linux/net/mac80211/scan.c

/*
 * Scanning implementation
 *
 * Copyright 2003, Jouni Malinen <jkmaline@cc.hut.fi>
 * Copyright 2004, Instant802 Networks, Inc.
 * Copyright 2005, Devicescape Software, Inc.
 * Copyright 2006-2007	Jiri Benc <jbenc@suse.cz>
 * Copyright 2007, Michael Wu <flamingice@sourmilk.net>
 *
 * 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/if_arp.h>
#include <linux/rtnetlink.h>
#include <linux/pm_qos_params.h>
#include <net/sch_generic.h>
#include <linux/slab.h>
#include <net/mac80211.h>

#include "ieee80211_i.h"
#include "driver-ops.h"
#include "mesh.h"

#define IEEE80211_PROBE_DELAY (HZ / 33)
#define IEEE80211_CHANNEL_TIME (HZ / 33)
#define IEEE80211_PASSIVE_CHANNEL_TIME (HZ / 8)

struct ieee80211_bss *
ieee80211_rx_bss_get(struct ieee80211_local *local, u8 *bssid, int freq,
		     u8 *ssid, u8 ssid_len)
{
	struct cfg80211_bss *cbss;

	cbss = cfg80211_get_bss(local->hw.wiphy,
				ieee80211_get_channel(local->hw.wiphy, freq),
				bssid, ssid, ssid_len, 0, 0);
	if (!cbss)
		return NULL;
	return (void *)cbss->priv;
}

static void ieee80211_rx_bss_free(struct cfg80211_bss *cbss)
{
	struct ieee80211_bss *bss = (void *)cbss->priv;

	kfree(bss_mesh_id(bss));
	kfree(bss_mesh_cfg(bss));
}

void ieee80211_rx_bss_put(struct ieee80211_local *local,
			  struct ieee80211_bss *bss)
{
	if (!bss)
		return;
	cfg80211_put_bss(container_of((void *)bss, struct cfg80211_bss, priv));
}

static bool is_uapsd_supported(struct ieee802_11_elems *elems)
{
	u8 qos_info;

	if (elems->wmm_info && elems->wmm_info_len == 7
	    && elems->wmm_info[5] == 1)
		qos_info = elems->wmm_info[6];
	else if (elems->wmm_param && elems->wmm_param_len == 24
		 && elems->wmm_param[5] == 1)
		qos_info = elems->wmm_param[6];
	else
		/* no valid wmm information or parameter element found */
		return false;

	return qos_info & IEEE80211_WMM_IE_AP_QOSINFO_UAPSD;
}

struct ieee80211_bss *
ieee80211_bss_info_update(struct ieee80211_local *local,
			  struct ieee80211_rx_status *rx_status,
			  struct ieee80211_mgmt *mgmt,
			  size_t len,
			  struct ieee802_11_elems *elems,
			  struct ieee80211_channel *channel,
			  bool beacon)
{
	struct cfg80211_bss *cbss;
	struct ieee80211_bss *bss;
	int clen, srlen;
	s32 signal = 0;

	if (local->hw.flags & IEEE80211_HW_SIGNAL_DBM)
		signal = rx_status->signal * 100;
	else if (local->hw.flags & IEEE80211_HW_SIGNAL_UNSPEC)
		signal = (rx_status->signal * 100) / local->hw.max_signal;

	cbss = cfg80211_inform_bss_frame(local->hw.wiphy, channel,
					 mgmt, len, signal, GFP_ATOMIC);

	if (!cbss)
		return NULL;

	cbss->free_priv = ieee80211_rx_bss_free;
	bss = (void *)cbss->priv;

	/* save the ERP value so that it is available at association time */
	if (elems->erp_info && elems->erp_info_len >= 1) {
		bss->erp_value = elems->erp_info[0];
		bss->has_erp_value = 1;
	}

	if (elems->tim) {
		struct ieee80211_tim_ie *tim_ie =
			(struct ieee80211_tim_ie *)elems->tim;
		bss->dtim_period = tim_ie->dtim_period;
	}

