Release 4.14 net/mac80211/mesh_hwmp.c

/*
 * Copyright (c) 2008, 2009 open80211s Ltd.
 * Author:     Luis Carlos Cobo <luisca@cozybit.com>
 *
 * 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 LINK_FAIL_THRESH 95


#define MAX_PREQ_QUEUE_LEN	64

static void mesh_queue_preq(struct mesh_path *, u8);



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

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1
33.33%
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static inline u16 u16_field_get(const u8 *preq_elem, int offset, bool ae)
{
	if (ae)
		offset += 6;
	return get_unaligned_le16(preq_elem + offset);
}

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/* 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 MAX_SANE_SN_DELTA 32



static inline u32 SN_DELTA(u32 x, u32 y)
{
	return x >= y ? x - y : y - x;
}

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#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,
				  const u8 *orig_addr, u32 orig_sn,
				  u8 target_flags, const u8 *target,
				  u32 target_sn, const u8 *da,
				  u8 hop_count, u8 ttl,
				  u32 lifetime, u32 metric, u32 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 = skb_put_zero(skb, 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", orig_addr);
		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;
	}
	*pos++ = ie_len;
	*pos++ = flags;
	*pos++ = hop_count;
	*pos++ = ttl;
	if (action == MPATH_PREP) {
		memcpy(pos, target, ETH_ALEN);
		pos += ETH_ALEN;
		put_unaligned_le32(target_sn, pos);
		pos += 4;
	} else {
		if (action == MPATH_PREQ) {
			put_unaligned_le32(preq_id, pos);
			pos += 4;
		}
		memcpy(pos, orig_addr, ETH_ALEN);
		pos += ETH_ALEN;
		put_unaligned_le32(orig_sn, pos);
		pos += 4;
	}
	put_unaligned_le32(lifetime, pos); /* interval for RANN */
	pos += 4;
	put_unaligned_le32(metric, pos);
	pos += 4;
	if (action == MPATH_PREQ) {
		*pos++ = 1; /* destination count */
		*pos++ = target_flags;
		memcpy(pos, target, ETH_ALEN);
		pos += ETH_ALEN;
		put_unaligned_le32(target_sn, pos);
		pos += 4;
	} else if (action == MPATH_PREP) {
		memcpy(pos, orig_addr, ETH_ALEN);
		pos += ETH_ALEN;
		put_unaligned_le32(orig_sn, pos);
		pos += 4;
	}

	ieee80211_tx_skb(sdata, skb);
	return 0;
}


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6
31.58%
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7
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Javier Cardona
2
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2
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/*  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);
	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;

	skb_reset_mac_header(skb);
	skb_reset_network_header(skb);
	skb_reset_transport_header(skb);

	/* 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;
	info->flags |= IEEE80211_TX_INTFL_NEED_TXPROCESSING;
	ieee80211_set_qos_hdr(sdata, skb);
	ieee80211_mps_set_frame_flags(sdata, NULL, hdr);
}

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/**
 * mesh_path_error_tx - Sends a PERR mesh management frame
 *
 * @ttl: allowed remaining hops
 * @target: broken destination
 * @target_sn: SN of the broken destination
 * @target_rcode: reason code for this PERR
 * @ra: node this frame is addressed to
 * @sdata: local mesh subif
 *
 * Note: This function may be called with driver locks taken that the driver
 * also acquires in the TX path.  To avoid a deadlock we don't transmit the
 * frame directly but add it to the pending queue instead.
 */


int mesh_path_error_tx(struct ieee80211_sub_if_data *sdata,
		       u8 ttl, const u8 *target, u32 target_sn,
		       u16 target_rcode, const u8 *ra)
{
	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 +
			    sdata->encrypt_headroom +
			    IEEE80211_ENCRYPT_TAILROOM +
			    hdr_len +
			    2 + 15 /* PERR IE */);
	if (!skb)
		return -1;
	skb_reserve(skb, local->tx_headroom + sdata->encrypt_headroom);
	mgmt = skb_put_zero(skb, 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 field has AE bit only as defined in
         * sec 8.4.2.117 IEEE802.11-2012
         */
	*pos = 0;
	pos++;
	memcpy(pos, target, ETH_ALEN);
	pos += ETH_ALEN;
	put_unaligned_le32(target_sn, pos);
	pos += 4;
	put_unaligned_le16(target_rcode, pos);

	/* 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;
}

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Johannes Berg
11
3.12%
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Chun-Yeow Yeoh
7
1.98%
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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.
         * feed failure as 100 and success as 0
         */
	ewma_mesh_fail_avg_add(&sta->mesh->fail_avg, failed * 100);
	if (ewma_mesh_fail_avg_read(&sta->mesh->fail_avg) >
			LINK_FAIL_THRESH)
		mesh_plink_broken(sta);
}

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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;
	unsigned long fail_avg =
		ewma_mesh_fail_avg_read(&sta->mesh->fail_avg);

