mesh_hwmp.c

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/*
 * Copyright (c) 2008, 2009 open80211s Ltd.
 * Author:     Luis Carlos Cobo <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/slab.h>
#include <linux/etherdevice.h>
#include <asm/unaligned.h>
#include "wme.h"
#include "mesh.h"

#define TEST_FRAME_LEN  8192
#define MAX_METRIC  0xffffffff
#define ARITH_SHIFT 8

#define MAX_PREQ_QUEUE_LEN  64

/* Destination only */
#define MP_F_DO 0x1
/* Reply and forward */
#define MP_F_RF 0x2
/* Unknown Sequence Number */
#define MP_F_USN    0x01
/* Reason code Present */
#define MP_F_RCODE  0x02

static void mesh_queue_preq(struct mesh_path *, u8);

static inline u32 u32_field_get(u8 *preq_elem, int offset, bool ae)
{
    if (ae)
        offset += 6;
    return get_unaligned_le32(preq_elem + offset);
}

static inline u32 u16_field_get(u8 *preq_elem, int offset, bool ae)
{
    if (ae)
        offset += 6;
    return get_unaligned_le16(preq_elem + offset);
}

/* HWMP IE processing macros */
#define AE_F            (1<<6)
#define AE_F_SET(x)     (*x & AE_F)
#define PREQ_IE_FLAGS(x)    (*(x))
#define PREQ_IE_HOPCOUNT(x) (*(x + 1))
#define PREQ_IE_TTL(x)      (*(x + 2))
#define PREQ_IE_PREQ_ID(x)  u32_field_get(x, 3, 0)
#define PREQ_IE_ORIG_ADDR(x)    (x + 7)
#define PREQ_IE_ORIG_SN(x)  u32_field_get(x, 13, 0)
#define PREQ_IE_LIFETIME(x) u32_field_get(x, 17, AE_F_SET(x))
#define PREQ_IE_METRIC(x)   u32_field_get(x, 21, AE_F_SET(x))
#define PREQ_IE_TARGET_F(x) (*(AE_F_SET(x) ? x + 32 : x + 26))
#define PREQ_IE_TARGET_ADDR(x)  (AE_F_SET(x) ? x + 33 : x + 27)
#define PREQ_IE_TARGET_SN(x)    u32_field_get(x, 33, AE_F_SET(x))


#define PREP_IE_FLAGS(x)    PREQ_IE_FLAGS(x)
#define PREP_IE_HOPCOUNT(x) PREQ_IE_HOPCOUNT(x)
#define PREP_IE_TTL(x)      PREQ_IE_TTL(x)
#define PREP_IE_ORIG_ADDR(x)    (AE_F_SET(x) ? x + 27 : x + 21)
#define PREP_IE_ORIG_SN(x)  u32_field_get(x, 27, AE_F_SET(x))
#define PREP_IE_LIFETIME(x) u32_field_get(x, 13, AE_F_SET(x))
#define PREP_IE_METRIC(x)   u32_field_get(x, 17, AE_F_SET(x))
#define PREP_IE_TARGET_ADDR(x)  (x + 3)
#define PREP_IE_TARGET_SN(x)    u32_field_get(x, 9, 0)

#define PERR_IE_TTL(x)      (*(x))
#define PERR_IE_TARGET_FLAGS(x) (*(x + 2))
#define PERR_IE_TARGET_ADDR(x)  (x + 3)
#define PERR_IE_TARGET_SN(x)    u32_field_get(x, 9, 0)
#define PERR_IE_TARGET_RCODE(x) u16_field_get(x, 13, 0)

#define MSEC_TO_TU(x) (x*1000/1024)
#define SN_GT(x, y) ((s32)(y - x) < 0)
#define SN_LT(x, y) ((s32)(x - y) < 0)

#define net_traversal_jiffies(s) \
    msecs_to_jiffies(s->u.mesh.mshcfg.dot11MeshHWMPnetDiameterTraversalTime)
#define default_lifetime(s) \
    MSEC_TO_TU(s->u.mesh.mshcfg.dot11MeshHWMPactivePathTimeout)
#define min_preq_int_jiff(s) \
    (msecs_to_jiffies(s->u.mesh.mshcfg.dot11MeshHWMPpreqMinInterval))
#define max_preq_retries(s) (s->u.mesh.mshcfg.dot11MeshHWMPmaxPREQretries)
#define disc_timeout_jiff(s) \
    msecs_to_jiffies(sdata->u.mesh.mshcfg.min_discovery_timeout)
#define root_path_confirmation_jiffies(s) \
    msecs_to_jiffies(sdata->u.mesh.mshcfg.dot11MeshHWMPconfirmationInterval)

enum mpath_frame_type {
    MPATH_PREQ = 0,
    MPATH_PREP,
    MPATH_PERR,
    MPATH_RANN
};

static const u8 broadcast_addr[ETH_ALEN] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};

static int mesh_path_sel_frame_tx(enum mpath_frame_type action, u8 flags,
        u8 *orig_addr, __le32 orig_sn, u8 target_flags, u8 *target,
        __le32 target_sn, const u8 *da, u8 hop_count, u8 ttl,
        __le32 lifetime, __le32 metric, __le32 preq_id,
        struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_local *local = sdata->local;
    struct sk_buff *skb;
    struct ieee80211_mgmt *mgmt;
    u8 *pos, ie_len;
    int hdr_len = offsetof(struct ieee80211_mgmt, u.action.u.mesh_action) +
              sizeof(mgmt->u.action.u.mesh_action);

