmp->dst, orig_node->orig);
        ether_addr_copy(icmp->orig, src);
        icmp->version = BATADV_COMPAT_VERSION;
        icmp->packet_type = BATADV_ICMP;
        icmp->ttl = BATADV_TTL;
        icmp->msg_type = BATADV_TP;
        icmp->uid = uid;

        icmp->subtype = BATADV_TP_MSG;
        memcpy(icmp->session, session, sizeof(icmp->session));
        icmp->seqno = htonl(seqno);
        icmp->timestamp = htonl(timestamp);

        data_len = len - sizeof(*icmp);
        data = skb_put(skb, data_len);
        batadv_tp_fill_prerandom(tp_vars, data, data_len);

        r = batadv_send_skb_to_orig(skb, orig_node, NULL);
        if (r == NET_XMIT_SUCCESS)
                return 0;

        return BATADV_TP_REASON_CANT_SEND;
}

/**
 * batadv_tp_recv_ack() - ACK receiving function
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: the buffer containing the received packet
 *
 * Process a received TP ACK packet
 */
static void batadv_tp_recv_ack(struct batadv_priv *bat_priv,
                               const struct sk_buff *skb)
{
        struct batadv_hard_iface *primary_if = NULL;
        struct batadv_orig_node *orig_node = NULL;
        const struct batadv_icmp_tp_packet *icmp;
        struct batadv_tp_vars *tp_vars;
        size_t packet_len, mss;
        u32 rtt, recv_ack, cwnd;
        unsigned char *dev_addr;

        packet_len = BATADV_TP_PLEN;
        mss = BATADV_TP_PLEN;
        packet_len += sizeof(struct batadv_unicast_packet);

        icmp = (struct batadv_icmp_tp_packet *)skb->data;

        /* find the tp_vars */
        tp_vars = batadv_tp_list_find_session(bat_priv, icmp->orig,
                                              icmp->session);
        if (unlikely(!tp_vars))
                return;

        if (unlikely(atomic_read(&tp_vars->sending) == 0))
                goto out;

        /* old ACK? silently drop it.. */
        if (batadv_seq_before(ntohl(icmp->seqno),
                              (u32)atomic_read(&tp_vars->last_acked)))
                goto out;

        primary_if = batadv_primary_if_get_selected(bat_priv);
        if (unlikely(!primary_if))
                goto out;

        orig_node = batadv_orig_hash_find(bat_priv, icmp->orig);
        if (unlikely(!orig_node))
                goto out;

        /* update RTO with the new sampled RTT, if any */
        rtt = jiffies_to_msecs(jiffies) - ntohl(icmp->timestamp);
        if (icmp->timestamp && rtt)
                batadv_tp_update_rto(tp_vars, rtt);

        /* ACK for new data... reset the timer */
        batadv_tp_reset_sender_timer(tp_vars);

        recv_ack = ntohl(icmp->seqno);

        /* check if this ACK is a duplicate */
        if (atomic_read(&tp_vars->last_acked) == recv_ack) {
                atomic_inc(&tp_vars->dup_acks);
                if (atomic_read(&tp_vars->dup_acks) != 3)
                        goto out;

                if (recv_ack >= tp_vars->recover)
                        goto out;

                /* if this is the third duplicate ACK do Fast Retransmit */
                batadv_tp_send_msg(tp_vars, primary_if->net_dev->dev_addr,
                                   orig_node, recv_ack, packet_len,
                                   icmp->session, icmp->uid,
                                   jiffies_to_msecs(jiffies));

                spin_lock_bh(&tp_vars->cwnd_lock);

