net/mac80211/scan.c

   1 /*
   2  * Scanning implementation
   3  *
   4  * Copyright 2003, Jouni Malinen <jkmaline@cc.hut.fi>
   5  * Copyright 2004, Instant802 Networks, Inc.
   6  * Copyright 2005, Devicescape Software, Inc.
   7  * Copyright 2006-2007  Jiri Benc <jbenc@suse.cz>
   8  * Copyright 2007, Michael Wu <flamingice@sourmilk.net>
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License version 2 as
  12  * published by the Free Software Foundation.
  13  */
  14
  15 /* TODO: figure out how to avoid that the "current BSS" expires */
  16
  17 #include <linux/wireless.h>
  18 #include <linux/if_arp.h>
  19 #include <linux/rtnetlink.h>
  20 #include <net/mac80211.h>
  21
  22 #include "ieee80211_i.h"
  23 #include "driver-ops.h"
  24 #include "mesh.h"
  25
  26 #define IEEE80211_PROBE_DELAY (HZ / 33)
  27 #define IEEE80211_CHANNEL_TIME (HZ / 33)
  28 #define IEEE80211_PASSIVE_CHANNEL_TIME (HZ / 8)
  29
  30 struct ieee80211_bss *
  31 ieee80211_rx_bss_get(struct ieee80211_local *local, u8 *bssid, int freq,
  32                      u8 *ssid, u8 ssid_len)
  33 {
  34         return (void *)cfg80211_get_bss(local->hw.wiphy,
  35                                         ieee80211_get_channel(local->hw.wiphy,
  36                                                               freq),
  37                                         bssid, ssid, ssid_len,
  38                                         0, 0);
  39 }
  40
  41 static void ieee80211_rx_bss_free(struct cfg80211_bss *cbss)
  42 {
  43         struct ieee80211_bss *bss = (void *)cbss;
  44
  45         kfree(bss_mesh_id(bss));
  46         kfree(bss_mesh_cfg(bss));
  47 }
  48
  49 void ieee80211_rx_bss_put(struct ieee80211_local *local,
  50                           struct ieee80211_bss *bss)
  51 {
  52         cfg80211_put_bss((struct cfg80211_bss *)bss);
  53 }
  54
  55 struct ieee80211_bss *
  56 ieee80211_bss_info_update(struct ieee80211_local *local,
  57                           struct ieee80211_rx_status *rx_status,
  58                           struct ieee80211_mgmt *mgmt,
  59                           size_t len,
  60                           struct ieee802_11_elems *elems,
  61                           struct ieee80211_channel *channel,
  62                           bool beacon)
  63 {
  64         struct ieee80211_bss *bss;
  65         int clen, srlen;
  66         s32 signal = 0;
  67
  68         if (local->hw.flags & IEEE80211_HW_SIGNAL_DBM)
  69                 signal = rx_status->signal * 100;
  70         else if (local->hw.flags & IEEE80211_HW_SIGNAL_UNSPEC)
  71                 signal = (rx_status->signal * 100) / local->hw.max_signal;
  72
  73         bss = (void *)cfg80211_inform_bss_frame(local->hw.wiphy, channel,
  74                                                 mgmt, len, signal, GFP_ATOMIC);
  75
  76         if (!bss)
  77                 return NULL;
  78
  79         bss->cbss.free_priv = ieee80211_rx_bss_free;
  80
  81         /* save the ERP value so that it is available at association time */
  82         if (elems->erp_info && elems->erp_info_len >= 1) {
  83                 bss->erp_value = elems->erp_info[0];
  84                 bss->has_erp_value = 1;
  85         }
  86
  87         if (elems->tim) {
  88                 struct ieee80211_tim_ie *tim_ie =
  89                         (struct ieee80211_tim_ie *)elems->tim;
  90                 bss->dtim_period = tim_ie->dtim_period;
  91         }
  92
  93         /* set default value for buggy AP/no TIM element */
  94         if (bss->dtim_period == 0)
  95                 bss->dtim_period = 1;
  96
  97         /* replace old supported rates if we get new values */
  98         srlen = 0;
  99         if (elems->supp_rates) {
 100                 clen = IEEE80211_MAX_SUPP_RATES;
 101                 if (clen > elems->supp_rates_len)