	/* If the beacon had no TIM IE, or it was invalid, use 1 */
	if (beacon && !bss->dtim_period)
		bss->dtim_period = 1;

	/* replace old supported rates if we get new values */
	srlen = 0;
	if (elems->supp_rates) {
		clen = IEEE80211_MAX_SUPP_RATES;
		if (clen > elems->supp_rates_len)
			clen = elems->supp_rates_len;
		memcpy(bss->supp_rates, elems->supp_rates, clen);
		srlen += clen;
	}
	if (elems->ext_supp_rates) {
		clen = IEEE80211_MAX_SUPP_RATES - srlen;
		if (clen > elems->ext_supp_rates_len)
			clen = elems->ext_supp_rates_len;
		memcpy(bss->supp_rates + srlen, elems->ext_supp_rates, clen);
		srlen += clen;
	}
	if (srlen)
		bss->supp_rates_len = srlen;

	bss->wmm_used = elems->wmm_param || elems->wmm_info;
	bss->uapsd_supported = is_uapsd_supported(elems);

	if (!beacon)
		bss->last_probe_resp = jiffies;

	return bss;
}

ieee80211_rx_result
ieee80211_scan_rx(struct ieee80211_sub_if_data *sdata, struct sk_buff *skb)
{
	struct ieee80211_rx_status *rx_status = IEEE80211_SKB_RXCB(skb);
	struct ieee80211_mgmt *mgmt;
	struct ieee80211_bss *bss;
	u8 *elements;
	struct ieee80211_channel *channel;
	size_t baselen;
	int freq;
	__le16 fc;
	bool presp, beacon = false;
	struct ieee802_11_elems elems;

	if (skb->len < 2)
		return RX_DROP_UNUSABLE;

	mgmt = (struct ieee80211_mgmt *) skb->data;
	fc = mgmt->frame_control;

	if (ieee80211_is_ctl(fc))
		return RX_CONTINUE;

	if (skb->len < 24)
		return RX_DROP_MONITOR;

	presp = ieee80211_is_probe_resp(fc);
	if (presp) {
		/* ignore ProbeResp to foreign address */
		if (memcmp(mgmt->da, sdata->vif.addr, ETH_ALEN))
			return RX_DROP_MONITOR;

		presp = true;
		elements = mgmt->u.probe_resp.variable;
		baselen = offsetof(struct ieee80211_mgmt, u.probe_resp.variable);
	} else {
		beacon = ieee80211_is_beacon(fc);
		baselen = offsetof(struct ieee80211_mgmt, u.beacon.variable);
		elements = mgmt->u.beacon.variable;
	}

	if (!presp && !beacon)
		return RX_CONTINUE;

	if (baselen > skb->len)
		return RX_DROP_MONITOR;

	ieee802_11_parse_elems(elements, skb->len - baselen, &elems);

	if (elems.ds_params && elems.ds_params_len == 1)
		freq = ieee80211_channel_to_frequency(elems.ds_params[0],
						      rx_status->band);
	else
		freq = rx_status->freq;

	channel = ieee80211_get_channel(sdata->local->hw.wiphy, freq);

	if (!channel || channel->flags & IEEE80211_CHAN_DISABLED)
		return RX_DROP_MONITOR;

	bss = ieee80211_bss_info_update(sdata->local, rx_status,
					mgmt, skb->len, &elems,
					channel, beacon);
	if (bss)
		ieee80211_rx_bss_put(sdata->local, bss);