                /* Fast Recovery */
                tp_vars->fast_recovery = true;
                /* Set recover to the last outstanding seqno when Fast Recovery
                 * is entered. RFC6582, Section 3.2, step 1
                 */
                tp_vars->recover = tp_vars->last_sent;
                tp_vars->ss_threshold = tp_vars->cwnd >> 1;
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Meter: Fast Recovery, (cur cwnd=%u) ss_thr=%u last_sent=%u recv_ack=%u\n",
                           tp_vars->cwnd, tp_vars->ss_threshold,
                           tp_vars->last_sent, recv_ack);
                tp_vars->cwnd = batadv_tp_cwnd(tp_vars->ss_threshold, 3 * mss,
                                               mss);
                tp_vars->dec_cwnd = 0;
                tp_vars->last_sent = recv_ack;

                spin_unlock_bh(&tp_vars->cwnd_lock);
        } else {
                /* count the acked data */
                atomic64_add(recv_ack - atomic_read(&tp_vars->last_acked),
                             &tp_vars->tot_sent);
                /* reset the duplicate ACKs counter */
                atomic_set(&tp_vars->dup_acks, 0);

                if (tp_vars->fast_recovery) {
                        /* partial ACK */
                        if (batadv_seq_before(recv_ack, tp_vars->recover)) {
                                /* this is another hole in the window. React
                                 * immediately as specified by NewReno (see
                                 * Section 3.2 of RFC6582 for details)
                                 */
                                dev_addr = primary_if->net_dev->dev_addr;
                                batadv_tp_send_msg(tp_vars, dev_addr,
                                                   orig_node, recv_ack,
                                                   packet_len, icmp->session,
                                                   icmp->uid,
                                                   jiffies_to_msecs(jiffies));
                                tp_vars->cwnd = batadv_tp_cwnd(tp_vars->cwnd,
                                                               mss, mss);
                        } else {
                                tp_vars->fast_recovery = false;
                                /* set cwnd to the value of ss_threshold at the
                                 * moment that Fast Recovery was entered.
                                 * RFC6582, Section 3.2, step 3
                                 */
                                cwnd = batadv_tp_cwnd(tp_vars->ss_threshold, 0,
                                                      mss);
                                tp_vars->cwnd = cwnd;
                        }
                        goto move_twnd;
                }

                if (recv_ack - atomic_read(&tp_vars->last_acked) >= mss)
                        batadv_tp_update_cwnd(tp_vars, mss);
move_twnd:
                /* move the Transmit Window */
                atomic_set(&tp_vars->last_acked, recv_ack);
        }

        wake_up(&tp_vars->more_bytes);
out:
        if (likely(primary_if))
                batadv_hardif_put(primary_if);
        if (likely(orig_node))
                batadv_orig_node_put(orig_node);
        if (likely(tp_vars))
                batadv_tp_vars_put(tp_vars);
}

/**
 * batadv_tp_avail() - check if congestion window is not full
 * @tp_vars: the private data of the current TP meter session
 * @payload_len: size of the payload of a single message
 *
 * Return: true when congestion window is not full, false otherwise
 */
static bool batadv_tp_avail(struct batadv_tp_vars *tp_vars,
                            size_t payload_len)
{
        u32 win_left, win_limit;

        win_limit = atomic_read(&tp_vars->last_acked) + tp_vars->cwnd;
        win_left = win_limit - tp_vars->last_sent;

        return win_left >= payload_len;
}

/**
 * batadv_tp_wait_available() - wait until congestion window becomes free or
 *  timeout is reached
 * @tp_vars: the private data of the current TP meter session
 * @plen: size of the payload of a single message
 *
 * Return: 0 if the condition evaluated to false after the timeout elapsed,
 *  1 if the condition evaluated to true after the timeout elapsed, the
 *  remaining jiffies (at least 1) if the condition evaluated to true before
 *  the timeout elapsed, or -ERESTARTSYS if it was interrupted by a signal.
 */
static int batadv_tp_wait_available(struct batadv_tp_vars *tp_vars, size_t plen)
{
        int ret;

        ret = wait_event_interruptible_timeout(tp_vars->more_bytes,
                                               batadv_tp_avail(tp_vars, plen),
                                               HZ / 10);

        return ret;
}

/**
 * batadv_tp_send() - main sending thread of a tp meter session
 * @arg: address of the related tp_vars
 *
 * Return: nothing, this function never returns
 */
static int batadv_tp_send(void *arg)
{
        struct batadv_tp_vars *tp_vars = arg;
        struct batadv_priv *bat_priv = tp_vars->bat_priv;
        struct batadv_hard_iface *primary_if = NULL;
        struct batadv_orig_node *orig_node = NULL;
        size_t payload_len, packet_len;
        int err = 0;