 102                         clen = elems->supp_rates_len;
 103                 memcpy(bss->supp_rates, elems->supp_rates, clen);
 104                 srlen += clen;
 105         }
 106         if (elems->ext_supp_rates) {
 107                 clen = IEEE80211_MAX_SUPP_RATES - srlen;
 108                 if (clen > elems->ext_supp_rates_len)
 109                         clen = elems->ext_supp_rates_len;
 110                 memcpy(bss->supp_rates + srlen, elems->ext_supp_rates, clen);
 111                 srlen += clen;
 112         }
 113         if (srlen)
 114                 bss->supp_rates_len = srlen;
 115
 116         bss->wmm_used = elems->wmm_param || elems->wmm_info;
 117
 118         if (!beacon)
 119                 bss->last_probe_resp = jiffies;
 120
 121         return bss;
 122 }
 123
 124 ieee80211_rx_result
 125 ieee80211_scan_rx(struct ieee80211_sub_if_data *sdata, struct sk_buff *skb)
 126 {
 127         struct ieee80211_rx_status *rx_status = IEEE80211_SKB_RXCB(skb);
 128         struct ieee80211_mgmt *mgmt;
 129         struct ieee80211_bss *bss;
 130         u8 *elements;
 131         struct ieee80211_channel *channel;
 132         size_t baselen;
 133         int freq;
 134         __le16 fc;
 135         bool presp, beacon = false;
 136         struct ieee802_11_elems elems;
 137
 138         if (skb->len < 2)
 139                 return RX_DROP_UNUSABLE;
 140
 141         mgmt = (struct ieee80211_mgmt *) skb->data;
 142         fc = mgmt->frame_control;
 143
 144         if (ieee80211_is_ctl(fc))
 145                 return RX_CONTINUE;
 146
 147         if (skb->len < 24)
 148                 return RX_DROP_MONITOR;
 149
 150         presp = ieee80211_is_probe_resp(fc);
 151         if (presp) {
 152                 /* ignore ProbeResp to foreign address */
 153                 if (memcmp(mgmt->da, sdata->dev->dev_addr, ETH_ALEN))
 154                         return RX_DROP_MONITOR;
 155
 156                 presp = true;
 157                 elements = mgmt->u.probe_resp.variable;
 158                 baselen = offsetof(struct ieee80211_mgmt, u.probe_resp.variable);
 159         } else {
 160                 beacon = ieee80211_is_beacon(fc);
 161                 baselen = offsetof(struct ieee80211_mgmt, u.beacon.variable);
 162                 elements = mgmt->u.beacon.variable;
 163         }
 164
 165         if (!presp && !beacon)
 166                 return RX_CONTINUE;
 167
 168         if (baselen > skb->len)
 169                 return RX_DROP_MONITOR;
 170
 171         ieee802_11_parse_elems(elements, skb->len - baselen, &elems);
 172
 173         if (elems.ds_params && elems.ds_params_len == 1)
 174                 freq = ieee80211_channel_to_frequency(elems.ds_params[0]);
 175         else
 176                 freq = rx_status->freq;
 177
 178         channel = ieee80211_get_channel(sdata->local->hw.wiphy, freq);
 179
 180         if (!channel || channel->flags & IEEE80211_CHAN_DISABLED)
 181                 return RX_DROP_MONITOR;
 182
 183         bss = ieee80211_bss_info_update(sdata->local, rx_status,
 184                                         mgmt, skb->len, &elems,
 185                                         channel, beacon);
 186         if (bss)
 187                 ieee80211_rx_bss_put(sdata->local, bss);
 188
 189         dev_kfree_skb(skb);
 190         return RX_QUEUED;
 191 }
 192
 193 /*
 194  * inform AP that we will go to sleep so that it will buffer the frames
 195  * while we scan
 196  */
 197 static void ieee80211_scan_ps_enable(struct ieee80211_sub_if_data *sdata)
 198 {
 199         struct ieee80211_local *local = sdata->local;
 200
 201         local->scan_ps_enabled = false;
 202
 203         /* FIXME: what to do when local->pspolling is true? */
 204
 205         del_timer_sync(&local->dynamic_ps_timer);
