wpa_supplicant/scan.c

/*
 * WPA Supplicant - Scanning
 * Copyright (c) 2003-2012, Jouni Malinen <j@w1.fi>
 *
 * This software may be distributed under the terms of the BSD license.
 * See README for more details.
 */

#include "utils/includes.h"

#include "utils/common.h"
#include "utils/eloop.h"
#include "common/ieee802_11_defs.h"
#include "common/wpa_ctrl.h"
#include "config.h"
#include "wpa_supplicant_i.h"
#include "driver_i.h"
#include "wps_supplicant.h"
#include "p2p_supplicant.h"
#include "p2p/p2p.h"
#include "hs20_supplicant.h"
#include "notify.h"
#include "bss.h"
#include "gas_query.h"
#include "scan.h"


static void wpa_supplicant_gen_assoc_event(struct wpa_supplicant *wpa_s)
{
	struct wpa_ssid *ssid;
	union wpa_event_data data;

	ssid = wpa_supplicant_get_ssid(wpa_s);
	if (ssid == NULL)
		return;

	if (wpa_s->current_ssid == NULL) {
		wpa_s->current_ssid = ssid;
		if (wpa_s->current_ssid != NULL)
			wpas_notify_network_changed(wpa_s);
	}
	wpa_supplicant_initiate_eapol(wpa_s);
	wpa_dbg(wpa_s, MSG_DEBUG, "Already associated with a configured "
		"network - generating associated event");
	os_memset(&data, 0, sizeof(data));
	wpa_supplicant_event(wpa_s, EVENT_ASSOC, &data);
}


#ifdef CONFIG_WPS
static int wpas_wps_in_use(struct wpa_supplicant *wpa_s,
			   enum wps_request_type *req_type)
{
	struct wpa_ssid *ssid;
	int wps = 0;

	for (ssid = wpa_s->conf->ssid; ssid; ssid = ssid->next) {
		if (!(ssid->key_mgmt & WPA_KEY_MGMT_WPS))
			continue;

		wps = 1;
		*req_type = wpas_wps_get_req_type(ssid);
		if (!ssid->eap.phase1)
			continue;

		if (os_strstr(ssid->eap.phase1, "pbc=1"))
			return 2;
	}

#ifdef CONFIG_P2P
	if (!wpa_s->global->p2p_disabled && wpa_s->global->p2p &&
	    !wpa_s->conf->p2p_disabled) {
		wpa_s->wps->dev.p2p = 1;
		if (!wps) {
			wps = 1;
			*req_type = WPS_REQ_ENROLLEE_INFO;
		}
	}
#endif /* CONFIG_P2P */

	return wps;
}
#endif /* CONFIG_WPS */


/**
 * wpa_supplicant_enabled_networks - Check whether there are enabled networks
 * @wpa_s: Pointer to wpa_supplicant data
 * Returns: 0 if no networks are enabled, >0 if networks are enabled
 *
 * This function is used to figure out whether any networks (or Interworking
 * with enabled credentials and auto_interworking) are present in the current
 * configuration.
 */
int wpa_supplicant_enabled_networks(struct wpa_supplicant *wpa_s)
{
	struct wpa_ssid *ssid = wpa_s->conf->ssid;
	int count = 0, disabled = 0;
	while (ssid) {
		if (!wpas_network_disabled(wpa_s, ssid))
			count++;
		else
			disabled++;
		ssid = ssid->next;
	}
	if (wpa_s->conf->cred && wpa_s->conf->interworking &&
	    wpa_s->conf->auto_interworking)
		count++;
	if (count == 0 && disabled > 0) {
		wpa_dbg(wpa_s, MSG_DEBUG, "No enabled networks (%d disabled "
			"networks)", disabled);
	}
	return count;
}


static void wpa_supplicant_assoc_try(struct wpa_supplicant *wpa_s,
				     struct wpa_ssid *ssid)
{
	while (ssid) {
		if (!wpas_network_disabled(wpa_s, ssid))
			break;
		ssid = ssid->next;
	}

	/* ap_scan=2 mode - try to associate with each SSID. */
	if (ssid == NULL) {
		wpa_dbg(wpa_s, MSG_DEBUG, "wpa_supplicant_assoc_try: Reached "
			"end of scan list - go back to beginning");
		wpa_s->prev_scan_ssid = WILDCARD_SSID_SCAN;
		wpa_supplicant_req_scan(wpa_s, 0, 0);
		return;
	}
	if (ssid->next) {
		/* Continue from the next SSID on the next attempt. */
		wpa_s->prev_scan_ssid = ssid;
	} else {
		/* Start from the beginning of the SSID list. */
		wpa_s->prev_scan_ssid = WILDCARD_SSID_SCAN;
	}
	wpa_supplicant_associate(wpa_s, NULL, ssid);
}


static int int_array_len(const int *a)
{
	int i;
	for (i = 0; a && a[i]; i++)
		;
	return i;
}


static void int_array_concat(int **res, const int *a)
{
	int reslen, alen, i;
	int *n;

	reslen = int_array_len(*res);
	alen = int_array_len(a);

	n = os_realloc_array(*res, reslen + alen + 1, sizeof(int));
	if (n == NULL) {
		os_free(*res);
		*res = NULL;
		return;
	}
	for (i = 0; i <= alen; i++)
		n[reslen + i] = a[i];
	*res = n;
}


static int freq_cmp(const void *a, const void *b)
{
	int _a = *(int *) a;
	int _b = *(int *) b;

	if (_a == 0)
		return 1;
	if (_b == 0)
		return -1;
	return _a - _b;
}


static void int_array_sort_unique(int *a)
{
	int alen;
	int i, j;

	if (a == NULL)
		return;

	alen = int_array_len(a);
	qsort(a, alen, sizeof(int), freq_cmp);

	i = 0;
	j = 1;
	while (a[i] && a[j]) {
		if (a[i] == a[j]) {
			j++;
			continue;
		}
		a[++i] = a[j++];
	}
	if (a[i])
		i++;
	a[i] = 0;
}


/**
 * wpa_supplicant_trigger_scan - Request driver to start a scan
 * @wpa_s: Pointer to wpa_supplicant data
 * @params: Scan parameters
 * Returns: 0 on success, -1 on failure
 */
int wpa_supplicant_trigger_scan(struct wpa_supplicant *wpa_s,
				struct wpa_driver_scan_params *params)
{
	int ret;

	wpa_supplicant_notify_scanning(wpa_s, 1);

	ret = wpa_drv_scan(wpa_s, params);
	if (ret) {
		wpa_supplicant_notify_scanning(wpa_s, 0);
		wpas_notify_scan_done(wpa_s, 0);
	} else {
		os_get_time(&wpa_s->scan_trigger_time);
		wpa_s->scan_runs++;
		wpa_s->normal_scans++;
	}

	return ret;
}


static void
wpa_supplicant_delayed_sched_scan_timeout(void *eloop_ctx, void *timeout_ctx)
{
	struct wpa_supplicant *wpa_s = eloop_ctx;

	wpa_dbg(wpa_s, MSG_DEBUG, "Starting delayed sched scan");

	if (wpa_supplicant_req_sched_scan(wpa_s))
		wpa_supplicant_req_scan(wpa_s, 0, 0);
}


static void
wpa_supplicant_sched_scan_timeout(void *eloop_ctx, void *timeout_ctx)
{
	struct wpa_supplicant *wpa_s = eloop_ctx;

	wpa_dbg(wpa_s, MSG_DEBUG, "Sched scan timeout - stopping it");

	wpa_s->sched_scan_timed_out = 1;
	wpa_supplicant_cancel_sched_scan(wpa_s);
}


static int
wpa_supplicant_start_sched_scan(struct wpa_supplicant *wpa_s,
				struct wpa_driver_scan_params *params,
				int interval)
{
	int ret;

	wpa_supplicant_notify_scanning(wpa_s, 1);
	ret = wpa_drv_sched_scan(wpa_s, params, interval * 1000);
	if (ret)
		wpa_supplicant_notify_scanning(wpa_s, 0);
	else
		wpa_s->sched_scanning = 1;

	return ret;
}


static int wpa_supplicant_stop_sched_scan(struct wpa_supplicant *wpa_s)
{
	int ret;

	ret = wpa_drv_stop_sched_scan(wpa_s);
	if (ret) {
		wpa_dbg(wpa_s, MSG_DEBUG, "stopping sched_scan failed!");
		/* TODO: what to do if stopping fails? */
		return -1;
	}

	return ret;
}


static struct wpa_driver_scan_filter *
wpa_supplicant_build_filter_ssids(struct wpa_config *conf, size_t *num_ssids)
{
	struct wpa_driver_scan_filter *ssids;
	struct wpa_ssid *ssid;
	size_t count;