        if (unlikely(tp_vars->role != BATADV_TP_SENDER)) {
                err = BATADV_TP_REASON_DST_UNREACHABLE;
                tp_vars->reason = err;
                goto out;
        }

        orig_node = batadv_orig_hash_find(bat_priv, tp_vars->other_end);
        if (unlikely(!orig_node)) {
                err = BATADV_TP_REASON_DST_UNREACHABLE;
                tp_vars->reason = err;
                goto out;
        }

        primary_if = batadv_primary_if_get_selected(bat_priv);
        if (unlikely(!primary_if)) {
                err = BATADV_TP_REASON_DST_UNREACHABLE;
                tp_vars->reason = err;
                goto out;
        }

        /* assume that all the hard_interfaces have a correctly
         * configured MTU, so use the soft_iface MTU as MSS.
         * This might not be true and in that case the fragmentation
         * should be used.
         * Now, try to send the packet as it is
         */
        payload_len = BATADV_TP_PLEN;
        BUILD_BUG_ON(sizeof(struct batadv_icmp_tp_packet) > BATADV_TP_PLEN);

        batadv_tp_reset_sender_timer(tp_vars);

        /* queue the worker in charge of terminating the test */
        queue_delayed_work(batadv_event_workqueue, &tp_vars->finish_work,
                           msecs_to_jiffies(tp_vars->test_length));

        while (atomic_read(&tp_vars->sending) != 0) {
                if (unlikely(!batadv_tp_avail(tp_vars, payload_len))) {
                        batadv_tp_wait_available(tp_vars, payload_len);
                        continue;
                }

                /* to emulate normal unicast traffic, add to the payload len
                 * the size of the unicast header
                 */
                packet_len = payload_len + sizeof(struct batadv_unicast_packet);

                err = batadv_tp_send_msg(tp_vars, primary_if->net_dev->dev_addr,
                                         orig_node, tp_vars->last_sent,
                                         packet_len,
                                         tp_vars->session, tp_vars->icmp_uid,
                                         jiffies_to_msecs(jiffies));

                /* something went wrong during the preparation/transmission */
                if (unlikely(err && err != BATADV_TP_REASON_CANT_SEND)) {
                        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                                   "Meter: %s() cannot send packets (%d)\n",
                                   __func__, err);
                        /* ensure nobody else tries to stop the thread now */
                        if (atomic_dec_and_test(&tp_vars->sending))
                                tp_vars->reason = err;
                        break;
                }

                /* right-shift the TWND */
                if (!err)
                        tp_vars->last_sent += payload_len;

                cond_resched();
        }

out:
        if (likely(primary_if))
                batadv_hardif_put(primary_if);
        if (likely(orig_node))
                batadv_orig_node_put(orig_node);

        batadv_tp_sender_end(bat_priv, tp_vars);
        batadv_tp_sender_cleanup(bat_priv, tp_vars);

        batadv_tp_vars_put(tp_vars);

        do_exit(0);
}

/**
 * batadv_tp_start_kthread() - start new thread which manages the tp meter
 *  sender
 * @tp_vars: the private data of the current TP meter session
 */
static void batadv_tp_start_kthread(struct batadv_tp_vars *tp_vars)
{
        struct task_struct *kthread;
        struct batadv_priv *bat_priv = tp_vars->bat_priv;
        u32 session_cookie;

        kref_get(&tp_vars->refcount);
        kthread = kthread_create(batadv_tp_send, tp_vars, "kbatadv_tp_meter");
        if (IS_ERR(kthread)) {
                session_cookie = batadv_tp_session_cookie(tp_vars->session,
                                                          tp_vars->icmp_uid);
                pr_err("batadv: cannot create tp meter kthread\n");
                batadv_tp_batctl_error_notify(BATADV_TP_REASON_MEMORY_ERROR,
                                              tp_vars->other_end,
                                              bat_priv, session_cookie);