 206         cancel_work_sync(&local->dynamic_ps_enable_work);
 207
 208         if (local->hw.conf.flags & IEEE80211_CONF_PS) {
 209                 local->scan_ps_enabled = true;
 210                 local->hw.conf.flags &= ~IEEE80211_CONF_PS;
 211                 ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_PS);
 212         }
 213
 214         if (!(local->scan_ps_enabled) ||
 215             !(local->hw.flags & IEEE80211_HW_PS_NULLFUNC_STACK))
 216                 /*
 217                  * If power save was enabled, no need to send a nullfunc
 218                  * frame because AP knows that we are sleeping. But if the
 219                  * hardware is creating the nullfunc frame for power save
 220                  * status (ie. IEEE80211_HW_PS_NULLFUNC_STACK is not
 221                  * enabled) and power save was enabled, the firmware just
 222                  * sent a null frame with power save disabled. So we need
 223                  * to send a new nullfunc frame to inform the AP that we
 224                  * are again sleeping.
 225                  */
 226                 ieee80211_send_nullfunc(local, sdata, 1);
 227 }
 228
 229 /* inform AP that we are awake again, unless power save is enabled */
 230 static void ieee80211_scan_ps_disable(struct ieee80211_sub_if_data *sdata)
 231 {
 232         struct ieee80211_local *local = sdata->local;
 233
 234         if (!local->ps_sdata)
 235                 ieee80211_send_nullfunc(local, sdata, 0);
 236         else if (local->scan_ps_enabled) {
 237                 /*
 238                  * In !IEEE80211_HW_PS_NULLFUNC_STACK case the hardware
 239                  * will send a nullfunc frame with the powersave bit set
 240                  * even though the AP already knows that we are sleeping.
 241                  * This could be avoided by sending a null frame with power
 242                  * save bit disabled before enabling the power save, but
 243                  * this doesn't gain anything.
 244                  *
 245                  * When IEEE80211_HW_PS_NULLFUNC_STACK is enabled, no need
 246                  * to send a nullfunc frame because AP already knows that
 247                  * we are sleeping, let's just enable power save mode in
 248                  * hardware.
 249                  */
 250                 local->hw.conf.flags |= IEEE80211_CONF_PS;
 251                 ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_PS);
 252         } else if (local->hw.conf.dynamic_ps_timeout > 0) {
 253                 /*
 254                  * If IEEE80211_CONF_PS was not set and the dynamic_ps_timer
 255                  * had been running before leaving the operating channel,
 256                  * restart the timer now and send a nullfunc frame to inform
 257                  * the AP that we are awake.
 258                  */
 259                 ieee80211_send_nullfunc(local, sdata, 0);
 260                 mod_timer(&local->dynamic_ps_timer, jiffies +
 261                           msecs_to_jiffies(local->hw.conf.dynamic_ps_timeout));
 262         }
 263 }
 264
 265 static void ieee80211_restore_scan_ies(struct ieee80211_local *local)
 266 {
 267         kfree(local->scan_req->ie);
 268         local->scan_req->ie = local->orig_ies;
 269         local->scan_req->ie_len = local->orig_ies_len;
 270 }
 271
 272 void ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
 273 {
 274         struct ieee80211_local *local = hw_to_local(hw);
 275         struct ieee80211_sub_if_data *sdata;
 276         bool was_hw_scan;
 277
 278         mutex_lock(&local->scan_mtx);
 279
 280         /*
 281          * It's ok to abort a not-yet-running scan (that
 282          * we have one at all will be verified by checking
 283          * local->scan_req next), but not to complete it
 284          * successfully.