	*num_ssids = 0;
	if (!conf->filter_ssids)
		return NULL;

	for (count = 0, ssid = conf->ssid; ssid; ssid = ssid->next) {
		if (ssid->ssid && ssid->ssid_len)
			count++;
	}
	if (count == 0)
		return NULL;
	ssids = os_zalloc(count * sizeof(struct wpa_driver_scan_filter));
	if (ssids == NULL)
		return NULL;

	for (ssid = conf->ssid; ssid; ssid = ssid->next) {
		if (!ssid->ssid || !ssid->ssid_len)
			continue;
		os_memcpy(ssids[*num_ssids].ssid, ssid->ssid, ssid->ssid_len);
		ssids[*num_ssids].ssid_len = ssid->ssid_len;
		(*num_ssids)++;
	}

	return ssids;
}


static void wpa_supplicant_optimize_freqs(
	struct wpa_supplicant *wpa_s, struct wpa_driver_scan_params *params)
{
#ifdef CONFIG_P2P
	if (params->freqs == NULL && wpa_s->p2p_in_provisioning &&
	    wpa_s->go_params) {
		/* Optimize provisioning state scan based on GO information */
		if (wpa_s->p2p_in_provisioning < 5 &&
		    wpa_s->go_params->freq > 0) {
			wpa_dbg(wpa_s, MSG_DEBUG, "P2P: Scan only GO "
				"preferred frequency %d MHz",
				wpa_s->go_params->freq);
			params->freqs = os_zalloc(2 * sizeof(int));
			if (params->freqs)
				params->freqs[0] = wpa_s->go_params->freq;
		} else if (wpa_s->p2p_in_provisioning < 8 &&
			   wpa_s->go_params->freq_list[0]) {
			wpa_dbg(wpa_s, MSG_DEBUG, "P2P: Scan only common "
				"channels");
			int_array_concat(&params->freqs,
					 wpa_s->go_params->freq_list);
			if (params->freqs)
				int_array_sort_unique(params->freqs);
		}
		wpa_s->p2p_in_provisioning++;
	}
#endif /* CONFIG_P2P */

#ifdef CONFIG_WPS
	if (params->freqs == NULL && wpa_s->after_wps && wpa_s->wps_freq) {
		/*
		 * Optimize post-provisioning scan based on channel used
		 * during provisioning.
		 */
		wpa_dbg(wpa_s, MSG_DEBUG, "WPS: Scan only frequency %u MHz "
			"that was used during provisioning", wpa_s->wps_freq);
		params->freqs = os_zalloc(2 * sizeof(int));
		if (params->freqs)
			params->freqs[0] = wpa_s->wps_freq;
		wpa_s->after_wps--;
	}

	if (params->freqs == NULL && wpa_s->known_wps_freq && wpa_s->wps_freq)
	{
		/* Optimize provisioning scan based on already known channel */
		wpa_dbg(wpa_s, MSG_DEBUG, "WPS: Scan only frequency %u MHz",
			wpa_s->wps_freq);
		params->freqs = os_zalloc(2 * sizeof(int));
		if (params->freqs)
			params->freqs[0] = wpa_s->wps_freq;
		wpa_s->known_wps_freq = 0; /* only do this once */
	}
#endif /* CONFIG_WPS */
}


#ifdef CONFIG_INTERWORKING
static void wpas_add_interworking_elements(struct wpa_supplicant *wpa_s,
					   struct wpabuf *buf)
{
	if (wpa_s->conf->interworking == 0)
		return;

	wpabuf_put_u8(buf, WLAN_EID_EXT_CAPAB);
	wpabuf_put_u8(buf, 4);
	wpabuf_put_u8(buf, 0x00);
	wpabuf_put_u8(buf, 0x00);
	wpabuf_put_u8(buf, 0x00);
	wpabuf_put_u8(buf, 0x80); /* Bit 31 - Interworking */

	wpabuf_put_u8(buf, WLAN_EID_INTERWORKING);
	wpabuf_put_u8(buf, is_zero_ether_addr(wpa_s->conf->hessid) ? 1 :
		      1 + ETH_ALEN);
	wpabuf_put_u8(buf, wpa_s->conf->access_network_type);
	/* No Venue Info */
	if (!is_zero_ether_addr(wpa_s->conf->hessid))
		wpabuf_put_data(buf, wpa_s->conf->hessid, ETH_ALEN);
}
#endif /* CONFIG_INTERWORKING */


static struct wpabuf * wpa_supplicant_extra_ies(struct wpa_supplicant *wpa_s)
{
	struct wpabuf *extra_ie = NULL;
#ifdef CONFIG_WPS
	int wps = 0;
	enum wps_request_type req_type = WPS_REQ_ENROLLEE_INFO;
#endif /* CONFIG_WPS */

#ifdef CONFIG_INTERWORKING
	if (wpa_s->conf->interworking &&
	    wpabuf_resize(&extra_ie, 100) == 0)
		wpas_add_interworking_elements(wpa_s, extra_ie);
#endif /* CONFIG_INTERWORKING */

#ifdef CONFIG_WPS
	wps = wpas_wps_in_use(wpa_s, &req_type);

	if (wps) {
		struct wpabuf *wps_ie;
		wps_ie = wps_build_probe_req_ie(wps == 2 ? DEV_PW_PUSHBUTTON :
						DEV_PW_DEFAULT,
						&wpa_s->wps->dev,
						wpa_s->wps->uuid, req_type,
						0, NULL);
		if (wps_ie) {
			if (wpabuf_resize(&extra_ie, wpabuf_len(wps_ie)) == 0)
				wpabuf_put_buf(extra_ie, wps_ie);
			wpabuf_free(wps_ie);
		}
	}

#ifdef CONFIG_P2P
	if (wps) {
		size_t ielen = p2p_scan_ie_buf_len(wpa_s->global->p2p);
		if (wpabuf_resize(&extra_ie, ielen) == 0)
			wpas_p2p_scan_ie(wpa_s, extra_ie);
	}
#endif /* CONFIG_P2P */