                /* drop reserved reference for kthread */
                batadv_tp_vars_put(tp_vars);

                /* cleanup of failed tp meter variables */
                batadv_tp_sender_cleanup(bat_priv, tp_vars);
                return;
        }

        wake_up_process(kthread);
}

/**
 * batadv_tp_start() - start a new tp meter session
 * @bat_priv: the bat priv with all the soft interface information
 * @dst: the receiver MAC address
 * @test_length: test length in milliseconds
 * @cookie: session cookie
 */
void batadv_tp_start(struct batadv_priv *bat_priv, const u8 *dst,
                     u32 test_length, u32 *cookie)
{
        struct batadv_tp_vars *tp_vars;
        u8 session_id[2];
        u8 icmp_uid;
        u32 session_cookie;

        get_random_bytes(session_id, sizeof(session_id));
        get_random_bytes(&icmp_uid, 1);
        session_cookie = batadv_tp_session_cookie(session_id, icmp_uid);
        *cookie = session_cookie;

        /* look for an already existing test towards this node */
        spin_lock_bh(&bat_priv->tp_list_lock);
        tp_vars = batadv_tp_list_find(bat_priv, dst);
        if (tp_vars) {
                spin_unlock_bh(&bat_priv->tp_list_lock);
                batadv_tp_vars_put(tp_vars);
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Meter: test to or from the same node already ongoing, aborting\n");
                batadv_tp_batctl_error_notify(BATADV_TP_REASON_ALREADY_ONGOING,
                                              dst, bat_priv, session_cookie);
                return;
        }

        if (!atomic_add_unless(&bat_priv->tp_num, 1, BATADV_TP_MAX_NUM)) {
                spin_unlock_bh(&bat_priv->tp_list_lock);
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Meter: too many ongoing sessions, aborting (SEND)\n");
                batadv_tp_batctl_error_notify(BATADV_TP_REASON_TOO_MANY, dst,
                                              bat_priv, session_cookie);
                return;
        }

        tp_vars = kmalloc(sizeof(*tp_vars), GFP_ATOMIC);
        if (!tp_vars) {
                spin_unlock_bh(&bat_priv->tp_list_lock);
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Meter: %s cannot allocate list elements\n",
                           __func__);
                batadv_tp_batctl_error_notify(BATADV_TP_REASON_MEMORY_ERROR,
                                              dst, bat_priv, session_cookie);
                return;
        }

        /* initialize tp_vars */
        ether_addr_copy(tp_vars->other_end, dst);
        kref_init(&tp_vars->refcount);
        tp_vars->role = BATADV_TP_SENDER;
        atomic_set(&tp_vars->sending, 1);
        memcpy(tp_vars->session, session_id, sizeof(session_id));
        tp_vars->icmp_uid = icmp_uid;

        tp_vars->last_sent = BATADV_TP_FIRST_SEQ;
        atomic_set(&tp_vars->last_acked, BATADV_TP_FIRST_SEQ);
        tp_vars->fast_recovery = false;
        tp_vars->recover = BATADV_TP_FIRST_SEQ;

        /* initialise the CWND to 3*MSS (Section 3.1 in RFC5681).
         * For batman-adv the MSS is the size of the payload received by the
         * soft_interface, hence its MTU
         */
        tp_vars->cwnd = BATADV_TP_PLEN * 3;
        /* at the beginning initialise the SS threshold to the biggest possible
         * window size, hence the AWND size
         */
        tp_vars->ss_threshold = BATADV_TP_AWND;