 285          */
 286         if (WARN_ON(!local->scanning && !aborted))
 287                 aborted = true;
 288
 289         if (WARN_ON(!local->scan_req)) {
 290                 mutex_unlock(&local->scan_mtx);
 291                 return;
 292         }
 293
 294         if (test_bit(SCAN_HW_SCANNING, &local->scanning))
 295                 ieee80211_restore_scan_ies(local);
 296
 297         if (local->scan_req != local->int_scan_req)
 298                 cfg80211_scan_done(local->scan_req, aborted);
 299         local->scan_req = NULL;
 300         local->scan_sdata = NULL;
 301
 302         was_hw_scan = test_bit(SCAN_HW_SCANNING, &local->scanning);
 303         local->scanning = 0;
 304         local->scan_channel = NULL;
 305
 306         /* we only have to protect scan_req and hw/sw scan */
 307         mutex_unlock(&local->scan_mtx);
 308
 309         ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
 310         if (was_hw_scan)
 311                 goto done;
 312
 313         ieee80211_configure_filter(local);
 314
 315         drv_sw_scan_complete(local);
 316
 317         mutex_lock(&local->iflist_mtx);
 318         list_for_each_entry(sdata, &local->interfaces, list) {
 319                 if (!netif_running(sdata->dev))
 320                         continue;
 321
 322                 /* Tell AP we're back */
 323                 if (sdata->vif.type == NL80211_IFTYPE_STATION) {
 324                         if (sdata->u.mgd.associated) {
 325                                 ieee80211_scan_ps_disable(sdata);
 326                                 netif_tx_wake_all_queues(sdata->dev);
 327                         }
 328                 } else
 329                         netif_tx_wake_all_queues(sdata->dev);
 330
 331                 /* re-enable beaconing */
 332                 if (sdata->vif.type == NL80211_IFTYPE_AP ||
 333                     sdata->vif.type == NL80211_IFTYPE_ADHOC ||
 334                     sdata->vif.type == NL80211_IFTYPE_MESH_POINT)
 335                         ieee80211_bss_info_change_notify(
 336                                 sdata, BSS_CHANGED_BEACON_ENABLED);
 337         }
 338         mutex_unlock(&local->iflist_mtx);
 339
 340  done:
 341         ieee80211_recalc_idle(local);
 342         ieee80211_mlme_notify_scan_completed(local);
 343         ieee80211_ibss_notify_scan_completed(local);
 344         ieee80211_mesh_notify_scan_completed(local);
 345 }
 346 EXPORT_SYMBOL(ieee80211_scan_completed);
 347
 348 static int ieee80211_start_sw_scan(struct ieee80211_local *local)
 349 {
 350         struct ieee80211_sub_if_data *sdata;
 351
 352         /*
 353          * Hardware/driver doesn't support hw_scan, so use software
 354          * scanning instead. First send a nullfunc frame with power save
 355          * bit on so that AP will buffer the frames for us while we are not
 356          * listening, then send probe requests to each channel and wait for
 357          * the responses. After all channels are scanned, tune back to the
 358          * original channel and send a nullfunc frame with power save bit
 359          * off to trigger the AP to send us all the buffered frames.
 360          *
 361          * Note that while local->sw_scanning is true everything else but
 362          * nullfunc frames and probe requests will be dropped in
 363          * ieee80211_tx_h_check_assoc().