#endif /* CONFIG_WPS */

#ifdef CONFIG_HS20
	if (wpa_s->conf->hs20 && wpabuf_resize(&extra_ie, 7) == 0)
		wpas_hs20_add_indication(extra_ie);
#endif /* CONFIG_HS20 */

	return extra_ie;
}


#ifdef CONFIG_P2P

/*
 * Check whether there are any enabled networks or credentials that could be
 * used for a non-P2P connection.
 */
static int non_p2p_network_enabled(struct wpa_supplicant *wpa_s)
{
	struct wpa_ssid *ssid;

	for (ssid = wpa_s->conf->ssid; ssid; ssid = ssid->next) {
		if (wpas_network_disabled(wpa_s, ssid))
			continue;
		if (!ssid->p2p_group)
			return 1;
	}

	if (wpa_s->conf->cred && wpa_s->conf->interworking &&
	    wpa_s->conf->auto_interworking)
		return 1;

	return 0;
}

#endif /* CONFIG_P2P */


static struct hostapd_hw_modes * get_mode(struct hostapd_hw_modes *modes,
					  u16 num_modes,
					  enum hostapd_hw_mode mode)
{
	u16 i;

	for (i = 0; i < num_modes; i++) {
		if (modes[i].mode == mode)
			return &modes[i];
	}

	return NULL;
}


static void wpa_setband_scan_freqs_list(struct wpa_supplicant *wpa_s,
					enum hostapd_hw_mode band,
					struct wpa_driver_scan_params *params)
{
	/* Include only supported channels for the specified band */
	struct hostapd_hw_modes *mode;
	int count, i;

	mode = get_mode(wpa_s->hw.modes, wpa_s->hw.num_modes, band);
	if (mode == NULL) {
		/* No channels supported in this band - use empty list */
		params->freqs = os_zalloc(sizeof(int));
		return;
	}

	params->freqs = os_zalloc((mode->num_channels + 1) * sizeof(int));
	if (params->freqs == NULL)
		return;
	for (count = 0, i = 0; i < mode->num_channels; i++) {
		if (mode->channels[i].flag & HOSTAPD_CHAN_DISABLED)
			continue;
		params->freqs[count++] = mode->channels[i].freq;
	}
}


static void wpa_setband_scan_freqs(struct wpa_supplicant *wpa_s,
				   struct wpa_driver_scan_params *params)
{
	if (wpa_s->hw.modes == NULL)
		return; /* unknown what channels the driver supports */
	if (params->freqs)
		return; /* already using a limited channel set */
	if (wpa_s->setband == WPA_SETBAND_5G)
		wpa_setband_scan_freqs_list(wpa_s, HOSTAPD_MODE_IEEE80211A,
					    params);
	else if (wpa_s->setband == WPA_SETBAND_2G)
		wpa_setband_scan_freqs_list(wpa_s, HOSTAPD_MODE_IEEE80211G,
					    params);
}


static void wpa_supplicant_scan(void *eloop_ctx, void *timeout_ctx)
{
	struct wpa_supplicant *wpa_s = eloop_ctx;
	struct wpa_ssid *ssid;
	enum scan_req_type scan_req = NORMAL_SCAN_REQ;
	int ret;
	struct wpabuf *extra_ie = NULL;
	struct wpa_driver_scan_params params;
	struct wpa_driver_scan_params *scan_params;
	size_t max_ssids;
	enum wpa_states prev_state;

	if (wpa_s->wpa_state == WPA_INTERFACE_DISABLED) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Skip scan - interface disabled");
		wpas_p2p_continue_after_scan(wpa_s);
		return;
	}

	if (wpa_s->disconnected && wpa_s->scan_req == NORMAL_SCAN_REQ) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Disconnected - do not scan");
		wpa_supplicant_set_state(wpa_s, WPA_DISCONNECTED);
		wpas_p2p_continue_after_scan(wpa_s);
		return;
	}
#ifdef ANDROID
	if (wpa_s->scanning) {
		/* If we are already in scanning state, we shall ignore this new scan request*/
		wpa_dbg(wpa_s, MSG_DEBUG, "Skip scan - already scanning");
		return;
	}
#endif
	if (!wpa_supplicant_enabled_networks(wpa_s) &&
	    wpa_s->scan_req == NORMAL_SCAN_REQ) {
		wpa_dbg(wpa_s, MSG_DEBUG, "No enabled networks - do not scan");
		wpa_supplicant_set_state(wpa_s, WPA_INACTIVE);
		wpas_p2p_continue_after_scan(wpa_s);
		return;
	}

	if (wpa_s->conf->ap_scan != 0 &&
	    (wpa_s->drv_flags & WPA_DRIVER_FLAGS_WIRED)) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Using wired authentication - "
			"overriding ap_scan configuration");
		wpa_s->conf->ap_scan = 0;
		wpas_notify_ap_scan_changed(wpa_s);
	}

	if (wpa_s->conf->ap_scan == 0) {
		wpa_supplicant_gen_assoc_event(wpa_s);
		return;
	}

#ifdef CONFIG_P2P
	if (wpas_p2p_in_progress(wpa_s) || wpas_wpa_is_in_progress(wpa_s, 0)) {
		if (wpa_s->sta_scan_pending &&
		    wpas_p2p_in_progress(wpa_s) == 2 &&
		    wpa_s->global->p2p_cb_on_scan_complete) {
			wpa_dbg(wpa_s, MSG_DEBUG, "Process pending station "
				"mode scan during P2P search");
		} else {
			wpa_dbg(wpa_s, MSG_DEBUG, "Delay station mode scan "
				"while P2P operation is in progress");
			wpa_s->sta_scan_pending = 1;
			wpa_supplicant_req_scan(wpa_s, 5, 0);
			return;
		}
	}
#endif /* CONFIG_P2P */

#ifdef CONFIG_GAS
	if (gas_query_in_progress(wpa_s->gas)) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Delay scan while GAS query is in progress");
		wpa_supplicant_req_scan(wpa_s, 1, 0);
		return;
	}
#endif /* CONFIG_GAS */

	if (wpa_s->conf->ap_scan == 2)
		max_ssids = 1;
	else {
		max_ssids = wpa_s->max_scan_ssids;
		if (max_ssids > WPAS_MAX_SCAN_SSIDS)
			max_ssids = WPAS_MAX_SCAN_SSIDS;
	}

	scan_req = wpa_s->scan_req;
	wpa_s->scan_req = NORMAL_SCAN_REQ;

	os_memset(&params, 0, sizeof(params));

	prev_state = wpa_s->wpa_state;
	if (wpa_s->wpa_state == WPA_DISCONNECTED ||
	    wpa_s->wpa_state == WPA_INACTIVE)
		wpa_supplicant_set_state(wpa_s, WPA_SCANNING);

	/*
	 * If autoscan has set its own scanning parameters
	 */
	if (wpa_s->autoscan_params != NULL) {
		scan_params = wpa_s->autoscan_params;
		goto scan;
	}

	if (scan_req != MANUAL_SCAN_REQ && wpa_s->connect_without_scan) {
		for (ssid = wpa_s->conf->ssid; ssid; ssid = ssid->next) {
			if (ssid == wpa_s->connect_without_scan)
				break;
		}
		wpa_s->connect_without_scan = NULL;
		if (ssid) {
			wpa_printf(MSG_DEBUG, "Start a pre-selected network "
				   "without scan step");
			wpa_supplicant_associate(wpa_s, NULL, ssid);
			return;
		}
	}

#ifdef CONFIG_P2P
	if ((wpa_s->p2p_in_provisioning || wpa_s->show_group_started) &&
	    wpa_s->go_params) {
		wpa_printf(MSG_DEBUG, "P2P: Use specific SSID for scan during P2P group formation (p2p_in_provisioning=%d show_group_started=%d)",
			   wpa_s->p2p_in_provisioning,
			   wpa_s->show_group_started);
		params.ssids[0].ssid = wpa_s->go_params->ssid;
		params.ssids[0].ssid_len = wpa_s->go_params->ssid_len;
		params.num_ssids = 1;
		goto ssid_list_set;
	}
#endif /* CONFIG_P2P */