        /* RTO initial value is 3 seconds.
         * Details in Section 2.1 of RFC6298
         */
        tp_vars->rto = 1000;
        tp_vars->srtt = 0;
        tp_vars->rttvar = 0;

        atomic64_set(&tp_vars->tot_sent, 0);

        kref_get(&tp_vars->refcount);
        timer_setup(&tp_vars->timer, batadv_tp_sender_timeout, 0);

        tp_vars->bat_priv = bat_priv;
        tp_vars->start_time = jiffies;

        init_waitqueue_head(&tp_vars->more_bytes);

        spin_lock_init(&tp_vars->unacked_lock);
        INIT_LIST_HEAD(&tp_vars->unacked_list);

        spin_lock_init(&tp_vars->cwnd_lock);

        tp_vars->prerandom_offset = 0;
        spin_lock_init(&tp_vars->prerandom_lock);

        kref_get(&tp_vars->refcount);
        hlist_add_head_rcu(&tp_vars->list, &bat_priv->tp_list);
        spin_unlock_bh(&bat_priv->tp_list_lock);

        tp_vars->test_length = test_length;
        if (!tp_vars->test_length)
                tp_vars->test_length = BATADV_TP_DEF_TEST_LENGTH;

        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                   "Meter: starting throughput meter towards %pM (length=%ums)\n",
                   dst, test_length);

        /* init work item for finished tp tests */
        INIT_DELAYED_WORK(&tp_vars->finish_work, batadv_tp_sender_finish);

        /* start tp kthread. This way the write() call issued from userspace can
         * happily return and avoid to block
         */
        batadv_tp_start_kthread(tp_vars);

        /* don't return reference to new tp_vars */
        batadv_tp_vars_put(tp_vars);
}

/**
 * batadv_tp_stop() - stop currently running tp meter session
 * @bat_priv: the bat priv with all the soft interface information
 * @dst: the receiver MAC address
 * @return_value: reason for tp meter session stop
 */
void batadv_tp_stop(struct batadv_priv *bat_priv, const u8 *dst,
                    u8 return_value)
{
        struct batadv_orig_node *orig_node;
        struct batadv_tp_vars *tp_vars;

        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                   "Meter: stopping test towards %pM\n", dst);

        orig_node = batadv_orig_hash_find(bat_priv, dst);
        if (!orig_node)
                return;

        tp_vars = batadv_tp_list_find(bat_priv, orig_node->orig);
        if (!tp_vars) {
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Meter: trying to interrupt an already over connection\n");
                goto out;
        }

        batadv_tp_sender_shutdown(tp_vars, return_value);
        batadv_tp_vars_put(tp_vars);
out:
        batadv_orig_node_put(orig_node);
}

/**
 * batadv_tp_reset_receiver_timer() - reset the receiver shutdown timer
 * @tp_vars: the private data of the current TP meter session
 *
 * start the receiver shutdown timer or reset it if already started
 */
static void batadv_tp_reset_receiver_timer(struct batadv_tp_vars *tp_vars)
{
        mod_timer(&tp_vars->timer,
                  jiffies + msecs_to_jiffies(BATADV_TP_RECV_TIMEOUT));
}

/**
 * batadv_tp_receiver_shutdown() - stop a tp meter receiver when timeout is
 *  reached without received ack
 * @t: address to timer_list inside tp_vars
 */
static void batadv_tp_receiver_shutdown(struct timer_list *t)
{
        struct batadv_tp_vars *tp_vars = from_timer(tp_vars, t, timer);
        struct batadv_tp_unacked *un, *safe;
        struct batadv_priv *bat_priv;

        bat_priv = tp_vars->bat_priv;

        /* if there is recent activity rearm the timer */
        if (!batadv_has_timed_out(tp_vars->last_recv_time,
                                  BATADV_TP_RECV_TIMEOUT)) {
                /* reset the receiver shutdown timer */
                batadv_tp_reset_receiver_timer(tp_vars);
                return;
        }

        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                   "Shutting down for inactivity (more than %dms) from %pM\n",
                   BATADV_TP_RECV_TIMEOUT, tp_vars->other_end);

        spin_lock_bh(&tp_vars->bat_priv->tp_list_lock);
        hlist_del_rcu(&tp_vars->list);
        spin_unlock_bh(&tp_vars->bat_priv->tp_list_lock);

        /* drop list reference */
        batadv_tp_vars_put(tp_vars);

        atomic_dec(&bat_priv->tp_num);

        spin_lock_bh(&tp_vars->unacked_lock);
        list_for_each_entry_safe(un, safe, &tp_vars->unacked_list, list) {
                list_del(&un->list);
                kfree(un);
        }
        spin_unlock_bh(&tp_vars->unacked_lock);

