scan.c

Go to the documentation of this file.

/*
 * Scanning implementation
 *
 * Copyright 2003, Jouni Malinen <[email protected]>
 * Copyright 2004, Instant802 Networks, Inc.
 * Copyright 2005, Devicescape Software, Inc.
 * Copyright 2006-2007  Jiri Benc <[email protected]>
 * Copyright 2007, Michael Wu <[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/if_arp.h>
#include <linux/etherdevice.h>
#include <linux/rtnetlink.h>
#include <linux/pm_qos.h>
#include <net/sch_generic.h>
#include <linux/slab.h>
#include <linux/export.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)

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;

    bss->device_ts = rx_status->device_timestamp;

    if (elems->parse_error) {
        if (beacon)
            bss->corrupt_data |= IEEE80211_BSS_CORRUPT_BEACON;
        else
            bss->corrupt_data |= IEEE80211_BSS_CORRUPT_PROBE_RESP;
    } else {
        if (beacon)
            bss->corrupt_data &= ~IEEE80211_BSS_CORRUPT_BEACON;
        else
            bss->corrupt_data &= ~IEEE80211_BSS_CORRUPT_PROBE_RESP;
    }

    /* save the ERP value so that it is available at association time */
    if (elems->erp_info && elems->erp_info_len >= 1 &&
            (!elems->parse_error ||
             !(bss->valid_data & IEEE80211_BSS_VALID_ERP))) {
        bss->erp_value = elems->erp_info[0];
        bss->has_erp_value = true;
        if (!elems->parse_error)
            bss->valid_data |= IEEE80211_BSS_VALID_ERP;
    }

    if (elems->tim && (!elems->parse_error ||
               !(bss->valid_data & IEEE80211_BSS_VALID_DTIM))) {
        struct ieee80211_tim_ie *tim_ie = elems->tim;
        bss->dtim_period = tim_ie->dtim_period;
        if (!elems->parse_error)
                bss->valid_data |= IEEE80211_BSS_VALID_DTIM;
    }

    /* 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 */
    if (!elems->parse_error ||
        !(bss->valid_data & IEEE80211_BSS_VALID_RATES)) {
        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;
            if (!elems->parse_error)
                bss->valid_data |= IEEE80211_BSS_VALID_RATES;
        }
    }

    if (!elems->parse_error ||
        !(bss->valid_data & IEEE80211_BSS_VALID_WMM)) {
        bss->wmm_used = elems->wmm_param || elems->wmm_info;
        bss->uapsd_supported = is_uapsd_supported(elems);
        if (!elems->parse_error)
            bss->valid_data |= IEEE80211_BSS_VALID_WMM;
    }

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

    return bss;
}

void ieee80211_scan_rx(struct ieee80211_local *local, struct sk_buff *skb)
{
    struct ieee80211_rx_status *rx_status = IEEE80211_SKB_RXCB(skb);
    struct ieee80211_sub_if_data *sdata1, *sdata2;
    struct ieee80211_mgmt *mgmt = (void *)skb->data;
    struct ieee80211_bss *bss;
    u8 *elements;
    struct ieee80211_channel *channel;
    size_t baselen;
    int freq;
    bool beacon;
    struct ieee802_11_elems elems;

    if (skb->len < 24 ||
        (!ieee80211_is_probe_resp(mgmt->frame_control) &&
         !ieee80211_is_beacon(mgmt->frame_control)))
        return;

    sdata1 = rcu_dereference(local->scan_sdata);
    sdata2 = rcu_dereference(local->sched_scan_sdata);

    if (likely(!sdata1 && !sdata2))
        return;

    if (ieee80211_is_probe_resp(mgmt->frame_control)) {
        /* ignore ProbeResp to foreign address */
        if ((!sdata1 || !ether_addr_equal(mgmt->da, sdata1->vif.addr)) &&
            (!sdata2 || !ether_addr_equal(mgmt->da, sdata2->vif.addr)))
            return;

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

    if (baselen > skb->len)
        return;

    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(local->hw.wiphy, freq);

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

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

/* 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,
                     req->rates[band], 0);
    local->hw_scan_req->ie_len = ielen;
    local->hw_scan_req->no_cck = req->no_cck;

    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);

    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;

        rc = drv_hw_scan(local,
            rcu_dereference_protected(local->scan_sdata,
                          lockdep_is_held(&local->mtx)),
            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;
    rcu_assign_pointer(local->scan_sdata, NULL);