	/* Find the starting point from which to continue scanning */
	ssid = wpa_s->conf->ssid;
	if (wpa_s->prev_scan_ssid != WILDCARD_SSID_SCAN) {
		while (ssid) {
			if (ssid == wpa_s->prev_scan_ssid) {
				ssid = ssid->next;
				break;
			}
			ssid = ssid->next;
		}
	}

	if (scan_req != MANUAL_SCAN_REQ && wpa_s->conf->ap_scan == 2) {
		wpa_s->connect_without_scan = NULL;
		wpa_s->prev_scan_wildcard = 0;
		wpa_supplicant_assoc_try(wpa_s, ssid);
		return;
#ifndef ANDROID
	} else if (wpa_s->conf->ap_scan == 2) {
		/*
		 * User-initiated scan request in ap_scan == 2; scan with
		 * wildcard SSID.
		 */
		ssid = NULL;
#endif
	} else {
		struct wpa_ssid *start = ssid, *tssid;
		int freqs_set = 0;
		if (ssid == NULL && max_ssids > 1)
			ssid = wpa_s->conf->ssid;
		while (ssid) {
			if (!wpas_network_disabled(wpa_s, ssid) &&
			    ssid->scan_ssid) {
				wpa_hexdump_ascii(MSG_DEBUG, "Scan SSID",
						  ssid->ssid, ssid->ssid_len);
				params.ssids[params.num_ssids].ssid =
					ssid->ssid;
				params.ssids[params.num_ssids].ssid_len =
					ssid->ssid_len;
				params.num_ssids++;
				if (params.num_ssids + 1 >= max_ssids)
					break;
			}
			ssid = ssid->next;
			if (ssid == start)
				break;
			if (ssid == NULL && max_ssids > 1 &&
			    start != wpa_s->conf->ssid)
				ssid = wpa_s->conf->ssid;
		}

		for (tssid = wpa_s->conf->ssid; tssid; tssid = tssid->next) {
			if (wpas_network_disabled(wpa_s, tssid))
				continue;
			if ((params.freqs || !freqs_set) && tssid->scan_freq) {
				int_array_concat(&params.freqs,
						 tssid->scan_freq);
			} else {
				os_free(params.freqs);
				params.freqs = NULL;
			}
			freqs_set = 1;
		}
		int_array_sort_unique(params.freqs);
	}

	if (ssid && max_ssids == 1) {
		/*
		 * If the driver is limited to 1 SSID at a time interleave
		 * wildcard SSID scans with specific SSID scans to avoid
		 * waiting a long time for a wildcard scan.
		 */
		if (!wpa_s->prev_scan_wildcard) {
			params.ssids[0].ssid = NULL;
			params.ssids[0].ssid_len = 0;
			wpa_s->prev_scan_wildcard = 1;
			wpa_dbg(wpa_s, MSG_DEBUG, "Starting AP scan for "
				"wildcard SSID (Interleave with specific)");
		} else {
			wpa_s->prev_scan_ssid = ssid;
			wpa_s->prev_scan_wildcard = 0;
			wpa_dbg(wpa_s, MSG_DEBUG,
				"Starting AP scan for specific SSID: %s",
				wpa_ssid_txt(ssid->ssid, ssid->ssid_len));
		}
	} else if (ssid) {
		/* max_ssids > 1 */

		wpa_s->prev_scan_ssid = ssid;
		wpa_dbg(wpa_s, MSG_DEBUG, "Include wildcard SSID in "
			"the scan request");
		params.num_ssids++;
	} else {
		wpa_s->prev_scan_ssid = WILDCARD_SSID_SCAN;
		params.num_ssids++;
		wpa_dbg(wpa_s, MSG_DEBUG, "Starting AP scan for wildcard "
			"SSID");
	}
#ifdef CONFIG_P2P
ssid_list_set:
#endif /* CONFIG_P2P */

	wpa_supplicant_optimize_freqs(wpa_s, &params);
	extra_ie = wpa_supplicant_extra_ies(wpa_s);

	if (params.freqs == NULL && wpa_s->next_scan_freqs) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Optimize scan based on previously "
			"generated frequency list");
		params.freqs = wpa_s->next_scan_freqs;
	} else
		os_free(wpa_s->next_scan_freqs);
	wpa_s->next_scan_freqs = NULL;
	wpa_setband_scan_freqs(wpa_s, &params);

	/* See if user specified frequencies. If so, scan only those. */
	if (wpa_s->conf->freq_list && !params.freqs) {
		wpa_dbg(wpa_s, MSG_DEBUG,
			"Optimize scan based on conf->freq_list");
		int_array_concat(&params.freqs, wpa_s->conf->freq_list);
	}

	/* Use current associated channel? */
	if (wpa_s->conf->scan_cur_freq && !params.freqs) {
		unsigned int num = wpa_s->num_multichan_concurrent;

		params.freqs = os_calloc(num + 1, sizeof(int));
		if (params.freqs) {
			num = get_shared_radio_freqs(wpa_s, params.freqs, num);
			if (num > 0) {
				wpa_dbg(wpa_s, MSG_DEBUG, "Scan only the "
					"current operating channels since "
					"scan_cur_freq is enabled");
			} else {
				os_free(params.freqs);
				params.freqs = NULL;
			}
		}
	}

	params.filter_ssids = wpa_supplicant_build_filter_ssids(
		wpa_s->conf, &params.num_filter_ssids);
	if (extra_ie) {
		params.extra_ies = wpabuf_head(extra_ie);
		params.extra_ies_len = wpabuf_len(extra_ie);
	}

#ifdef CONFIG_P2P
	if (wpa_s->p2p_in_provisioning ||
	    (wpa_s->show_group_started && wpa_s->go_params)) {
		/*
		 * The interface may not yet be in P2P mode, so we have to
		 * explicitly request P2P probe to disable CCK rates.
		 */
		params.p2p_probe = 1;
	}
#endif /* CONFIG_P2P */

	scan_params = &params;

scan:
#ifdef CONFIG_P2P
	/*
	 * If the driver does not support multi-channel concurrency and a
	 * virtual interface that shares the same radio with the wpa_s interface
	 * is operating there may not be need to scan other channels apart from
	 * the current operating channel on the other virtual interface. Filter
	 * out other channels in case we are trying to find a connection for a
	 * station interface when we are not configured to prefer station
	 * connection and a concurrent operation is already in process.
	 */
	if (wpa_s->scan_for_connection && scan_req == NORMAL_SCAN_REQ &&
	    !scan_params->freqs && !params.freqs &&
	    wpas_is_p2p_prioritized(wpa_s) &&
	    wpa_s->p2p_group_interface == NOT_P2P_GROUP_INTERFACE &&
	    non_p2p_network_enabled(wpa_s)) {
		unsigned int num = wpa_s->num_multichan_concurrent;

		params.freqs = os_calloc(num + 1, sizeof(int));
		if (params.freqs) {
			num = get_shared_radio_freqs(wpa_s, params.freqs, num);
			if (num > 0 && num == wpa_s->num_multichan_concurrent) {
				wpa_dbg(wpa_s, MSG_DEBUG, "Scan only the current operating channels since all channels are already used");
			} else {
				os_free(params.freqs);
				params.freqs = NULL;
			}
		}
	}
#endif /* CONFIG_P2P */

	ret = wpa_supplicant_trigger_scan(wpa_s, scan_params);

	wpabuf_free(extra_ie);
	os_free(params.freqs);
	os_free(params.filter_ssids);

	if (ret) {
		wpa_msg(wpa_s, MSG_WARNING, "Failed to initiate AP scan");
		if (prev_state != wpa_s->wpa_state)
			wpa_supplicant_set_state(wpa_s, prev_state);
		/* Restore scan_req since we will try to scan again */
		wpa_s->scan_req = scan_req;
		wpa_supplicant_req_scan(wpa_s, 1, 0);
	} else {
		wpa_s->scan_for_connection = 0;
	}
}


void wpa_supplicant_update_scan_int(struct wpa_supplicant *wpa_s, int sec)
{
	struct os_time remaining, new_int;
	int cancelled;

	cancelled = eloop_cancel_timeout_one(wpa_supplicant_scan, wpa_s, NULL,
					     &remaining);

	new_int.sec = sec;
	new_int.usec = 0;
	if (cancelled && os_time_before(&remaining, &new_int)) {
		new_int.sec = remaining.sec;
		new_int.usec = remaining.usec;
	}

	if (cancelled) {
		eloop_register_timeout(new_int.sec, new_int.usec,
				       wpa_supplicant_scan, wpa_s, NULL);
	}
	wpa_s->scan_interval = sec;
}