        /* drop reference of timer */
        batadv_tp_vars_put(tp_vars);
}

/**
 * batadv_tp_send_ack() - send an ACK packet
 * @bat_priv: the bat priv with all the soft interface information
 * @dst: the mac address of the destination originator
 * @seq: the sequence number to ACK
 * @timestamp: the timestamp to echo back in the ACK
 * @session: session identifier
 * @socket_index: local ICMP socket identifier
 *
 * Return: 0 on success, a positive integer representing the reason of the
 * failure otherwise
 */
static int batadv_tp_send_ack(struct batadv_priv *bat_priv, const u8 *dst,
                              u32 seq, __be32 timestamp, const u8 *session,
                              int socket_index)
{
        struct batadv_hard_iface *primary_if = NULL;
        struct batadv_orig_node *orig_node;
        struct batadv_icmp_tp_packet *icmp;
        struct sk_buff *skb;
        int r, ret;

        orig_node = batadv_orig_hash_find(bat_priv, dst);
        if (unlikely(!orig_node)) {
                ret = BATADV_TP_REASON_DST_UNREACHABLE;
                goto out;
        }

        primary_if = batadv_primary_if_get_selected(bat_priv);
        if (unlikely(!primary_if)) {
                ret = BATADV_TP_REASON_DST_UNREACHABLE;
                goto out;
        }

        skb = netdev_alloc_skb_ip_align(NULL, sizeof(*icmp) + ETH_HLEN);
        if (unlikely(!skb)) {
                ret = BATADV_TP_REASON_MEMORY_ERROR;
                goto out;
        }

        skb_reserve(skb, ETH_HLEN);
        icmp = skb_put(skb, sizeof(*icmp));
        icmp->packet_type = BATADV_ICMP;
        icmp->version = BATADV_COMPAT_VERSION;
        icmp->ttl = BATADV_TTL;
        icmp->msg_type = BATADV_TP;
        ether_addr_copy(icmp->dst, orig_node->orig);
        ether_addr_copy(icmp->orig, primary_if->net_dev->dev_addr);
        icmp->uid = socket_index;

        icmp->subtype = BATADV_TP_ACK;
        memcpy(icmp->session, session, sizeof(icmp->session));
        icmp->seqno = htonl(seq);
        icmp->timestamp = timestamp;

        /* send the ack */
        r = batadv_send_skb_to_orig(skb, orig_node, NULL);
        if (unlikely(r < 0) || r == NET_XMIT_DROP) {
                ret = BATADV_TP_REASON_DST_UNREACHABLE;
                goto out;
        }
        ret = 0;

out:
        if (likely(orig_node))
                batadv_orig_node_put(orig_node);
        if (likely(primary_if))
                batadv_hardif_put(primary_if);

        return ret;
}

/**
 * batadv_tp_handle_out_of_order() - store an out of order packet
 * @tp_vars: the private data of the current TP meter session
 * @skb: the buffer containing the received packet
 *
 * Store the out of order packet in the unacked list for late processing. This
 * packets are kept in this list so that they can be ACKed at once as soon as
 * all the previous packets have been received
 *
 * Return: true if the packed has been successfully processed, false otherwise
 */
static bool batadv_tp_handle_out_of_order(struct batadv_tp_vars *tp_vars,
                                          const struct sk_buff *skb)
{
        const struct batadv_icmp_tp_packet *icmp;
        struct batadv_tp_unacked *un, *new;
        u32 payload_len;
        bool added = false;

        new = kmalloc(sizeof(*new), GFP_ATOMIC);
        if (unlikely(!new))
                return false;

        icmp = (struct batadv_icmp_tp_packet *)skb->data;

        new->seqno = ntohl(icmp->seqno);
        payload_len = skb->len - sizeof(struct batadv_unicast_packet);
        new->len = payload_len;

        spin_lock_bh(&tp_vars->unacked_lock);
        /* if the list is empty immediately attach this new object */
        if (list_empty(&tp_vars->unacked_list)) {
                list_add(&new->list, &tp_vars->unacked_list);
                goto out;
        }