 364          */
 365         drv_sw_scan_start(local);
 366
 367         mutex_lock(&local->iflist_mtx);
 368         list_for_each_entry(sdata, &local->interfaces, list) {
 369                 if (!netif_running(sdata->dev))
 370                         continue;
 371
 372                 /* disable beaconing */
 373                 if (sdata->vif.type == NL80211_IFTYPE_AP ||
 374                     sdata->vif.type == NL80211_IFTYPE_ADHOC ||
 375                     sdata->vif.type == NL80211_IFTYPE_MESH_POINT)
 376                         ieee80211_bss_info_change_notify(
 377                                 sdata, BSS_CHANGED_BEACON_ENABLED);
 378
 379                 /*
 380                  * only handle non-STA interfaces here, STA interfaces
 381                  * are handled in the scan state machine
 382                  */
 383                 if (sdata->vif.type != NL80211_IFTYPE_STATION)
 384                         netif_tx_stop_all_queues(sdata->dev);
 385         }
 386         mutex_unlock(&local->iflist_mtx);
 387
 388         local->next_scan_state = SCAN_DECISION;
 389         local->scan_channel_idx = 0;
 390
 391         ieee80211_configure_filter(local);
 392
 393         /* TODO: start scan as soon as all nullfunc frames are ACKed */
 394         ieee80211_queue_delayed_work(&local->hw,
 395                                      &local->scan_work,
 396                                      IEEE80211_CHANNEL_TIME);
 397
 398         return 0;
 399 }
 400
 401
 402 static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 403                                   struct cfg80211_scan_request *req)
 404 {
 405         struct ieee80211_local *local = sdata->local;
 406         struct ieee80211_if_managed *ifmgd = &sdata->u.mgd;
 407         int rc;
 408
 409         if (local->scan_req)
 410                 return -EBUSY;
 411
 412         if (req != local->int_scan_req &&
 413             sdata->vif.type == NL80211_IFTYPE_STATION &&
 414             !list_empty(&ifmgd->work_list)) {
 415                 /* actually wait for the work it's doing to finish/time out */
 416                 set_bit(IEEE80211_STA_REQ_SCAN, &ifmgd->request);
 417                 local->scan_req = req;
 418                 local->scan_sdata = sdata;
 419                 return 0;
 420         }
 421
 422         if (local->ops->hw_scan) {
 423                 u8 *ies;
 424                 int ielen;
 425
 426                 ies = kmalloc(2 + IEEE80211_MAX_SSID_LEN +
 427                               local->scan_ies_len + req->ie_len, GFP_KERNEL);
 428                 if (!ies)
 429                         return -ENOMEM;
 430
 431                 ielen = ieee80211_build_preq_ies(local, ies,
 432                                                  req->ie, req->ie_len);
 433                 local->orig_ies = req->ie;
 434                 local->orig_ies_len = req->ie_len;
 435                 req->ie = ies;
 436                 req->ie_len = ielen;
 437         }
 438
 439         local->scan_req = req;
 440         local->scan_sdata = sdata;
 441
 442         if (local->ops->hw_scan)
 443                 __set_bit(SCAN_HW_SCANNING, &local->scanning);
 444         else
 445                 __set_bit(SCAN_SW_SCANNING, &local->scanning);
 446         /*
 447          * Kicking off the scan need not be protected,
 448          * only the scan variable stuff, since now
 449          * local->scan_req is assigned and other callers
 450          * will abort their scan attempts.
 451          *
 452          * This avoids getting a scan_mtx -> iflist_mtx
 453          * dependency, so that the scan completed calls
 454          * have more locking freedom.