/**
 * wpa_supplicant_req_scan - Schedule a scan for neighboring access points
 * @wpa_s: Pointer to wpa_supplicant data
 * @sec: Number of seconds after which to scan
 * @usec: Number of microseconds after which to scan
 *
 * This function is used to schedule a scan for neighboring access points after
 * the specified time.
 */
void wpa_supplicant_req_scan(struct wpa_supplicant *wpa_s, int sec, int usec)
{
#ifndef ANDROID
	/* If there's at least one network that should be specifically scanned
	 * then don't cancel the scan and reschedule.  Some drivers do
	 * background scanning which generates frequent scan results, and that
	 * causes the specific SSID scan to get continually pushed back and
	 * never happen, which causes hidden APs to never get probe-scanned.
	 */
	if (eloop_is_timeout_registered(wpa_supplicant_scan, wpa_s, NULL) &&
	    wpa_s->conf->ap_scan == 1) {
		struct wpa_ssid *ssid = wpa_s->conf->ssid;

		while (ssid) {
			if (!wpas_network_disabled(wpa_s, ssid) &&
			    ssid->scan_ssid)
				break;
			ssid = ssid->next;
		}
		if (ssid) {
			wpa_dbg(wpa_s, MSG_DEBUG, "Not rescheduling scan to "
			        "ensure that specific SSID scans occur");
			return;
		}
	}
#endif
	wpa_dbg(wpa_s, MSG_DEBUG, "Setting scan request: %d sec %d usec",
		sec, usec);
	eloop_cancel_timeout(wpa_supplicant_scan, wpa_s, NULL);
	eloop_register_timeout(sec, usec, wpa_supplicant_scan, wpa_s, NULL);
}


/**
 * wpa_supplicant_delayed_sched_scan - Request a delayed scheduled scan
 * @wpa_s: Pointer to wpa_supplicant data
 * @sec: Number of seconds after which to scan
 * @usec: Number of microseconds after which to scan
 * Returns: 0 on success or -1 otherwise
 *
 * This function is used to schedule periodic scans for neighboring
 * access points after the specified time.
 */
int wpa_supplicant_delayed_sched_scan(struct wpa_supplicant *wpa_s,
				      int sec, int usec)
{
	if (!wpa_s->sched_scan_supported)
		return -1;

	eloop_register_timeout(sec, usec,
			       wpa_supplicant_delayed_sched_scan_timeout,
			       wpa_s, NULL);

	return 0;
}


/**
 * wpa_supplicant_req_sched_scan - Start a periodic scheduled scan
 * @wpa_s: Pointer to wpa_supplicant data
 * Returns: 0 is sched_scan was started or -1 otherwise
 *
 * This function is used to schedule periodic scans for neighboring
 * access points repeating the scan continuously.
 */
int wpa_supplicant_req_sched_scan(struct wpa_supplicant *wpa_s)
{
	struct wpa_driver_scan_params params;
	struct wpa_driver_scan_params *scan_params;
	enum wpa_states prev_state;
	struct wpa_ssid *ssid = NULL;
	struct wpabuf *extra_ie = NULL;
	int ret;
	unsigned int max_sched_scan_ssids;
	int wildcard = 0;
	int need_ssids;

	if (!wpa_s->sched_scan_supported)
		return -1;

	if (wpa_s->max_sched_scan_ssids > WPAS_MAX_SCAN_SSIDS)
		max_sched_scan_ssids = WPAS_MAX_SCAN_SSIDS;
	else
		max_sched_scan_ssids = wpa_s->max_sched_scan_ssids;
	if (max_sched_scan_ssids < 1 || wpa_s->conf->disable_scan_offload)
		return -1;

	if (wpa_s->sched_scanning) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Already sched scanning");
		return 0;
	}

	need_ssids = 0;
	for (ssid = wpa_s->conf->ssid; ssid; ssid = ssid->next) {
		if (!wpas_network_disabled(wpa_s, ssid) && !ssid->scan_ssid) {
			/* Use wildcard SSID to find this network */
			wildcard = 1;
		} else if (!wpas_network_disabled(wpa_s, ssid) &&
			   ssid->ssid_len)
			need_ssids++;

#ifdef CONFIG_WPS
		if (!wpas_network_disabled(wpa_s, ssid) &&
		    ssid->key_mgmt == WPA_KEY_MGMT_WPS) {
			/*
			 * Normal scan is more reliable and faster for WPS
			 * operations and since these are for short periods of
			 * time, the benefit of trying to use sched_scan would
			 * be limited.
			 */
			wpa_dbg(wpa_s, MSG_DEBUG, "Use normal scan instead of "
				"sched_scan for WPS");
			return -1;
		}
#endif /* CONFIG_WPS */
	}
	if (wildcard)
		need_ssids++;

	if (wpa_s->normal_scans < 3 &&
	    (need_ssids <= wpa_s->max_scan_ssids ||
	     wpa_s->max_scan_ssids >= (int) max_sched_scan_ssids)) {
		/*
		 * When normal scan can speed up operations, use that for the
		 * first operations before starting the sched_scan to allow
		 * user space sleep more. We do this only if the normal scan
		 * has functionality that is suitable for this or if the
		 * sched_scan does not have better support for multiple SSIDs.
		 */
		wpa_dbg(wpa_s, MSG_DEBUG, "Use normal scan instead of "
			"sched_scan for initial scans (normal_scans=%d)",
			wpa_s->normal_scans);
		return -1;
	}

	os_memset(&params, 0, sizeof(params));

	/* If we can't allocate space for the filters, we just don't filter */
	params.filter_ssids = os_zalloc(wpa_s->max_match_sets *
					sizeof(struct wpa_driver_scan_filter));

	prev_state = wpa_s->wpa_state;
	if (wpa_s->wpa_state == WPA_DISCONNECTED ||
	    wpa_s->wpa_state == WPA_INACTIVE)
		wpa_supplicant_set_state(wpa_s, WPA_SCANNING);

	if (wpa_s->autoscan_params != NULL) {
		scan_params = wpa_s->autoscan_params;
		goto scan;
	}

	/* Find the starting point from which to continue scanning */
	ssid = wpa_s->conf->ssid;
	if (wpa_s->prev_sched_ssid) {
		while (ssid) {
			if (ssid == wpa_s->prev_sched_ssid) {
				ssid = ssid->next;
				break;
			}
			ssid = ssid->next;
		}
	}

	if (!ssid || !wpa_s->prev_sched_ssid) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Beginning of SSID list");
		if (wpa_s->conf->sched_scan_interval)
			wpa_s->sched_scan_interval =
				wpa_s->conf->sched_scan_interval;
		if (wpa_s->sched_scan_interval == 0)
			wpa_s->sched_scan_interval = 10;
		wpa_s->sched_scan_timeout = max_sched_scan_ssids * 2;
		wpa_s->first_sched_scan = 1;
		ssid = wpa_s->conf->ssid;
		wpa_s->prev_sched_ssid = ssid;
	}

	if (wildcard) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Add wildcard SSID to sched_scan");
		params.num_ssids++;
	}

	while (ssid) {
		if (wpas_network_disabled(wpa_s, ssid))
			goto next;