	/* If we are on-operating-channel, and this packet is for the
	 * current channel, pass the pkt on up the stack so that
	 * the rest of the stack can make use of it.
	 */
	if (ieee80211_cfg_on_oper_channel(sdata->local)
	    && (channel == sdata->local->oper_channel))
		return RX_CONTINUE;

	dev_kfree_skb(skb);
	return RX_QUEUED;
}

/* return false if no more work */
static bool ieee80211_prep_hw_scan(struct ieee80211_local *local)
{
	struct cfg80211_scan_request *req = local->scan_req;
	enum ieee80211_band band;
	int i, ielen, n_chans;

	do {
		if (local->hw_scan_band == IEEE80211_NUM_BANDS)
			return false;

		band = local->hw_scan_band;
		n_chans = 0;
		for (i = 0; i < req->n_channels; i++) {
			if (req->channels[i]->band == band) {
				local->hw_scan_req->channels[n_chans] =
							req->channels[i];
				n_chans++;
			}
		}

		local->hw_scan_band++;
	} while (!n_chans);

	local->hw_scan_req->n_channels = n_chans;

	ielen = ieee80211_build_preq_ies(local, (u8 *)local->hw_scan_req->ie,
					 req->ie, req->ie_len, band, (u32) -1,
					 0);
	local->hw_scan_req->ie_len = ielen;

	return true;
}

static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted,
				       bool was_hw_scan)
{
	struct ieee80211_local *local = hw_to_local(hw);
	bool on_oper_chan;
	bool enable_beacons = false;

	lockdep_assert_held(&local->mtx);

	/*
	 * It's ok to abort a not-yet-running scan (that
	 * we have one at all will be verified by checking
	 * local->scan_req next), but not to complete it
	 * successfully.
	 */
	if (WARN_ON(!local->scanning && !aborted))
		aborted = true;

	if (WARN_ON(!local->scan_req))
		return;

	if (was_hw_scan && !aborted && ieee80211_prep_hw_scan(local)) {
		int rc = drv_hw_scan(local, local->scan_sdata, local->hw_scan_req);
		if (rc == 0)
			return;
	}

	kfree(local->hw_scan_req);
	local->hw_scan_req = NULL;

	if (local->scan_req != local->int_scan_req)
		cfg80211_scan_done(local->scan_req, aborted);
	local->scan_req = NULL;
	local->scan_sdata = NULL;

	local->scanning = 0;
	local->scan_channel = NULL;

	on_oper_chan = ieee80211_cfg_on_oper_channel(local);

	if (was_hw_scan || !on_oper_chan)
		ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
	else
		/* Set power back to normal operating levels. */
		ieee80211_hw_config(local, 0);

	if (!was_hw_scan) {
		bool on_oper_chan2;
		ieee80211_configure_filter(local);
		drv_sw_scan_complete(local);
		on_oper_chan2 = ieee80211_cfg_on_oper_channel(local);
		/* We should always be on-channel at this point. */
		WARN_ON(!on_oper_chan2);
		if (on_oper_chan2 && (on_oper_chan != on_oper_chan2))
			enable_beacons = true;

		ieee80211_offchannel_return(local, enable_beacons, true);
	}

	ieee80211_recalc_idle(local);

	ieee80211_mlme_notify_scan_completed(local);
	ieee80211_ibss_notify_scan_completed(local);
	ieee80211_mesh_notify_scan_completed(local);
	ieee80211_queue_work(&local->hw, &local->work_work);
}

void ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
{
	struct ieee80211_local *local = hw_to_local(hw);

	trace_api_scan_completed(local, aborted);

	set_bit(SCAN_COMPLETED, &local->scanning);
	if (aborted)
		set_bit(SCAN_ABORTED, &local->scanning);
	ieee80211_queue_delayed_work(&local->hw, &local->scan_work, 0);
}
EXPORT_SYMBOL(ieee80211_scan_completed);

static int ieee80211_start_sw_scan(struct ieee80211_local *local)
{
	/*
	 * Hardware/driver doesn't support hw_scan, so use software
	 * scanning instead. First send a nullfunc frame with power save
	 * bit on so that AP will buffer the frames for us while we are not
	 * listening, then send probe requests to each channel and wait for
	 * the responses. After all channels are scanned, tune back to the
	 * original channel and send a nullfunc frame with power save bit
	 * off to trigger the AP to send us all the buffered frames.
	 *
	 * Note that while local->sw_scanning is true everything else but
	 * nullfunc frames and probe requests will be dropped in
	 * ieee80211_tx_h_check_assoc().
	 */
	drv_sw_scan_start(local);

	local->leave_oper_channel_time = 0;
	local->next_scan_state = SCAN_DECISION;
	local->scan_channel_idx = 0;