 455          */
 456
 457         ieee80211_recalc_idle(local);
 458         mutex_unlock(&local->scan_mtx);
 459
 460         if (local->ops->hw_scan)
 461                 rc = drv_hw_scan(local, local->scan_req);
 462         else
 463                 rc = ieee80211_start_sw_scan(local);
 464
 465         mutex_lock(&local->scan_mtx);
 466
 467         if (rc) {
 468                 if (local->ops->hw_scan)
 469                         ieee80211_restore_scan_ies(local);
 470                 local->scanning = 0;
 471
 472                 ieee80211_recalc_idle(local);
 473
 474                 local->scan_req = NULL;
 475                 local->scan_sdata = NULL;
 476         }
 477
 478         return rc;
 479 }
 480
 481 static int ieee80211_scan_state_decision(struct ieee80211_local *local,
 482                                          unsigned long *next_delay)
 483 {
 484         bool associated = false;
 485         struct ieee80211_sub_if_data *sdata;
 486
 487         /* if no more bands/channels left, complete scan and advance to the idle state */
 488         if (local->scan_channel_idx >= local->scan_req->n_channels) {
 489                 ieee80211_scan_completed(&local->hw, false);
 490                 return 1;
 491         }
 492
 493         /* check if at least one STA interface is associated */
 494         mutex_lock(&local->iflist_mtx);
 495         list_for_each_entry(sdata, &local->interfaces, list) {
 496                 if (!netif_running(sdata->dev))
 497                         continue;
 498
 499                 if (sdata->vif.type == NL80211_IFTYPE_STATION) {
 500                         if (sdata->u.mgd.associated) {
 501                                 associated = true;
 502                                 break;
 503                         }
 504                 }
 505         }
 506         mutex_unlock(&local->iflist_mtx);
 507
 508         if (local->scan_channel) {
 509                 /*
 510                  * we're currently scanning a different channel, let's
 511                  * switch back to the operating channel now if at least
 512                  * one interface is associated. Otherwise just scan the
 513                  * next channel
 514                  */
 515                 if (associated)
 516                         local->next_scan_state = SCAN_ENTER_OPER_CHANNEL;
 517                 else
 518                         local->next_scan_state = SCAN_SET_CHANNEL;
 519         } else {
 520                 /*
 521                  * we're on the operating channel currently, let's
 522                  * leave that channel now to scan another one
 523                  */
 524                 local->next_scan_state = SCAN_LEAVE_OPER_CHANNEL;
 525         }
 526
 527         *next_delay = 0;
 528         return 0;
 529 }
 530
 531 static void ieee80211_scan_state_leave_oper_channel(struct ieee80211_local *local,
 532                                                     unsigned long *next_delay)
 533 {
 534         struct ieee80211_sub_if_data *sdata;
 535
 536         /*
 537          * notify the AP about us leaving the channel and stop all STA interfaces
 538          */
 539         mutex_lock(&local->iflist_mtx);
 540         list_for_each_entry(sdata, &local->interfaces, list) {
 541                 if (!netif_running(sdata->dev))
 542                         continue;
 543
 544                 if (sdata->vif.type == NL80211_IFTYPE_STATION) {
 545                         netif_tx_stop_all_queues(sdata->dev);
 546                         if (sdata->u.mgd.associated)
 547                                 ieee80211_scan_ps_enable(sdata);
 548                 }
 549         }
 550         mutex_unlock(&local->iflist_mtx);
 551
 552         __set_bit(SCAN_OFF_CHANNEL, &local->scanning);
 553
 554         /* advance to the next channel to be scanned */
 555         *next_delay = HZ / 10;
 556         local->next_scan_state = SCAN_SET_CHANNEL;
 557 }
 558
 559 static void ieee80211_scan_state_enter_oper_channel(struct ieee80211_local *local,