		if (params.num_filter_ssids < wpa_s->max_match_sets &&
		    params.filter_ssids && ssid->ssid && ssid->ssid_len) {
			wpa_dbg(wpa_s, MSG_DEBUG, "add to filter ssid: %s",
				wpa_ssid_txt(ssid->ssid, ssid->ssid_len));
			os_memcpy(params.filter_ssids[params.num_filter_ssids].ssid,
				  ssid->ssid, ssid->ssid_len);
			params.filter_ssids[params.num_filter_ssids].ssid_len =
				ssid->ssid_len;
			params.num_filter_ssids++;
		} else if (params.filter_ssids && ssid->ssid && ssid->ssid_len)
		{
			wpa_dbg(wpa_s, MSG_DEBUG, "Not enough room for SSID "
				"filter for sched_scan - drop filter");
			os_free(params.filter_ssids);
			params.filter_ssids = NULL;
			params.num_filter_ssids = 0;
		}

		if (ssid->scan_ssid && ssid->ssid && ssid->ssid_len) {
			if (params.num_ssids == max_sched_scan_ssids)
				break; /* only room for broadcast SSID */
			wpa_dbg(wpa_s, MSG_DEBUG,
				"add to active scan ssid: %s",
				wpa_ssid_txt(ssid->ssid, ssid->ssid_len));
			params.ssids[params.num_ssids].ssid =
				ssid->ssid;
			params.ssids[params.num_ssids].ssid_len =
				ssid->ssid_len;
			params.num_ssids++;
			if (params.num_ssids >= max_sched_scan_ssids) {
				wpa_s->prev_sched_ssid = ssid;
				do {
					ssid = ssid->next;
				} while (ssid &&
					 (wpas_network_disabled(wpa_s, ssid) ||
					  !ssid->scan_ssid));
				break;
			}
		}

	next:
		wpa_s->prev_sched_ssid = ssid;
		ssid = ssid->next;
	}

	if (params.num_filter_ssids == 0) {
		os_free(params.filter_ssids);
		params.filter_ssids = NULL;
	}

	extra_ie = wpa_supplicant_extra_ies(wpa_s);
	if (extra_ie) {
		params.extra_ies = wpabuf_head(extra_ie);
		params.extra_ies_len = wpabuf_len(extra_ie);
	}

	scan_params = &params;

scan:
	if (ssid || !wpa_s->first_sched_scan) {
		wpa_dbg(wpa_s, MSG_DEBUG,
			"Starting sched scan: interval %d timeout %d",
			wpa_s->sched_scan_interval, wpa_s->sched_scan_timeout);
	} else {
		wpa_dbg(wpa_s, MSG_DEBUG,
			"Starting sched scan: interval %d (no timeout)",
			wpa_s->sched_scan_interval);
	}

	wpa_setband_scan_freqs(wpa_s, scan_params);

	ret = wpa_supplicant_start_sched_scan(wpa_s, scan_params,
					      wpa_s->sched_scan_interval);
	wpabuf_free(extra_ie);
	os_free(params.filter_ssids);
	if (ret) {
		wpa_msg(wpa_s, MSG_WARNING, "Failed to initiate sched scan");
		if (prev_state != wpa_s->wpa_state)
			wpa_supplicant_set_state(wpa_s, prev_state);
		return ret;
	}

	/* If we have more SSIDs to scan, add a timeout so we scan them too */
	if (ssid || !wpa_s->first_sched_scan) {
		wpa_s->sched_scan_timed_out = 0;
		eloop_register_timeout(wpa_s->sched_scan_timeout, 0,
				       wpa_supplicant_sched_scan_timeout,
				       wpa_s, NULL);
		wpa_s->first_sched_scan = 0;
		wpa_s->sched_scan_timeout /= 2;
		wpa_s->sched_scan_interval *= 2;
		if (wpa_s->sched_scan_timeout < wpa_s->sched_scan_interval) {
			wpa_s->sched_scan_interval = 10;
			wpa_s->sched_scan_timeout = max_sched_scan_ssids * 2;
		}
	}

	/* If there is no more ssids, start next time from the beginning */
	if (!ssid)
		wpa_s->prev_sched_ssid = NULL;

	return 0;
}


/**
 * wpa_supplicant_cancel_scan - Cancel a scheduled scan request
 * @wpa_s: Pointer to wpa_supplicant data
 *
 * This function is used to cancel a scan request scheduled with
 * wpa_supplicant_req_scan().
 */
void wpa_supplicant_cancel_scan(struct wpa_supplicant *wpa_s)
{
	wpa_dbg(wpa_s, MSG_DEBUG, "Cancelling scan request");
	eloop_cancel_timeout(wpa_supplicant_scan, wpa_s, NULL);
	wpas_p2p_continue_after_scan(wpa_s);
#ifdef ANDROID
	wpa_supplicant_notify_scanning(wpa_s, 0);
#endif
}


/**
 * wpa_supplicant_cancel_delayed_sched_scan - Stop a delayed scheduled scan
 * @wpa_s: Pointer to wpa_supplicant data
 *
 * This function is used to stop a delayed scheduled scan.
 */
void wpa_supplicant_cancel_delayed_sched_scan(struct wpa_supplicant *wpa_s)
{
	if (!wpa_s->sched_scan_supported)
		return;

	wpa_dbg(wpa_s, MSG_DEBUG, "Cancelling delayed sched scan");
	eloop_cancel_timeout(wpa_supplicant_delayed_sched_scan_timeout,
			     wpa_s, NULL);
}


/**
 * wpa_supplicant_cancel_sched_scan - Stop running scheduled scans
 * @wpa_s: Pointer to wpa_supplicant data
 *
 * This function is used to stop a periodic scheduled scan.
 */
void wpa_supplicant_cancel_sched_scan(struct wpa_supplicant *wpa_s)
{
	if (!wpa_s->sched_scanning)
		return;

	wpa_dbg(wpa_s, MSG_DEBUG, "Cancelling sched scan");
	eloop_cancel_timeout(wpa_supplicant_sched_scan_timeout, wpa_s, NULL);
	wpa_supplicant_stop_sched_scan(wpa_s);
}


/**
 * wpa_supplicant_notify_scanning - Indicate possible scan state change
 * @wpa_s: Pointer to wpa_supplicant data
 * @scanning: Whether scanning is currently in progress
 *
 * This function is to generate scanning notifycations. It is called whenever
 * there may have been a change in scanning (scan started, completed, stopped).
 * wpas_notify_scanning() is called whenever the scanning state changed from the
 * previously notified state.
 */
void wpa_supplicant_notify_scanning(struct wpa_supplicant *wpa_s,
				    int scanning)
{
	if (wpa_s->scanning != scanning) {
		wpa_s->scanning = scanning;
		wpas_notify_scanning(wpa_s);
	}
}


static int wpa_scan_get_max_rate(const struct wpa_scan_res *res)
{
	int rate = 0;
	const u8 *ie;
	int i;

	ie = wpa_scan_get_ie(res, WLAN_EID_SUPP_RATES);
	for (i = 0; ie && i < ie[1]; i++) {
		if ((ie[i + 2] & 0x7f) > rate)
			rate = ie[i + 2] & 0x7f;
	}

	ie = wpa_scan_get_ie(res, WLAN_EID_EXT_SUPP_RATES);
	for (i = 0; ie && i < ie[1]; i++) {
		if ((ie[i + 2] & 0x7f) > rate)
			rate = ie[i + 2] & 0x7f;
	}

	return rate;
}


/**
 * wpa_scan_get_ie - Fetch a specified information element from a scan result
 * @res: Scan result entry
 * @ie: Information element identitifier (WLAN_EID_*)
 * Returns: Pointer to the information element (id field) or %NULL if not found
 *
 * This function returns the first matching information element in the scan
 * result.
 */
const u8 * wpa_scan_get_ie(const struct wpa_scan_res *res, u8 ie)
{
	const u8 *end, *pos;

	pos = (const u8 *) (res + 1);
	end = pos + res->ie_len;

	while (pos + 1 < end) {
		if (pos + 2 + pos[1] > end)
			break;
		if (pos[0] == ie)
			return pos;
		pos += 2 + pos[1];
	}