    skb = dev_alloc_skb(local->tx_headroom +
                hdr_len +
                2 + 37); /* max HWMP IE */
    if (!skb)
        return -1;
    skb_reserve(skb, local->tx_headroom);
    mgmt = (struct ieee80211_mgmt *) skb_put(skb, hdr_len);
    memset(mgmt, 0, hdr_len);
    mgmt->frame_control = cpu_to_le16(IEEE80211_FTYPE_MGMT |
                      IEEE80211_STYPE_ACTION);

    memcpy(mgmt->da, da, ETH_ALEN);
    memcpy(mgmt->sa, sdata->vif.addr, ETH_ALEN);
    /* BSSID == SA */
    memcpy(mgmt->bssid, sdata->vif.addr, ETH_ALEN);
    mgmt->u.action.category = WLAN_CATEGORY_MESH_ACTION;
    mgmt->u.action.u.mesh_action.action_code =
                    WLAN_MESH_ACTION_HWMP_PATH_SELECTION;

    switch (action) {
    case MPATH_PREQ:
        mhwmp_dbg(sdata, "sending PREQ to %pM\n", target);
        ie_len = 37;
        pos = skb_put(skb, 2 + ie_len);
        *pos++ = WLAN_EID_PREQ;
        break;
    case MPATH_PREP:
        mhwmp_dbg(sdata, "sending PREP to %pM\n", target);
        ie_len = 31;
        pos = skb_put(skb, 2 + ie_len);
        *pos++ = WLAN_EID_PREP;
        break;
    case MPATH_RANN:
        mhwmp_dbg(sdata, "sending RANN from %pM\n", orig_addr);
        ie_len = sizeof(struct ieee80211_rann_ie);
        pos = skb_put(skb, 2 + ie_len);
        *pos++ = WLAN_EID_RANN;
        break;
    default:
        kfree_skb(skb);
        return -ENOTSUPP;
        break;
    }
    *pos++ = ie_len;
    *pos++ = flags;
    *pos++ = hop_count;
    *pos++ = ttl;
    if (action == MPATH_PREP) {
        memcpy(pos, target, ETH_ALEN);
        pos += ETH_ALEN;
        memcpy(pos, &target_sn, 4);
        pos += 4;
    } else {
        if (action == MPATH_PREQ) {
            memcpy(pos, &preq_id, 4);
            pos += 4;
        }
        memcpy(pos, orig_addr, ETH_ALEN);
        pos += ETH_ALEN;
        memcpy(pos, &orig_sn, 4);
        pos += 4;
    }
    memcpy(pos, &lifetime, 4);  /* interval for RANN */
    pos += 4;
    memcpy(pos, &metric, 4);
    pos += 4;
    if (action == MPATH_PREQ) {
        *pos++ = 1; /* destination count */
        *pos++ = target_flags;
        memcpy(pos, target, ETH_ALEN);
        pos += ETH_ALEN;
        memcpy(pos, &target_sn, 4);
        pos += 4;
    } else if (action == MPATH_PREP) {
        memcpy(pos, orig_addr, ETH_ALEN);
        pos += ETH_ALEN;
        memcpy(pos, &orig_sn, 4);
        pos += 4;
    }

    ieee80211_tx_skb(sdata, skb);
    return 0;
}


/*  Headroom is not adjusted.  Caller should ensure that skb has sufficient
 *  headroom in case the frame is encrypted. */
static void prepare_frame_for_deferred_tx(struct ieee80211_sub_if_data *sdata,
        struct sk_buff *skb)
{
    struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);

    skb_set_mac_header(skb, 0);
    skb_set_network_header(skb, 0);
    skb_set_transport_header(skb, 0);

    /* Send all internal mgmt frames on VO. Accordingly set TID to 7. */
    skb_set_queue_mapping(skb, IEEE80211_AC_VO);
    skb->priority = 7;

    info->control.vif = &sdata->vif;
    ieee80211_set_qos_hdr(sdata, skb);
}

int mesh_path_error_tx(u8 ttl, u8 *target, __le32 target_sn,
               __le16 target_rcode, const u8 *ra,
               struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_local *local = sdata->local;
    struct sk_buff *skb;
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct ieee80211_mgmt *mgmt;
    u8 *pos, ie_len;
    int hdr_len = offsetof(struct ieee80211_mgmt, u.action.u.mesh_action) +
              sizeof(mgmt->u.action.u.mesh_action);

    if (time_before(jiffies, ifmsh->next_perr))
        return -EAGAIN;

    skb = dev_alloc_skb(local->tx_headroom +
                hdr_len +
                2 + 15 /* PERR IE */);
    if (!skb)
        return -1;
    skb_reserve(skb, local->tx_headroom);
    mgmt = (struct ieee80211_mgmt *) skb_put(skb, hdr_len);
    memset(mgmt, 0, hdr_len);
    mgmt->frame_control = cpu_to_le16(IEEE80211_FTYPE_MGMT |
                      IEEE80211_STYPE_ACTION);

    memcpy(mgmt->da, ra, ETH_ALEN);
    memcpy(mgmt->sa, sdata->vif.addr, ETH_ALEN);
    /* BSSID == SA */
    memcpy(mgmt->bssid, sdata->vif.addr, ETH_ALEN);
    mgmt->u.action.category = WLAN_CATEGORY_MESH_ACTION;
    mgmt->u.action.u.mesh_action.action_code =
                    WLAN_MESH_ACTION_HWMP_PATH_SELECTION;
    ie_len = 15;
    pos = skb_put(skb, 2 + ie_len);
    *pos++ = WLAN_EID_PERR;
    *pos++ = ie_len;
    /* ttl */
    *pos++ = ttl;
    /* number of destinations */
    *pos++ = 1;
    /*
     * flags bit, bit 1 is unset if we know the sequence number and
     * bit 2 is set if we have a reason code
     */
    *pos = 0;
    if (!target_sn)
        *pos |= MP_F_USN;
    if (target_rcode)
        *pos |= MP_F_RCODE;
    pos++;
    memcpy(pos, target, ETH_ALEN);
    pos += ETH_ALEN;
    memcpy(pos, &target_sn, 4);
    pos += 4;
    memcpy(pos, &target_rcode, 2);