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

    /* Set power back to normal operating levels. */
    ieee80211_hw_config(local, 0);

    if (!was_hw_scan) {
        ieee80211_configure_filter(local);
        drv_sw_scan_complete(local);
        ieee80211_offchannel_return(local, true);
    }

    ieee80211_recalc_idle(local);

    ieee80211_mlme_notify_scan_completed(local);
    ieee80211_ibss_notify_scan_completed(local);
    ieee80211_mesh_notify_scan_completed(local);
    ieee80211_start_next_roc(local);
}

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

    ieee80211_offchannel_stop_vifs(local, true);

    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, 0);

    return 0;
}

static bool ieee80211_can_scan(struct ieee80211_local *local,
                   struct ieee80211_sub_if_data *sdata)
{
    if (!list_empty(&local->roc_list))
        return false;

    if (sdata->vif.type == NL80211_IFTYPE_STATION &&
        sdata->u.mgd.flags & (IEEE80211_STA_BEACON_POLL |
                  IEEE80211_STA_CONNECTION_POLL))
        return false;

    return true;
}

void ieee80211_run_deferred_scan(struct ieee80211_local *local)
{
    lockdep_assert_held(&local->mtx);

    if (!local->scan_req || local->scanning)
        return;

    if (!ieee80211_can_scan(local,
                rcu_dereference_protected(
                    local->scan_sdata,
                    lockdep_is_held(&local->mtx))))
        return;

    ieee80211_queue_delayed_work(&local->hw, &local->scan_work,
                     round_jiffies_relative(0));
}

static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
                        unsigned long *next_delay)
{
    int i;
    struct ieee80211_sub_if_data *sdata;
    enum ieee80211_band band = local->hw.conf.channel->band;

    sdata = rcu_dereference_protected(local->scan_sdata,
                      lockdep_is_held(&local->mtx));

    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,
            local->scan_req->rates[band], false,
            local->scan_req->no_cck,
            local->hw.conf.channel);

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

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 (!ieee80211_can_scan(local, sdata)) {
        /* wait for the work to finish/time out */
        local->scan_req = req;
        rcu_assign_pointer(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;
    rcu_assign_pointer(local->scan_sdata, sdata);

    if (local->ops->hw_scan) {
        __set_bit(SCAN_HW_SCANNING, &local->scanning);
    } else if ((req->n_channels == 1) &&
           (req->channels[0] == local->oper_channel)) {
        /*
         * If we are scanning only on the operating channel
         * then we do not need to stop normal activities
         */
        unsigned long next_delay;

        __set_bit(SCAN_ONCHANNEL_SCANNING, &local->scanning);

        ieee80211_recalc_idle(local);

        /* Notify driver scan is starting, keep order of operations
         * same as normal software scan, in case that matters. */
        drv_sw_scan_start(local);

        ieee80211_configure_filter(local); /* accept probe-responses */

        /* We need to ensure power level is at max for scanning. */
        ieee80211_hw_config(local, 0);

        if ((req->channels[0]->flags &
             IEEE80211_CHAN_PASSIVE_SCAN) ||
            !local->scan_req->n_ssids) {
            next_delay = IEEE80211_PASSIVE_CHANNEL_TIME;
        } else {
            ieee80211_scan_state_send_probe(local, &next_delay);
            next_delay = IEEE80211_CHANNEL_TIME;
        }

        /* Now, just wait a bit and we are all done! */
        ieee80211_queue_delayed_work(&local->hw, &local->scan_work,
                         next_delay);
        return 0;
    } else {
        /* Do normal software scan */
        __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;
        rcu_assign_pointer(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];

    /*
     * 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_SUSPEND;
    else
        local->next_scan_state = SCAN_SET_CHANNEL;

    *next_delay = 0;
}

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;

    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_suspend(struct ieee80211_local *local,
                     unsigned long *next_delay)
{
    /* switch back to the operating channel */
    local->scan_channel = NULL;
    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, false);

    *next_delay = HZ / 5;
    /* afterwards, resume scan & go to next channel */
    local->next_scan_state = SCAN_RESUME;
}

static void ieee80211_scan_state_resume(struct ieee80211_local *local,
                    unsigned long *next_delay)
{
    /* PS already is in off-channel mode */
    ieee80211_offchannel_stop_vifs(local, false);

    if (local->ops->flush) {
        drv_flush(local, false);
        *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;
}