	/* We always want to use off-channel PS, even if we
	 * are not really leaving oper-channel.  Don't
	 * tell the AP though, as long as we are on-channel.
	 */
	ieee80211_offchannel_enable_all_ps(local, false);

	ieee80211_configure_filter(local);

	/* We need to set power level at maximum rate for scanning. */
	ieee80211_hw_config(local, 0);

	ieee80211_queue_delayed_work(&local->hw,
				     &local->scan_work,
				     IEEE80211_CHANNEL_TIME);

	return 0;
}


static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
				  struct cfg80211_scan_request *req)
{
	struct ieee80211_local *local = sdata->local;
	int rc;

	lockdep_assert_held(&local->mtx);

	if (local->scan_req)
		return -EBUSY;

	if (!list_empty(&local->work_list)) {
		/* wait for the work to finish/time out */
		local->scan_req = req;
		local->scan_sdata = sdata;
		return 0;
	}

	if (local->ops->hw_scan) {
		u8 *ies;

		local->hw_scan_req = kmalloc(
				sizeof(*local->hw_scan_req) +
				req->n_channels * sizeof(req->channels[0]) +
				2 + IEEE80211_MAX_SSID_LEN + local->scan_ies_len +
				req->ie_len, GFP_KERNEL);
		if (!local->hw_scan_req)
			return -ENOMEM;

		local->hw_scan_req->ssids = req->ssids;
		local->hw_scan_req->n_ssids = req->n_ssids;
		ies = (u8 *)local->hw_scan_req +
			sizeof(*local->hw_scan_req) +
			req->n_channels * sizeof(req->channels[0]);
		local->hw_scan_req->ie = ies;

		local->hw_scan_band = 0;

		/*
		 * After allocating local->hw_scan_req, we must
		 * go through until ieee80211_prep_hw_scan(), so
		 * anything that might be changed here and leave
		 * this function early must not go after this
		 * allocation.
		 */
	}

	local->scan_req = req;
	local->scan_sdata = sdata;

	if (local->ops->hw_scan)
		__set_bit(SCAN_HW_SCANNING, &local->scanning);
	else
		__set_bit(SCAN_SW_SCANNING, &local->scanning);

	ieee80211_recalc_idle(local);

	if (local->ops->hw_scan) {
		WARN_ON(!ieee80211_prep_hw_scan(local));
		rc = drv_hw_scan(local, sdata, local->hw_scan_req);
	} else
		rc = ieee80211_start_sw_scan(local);

	if (rc) {
		kfree(local->hw_scan_req);
		local->hw_scan_req = NULL;
		local->scanning = 0;

		ieee80211_recalc_idle(local);

		local->scan_req = NULL;
		local->scan_sdata = NULL;
	}

	return rc;
}

static unsigned long
ieee80211_scan_get_channel_time(struct ieee80211_channel *chan)
{
	/*
	 * TODO: channel switching also consumes quite some time,
	 * add that delay as well to get a better estimation
	 */
	if (chan->flags & IEEE80211_CHAN_PASSIVE_SCAN)
		return IEEE80211_PASSIVE_CHANNEL_TIME;
	return IEEE80211_PROBE_DELAY + IEEE80211_CHANNEL_TIME;
}

static void ieee80211_scan_state_decision(struct ieee80211_local *local,
					  unsigned long *next_delay)
{
	bool associated = false;
	bool tx_empty = true;
	bool bad_latency;
	bool listen_int_exceeded;
	unsigned long min_beacon_int = 0;
	struct ieee80211_sub_if_data *sdata;
	struct ieee80211_channel *next_chan;