 560                                                     unsigned long *next_delay)
 561 {
 562         struct ieee80211_sub_if_data *sdata = local->scan_sdata;
 563
 564         /* switch back to the operating channel */
 565         local->scan_channel = NULL;
 566         ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
 567
 568         /*
 569          * notify the AP about us being back and restart all STA interfaces
 570          */
 571         mutex_lock(&local->iflist_mtx);
 572         list_for_each_entry(sdata, &local->interfaces, list) {
 573                 if (!netif_running(sdata->dev))
 574                         continue;
 575
 576                 /* Tell AP we're back */
 577                 if (sdata->vif.type == NL80211_IFTYPE_STATION) {
 578                         if (sdata->u.mgd.associated)
 579                                 ieee80211_scan_ps_disable(sdata);
 580                         netif_tx_wake_all_queues(sdata->dev);
 581                 }
 582         }
 583         mutex_unlock(&local->iflist_mtx);
 584
 585         __clear_bit(SCAN_OFF_CHANNEL, &local->scanning);
 586
 587         *next_delay = HZ / 5;
 588         local->next_scan_state = SCAN_DECISION;
 589 }
 590
 591 static void ieee80211_scan_state_set_channel(struct ieee80211_local *local,
 592                                              unsigned long *next_delay)
 593 {
 594         int skip;
 595         struct ieee80211_channel *chan;
 596         struct ieee80211_sub_if_data *sdata = local->scan_sdata;
 597
 598         skip = 0;
 599         chan = local->scan_req->channels[local->scan_channel_idx];
 600
 601         if (chan->flags & IEEE80211_CHAN_DISABLED ||
 602             (sdata->vif.type == NL80211_IFTYPE_ADHOC &&
 603              chan->flags & IEEE80211_CHAN_NO_IBSS))
 604                 skip = 1;
 605
 606         if (!skip) {
 607                 local->scan_channel = chan;
 608                 if (ieee80211_hw_config(local,
 609                                         IEEE80211_CONF_CHANGE_CHANNEL))
 610                         skip = 1;
 611         }
 612
 613         /* advance state machine to next channel/band */
 614         local->scan_channel_idx++;
 615
 616         if (skip) {
 617                 /* if we skip this channel return to the decision state */
 618                 local->next_scan_state = SCAN_DECISION;
 619                 return;
 620         }
 621
 622         /*
 623          * Probe delay is used to update the NAV, cf. 11.1.3.2.2
 624          * (which unfortunately doesn't say _why_ step a) is done,
 625          * but it waits for the probe delay or until a frame is
 626          * received - and the received frame would update the NAV).
 627          * For now, we do not support waiting until a frame is
 628          * received.
 629          *
 630          * In any case, it is not necessary for a passive scan.
 631          */
 632         if (chan->flags & IEEE80211_CHAN_PASSIVE_SCAN ||
 633             !local->scan_req->n_ssids) {
 634                 *next_delay = IEEE80211_PASSIVE_CHANNEL_TIME;
 635                 local->next_scan_state = SCAN_DECISION;
 636                 return;
 637         }
 638
 639         /* active scan, send probes */
 640         *next_delay = IEEE80211_PROBE_DELAY;
 641         local->next_scan_state = SCAN_SEND_PROBE;
 642 }
 643
 644 static void ieee80211_scan_state_send_probe(struct ieee80211_local *local,
 645                                             unsigned long *next_delay)
 646 {
 647         int i;
 648         struct ieee80211_sub_if_data *sdata = local->scan_sdata;
 649
 650         for (i = 0; i < local->scan_req->n_ssids; i++)
 651                 ieee80211_send_probe_req(
 652                         sdata, NULL,
 653                         local->scan_req->ssids[i].ssid,
 654                         local->scan_req->ssids[i].ssid_len,
 655                         local->scan_req->ie, local->scan_req->ie_len);
 656
 657         /*
 658          * After sending probe requests, wait for probe responses
 659          * on the channel.