    /* see note in function header */
    prepare_frame_for_deferred_tx(sdata, skb);
    ifmsh->next_perr = TU_TO_EXP_TIME(
                   ifmsh->mshcfg.dot11MeshHWMPperrMinInterval);
    ieee80211_add_pending_skb(local, skb);
    return 0;
}

void ieee80211s_update_metric(struct ieee80211_local *local,
        struct sta_info *sta, struct sk_buff *skb)
{
    struct ieee80211_tx_info *txinfo = IEEE80211_SKB_CB(skb);
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
    int failed;

    if (!ieee80211_is_data(hdr->frame_control))
        return;

    failed = !(txinfo->flags & IEEE80211_TX_STAT_ACK);

    /* moving average, scaled to 100 */
    sta->fail_avg = ((80 * sta->fail_avg + 5) / 100 + 20 * failed);
    if (sta->fail_avg > 95)
        mesh_plink_broken(sta);
}

static u32 airtime_link_metric_get(struct ieee80211_local *local,
                   struct sta_info *sta)
{
    struct rate_info rinfo;
    /* This should be adjusted for each device */
    int device_constant = 1 << ARITH_SHIFT;
    int test_frame_len = TEST_FRAME_LEN << ARITH_SHIFT;
    int s_unit = 1 << ARITH_SHIFT;
    int rate, err;
    u32 tx_time, estimated_retx;
    u64 result;

    if (sta->fail_avg >= 100)
        return MAX_METRIC;

    sta_set_rate_info_tx(sta, &sta->last_tx_rate, &rinfo);
    rate = cfg80211_calculate_bitrate(&rinfo);
    if (WARN_ON(!rate))
        return MAX_METRIC;

    err = (sta->fail_avg << ARITH_SHIFT) / 100;

    /* bitrate is in units of 100 Kbps, while we need rate in units of
     * 1Mbps. This will be corrected on tx_time computation.
     */
    tx_time = (device_constant + 10 * test_frame_len / rate);
    estimated_retx = ((1 << (2 * ARITH_SHIFT)) / (s_unit - err));
    result = (tx_time * estimated_retx) >> (2 * ARITH_SHIFT) ;
    return (u32)result;
}

static u32 hwmp_route_info_get(struct ieee80211_sub_if_data *sdata,
                struct ieee80211_mgmt *mgmt,
                u8 *hwmp_ie, enum mpath_frame_type action)
{
    struct ieee80211_local *local = sdata->local;
    struct mesh_path *mpath;
    struct sta_info *sta;
    bool fresh_info;
    u8 *orig_addr, *ta;
    u32 orig_sn, orig_metric;
    unsigned long orig_lifetime, exp_time;
    u32 last_hop_metric, new_metric;
    bool process = true;

    rcu_read_lock();
    sta = sta_info_get(sdata, mgmt->sa);
    if (!sta) {
        rcu_read_unlock();
        return 0;
    }

    last_hop_metric = airtime_link_metric_get(local, sta);
    /* Update and check originator routing info */
    fresh_info = true;

    switch (action) {
    case MPATH_PREQ:
        orig_addr = PREQ_IE_ORIG_ADDR(hwmp_ie);
        orig_sn = PREQ_IE_ORIG_SN(hwmp_ie);
        orig_lifetime = PREQ_IE_LIFETIME(hwmp_ie);
        orig_metric = PREQ_IE_METRIC(hwmp_ie);
        break;
    case MPATH_PREP:
        /* Originator here refers to the MP that was the target in the
         * Path Request. We divert from the nomenclature in the draft
         * so that we can easily use a single function to gather path
         * information from both PREQ and PREP frames.
         */
        orig_addr = PREP_IE_TARGET_ADDR(hwmp_ie);
        orig_sn = PREP_IE_TARGET_SN(hwmp_ie);
        orig_lifetime = PREP_IE_LIFETIME(hwmp_ie);
        orig_metric = PREP_IE_METRIC(hwmp_ie);
        break;
    default:
        rcu_read_unlock();
        return 0;
    }
    new_metric = orig_metric + last_hop_metric;
    if (new_metric < orig_metric)
        new_metric = MAX_METRIC;
    exp_time = TU_TO_EXP_TIME(orig_lifetime);

    if (ether_addr_equal(orig_addr, sdata->vif.addr)) {
        /* This MP is the originator, we are not interested in this
         * frame, except for updating transmitter's path info.
         */
        process = false;
        fresh_info = false;
    } else {
        mpath = mesh_path_lookup(orig_addr, sdata);
        if (mpath) {
            spin_lock_bh(&mpath->state_lock);
            if (mpath->flags & MESH_PATH_FIXED)
                fresh_info = false;
            else if ((mpath->flags & MESH_PATH_ACTIVE) &&
                (mpath->flags & MESH_PATH_SN_VALID)) {
                if (SN_GT(mpath->sn, orig_sn) ||
                    (mpath->sn == orig_sn &&
                     new_metric >= mpath->metric)) {
                    process = false;
                    fresh_info = false;
                }
            }
        } else {
            mesh_path_add(orig_addr, sdata);
            mpath = mesh_path_lookup(orig_addr, sdata);
            if (!mpath) {
                rcu_read_unlock();
                return 0;
            }
            spin_lock_bh(&mpath->state_lock);
        }

        if (fresh_info) {
            mesh_path_assign_nexthop(mpath, sta);
            mpath->flags |= MESH_PATH_SN_VALID;
            mpath->metric = new_metric;
            mpath->sn = orig_sn;
            mpath->exp_time = time_after(mpath->exp_time, exp_time)
                      ?  mpath->exp_time : exp_time;
            mesh_path_activate(mpath);
            spin_unlock_bh(&mpath->state_lock);
            mesh_path_tx_pending(mpath);
            /* draft says preq_id should be saved to, but there does
             * not seem to be any use for it, skipping by now
             */
        } else
            spin_unlock_bh(&mpath->state_lock);
    }