        /* otherwise loop over the list and either drop the packet because this
         * is a duplicate or store it at the right position.
         *
         * The iteration is done in the reverse way because it is likely that
         * the last received packet (the one being processed now) has a bigger
         * seqno than all the others already stored.
         */
        list_for_each_entry_reverse(un, &tp_vars->unacked_list, list) {
                /* check for duplicates */
                if (new->seqno == un->seqno) {
                        if (new->len > un->len)
                                un->len = new->len;
                        kfree(new);
                        added = true;
                        break;
                }

                /* look for the right position */
                if (batadv_seq_before(new->seqno, un->seqno))
                        continue;

                /* as soon as an entry having a bigger seqno is found, the new
                 * one is attached _after_ it. In this way the list is kept in
                 * ascending order
                 */
                list_add_tail(&new->list, &un->list);
                added = true;
                break;
        }

        /* received packet with smallest seqno out of order; add it to front */
        if (!added)
                list_add(&new->list, &tp_vars->unacked_list);

out:
        spin_unlock_bh(&tp_vars->unacked_lock);

        return true;
}

/**
 * batadv_tp_ack_unordered() - update number received bytes in current stream
 *  without gaps
 * @tp_vars: the private data of the current TP meter session
 */
static void batadv_tp_ack_unordered(struct batadv_tp_vars *tp_vars)
{
        struct batadv_tp_unacked *un, *safe;
        u32 to_ack;

        /* go through the unacked packet list and possibly ACK them as
         * well
         */
        spin_lock_bh(&tp_vars->unacked_lock);
        list_for_each_entry_safe(un, safe, &tp_vars->unacked_list, list) {
                /* the list is ordered, therefore it is possible to stop as soon
                 * there is a gap between the last acked seqno and the seqno of
                 * the packet under inspection
                 */
                if (batadv_seq_before(tp_vars->last_recv, un->seqno))
                        break;

                to_ack = un->seqno + un->len - tp_vars->last_recv;

                if (batadv_seq_before(tp_vars->last_recv, un->seqno + un->len))
                        tp_vars->last_recv += to_ack;

                list_del(&un->list);
                kfree(un);
        }
        spin_unlock_bh(&tp_vars->unacked_lock);
}

/**
 * batadv_tp_init_recv() - return matching or create new receiver tp_vars
 * @bat_priv: the bat priv with all the soft interface information
 * @icmp: received icmp tp msg
 *
 * Return: corresponding tp_vars or NULL on errors
 */
static struct batadv_tp_vars *
batadv_tp_init_recv(struct batadv_priv *bat_priv,
                    const struct batadv_icmp_tp_packet *icmp)
{
        struct batadv_tp_vars *tp_vars;

        spin_lock_bh(&bat_priv->tp_list_lock);
        tp_vars = batadv_tp_list_find_session(bat_priv, icmp->orig,
                                              icmp->session);
        if (tp_vars)
                goto out_unlock;

        if (!atomic_add_unless(&bat_priv->tp_num, 1, BATADV_TP_MAX_NUM)) {
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Meter: too many ongoing sessions, aborting (RECV)\n");
                goto out_unlock;
        }

        tp_vars = kmalloc(sizeof(*tp_vars), GFP_ATOMIC);
        if (!tp_vars)
                goto out_unlock;

        ether_addr_copy(tp_vars->other_end, icmp->orig);
        tp_vars->role = BATADV_TP_RECEIVER;
        memcpy(tp_vars->session, icmp->session, sizeof(tp_vars->session));
        tp_vars->last_recv = BATADV_TP_FIRST_SEQ;
        tp_vars->bat_priv = bat_priv;
        kref_init(&tp_vars->refcount);

        spin_lock_init(&tp_vars->unacked_lock);
        INIT_LIST_HEAD(&tp_vars->unacked_list);

        kref_get(&tp_vars->refcount);
        hlist_add_head_rcu(&tp_vars->list, &bat_priv->tp_list);

        kref_get(&tp_vars->refcount);
        timer_setup(&tp_vars->timer, batadv_tp_receiver_shutdown, 0);