	/*
	 * check if at least one STA interface is associated,
	 * check if at least one STA interface has pending tx frames
	 * and grab the lowest used beacon interval
	 */
	mutex_lock(&local->iflist_mtx);
	list_for_each_entry(sdata, &local->interfaces, list) {
		if (!ieee80211_sdata_running(sdata))
			continue;

		if (sdata->vif.type == NL80211_IFTYPE_STATION) {
			if (sdata->u.mgd.associated) {
				associated = true;

				if (sdata->vif.bss_conf.beacon_int <
				    min_beacon_int || min_beacon_int == 0)
					min_beacon_int =
						sdata->vif.bss_conf.beacon_int;

				if (!qdisc_all_tx_empty(sdata->dev)) {
					tx_empty = false;
					break;
				}
			}
		}
	}
	mutex_unlock(&local->iflist_mtx);

	next_chan = local->scan_req->channels[local->scan_channel_idx];

	if (ieee80211_cfg_on_oper_channel(local)) {
		/* We're currently on operating channel. */
		if (next_chan == local->oper_channel)
			/* We don't need to move off of operating channel. */
			local->next_scan_state = SCAN_SET_CHANNEL;
		else
			/*
			 * We do need to leave operating channel, as next
			 * scan is somewhere else.
			 */
			local->next_scan_state = SCAN_LEAVE_OPER_CHANNEL;
	} else {
		/*
		 * we're currently scanning a different channel, let's
		 * see if we can scan another channel without interfering
		 * with the current traffic situation.
		 *
		 * Since we don't know if the AP has pending frames for us
		 * we can only check for our tx queues and use the current
		 * pm_qos requirements for rx. Hence, if no tx traffic occurs
		 * at all we will scan as many channels in a row as the pm_qos
		 * latency allows us to. Additionally we also check for the
		 * currently negotiated listen interval to prevent losing
		 * frames unnecessarily.
		 *
		 * Otherwise switch back to the operating channel.
		 */

		bad_latency = time_after(jiffies +
				ieee80211_scan_get_channel_time(next_chan),
				local->leave_oper_channel_time +
				usecs_to_jiffies(pm_qos_request(PM_QOS_NETWORK_LATENCY)));

		listen_int_exceeded = time_after(jiffies +
				ieee80211_scan_get_channel_time(next_chan),
				local->leave_oper_channel_time +
				usecs_to_jiffies(min_beacon_int * 1024) *
				local->hw.conf.listen_interval);

		if (associated && ( !tx_empty || bad_latency ||
		    listen_int_exceeded))
			local->next_scan_state = SCAN_ENTER_OPER_CHANNEL;
		else
			local->next_scan_state = SCAN_SET_CHANNEL;
	}

	*next_delay = 0;
}

static void ieee80211_scan_state_leave_oper_channel(struct ieee80211_local *local,
						    unsigned long *next_delay)
{
	/* PS will already be in off-channel mode,
	 * we do that once at the beginning of scanning.
	 */
	ieee80211_offchannel_stop_vifs(local, false);

	/*
	 * What if the nullfunc frames didn't arrive?
	 */
	drv_flush(local, false);
	if (local->ops->flush)
		*next_delay = 0;
	else
		*next_delay = HZ / 10;

	/* remember when we left the operating channel */
	local->leave_oper_channel_time = jiffies;

	/* advance to the next channel to be scanned */
	local->next_scan_state = SCAN_SET_CHANNEL;
}

static void ieee80211_scan_state_enter_oper_channel(struct ieee80211_local *local,
						    unsigned long *next_delay)
{
	/* switch back to the operating channel */
	local->scan_channel = NULL;
	if (!ieee80211_cfg_on_oper_channel(local))
		ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);

	/*
	 * Re-enable vifs and beaconing.  Leave PS
	 * in off-channel state..will put that back
	 * on-channel at the end of scanning.
	 */
	ieee80211_offchannel_return(local, true, false);