	/* Try to get rate based on HW/SW RC algorithm.
         * Rate is returned in units of Kbps, correct this
         * to comply with airtime calculation units
         * Round up in case we get rate < 100Kbps
         */
	rate = DIV_ROUND_UP(sta_get_expected_throughput(sta), 100);

	if (rate) {
		err = 0;
	} else {
		if (fail_avg > LINK_FAIL_THRESH)
			return MAX_METRIC;

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

		err = (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;
}

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/**
 * hwmp_route_info_get - Update routing info to originator and transmitter
 *
 * @sdata: local mesh subif
 * @mgmt: mesh management frame
 * @hwmp_ie: hwmp information element (PREP or PREQ)
 * @action: type of hwmp ie
 *
 * This function updates the path routing information to the originator and the
 * transmitter of a HWMP PREQ or PREP frame.
 *
 * Returns: metric to frame originator or 0 if the frame should not be further
 * processed
 *
 * Notes: this function is the only place (besides user-provided info) where
 * path routing information is updated.
 */


static u32 hwmp_route_info_get(struct ieee80211_sub_if_data *sdata,
			       struct ieee80211_mgmt *mgmt,
			       const 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;
	const 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(sdata, orig_addr);
		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 if (!(mpath->flags & MESH_PATH_ACTIVE)) {
				bool have_sn, newer_sn, bounced;

				have_sn = mpath->flags & MESH_PATH_SN_VALID;
				newer_sn = have_sn && SN_GT(orig_sn, mpath->sn);
				bounced = have_sn &&
					  (SN_DELTA(orig_sn, mpath->sn) >
							MAX_SANE_SN_DELTA);

				if (!have_sn || newer_sn) {
					/* if SN is newer than what we had
                                         * then we can take it */;
				} else if (bounced) {
					/* if SN is way different than what
                                         * we had then assume the other side
                                         * rebooted or restarted */;
				} else {
					process = false;
					fresh_info = false;
				}
			}
		} else {
			mpath = mesh_path_add(sdata, orig_addr);
			if (IS_ERR(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);
			ewma_mesh_fail_avg_init(&sta->mesh->fail_avg);
			/* init it at a low value - 0 start is tricky */
			ewma_mesh_fail_avg_add(&sta->mesh->fail_avg, 1);
			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(sdata, ta);
		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 {
			mpath = mesh_path_add(sdata, ta);
			if (IS_ERR(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);
			ewma_mesh_fail_avg_init(&sta->mesh->fail_avg);
			/* init it at a low value - 0 start is tricky */
			ewma_mesh_fail_avg_add(&sta->mesh->fail_avg, 1);
			mesh_path_tx_pending(mpath);
		} else
			spin_unlock_bh(&mpath->state_lock);
	}

	rcu_read_unlock();

	return process ? new_metric : 0;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Luis Carlos Cobo Rus
578
74.39%
1
6.67%
Jesse Jones
90
11.58%
1
6.67%
Rajkumar Manoharan
46
5.92%
1
6.67%
Johannes Berg
22
2.83%
5
33.33%
Rui Paulo
17
2.19%
2
13.33%
Jasper Bryant-Greene
10
1.29%
1
6.67%
Bob Copeland
8
1.03%
1
6.67%
Thomas Pedersen
3
0.39%
1
6.67%
Joe Perches
2
0.26%
1
6.67%
Marco Porsch
1
0.13%
1
6.67%
Total
777
100.00%
15
100.00%



static void hwmp_preq_frame_process(struct ieee80211_sub_if_data *sdata,
				    struct ieee80211_mgmt *mgmt,
				    const u8 *preq_elem, u32 orig_metric)
{
	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
	struct mesh_path *mpath = NULL;
	const u8 *target_addr, *orig_addr;
	const u8 *da;
	u8 target_flags, ttl, flags;
	u32 orig_sn, target_sn, lifetime, target_metric = 0;
	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);
	/* 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;
		target_metric = 0;
		if (time_after(jiffies, ifmsh->last_sn_update +
					net_traversal_jiffies(sdata)) ||
		    time_before(jiffies, ifmsh->last_sn_update)) {
			++ifmsh->sn;
			ifmsh->last_sn_update = jiffies;
		}
		target_sn = ifmsh->sn;
	} else if (is_broadcast_ether_addr(target_addr) &&
		   (target_flags & IEEE80211_PREQ_TO_FLAG)) {
		rcu_read_lock();
		mpath = mesh_path_lookup(sdata, orig_addr);
		if (mpath) {
			if (flags & IEEE80211_PREQ_PROACTIVE_PREP_FLAG) {
				reply = true;
				target_addr = sdata->vif.addr;
				target_sn = ++ifmsh->sn;
				target_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(sdata, target_addr);
		if (mpath) {
			if ((!(mpath->flags & MESH_PATH_SN_VALID)) ||
					SN_LT<