	return NULL;
}


/**
 * wpa_scan_get_vendor_ie - Fetch vendor information element from a scan result
 * @res: Scan result entry
 * @vendor_type: Vendor type (four octets starting the IE payload)
 * Returns: Pointer to the information element (id field) or %NULL if not found
 *
 * This function returns the first matching information element in the scan
 * result.
 */
const u8 * wpa_scan_get_vendor_ie(const struct wpa_scan_res *res,
				  u32 vendor_type)
{
	const u8 *end, *pos;

	pos = (const u8 *) (res + 1);
	end = pos + res->ie_len;

	while (pos + 1 < end) {
		if (pos + 2 + pos[1] > end)
			break;
		if (pos[0] == WLAN_EID_VENDOR_SPECIFIC && pos[1] >= 4 &&
		    vendor_type == WPA_GET_BE32(&pos[2]))
			return pos;
		pos += 2 + pos[1];
	}

	return NULL;
}


/**
 * wpa_scan_get_vendor_ie_beacon - Fetch vendor information from a scan result
 * @res: Scan result entry
 * @vendor_type: Vendor type (four octets starting the IE payload)
 * Returns: Pointer to the information element (id field) or %NULL if not found
 *
 * This function returns the first matching information element in the scan
 * result.
 *
 * This function is like wpa_scan_get_vendor_ie(), but uses IE buffer only
 * from Beacon frames instead of either Beacon or Probe Response frames.
 */
const u8 * wpa_scan_get_vendor_ie_beacon(const struct wpa_scan_res *res,
					 u32 vendor_type)
{
	const u8 *end, *pos;

	if (res->beacon_ie_len == 0)
		return NULL;

	pos = (const u8 *) (res + 1);
	pos += res->ie_len;
	end = pos + res->beacon_ie_len;

	while (pos + 1 < end) {
		if (pos + 2 + pos[1] > end)
			break;
		if (pos[0] == WLAN_EID_VENDOR_SPECIFIC && pos[1] >= 4 &&
		    vendor_type == WPA_GET_BE32(&pos[2]))
			return pos;
		pos += 2 + pos[1];
	}

	return NULL;
}


/**
 * wpa_scan_get_vendor_ie_multi - Fetch vendor IE data from a scan result
 * @res: Scan result entry
 * @vendor_type: Vendor type (four octets starting the IE payload)
 * Returns: Pointer to the information element payload or %NULL if not found
 *
 * This function returns concatenated payload of possibly fragmented vendor
 * specific information elements in the scan result. The caller is responsible
 * for freeing the returned buffer.
 */
struct wpabuf * wpa_scan_get_vendor_ie_multi(const struct wpa_scan_res *res,
					     u32 vendor_type)
{
	struct wpabuf *buf;
	const u8 *end, *pos;

	buf = wpabuf_alloc(res->ie_len);
	if (buf == NULL)
		return NULL;

	pos = (const u8 *) (res + 1);
	end = pos + res->ie_len;

	while (pos + 1 < end) {
		if (pos + 2 + pos[1] > end)
			break;
		if (pos[0] == WLAN_EID_VENDOR_SPECIFIC && pos[1] >= 4 &&
		    vendor_type == WPA_GET_BE32(&pos[2]))
			wpabuf_put_data(buf, pos + 2 + 4, pos[1] - 4);
		pos += 2 + pos[1];
	}

	if (wpabuf_len(buf) == 0) {
		wpabuf_free(buf);
		buf = NULL;
	}

	return buf;
}


/*
 * Channels with a great SNR can operate at full rate. What is a great SNR?
 * This doc https://supportforums.cisco.com/docs/DOC-12954 says, "the general
 * rule of thumb is that any SNR above 20 is good." This one
 * http://www.cisco.com/en/US/tech/tk722/tk809/technologies_q_and_a_item09186a00805e9a96.shtml#qa23
 * recommends 25 as a minimum SNR for 54 Mbps data rate. 30 is chosen here as a
 * conservative value.
 */
#define GREAT_SNR 30

/* Compare function for sorting scan results. Return >0 if @b is considered
 * better. */
static int wpa_scan_result_compar(const void *a, const void *b)
{
#define IS_5GHZ(n) (n > 4000)
#define MIN(a,b) a < b ? a : b
	struct wpa_scan_res **_wa = (void *) a;
	struct wpa_scan_res **_wb = (void *) b;
	struct wpa_scan_res *wa = *_wa;
	struct wpa_scan_res *wb = *_wb;
	int wpa_a, wpa_b, maxrate_a, maxrate_b;
	int snr_a, snr_b;

	/* WPA/WPA2 support preferred */
	wpa_a = wpa_scan_get_vendor_ie(wa, WPA_IE_VENDOR_TYPE) != NULL ||
		wpa_scan_get_ie(wa, WLAN_EID_RSN) != NULL;
	wpa_b = wpa_scan_get_vendor_ie(wb, WPA_IE_VENDOR_TYPE) != NULL ||
		wpa_scan_get_ie(wb, WLAN_EID_RSN) != NULL;

	if (wpa_b && !wpa_a)
		return 1;
	if (!wpa_b && wpa_a)
		return -1;

	/* privacy support preferred */
	if ((wa->caps & IEEE80211_CAP_PRIVACY) == 0 &&
	    (wb->caps & IEEE80211_CAP_PRIVACY))
		return 1;
	if ((wa->caps & IEEE80211_CAP_PRIVACY) &&
	    (wb->caps & IEEE80211_CAP_PRIVACY) == 0)
		return -1;

	if ((wa->flags & wb->flags & WPA_SCAN_LEVEL_DBM) &&
	    !((wa->flags | wb->flags) & WPA_SCAN_NOISE_INVALID)) {
		snr_a = MIN(wa->level - wa->noise, GREAT_SNR);
		snr_b = MIN(wb->level - wb->noise, GREAT_SNR);
	} else {
		/* Not suitable information to calculate SNR, so use level */
		snr_a = wa->level;
		snr_b = wb->level;
	}

	/* best/max rate preferred if SNR close enough */
        if ((snr_a && snr_b && abs(snr_b - snr_a) < 5) ||
	    (wa->qual && wb->qual && abs(wb->qual - wa->qual) < 10)) {
		maxrate_a = wpa_scan_get_max_rate(wa);
		maxrate_b = wpa_scan_get_max_rate(wb);
		if (maxrate_a != maxrate_b)
			return maxrate_b - maxrate_a;
		if (IS_5GHZ(wa->freq) ^ IS_5GHZ(wb->freq))
			return IS_5GHZ(wa->freq) ? -1 : 1;
	}

	/* use freq for channel preference */

	/* all things being equal, use SNR; if SNRs are
	 * identical, use quality values since some drivers may only report
	 * that value and leave the signal level zero */
	if (snr_b == snr_a)
		return wb->qual - wa->qual;
	return snr_b - snr_a;
#undef MIN
#undef IS_5GHZ
}


#ifdef CONFIG_WPS
/* Compare function for sorting scan results when searching a WPS AP for
 * provisioning. Return >0 if @b is considered better. */
static int wpa_scan_result_wps_compar(const void *a, const void *b)
{
	struct wpa_scan_res **_wa = (void *) a;
	struct wpa_scan_res **_wb = (void *) b;
	struct wpa_scan_res *wa = *_wa;
	struct wpa_scan_res *wb = *_wb;
	int uses_wps_a, uses_wps_b;
	struct wpabuf *wps_a, *wps_b;
	int res;