    /* Update and check transmitter routing info */
    ta = mgmt->sa;
    if (ether_addr_equal(orig_addr, ta))
        fresh_info = false;
    else {
        fresh_info = true;

        mpath = mesh_path_lookup(ta, sdata);
        if (mpath) {
            spin_lock_bh(&mpath->state_lock);
            if ((mpath->flags & MESH_PATH_FIXED) ||
                ((mpath->flags & MESH_PATH_ACTIVE) &&
                    (last_hop_metric > mpath->metric)))
                fresh_info = false;
        } else {
            mesh_path_add(ta, sdata);
            mpath = mesh_path_lookup(ta, sdata);
            if (!mpath) {
                rcu_read_unlock();
                return 0;
            }
            spin_lock_bh(&mpath->state_lock);
        }

        if (fresh_info) {
            mesh_path_assign_nexthop(mpath, sta);
            mpath->metric = last_hop_metric;
            mpath->exp_time = time_after(mpath->exp_time, exp_time)
                      ?  mpath->exp_time : exp_time;
            mesh_path_activate(mpath);
            spin_unlock_bh(&mpath->state_lock);
            mesh_path_tx_pending(mpath);
        } else
            spin_unlock_bh(&mpath->state_lock);
    }

    rcu_read_unlock();

    return process ? new_metric : 0;
}

static void hwmp_preq_frame_process(struct ieee80211_sub_if_data *sdata,
                    struct ieee80211_mgmt *mgmt,
                    u8 *preq_elem, u32 metric)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct mesh_path *mpath = NULL;
    u8 *target_addr, *orig_addr;
    const u8 *da;
    u8 target_flags, ttl, flags;
    u32 orig_sn, target_sn, lifetime, orig_metric;
    bool reply = false;
    bool forward = true;
    bool root_is_gate;

    /* Update target SN, if present */
    target_addr = PREQ_IE_TARGET_ADDR(preq_elem);
    orig_addr = PREQ_IE_ORIG_ADDR(preq_elem);
    target_sn = PREQ_IE_TARGET_SN(preq_elem);
    orig_sn = PREQ_IE_ORIG_SN(preq_elem);
    target_flags = PREQ_IE_TARGET_F(preq_elem);
    orig_metric = metric;
    /* Proactive PREQ gate announcements */
    flags = PREQ_IE_FLAGS(preq_elem);
    root_is_gate = !!(flags & RANN_FLAG_IS_GATE);

    mhwmp_dbg(sdata, "received PREQ from %pM\n", orig_addr);

    if (ether_addr_equal(target_addr, sdata->vif.addr)) {
        mhwmp_dbg(sdata, "PREQ is for us\n");
        forward = false;
        reply = true;
        metric = 0;
        if (time_after(jiffies, ifmsh->last_sn_update +
                    net_traversal_jiffies(sdata)) ||
            time_before(jiffies, ifmsh->last_sn_update)) {
            target_sn = ++ifmsh->sn;
            ifmsh->last_sn_update = jiffies;
        }
    } else if (is_broadcast_ether_addr(target_addr) &&
           (target_flags & IEEE80211_PREQ_TO_FLAG)) {
        rcu_read_lock();
        mpath = mesh_path_lookup(orig_addr, sdata);
        if (mpath) {
            if (flags & IEEE80211_PREQ_PROACTIVE_PREP_FLAG) {
                reply = true;
                target_addr = sdata->vif.addr;
                target_sn = ++ifmsh->sn;
                metric = 0;
                ifmsh->last_sn_update = jiffies;
            }
            if (root_is_gate)
                mesh_path_add_gate(mpath);
        }
        rcu_read_unlock();
    } else {
        rcu_read_lock();
        mpath = mesh_path_lookup(target_addr, sdata);
        if (mpath) {
            if ((!(mpath->flags & MESH_PATH_SN_VALID)) ||
                    SN_LT(mpath->sn, target_sn)) {
                mpath->sn = target_sn;
                mpath->flags |= MESH_PATH_SN_VALID;
            } else if ((!(target_flags & MP_F_DO)) &&
                    (mpath->flags & MESH_PATH_ACTIVE)) {
                reply = true;
                metric = mpath->metric;
                target_sn = mpath->sn;
                if (target_flags & MP_F_RF)
                    target_flags |= MP_F_DO;
                else
                    forward = false;
            }
        }
        rcu_read_unlock();
    }

    if (reply) {
        lifetime = PREQ_IE_LIFETIME(preq_elem);
        ttl = ifmsh->mshcfg.element_ttl;
        if (ttl != 0) {
            mhwmp_dbg(sdata, "replying to the PREQ\n");
            mesh_path_sel_frame_tx(MPATH_PREP, 0, orig_addr,
                cpu_to_le32(orig_sn), 0, target_addr,
                cpu_to_le32(target_sn), mgmt->sa, 0, ttl,
                cpu_to_le32(lifetime), cpu_to_le32(metric),
                0, sdata);
        } else {
            ifmsh->mshstats.dropped_frames_ttl++;
        }
    }

    if (forward && ifmsh->mshcfg.dot11MeshForwarding) {
        u32 preq_id;
        u8 hopcount;