	*next_delay = HZ / 5;
	local->next_scan_state = SCAN_DECISION;
}

static void ieee80211_scan_state_set_channel(struct ieee80211_local *local,
					     unsigned long *next_delay)
{
	int skip;
	struct ieee80211_channel *chan;

	skip = 0;
	chan = local->scan_req->channels[local->scan_channel_idx];

	local->scan_channel = chan;

	/* Only call hw-config if we really need to change channels. */
	if (chan != local->hw.conf.channel)
		if (ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL))
			skip = 1;

	/* advance state machine to next channel/band */
	local->scan_channel_idx++;

	if (skip) {
		/* if we skip this channel return to the decision state */
		local->next_scan_state = SCAN_DECISION;
		return;
	}

	/*
	 * Probe delay is used to update the NAV, cf. 11.1.3.2.2
	 * (which unfortunately doesn't say _why_ step a) is done,
	 * but it waits for the probe delay or until a frame is
	 * received - and the received frame would update the NAV).
	 * For now, we do not support waiting until a frame is
	 * received.
	 *
	 * In any case, it is not necessary for a passive scan.
	 */
	if (chan->flags & IEEE80211_CHAN_PASSIVE_SCAN ||
	    !local->scan_req->n_ssids) {
		*next_delay = IEEE80211_PASSIVE_CHANNEL_TIME;
		local->next_scan_state = SCAN_DECISION;
		return;
	}

	/* active scan, send probes */
	*next_delay = IEEE80211_PROBE_DELAY;
	local->next_scan_state = SCAN_SEND_PROBE;
}

static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
					    unsigned long *next_delay)
{
	int i;
	struct ieee80211_sub_if_data *sdata = local->scan_sdata;

	for (i = 0; i < local->scan_req->n_ssids; i++)
		ieee80211_send_probe_req(
			sdata, NULL,
			local->scan_req->ssids[i].ssid,
			local->scan_req->ssids[i].ssid_len,
			local->scan_req->ie, local->scan_req->ie_len);

	/*
	 * After sending probe requests, wait for probe responses
	 * on the channel.
	 */
	*next_delay = IEEE80211_CHANNEL_TIME;
	local->next_scan_state = SCAN_DECISION;
}

void ieee80211_scan_work(struct work_struct *work)
{
	struct ieee80211_local *local =
		container_of(work, struct ieee80211_local, scan_work.work);
	struct ieee80211_sub_if_data *sdata;
	unsigned long next_delay = 0;
	bool aborted, hw_scan;

	mutex_lock(&local->mtx);

	sdata = local->scan_sdata;

	if (test_and_clear_bit(SCAN_COMPLETED, &local->scanning)) {
		aborted = test_and_clear_bit(SCAN_ABORTED, &local->scanning);
		goto out_complete;
	}

	if (!sdata || !local->scan_req)
		goto out;

	if (local->scan_req && !local->scanning) {
		struct cfg80211_scan_request *req = local->scan_req;
		int rc;

		local->scan_req = NULL;
		local->scan_sdata = NULL;

		rc = __ieee80211_start_scan(sdata, req);
		if (rc) {
			/* need to complete scan in cfg80211 */
			local->scan_req = req;
			aborted = true;
			goto out_complete;
		} else
			goto out;
	}

	/*
	 * Avoid re-scheduling when the sdata is going away.
	 */
	if (!ieee80211_sdata_running(sdata)) {
		aborted = true;
		goto out_complete;
	}

	/*
	 * as long as no delay is required advance immediately
	 * without scheduling a new work
	 */
	do {
		switch (local->next_scan_state) {
		case SCAN_DECISION:
			/* if no more bands/channels left, complete scan */
			if (local->scan_channel_idx >= local->scan_req->n_channels) {
				aborted = false;
				goto out_complete;
			}
			ieee80211_scan_state_decision(local, &next_delay);
			break;
		case SCAN_SET_CHANNEL:
			ieee80211_scan_state_set_channel(local, &next_delay);
			break;
		case SCAN_SEND_PROBE:
			ieee80211_scan_state_send_probe(local, &next_delay);
			break;
		case SCAN_LEAVE_OPER_CHANNEL:
			ieee80211_scan_state_leave_oper_channel(local, &next_delay);
			break;
		case SCAN_ENTER_OPER_CHANNEL:
			ieee80211_scan_state_enter_oper_channel(local, &next_delay);
			break;
		}
	} while (next_delay == 0);