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 = rcu_dereference_protected(local->scan_sdata,
                      lockdep_is_held(&local->mtx));

    /* When scanning on-channel, the first-callback means completed. */
    if (test_bit(SCAN_ONCHANNEL_SCANNING, &local->scanning)) {
        aborted = test_and_clear_bit(SCAN_ABORTED, &local->scanning);
        goto out_complete;
    }

    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;
        rcu_assign_pointer(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 {
        if (!ieee80211_sdata_running(sdata)) {
            aborted = true;
            goto out_complete;
        }

        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_SUSPEND:
            ieee80211_scan_state_suspend(local, &next_delay);
            break;
        case SCAN_RESUME:
            ieee80211_scan_state_resume(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)
{
    /*
     * We are 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 we only call the cancel_hw_scan() callback, but the low-level
     * driver is still responsible for calling ieee80211_scan_completed()
     * after the scan was completed/aborted.
     */

    mutex_lock(&local->mtx);
    if (!local->scan_req)
        goto out;

    if (test_bit(SCAN_HW_SCANNING, &local->scanning)) {
        if (local->ops->cancel_hw_scan)
            drv_cancel_hw_scan(local,
                rcu_dereference_protected(local->scan_sdata,
                        lockdep_is_held(&local->mtx)));
        goto out;
    }

    /*
     * 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);
out:
    mutex_unlock(&local->mtx);
}

int ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
                       struct cfg80211_sched_scan_request *req)
{
    struct ieee80211_local *local = sdata->local;
    struct ieee80211_sched_scan_ies sched_scan_ies = {};
    int ret, i;

    mutex_lock(&local->mtx);

    if (rcu_access_pointer(local->sched_scan_sdata)) {
        ret = -EBUSY;
        goto out;
    }

    if (!local->ops->sched_scan_start) {
        ret = -ENOTSUPP;
        goto out;
    }

    for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
        if (!local->hw.wiphy->bands[i])
            continue;

        sched_scan_ies.ie[i] = kzalloc(2 + IEEE80211_MAX_SSID_LEN +
                           local->scan_ies_len +
                           req->ie_len,
                           GFP_KERNEL);
        if (!sched_scan_ies.ie[i]) {
            ret = -ENOMEM;
            goto out_free;
        }

        sched_scan_ies.len[i] =
            ieee80211_build_preq_ies(local, sched_scan_ies.ie[i],
                         req->ie, req->ie_len, i,
                         (u32) -1, 0);
    }

    ret = drv_sched_scan_start(local, sdata, req, &sched_scan_ies);
    if (ret == 0)
        rcu_assign_pointer(local->sched_scan_sdata, sdata);

out_free:
    while (i > 0)
        kfree(sched_scan_ies.ie[--i]);
out:
    mutex_unlock(&local->mtx);
    return ret;
}

int ieee80211_request_sched_scan_stop(struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_local *local = sdata->local;
    int ret = 0;

    mutex_lock(&local->mtx);

    if (!local->ops->sched_scan_stop) {
        ret = -ENOTSUPP;
        goto out;
    }

    if (rcu_access_pointer(local->sched_scan_sdata))
        drv_sched_scan_stop(local, sdata);

out:
    mutex_unlock(&local->mtx);

    return ret;
}

void ieee80211_sched_scan_results(struct ieee80211_hw *hw)
{
    struct ieee80211_local *local = hw_to_local(hw);

    trace_api_sched_scan_results(local);

    cfg80211_sched_scan_results(hw->wiphy);
}
EXPORT_SYMBOL(ieee80211_sched_scan_results);

void ieee80211_sched_scan_stopped_work(struct work_struct *work)
{
    struct ieee80211_local *local =
        container_of(work, struct ieee80211_local,
                 sched_scan_stopped_work);

    mutex_lock(&local->mtx);

    if (!rcu_access_pointer(local->sched_scan_sdata)) {
        mutex_unlock(&local->mtx);
        return;
    }

    rcu_assign_pointer(local->sched_scan_sdata, NULL);

    mutex_unlock(&local->mtx);

    cfg80211_sched_scan_stopped(local->hw.wiphy);
}

void ieee80211_sched_scan_stopped(struct ieee80211_hw *hw)
{
    struct ieee80211_local *local = hw_to_local(hw);

    trace_api_sched_scan_stopped(local);

    ieee80211_queue_work(&local->hw, &local->sched_scan_stopped_work);
}
EXPORT_SYMBOL(ieee80211_sched_scan_stopped);