        ttl = PREQ_IE_TTL(preq_elem);
        lifetime = PREQ_IE_LIFETIME(preq_elem);
        if (ttl <= 1) {
            ifmsh->mshstats.dropped_frames_ttl++;
            return;
        }
        mhwmp_dbg(sdata, "forwarding the PREQ from %pM\n", orig_addr);
        --ttl;
        preq_id = PREQ_IE_PREQ_ID(preq_elem);
        hopcount = PREQ_IE_HOPCOUNT(preq_elem) + 1;
        da = (mpath && mpath->is_root) ?
            mpath->rann_snd_addr : broadcast_addr;

        if (flags & IEEE80211_PREQ_PROACTIVE_PREP_FLAG) {
            target_addr = PREQ_IE_TARGET_ADDR(preq_elem);
            target_sn = PREQ_IE_TARGET_SN(preq_elem);
            metric = orig_metric;
        }

        mesh_path_sel_frame_tx(MPATH_PREQ, flags, orig_addr,
                cpu_to_le32(orig_sn), target_flags, target_addr,
                cpu_to_le32(target_sn), da,
                hopcount, ttl, cpu_to_le32(lifetime),
                cpu_to_le32(metric), cpu_to_le32(preq_id),
                sdata);
        if (!is_multicast_ether_addr(da))
            ifmsh->mshstats.fwded_unicast++;
        else
            ifmsh->mshstats.fwded_mcast++;
        ifmsh->mshstats.fwded_frames++;
    }
}


static inline struct sta_info *
next_hop_deref_protected(struct mesh_path *mpath)
{
    return rcu_dereference_protected(mpath->next_hop,
                     lockdep_is_held(&mpath->state_lock));
}


static void hwmp_prep_frame_process(struct ieee80211_sub_if_data *sdata,
                    struct ieee80211_mgmt *mgmt,
                    u8 *prep_elem, u32 metric)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct mesh_path *mpath;
    u8 *target_addr, *orig_addr;
    u8 ttl, hopcount, flags;
    u8 next_hop[ETH_ALEN];
    u32 target_sn, orig_sn, lifetime;

    mhwmp_dbg(sdata, "received PREP from %pM\n",
          PREP_IE_ORIG_ADDR(prep_elem));

    orig_addr = PREP_IE_ORIG_ADDR(prep_elem);
    if (ether_addr_equal(orig_addr, sdata->vif.addr))
        /* destination, no forwarding required */
        return;

    if (!ifmsh->mshcfg.dot11MeshForwarding)
        return;

    ttl = PREP_IE_TTL(prep_elem);
    if (ttl <= 1) {
        sdata->u.mesh.mshstats.dropped_frames_ttl++;
        return;
    }

    rcu_read_lock();
    mpath = mesh_path_lookup(orig_addr, sdata);
    if (mpath)
        spin_lock_bh(&mpath->state_lock);
    else
        goto fail;
    if (!(mpath->flags & MESH_PATH_ACTIVE)) {
        spin_unlock_bh(&mpath->state_lock);
        goto fail;
    }
    memcpy(next_hop, next_hop_deref_protected(mpath)->sta.addr, ETH_ALEN);
    spin_unlock_bh(&mpath->state_lock);
    --ttl;
    flags = PREP_IE_FLAGS(prep_elem);
    lifetime = PREP_IE_LIFETIME(prep_elem);
    hopcount = PREP_IE_HOPCOUNT(prep_elem) + 1;
    target_addr = PREP_IE_TARGET_ADDR(prep_elem);
    target_sn = PREP_IE_TARGET_SN(prep_elem);
    orig_sn = PREP_IE_ORIG_SN(prep_elem);

    mesh_path_sel_frame_tx(MPATH_PREP, flags, orig_addr,
        cpu_to_le32(orig_sn), 0, target_addr,
        cpu_to_le32(target_sn), next_hop, hopcount,
        ttl, cpu_to_le32(lifetime), cpu_to_le32(metric),
        0, sdata);
    rcu_read_unlock();

    sdata->u.mesh.mshstats.fwded_unicast++;
    sdata->u.mesh.mshstats.fwded_frames++;
    return;

fail:
    rcu_read_unlock();
    sdata->u.mesh.mshstats.dropped_frames_no_route++;
}

static void hwmp_perr_frame_process(struct ieee80211_sub_if_data *sdata,
                 struct ieee80211_mgmt *mgmt, u8 *perr_elem)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct mesh_path *mpath;
    u8 ttl;
    u8 *ta, *target_addr;
    u32 target_sn;
    u16 target_rcode;

    ta = mgmt->sa;
    ttl = PERR_IE_TTL(perr_elem);
    if (ttl <= 1) {
        ifmsh->mshstats.dropped_frames_ttl++;
        return;
    }
    ttl--;
    target_addr = PERR_IE_TARGET_ADDR(perr_elem);
    target_sn = PERR_IE_TARGET_SN(perr_elem);
    target_rcode = PERR_IE_TARGET_RCODE(perr_elem);

    rcu_read_lock();
    mpath = mesh_path_lookup(target_addr, sdata);
    if (mpath) {
        struct sta_info *sta;

        spin_lock_bh(&mpath->state_lock);
        sta = next_hop_deref_protected(mpath);
        if (mpath->flags & MESH_PATH_ACTIVE &&
            ether_addr_equal(ta, sta->sta.addr) &&
            (!(mpath->flags & MESH_PATH_SN_VALID) ||
            SN_GT(target_sn, mpath->sn))) {
            mpath->flags &= ~MESH_PATH_ACTIVE;
            mpath->sn = target_sn;
            spin_unlock_bh(&mpath->state_lock);
            if (!ifmsh->mshcfg.dot11MeshForwarding)
                goto endperr;
            mesh_path_error_tx(ttl, target_addr, cpu_to_le32(target_sn),
                       cpu_to_le16(target_rcode),
                       broadcast_addr, sdata);
        } else
            spin_unlock_bh(&mpath->state_lock);
    }
endperr:
    rcu_read_unlock();
}