	/* Optimization - check WPS IE existence before allocated memory and
	 * doing full reassembly. */
	uses_wps_a = wpa_scan_get_vendor_ie(wa, WPS_IE_VENDOR_TYPE) != NULL;
	uses_wps_b = wpa_scan_get_vendor_ie(wb, WPS_IE_VENDOR_TYPE) != NULL;
	if (uses_wps_a && !uses_wps_b)
		return -1;
	if (!uses_wps_a && uses_wps_b)
		return 1;

	if (uses_wps_a && uses_wps_b) {
		wps_a = wpa_scan_get_vendor_ie_multi(wa, WPS_IE_VENDOR_TYPE);
		wps_b = wpa_scan_get_vendor_ie_multi(wb, WPS_IE_VENDOR_TYPE);
		res = wps_ap_priority_compar(wps_a, wps_b);
		wpabuf_free(wps_a);
		wpabuf_free(wps_b);
		if (res)
			return res;
	}

	/*
	 * Do not use current AP security policy as a sorting criteria during
	 * WPS provisioning step since the AP may get reconfigured at the
	 * completion of provisioning.
	 */

	/* all things being equal, use signal level; if signal levels are
	 * identical, use quality values since some drivers may only report
	 * that value and leave the signal level zero */
	if (wb->level == wa->level)
		return wb->qual - wa->qual;
	return wb->level - wa->level;
}
#endif /* CONFIG_WPS */


static void dump_scan_res(struct wpa_scan_results *scan_res)
{
#ifndef CONFIG_NO_STDOUT_DEBUG
	size_t i;

	if (scan_res->res == NULL || scan_res->num == 0)
		return;

	wpa_printf(MSG_EXCESSIVE, "Sorted scan results");

	for (i = 0; i < scan_res->num; i++) {
		struct wpa_scan_res *r = scan_res->res[i];
		u8 *pos;
		if ((r->flags & (WPA_SCAN_LEVEL_DBM | WPA_SCAN_NOISE_INVALID))
		    == WPA_SCAN_LEVEL_DBM) {
			int snr = r->level - r->noise;
			wpa_printf(MSG_EXCESSIVE, MACSTR " freq=%d qual=%d "
				   "noise=%d level=%d snr=%d%s flags=0x%x "
				   "age=%u",
				   MAC2STR(r->bssid), r->freq, r->qual,
				   r->noise, r->level, snr,
				   snr >= GREAT_SNR ? "*" : "", r->flags,
				   r->age);
		} else {
			wpa_printf(MSG_EXCESSIVE, MACSTR " freq=%d qual=%d "
				   "noise=%d level=%d flags=0x%x age=%u",
				   MAC2STR(r->bssid), r->freq, r->qual,
				   r->noise, r->level, r->flags, r->age);
		}
		pos = (u8 *) (r + 1);
		if (r->ie_len)
			wpa_hexdump(MSG_EXCESSIVE, "IEs", pos, r->ie_len);
		pos += r->ie_len;
		if (r->beacon_ie_len)
			wpa_hexdump(MSG_EXCESSIVE, "Beacon IEs",
				    pos, r->beacon_ie_len);
	}
#endif /* CONFIG_NO_STDOUT_DEBUG */
}


/**
 * wpa_supplicant_filter_bssid_match - Is the specified BSSID allowed
 * @wpa_s: Pointer to wpa_supplicant data
 * @bssid: BSSID to check
 * Returns: 0 if the BSSID is filtered or 1 if not
 *
 * This function is used to filter out specific BSSIDs from scan reslts mainly
 * for testing purposes (SET bssid_filter ctrl_iface command).
 */
int wpa_supplicant_filter_bssid_match(struct wpa_supplicant *wpa_s,
				      const u8 *bssid)
{
	size_t i;

	if (wpa_s->bssid_filter == NULL)
		return 1;

	for (i = 0; i < wpa_s->bssid_filter_count; i++) {
		if (os_memcmp(wpa_s->bssid_filter + i * ETH_ALEN, bssid,
			      ETH_ALEN) == 0)
			return 1;
	}

	return 0;
}


static void filter_scan_res(struct wpa_supplicant *wpa_s,
			    struct wpa_scan_results *res)
{
	size_t i, j;

	if (wpa_s->bssid_filter == NULL)
		return;

	for (i = 0, j = 0; i < res->num; i++) {
		if (wpa_supplicant_filter_bssid_match(wpa_s,
						      res->res[i]->bssid)) {
			res->res[j++] = res->res[i];
		} else {
			os_free(res->res[i]);
			res->res[i] = NULL;
		}
	}

	if (res->num != j) {
		wpa_printf(MSG_DEBUG, "Filtered out %d scan results",
			   (int) (res->num - j));
		res->num = j;
	}
}


/**
 * wpa_supplicant_get_scan_results - Get scan results
 * @wpa_s: Pointer to wpa_supplicant data
 * @info: Information about what was scanned or %NULL if not available
 * @new_scan: Whether a new scan was performed
 * Returns: Scan results, %NULL on failure
 *
 * This function request the current scan results from the driver and updates
 * the local BSS list wpa_s->bss. The caller is responsible for freeing the
 * results with wpa_scan_results_free().
 */
struct wpa_scan_results *
wpa_supplicant_get_scan_results(struct wpa_supplicant *wpa_s,
				struct scan_info *info, int new_scan)
{
	struct wpa_scan_results *scan_res;
	size_t i;
	int (*compar)(const void *, const void *) = wpa_scan_result_compar;

	scan_res = wpa_drv_get_scan_results2(wpa_s);
	if (scan_res == NULL) {
		wpa_dbg(wpa_s, MSG_DEBUG, "Failed to get scan results");
		return NULL;
	}
	if (scan_res->fetch_time.sec == 0) {
		/*
		 * Make sure we have a valid timestamp if the driver wrapper
		 * does not set this.
		 */
		os_get_time(&scan_res->fetch_time);
	}
	filter_scan_res(wpa_s, scan_res);

#ifdef CONFIG_WPS
	if (wpas_wps_in_progress(wpa_s)) {
		wpa_dbg(wpa_s, MSG_DEBUG, "WPS: Order scan results with WPS "
			"provisioning rules");
		compar = wpa_scan_result_wps_compar;
	}
#endif /* CONFIG_WPS */

	qsort(scan_res->res, scan_res->num, sizeof(struct wpa_scan_res *),
	      compar);
	dump_scan_res(scan_res);

	wpa_bss_update_start(wpa_s);
	for (i = 0; i < scan_res->num; i++)
		wpa_bss_update_scan_res(wpa_s, scan_res->res[i],
					&scan_res->fetch_time);
	wpa_bss_update_end(wpa_s, info, new_scan);

	return scan_res;
}


/**
 * wpa_supplicant_update_scan_results - Update scan results from the driver
 * @wpa_s: Pointer to wpa_supplicant data
 * Returns: 0 on success, -1 on failure
 *
 * This function updates the BSS table within wpa_supplicant based on the
 * currently available scan results from the driver without requesting a new
 * scan. This is used in cases where the driver indicates an association
 * (including roaming within ESS) and wpa_supplicant does not yet have the
 * needed information to complete the connection (e.g., to perform validation
 * steps in 4-way handshake).
 */
int wpa_supplicant_update_scan_results(struct wpa_supplicant *wpa_s)
{
	struct wpa_scan_results *scan_res;
	scan_res = wpa_supplicant_get_scan_results(wpa_s, NULL, 0);
	if (scan_res == NULL)
		return -1;
	wpa_scan_results_free(scan_res);

	return 0;
}


/**
 * scan_only_handler - Reports scan results
 */
void scan_only_handler(struct wpa_supplicant *wpa_s,
		       struct wpa_scan_results *scan_res)
{
	wpa_dbg(wpa_s, MSG_DEBUG, "Scan-only results received");
	wpa_msg_ctrl(wpa_s, MSG_INFO, WPA_EVENT_SCAN_RESULTS);
	wpas_notify_scan_results(wpa_s);
	wpas_notify_scan_done(wpa_s, 1);
}


int wpas_scan_scheduled(struct wpa_supplicant *wpa_s)
{
	return eloop_is_timeout_registered(wpa_supplicant_scan, wpa_s, NULL);
}