 660          */
 661         *next_delay = IEEE80211_CHANNEL_TIME;
 662         local->next_scan_state = SCAN_DECISION;
 663 }
 664
 665 void ieee80211_scan_work(struct work_struct *work)
 666 {
 667         struct ieee80211_local *local =
 668                 container_of(work, struct ieee80211_local, scan_work.work);
 669         struct ieee80211_sub_if_data *sdata = local->scan_sdata;
 670         unsigned long next_delay = 0;
 671
 672         mutex_lock(&local->scan_mtx);
 673         if (!sdata || !local->scan_req) {
 674                 mutex_unlock(&local->scan_mtx);
 675                 return;
 676         }
 677
 678         if (local->scan_req && !local->scanning) {
 679                 struct cfg80211_scan_request *req = local->scan_req;
 680                 int rc;
 681
 682                 local->scan_req = NULL;
 683                 local->scan_sdata = NULL;
 684
 685                 rc = __ieee80211_start_scan(sdata, req);
 686                 mutex_unlock(&local->scan_mtx);
 687
 688                 if (rc)
 689                         ieee80211_scan_completed(&local->hw, true);
 690                 return;
 691         }
 692
 693         mutex_unlock(&local->scan_mtx);
 694
 695         /*
 696          * Avoid re-scheduling when the sdata is going away.
 697          */
 698         if (!netif_running(sdata->dev)) {
 699                 ieee80211_scan_completed(&local->hw, true);
 700                 return;
 701         }
 702
 703         /*
 704          * as long as no delay is required advance immediately
 705          * without scheduling a new work
 706          */
 707         do {
 708                 switch (local->next_scan_state) {
 709                 case SCAN_DECISION:
 710                         if (ieee80211_scan_state_decision(local, &next_delay))
 711                                 return;
 712                         break;
 713                 case SCAN_SET_CHANNEL:
 714                         ieee80211_scan_state_set_channel(local, &next_delay);
 715                         break;
 716                 case SCAN_SEND_PROBE:
 717                         ieee80211_scan_state_send_probe(local, &next_delay);
 718                         break;
 719                 case SCAN_LEAVE_OPER_CHANNEL:
 720                         ieee80211_scan_state_leave_oper_channel(local, &next_delay);
 721                         break;
 722                 case SCAN_ENTER_OPER_CHANNEL:
 723                         ieee80211_scan_state_enter_oper_channel(local, &next_delay);
 724                         break;
 725                 }
 726         } while (next_delay == 0);
 727
 728         ieee80211_queue_delayed_work(&local->hw, &local->scan_work, next_delay);
 729 }
 730
 731 int ieee80211_request_scan(struct ieee80211_sub_if_data *sdata,
 732                            struct cfg80211_scan_request *req)
 733 {
 734         int res;
 735
 736         mutex_lock(&sdata->local->scan_mtx);
 737         res = __ieee80211_start_scan(sdata, req);
 738         mutex_unlock(&sdata->local->scan_mtx);
 739
 740         return res;
 741 }
 742
 743 int ieee80211_request_internal_scan(struct ieee80211_sub_if_data *sdata,
 744                                     const u8 *ssid, u8 ssid_len)
 745 {
 746         struct ieee80211_local *local = sdata->local;
 747         int ret = -EBUSY;
 748
 749         mutex_lock(&local->scan_mtx);
 750
 751         /* busy scanning */
 752         if (local->scan_req)
 753                 goto unlock;
 754
 755         memcpy(local->int_scan_req->ssids[0].ssid, ssid, IEEE80211_MAX_SSID_LEN);
 756         local->int_scan_req->ssids[0].ssid_len = ssid_len;
 757
 758         ret = __ieee80211_start_scan(sdata, sdata->local->int_scan_req);
 759  unlock:
 760         mutex_unlock(&local->scan_mtx);
 761         return ret;
 762 }
 763
 764 void ieee80211_scan_cancel(struct ieee80211_local *local)
 765 {
 766         bool abortscan;
 767
 768         cancel_delayed_work_sync(&local->scan_work);
 769
 770         /*
 771          * Only call this function when a scan can't be
 772          * queued -- mostly at suspend under RTNL.
 773          */
 774         mutex_lock(&local->scan_mtx);
 775         abortscan = test_bit(SCAN_SW_SCANNING, &local->scanning) ||
 776                     (!local->scanning && local->scan_req);
 777         mutex_unlock(&local->scan_mtx);
 778
 779         if (abortscan)
 780                 ieee80211_scan_completed(&local->hw, true);
 781 }