static void hwmp_rann_frame_process(struct ieee80211_sub_if_data *sdata,
                struct ieee80211_mgmt *mgmt,
                struct ieee80211_rann_ie *rann)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct ieee80211_local *local = sdata->local;
    struct sta_info *sta;
    struct mesh_path *mpath;
    u8 ttl, flags, hopcount;
    u8 *orig_addr;
    u32 orig_sn, metric, metric_txsta, interval;
    bool root_is_gate;

    ttl = rann->rann_ttl;
    flags = rann->rann_flags;
    root_is_gate = !!(flags & RANN_FLAG_IS_GATE);
    orig_addr = rann->rann_addr;
    orig_sn = le32_to_cpu(rann->rann_seq);
    interval = le32_to_cpu(rann->rann_interval);
    hopcount = rann->rann_hopcount;
    hopcount++;
    metric = le32_to_cpu(rann->rann_metric);

    /*  Ignore our own RANNs */
    if (ether_addr_equal(orig_addr, sdata->vif.addr))
        return;

    mhwmp_dbg(sdata,
          "received RANN from %pM via neighbour %pM (is_gate=%d)\n",
          orig_addr, mgmt->sa, root_is_gate);

    rcu_read_lock();
    sta = sta_info_get(sdata, mgmt->sa);
    if (!sta) {
        rcu_read_unlock();
        return;
    }

    metric_txsta = airtime_link_metric_get(local, sta);

    mpath = mesh_path_lookup(orig_addr, sdata);
    if (!mpath) {
        mesh_path_add(orig_addr, sdata);
        mpath = mesh_path_lookup(orig_addr, sdata);
        if (!mpath) {
            rcu_read_unlock();
            sdata->u.mesh.mshstats.dropped_frames_no_route++;
            return;
        }
    }

    if (!(SN_LT(mpath->sn, orig_sn)) &&
        !(mpath->sn == orig_sn && metric < mpath->rann_metric)) {
        rcu_read_unlock();
        return;
    }

    if ((!(mpath->flags & (MESH_PATH_ACTIVE | MESH_PATH_RESOLVING)) ||
         (time_after(jiffies, mpath->last_preq_to_root +
                  root_path_confirmation_jiffies(sdata)) ||
         time_before(jiffies, mpath->last_preq_to_root))) &&
         !(mpath->flags & MESH_PATH_FIXED) && (ttl != 0)) {
        mhwmp_dbg(sdata,
              "time to refresh root mpath %pM\n",
              orig_addr);
        mesh_queue_preq(mpath, PREQ_Q_F_START | PREQ_Q_F_REFRESH);
        mpath->last_preq_to_root = jiffies;
    }

    mpath->sn = orig_sn;
    mpath->rann_metric = metric + metric_txsta;
    mpath->is_root = true;
    /* Recording RANNs sender address to send individually
     * addressed PREQs destined for root mesh STA */
    memcpy(mpath->rann_snd_addr, mgmt->sa, ETH_ALEN);

    if (root_is_gate)
        mesh_path_add_gate(mpath);

    if (ttl <= 1) {
        ifmsh->mshstats.dropped_frames_ttl++;
        rcu_read_unlock();
        return;
    }
    ttl--;

    if (ifmsh->mshcfg.dot11MeshForwarding) {
        mesh_path_sel_frame_tx(MPATH_RANN, flags, orig_addr,
                       cpu_to_le32(orig_sn),
                       0, NULL, 0, broadcast_addr,
                       hopcount, ttl, cpu_to_le32(interval),
                       cpu_to_le32(metric + metric_txsta),
                       0, sdata);
    }

    rcu_read_unlock();
}


void mesh_rx_path_sel_frame(struct ieee80211_sub_if_data *sdata,
                struct ieee80211_mgmt *mgmt,
                size_t len)
{
    struct ieee802_11_elems elems;
    size_t baselen;
    u32 last_hop_metric;
    struct sta_info *sta;

    /* need action_code */
    if (len < IEEE80211_MIN_ACTION_SIZE + 1)
        return;

    rcu_read_lock();
    sta = sta_info_get(sdata, mgmt->sa);
    if (!sta || sta->plink_state != NL80211_PLINK_ESTAB) {
        rcu_read_unlock();
        return;
    }
    rcu_read_unlock();

    baselen = (u8 *) mgmt->u.action.u.mesh_action.variable - (u8 *) mgmt;
    ieee802_11_parse_elems(mgmt->u.action.u.mesh_action.variable,
            len - baselen, &elems);

    if (elems.preq) {
        if (elems.preq_len != 37)
            /* Right now we support just 1 destination and no AE */
            return;
        last_hop_metric = hwmp_route_info_get(sdata, mgmt, elems.preq,
                              MPATH_PREQ);
        if (last_hop_metric)
            hwmp_preq_frame_process(sdata, mgmt, elems.preq,
                        last_hop_metric);
    }
    if (elems.prep) {
        if (elems.prep_len != 31)
            /* Right now we support no AE */
            return;
        last_hop_metric = hwmp_route_info_get(sdata, mgmt, elems.prep,
                              MPATH_PREP);
        if (last_hop_metric)
            hwmp_prep_frame_process(sdata, mgmt, elems.prep,
                        last_hop_metric);
    }
    if (elems.perr) {
        if (elems.perr_len != 15)
            /* Right now we support only one destination per PERR */
            return;
        hwmp_perr_frame_process(sdata, mgmt, elems.perr);
    }
    if (elems.rann)
        hwmp_rann_frame_process(sdata, mgmt, elems.rann);
}