        batadv_tp_reset_receiver_timer(tp_vars);

out_unlock:
        spin_unlock_bh(&bat_priv->tp_list_lock);

        return tp_vars;
}

/**
 * batadv_tp_recv_msg() - process a single data message
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: the buffer containing the received packet
 *
 * Process a received TP MSG packet
 */
static void batadv_tp_recv_msg(struct batadv_priv *bat_priv,
                               const struct sk_buff *skb)
{
        const struct batadv_icmp_tp_packet *icmp;
        struct batadv_tp_vars *tp_vars;
        size_t packet_size;
        u32 seqno;

        icmp = (struct batadv_icmp_tp_packet *)skb->data;

        seqno = ntohl(icmp->seqno);
        /* check if this is the first seqno. This means that if the
         * first packet is lost, the tp meter does not work anymore!
         */
        if (seqno == BATADV_TP_FIRST_SEQ) {
                tp_vars = batadv_tp_init_recv(bat_priv, icmp);
                if (!tp_vars) {
                        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                                   "Meter: seqno != BATADV_TP_FIRST_SEQ cannot initiate connection\n");
                        goto out;
                }
        } else {
                tp_vars = batadv_tp_list_find_session(bat_priv, icmp->orig,
                                                      icmp->session);
                if (!tp_vars) {
                        batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                                   "Unexpected packet from %pM!\n",
                                   icmp->orig);
                        goto out;
                }
        }

        if (unlikely(tp_vars->role != BATADV_TP_RECEIVER)) {
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Meter: dropping packet: not expected (role=%u)\n",
                           tp_vars->role);
                goto out;
        }

        tp_vars->last_recv_time = jiffies;

        /* if the packet is a duplicate, it may be the case that an ACK has been
         * lost. Resend the ACK
         */
        if (batadv_seq_before(seqno, tp_vars->last_recv))
                goto send_ack;

        /* if the packet is out of order enqueue it */
        if (ntohl(icmp->seqno) != tp_vars->last_recv) {
                /* exit immediately (and do not send any ACK) if the packet has
                 * not been enqueued correctly
                 */
                if (!batadv_tp_handle_out_of_order(tp_vars, skb))
                        goto out;

                /* send a duplicate ACK */
                goto send_ack;
        }

        /* if everything was fine count the ACKed bytes */
        packet_size = skb->len - sizeof(struct batadv_unicast_packet);
        tp_vars->last_recv += packet_size;

        /* check if this ordered message filled a gap.... */
        batadv_tp_ack_unordered(tp_vars);

send_ack:
        /* send the ACK. If the received packet was out of order, the ACK that
         * is going to be sent is a duplicate (the sender will count them and
         * possibly enter Fast Retransmit as soon as it has reached 3)
         */
        batadv_tp_send_ack(bat_priv, icmp->orig, tp_vars->last_recv,
                           icmp->timestamp, icmp->session, icmp->uid);
out:
        if (likely(tp_vars))
                batadv_tp_vars_put(tp_vars);
}

/**
 * batadv_tp_meter_recv() - main TP Meter receiving function
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: the buffer containing the received packet
 */
void batadv_tp_meter_recv(struct batadv_priv *bat_priv, struct sk_buff *skb)
{
        struct batadv_icmp_tp_packet *icmp;

        icmp = (struct batadv_icmp_tp_packet *)skb->data;

        switch (icmp->subtype) {
        case BATADV_TP_MSG:
                batadv_tp_recv_msg(bat_priv, skb);
                break;
        case BATADV_TP_ACK:
                batadv_tp_recv_ack(bat_priv, skb);
                break;
        default:
                batadv_dbg(BATADV_DBG_TP_METER, bat_priv,
                           "Received unknown TP Metric packet type %u\n",
                           icmp->subtype);
        }
        consume_skb(skb);
}

/**
 * batadv_tp_meter_init() - initialize global tp_meter structures
 */
void __init batadv_tp_meter_init(void)
{
        get_random_bytes(batadv_tp_prerandom, sizeof(batadv_tp_prerandom));
}