	ieee80211_queue_delayed_work(&local->hw, &local->scan_work, next_delay);
	goto out;

out_complete:
	hw_scan = test_bit(SCAN_HW_SCANNING, &local->scanning);
	__ieee80211_scan_completed(&local->hw, aborted, hw_scan);
out:
	mutex_unlock(&local->mtx);
}

int ieee80211_request_scan(struct ieee80211_sub_if_data *sdata,
			   struct cfg80211_scan_request *req)
{
	int res;

	mutex_lock(&sdata->local->mtx);
	res = __ieee80211_start_scan(sdata, req);
	mutex_unlock(&sdata->local->mtx);

	return res;
}

int ieee80211_request_internal_scan(struct ieee80211_sub_if_data *sdata,
				    const u8 *ssid, u8 ssid_len,
				    struct ieee80211_channel *chan)
{
	struct ieee80211_local *local = sdata->local;
	int ret = -EBUSY;
	enum ieee80211_band band;

	mutex_lock(&local->mtx);

	/* busy scanning */
	if (local->scan_req)
		goto unlock;

	/* fill internal scan request */
	if (!chan) {
		int i, nchan = 0;

		for (band = 0; band < IEEE80211_NUM_BANDS; band++) {
			if (!local->hw.wiphy->bands[band])
				continue;
			for (i = 0;
			     i < local->hw.wiphy->bands[band]->n_channels;
			     i++) {
				local->int_scan_req->channels[nchan] =
				    &local->hw.wiphy->bands[band]->channels[i];
				nchan++;
			}
		}

		local->int_scan_req->n_channels = nchan;
	} else {
		local->int_scan_req->channels[0] = chan;
		local->int_scan_req->n_channels = 1;
	}

	local->int_scan_req->ssids = &local->scan_ssid;
	local->int_scan_req->n_ssids = 1;
	memcpy(local->int_scan_req->ssids[0].ssid, ssid, IEEE80211_MAX_SSID_LEN);
	local->int_scan_req->ssids[0].ssid_len = ssid_len;

	ret = __ieee80211_start_scan(sdata, sdata->local->int_scan_req);
 unlock:
	mutex_unlock(&local->mtx);
	return ret;
}

/*
 * Only call this function when a scan can't be queued -- under RTNL.
 */
void ieee80211_scan_cancel(struct ieee80211_local *local)
{
	bool abortscan;

	/*
	 * We are only canceling software scan, or deferred scan that was not
	 * yet really started (see __ieee80211_start_scan ).
	 *
	 * Regarding hardware scan:
	 * - we can not call  __ieee80211_scan_completed() as when
	 *   SCAN_HW_SCANNING bit is set this function change
	 *   local->hw_scan_req to operate on 5G band, what race with
	 *   driver which can use local->hw_scan_req
	 *
	 * - we can not cancel scan_work since driver can schedule it
	 *   by ieee80211_scan_completed(..., true) to finish scan
	 *
	 * Hence low lever driver is responsible for canceling HW scan.
	 */

	mutex_lock(&local->mtx);
	abortscan = local->scan_req && !test_bit(SCAN_HW_SCANNING, &local->scanning);
	if (abortscan) {
		/*
		 * The scan is canceled, but stop work from being pending.
		 *
		 * If the work is currently running, it must be blocked on
		 * the mutex, but we'll set scan_sdata = NULL and it'll
		 * simply exit once it acquires the mutex.
		 */
		cancel_delayed_work(&local->scan_work);
		/* and clean up */
		__ieee80211_scan_completed(&local->hw, true, false);
	}
	mutex_unlock(&local->mtx);
}