static void mesh_queue_preq(struct mesh_path *mpath, u8 flags)
{
    struct ieee80211_sub_if_data *sdata = mpath->sdata;
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct mesh_preq_queue *preq_node;

    preq_node = kmalloc(sizeof(struct mesh_preq_queue), GFP_ATOMIC);
    if (!preq_node) {
        mhwmp_dbg(sdata, "could not allocate PREQ node\n");
        return;
    }

    spin_lock_bh(&ifmsh->mesh_preq_queue_lock);
    if (ifmsh->preq_queue_len == MAX_PREQ_QUEUE_LEN) {
        spin_unlock_bh(&ifmsh->mesh_preq_queue_lock);
        kfree(preq_node);
        if (printk_ratelimit())
            mhwmp_dbg(sdata, "PREQ node queue full\n");
        return;
    }

    spin_lock(&mpath->state_lock);
    if (mpath->flags & MESH_PATH_REQ_QUEUED) {
        spin_unlock(&mpath->state_lock);
        spin_unlock_bh(&ifmsh->mesh_preq_queue_lock);
        kfree(preq_node);
        return;
    }

    memcpy(preq_node->dst, mpath->dst, ETH_ALEN);
    preq_node->flags = flags;

    mpath->flags |= MESH_PATH_REQ_QUEUED;
    spin_unlock(&mpath->state_lock);

    list_add_tail(&preq_node->list, &ifmsh->preq_queue.list);
    ++ifmsh->preq_queue_len;
    spin_unlock_bh(&ifmsh->mesh_preq_queue_lock);

    if (time_after(jiffies, ifmsh->last_preq + min_preq_int_jiff(sdata)))
        ieee80211_queue_work(&sdata->local->hw, &sdata->work);

    else if (time_before(jiffies, ifmsh->last_preq)) {
        /* avoid long wait if did not send preqs for a long time
         * and jiffies wrapped around
         */
        ifmsh->last_preq = jiffies - min_preq_int_jiff(sdata) - 1;
        ieee80211_queue_work(&sdata->local->hw, &sdata->work);
    } else
        mod_timer(&ifmsh->mesh_path_timer, ifmsh->last_preq +
                        min_preq_int_jiff(sdata));
}

void mesh_path_start_discovery(struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct mesh_preq_queue *preq_node;
    struct mesh_path *mpath;
    u8 ttl, target_flags;
    const u8 *da;
    u32 lifetime;

    spin_lock_bh(&ifmsh->mesh_preq_queue_lock);
    if (!ifmsh->preq_queue_len ||
        time_before(jiffies, ifmsh->last_preq +
                min_preq_int_jiff(sdata))) {
        spin_unlock_bh(&ifmsh->mesh_preq_queue_lock);
        return;
    }

    preq_node = list_first_entry(&ifmsh->preq_queue.list,
            struct mesh_preq_queue, list);
    list_del(&preq_node->list);
    --ifmsh->preq_queue_len;
    spin_unlock_bh(&ifmsh->mesh_preq_queue_lock);

    rcu_read_lock();
    mpath = mesh_path_lookup(preq_node->dst, sdata);
    if (!mpath)
        goto enddiscovery;

    spin_lock_bh(&mpath->state_lock);
    mpath->flags &= ~MESH_PATH_REQ_QUEUED;
    if (preq_node->flags & PREQ_Q_F_START) {
        if (mpath->flags & MESH_PATH_RESOLVING) {
            spin_unlock_bh(&mpath->state_lock);
            goto enddiscovery;
        } else {
            mpath->flags &= ~MESH_PATH_RESOLVED;
            mpath->flags |= MESH_PATH_RESOLVING;
            mpath->discovery_retries = 0;
            mpath->discovery_timeout = disc_timeout_jiff(sdata);
        }
    } else if (!(mpath->flags & MESH_PATH_RESOLVING) ||
            mpath->flags & MESH_PATH_RESOLVED) {
        mpath->flags &= ~MESH_PATH_RESOLVING;
        spin_unlock_bh(&mpath->state_lock);
        goto enddiscovery;
    }

    ifmsh->last_preq = jiffies;

    if (time_after(jiffies, ifmsh->last_sn_update +
                net_traversal_jiffies(sdata)) ||
        time_before(jiffies, ifmsh->last_sn_update)) {
        ++ifmsh->sn;
        sdata->u.mesh.last_sn_update = jiffies;
    }
    lifetime = default_lifetime(sdata);
    ttl = sdata->u.mesh.mshcfg.element_ttl;
    if (ttl == 0) {
        sdata->u.mesh.mshstats.dropped_frames_ttl++;
        spin_unlock_bh(&mpath->state_lock);
        goto enddiscovery;
    }

    if (preq_node->flags & PREQ_Q_F_REFRESH)
        target_flags = MP_F_DO;
    else
        target_flags = MP_F_RF;

    spin_unlock_bh(&mpath->state_lock);
    da = (mpath->is_root) ? mpath->rann_snd_addr : broadcast_addr;
    mesh_path_sel_frame_tx(MPATH_PREQ, 0, sdata->vif.addr,
            cpu_to_le32(ifmsh->sn), target_flags, mpath->dst,
            cpu_to_le32(mpath->sn), da, 0,
            ttl, cpu_to_le32(lifetime), 0,
            cpu_to_le32(ifmsh->preq_id++), sdata);
    mod_timer(&mpath->timer, jiffies + mpath->discovery_timeout);

enddiscovery:
    rcu_read_unlock();
    kfree(preq_node);
}

int mesh_nexthop_resolve(struct sk_buff *skb,
             struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
    struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
    struct mesh_path *mpath;
    struct sk_buff *skb_to_free = NULL;
    u8 *target_addr = hdr->addr3;
    int err = 0;

    rcu_read_lock();
    err = mesh_nexthop_lookup(skb, sdata);
    if (!err)
        goto endlookup;

    /* no nexthop found, start resolving */
    mpath = mesh_path_lookup(target_addr, sdata);
    if (!mpath) {
        mesh_path_add(target_addr, sdata);
        mpath = mesh_path_lookup(target_addr, sdata);
        if (!mpath) {
            mesh_path_discard_frame(skb, sdata);
            err = -ENOSPC;
            goto endlookup;
        }
    }

    if (!(mpath->flags & MESH_PATH_RESOLVING))
        mesh_queue_preq(mpath, PREQ_Q_F_START);

    if (skb_queue_len(&mpath->frame_queue) >= MESH_FRAME_QUEUE_LEN)
        skb_to_free = skb_dequeue(&mpath->frame_queue);

    info->flags |= IEEE80211_TX_INTFL_NEED_TXPROCESSING;
    ieee80211_set_qos_hdr(sdata, skb);
    skb_queue_tail(&mpath->frame_queue, skb);
    err = -ENOENT;
    if (skb_to_free)
        mesh_path_discard_frame(skb_to_free, sdata);

endlookup:
    rcu_read_unlock();
    return err;
}
int mesh_nexthop_lookup(struct sk_buff *skb,
            struct ieee80211_sub_if_data *sdata)
{
    struct mesh_path *mpath;
    struct sta_info *next_hop;
    struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
    u8 *target_addr = hdr->addr3;
    int err = -ENOENT;

    rcu_read_lock();
    mpath = mesh_path_lookup(target_addr, sdata);

    if (!mpath || !(mpath->flags & MESH_PATH_ACTIVE))
        goto endlookup;

    if (time_after(jiffies,
               mpath->exp_time -
               msecs_to_jiffies(sdata->u.mesh.mshcfg.path_refresh_time)) &&
        ether_addr_equal(sdata->vif.addr, hdr->addr4) &&
        !(mpath->flags & MESH_PATH_RESOLVING) &&
        !(mpath->flags & MESH_PATH_FIXED))
        mesh_queue_preq(mpath, PREQ_Q_F_START | PREQ_Q_F_REFRESH);

    next_hop = rcu_dereference(mpath->next_hop);
    if (next_hop) {
        memcpy(hdr->addr1, next_hop->sta.addr, ETH_ALEN);
        memcpy(hdr->addr2, sdata->vif.addr, ETH_ALEN);
        err = 0;
    }

endlookup:
    rcu_read_unlock();
    return err;
}

void mesh_path_timer(unsigned long data)
{
    struct mesh_path *mpath = (void *) data;
    struct ieee80211_sub_if_data *sdata = mpath->sdata;
    int ret;

    if (sdata->local->quiescing)
        return;

    spin_lock_bh(&mpath->state_lock);
    if (mpath->flags & MESH_PATH_RESOLVED ||
            (!(mpath->flags & MESH_PATH_RESOLVING))) {
        mpath->flags &= ~(MESH_PATH_RESOLVING | MESH_PATH_RESOLVED);
        spin_unlock_bh(&mpath->state_lock);
    } else if (mpath->discovery_retries < max_preq_retries(sdata)) {
        ++mpath->discovery_retries;
        mpath->discovery_timeout *= 2;
        mpath->flags &= ~MESH_PATH_REQ_QUEUED;
        spin_unlock_bh(&mpath->state_lock);
        mesh_queue_preq(mpath, 0);
    } else {
        mpath->flags = 0;
        mpath->exp_time = jiffies;
        spin_unlock_bh(&mpath->state_lock);
        if (!mpath->is_gate && mesh_gate_num(sdata) > 0) {
            ret = mesh_path_send_to_gates(mpath);
            if (ret)
                mhwmp_dbg(sdata, "no gate was reachable\n");
        } else
            mesh_path_flush_pending(mpath);
    }
}

void
mesh_path_tx_root_frame(struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    u32 interval = ifmsh->mshcfg.dot11MeshHWMPRannInterval;
    u8 flags, target_flags = 0;

    flags = (ifmsh->mshcfg.dot11MeshGateAnnouncementProtocol)
            ? RANN_FLAG_IS_GATE : 0;

    switch (ifmsh->mshcfg.dot11MeshHWMPRootMode) {
    case IEEE80211_PROACTIVE_RANN:
        mesh_path_sel_frame_tx(MPATH_RANN, flags, sdata->vif.addr,
                   cpu_to_le32(++ifmsh->sn),
                   0, NULL, 0, broadcast_addr,
                   0, ifmsh->mshcfg.element_ttl,
                   cpu_to_le32(interval), 0, 0, sdata);
        break;
    case IEEE80211_PROACTIVE_PREQ_WITH_PREP:
        flags |= IEEE80211_PREQ_PROACTIVE_PREP_FLAG;
    case IEEE80211_PROACTIVE_PREQ_NO_PREP:
        interval = ifmsh->mshcfg.dot11MeshHWMPactivePathToRootTimeout;
        target_flags |= IEEE80211_PREQ_TO_FLAG |
                IEEE80211_PREQ_USN_FLAG;
        mesh_path_sel_frame_tx(MPATH_PREQ, flags, sdata->vif.addr,
                cpu_to_le32(++ifmsh->sn), target_flags,
                (u8 *) broadcast_addr, 0, broadcast_addr,
                0, ifmsh->mshcfg.element_ttl,
                cpu_to_le32(interval),
                0, cpu_to_le32(ifmsh->preq_id++), sdata);
        break;
    default:
        mhwmp_dbg(sdata, "Proactive mechanism not supported\n");
        return;
    }
}