bgscan_simple.c

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/*
 * WPA Supplicant - background scan and roaming module: simple
 * Copyright (c) 2009-2010, Jouni Malinen <j@w1.fi>
 *
 * 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.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 */

#include "includes.h"

#include "common.h"
#include "eloop.h"
#include "drivers/driver.h"
#include "config_ssid.h"
#include "wpa_supplicant_i.h"
#include "driver_i.h"
#include "scan.h"
#include "bgscan.h"

struct bgscan_simple_data {
        struct wpa_supplicant *wpa_s;
        const struct wpa_ssid *ssid;
        int scan_interval;
        int signal_threshold;
        int short_interval; /* use if signal < threshold */
        int long_interval; /* use if signal > threshold */
        struct os_time last_bgscan;
};


static void bgscan_simple_timeout(void *eloop_ctx, void *timeout_ctx)
{
        struct bgscan_simple_data *data = eloop_ctx;
        struct wpa_supplicant *wpa_s = data->wpa_s;
        struct wpa_driver_scan_params params;

        os_memset(&params, 0, sizeof(params));
        params.num_ssids = 1;
        params.ssids[0].ssid = data->ssid->ssid;
        params.ssids[0].ssid_len = data->ssid->ssid_len;
        params.freqs = data->ssid->scan_freq;

        /*
         * A more advanced bgscan module would learn about most like channels
         * over time and request scans only for some channels (probing others
         * every now and then) to reduce effect on the data connection.
         */

        wpa_printf(MSG_DEBUG, "bgscan simple: Request a background scan");
        if (wpa_supplicant_trigger_scan(wpa_s, &params)) {
                wpa_printf(MSG_DEBUG, "bgscan simple: Failed to trigger scan");
                eloop_register_timeout(data->scan_interval, 0,
                                       bgscan_simple_timeout, data, NULL);
        } else
                os_get_time(&data->last_bgscan);
}


static int bgscan_simple_get_params(struct bgscan_simple_data *data,
                                    const char *params)
{
        const char *pos;

        if (params == NULL)
                return 0;

        data->short_interval = atoi(params);

        pos = os_strchr(params, ':');
        if (pos == NULL)
                return 0;
        pos++;
        data->signal_threshold = atoi(pos);
        pos = os_strchr(pos, ':');
        if (pos == NULL) {
                wpa_printf(MSG_ERROR, "bgscan simple: Missing scan interval "
                           "for high signal");
                return -1;
        }
        pos++;
        data->long_interval = atoi(pos);

        return 0;
}


static void * bgscan_simple_init(struct wpa_supplicant *wpa_s,
                                 const char *params,
                                 const struct wpa_ssid *ssid)
{
        struct bgscan_simple_data *data;

        data = os_zalloc(sizeof(*data));
        if (data == NULL)
                return NULL;
        data->wpa_s = wpa_s;
        data->ssid = ssid;
        if (bgscan_simple_get_params(data, params) < 0) {
                os_free(data);
                return NULL;
        }
        if (data->short_interval <= 0)
                data->short_interval = 30;
        if (data->long_interval <= 0)
                data->long_interval = 30;

        wpa_printf(MSG_DEBUG, "bgscan simple: Signal strength threshold %d  "
                   "Short bgscan interval %d  Long bgscan interval %d",
                   data->signal_threshold, data->short_interval,
                   data->long_interval);

        if (data->signal_threshold &&
            wpa_drv_signal_monitor(wpa_s, data->signal_threshold, 4) < 0) {
                wpa_printf(MSG_ERROR, "bgscan simple: Failed to enable "
                           "signal strength monitoring");
        }

        data->scan_interval = data->short_interval;
        eloop_register_timeout(data->scan_interval, 0, bgscan_simple_timeout,
                               data, NULL);
        return data;
}


static void bgscan_simple_deinit(void *priv)
{
        struct bgscan_simple_data *data = priv;
        eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
        if (data->signal_threshold)
                wpa_drv_signal_monitor(data->wpa_s, 0, 0);
        os_free(data);
}


static int bgscan_simple_notify_scan(void *priv)
{
        struct bgscan_simple_data *data = priv;

        wpa_printf(MSG_DEBUG, "bgscan simple: scan result notification");

        eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
        eloop_register_timeout(data->scan_interval, 0, bgscan_simple_timeout,
                               data, NULL);

        /*
         * A more advanced bgscan could process scan results internally, select
         * the BSS and request roam if needed. This sample uses the existing
         * BSS/ESS selection routine. Change this to return 1 if selection is
         * done inside the bgscan module.
         */

        return 0;
}


static void bgscan_simple_notify_beacon_loss(void *priv)
{
        wpa_printf(MSG_DEBUG, "bgscan simple: beacon loss");
        /* TODO: speed up background scanning */
}


static void bgscan_simple_notify_signal_change(void *priv, int above)
{
        struct bgscan_simple_data *data = priv;

        if (data->short_interval == data->long_interval ||
            data->signal_threshold == 0)
                return;

        wpa_printf(MSG_DEBUG, "bgscan simple: signal level changed "
                   "(above=%d)", above);
        if (data->scan_interval == data->long_interval && !above) {
                wpa_printf(MSG_DEBUG, "bgscan simple: Trigger immediate scan "
                           "and start using short bgscan interval");
                data->scan_interval = data->short_interval;
                eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
                eloop_register_timeout(0, 0, bgscan_simple_timeout, data,
                                       NULL);
        } else if (data->scan_interval == data->short_interval && above) {
                wpa_printf(MSG_DEBUG, "bgscan simple: Start using long bgscan "
                           "interval");
                data->scan_interval = data->long_interval;
                eloop_cancel_timeout(bgscan_simple_timeout, data, NULL);
                eloop_register_timeout(data->scan_interval, 0,
                                       bgscan_simple_timeout, data, NULL);
        } else if (!above) {
                struct os_time now;
                /*
                 * Signal dropped further 4 dB. Request a new scan if we have
                 * not yet scanned in a while.
                 */
                os_get_time(&now);
                if (now.sec > data->last_bgscan.sec + 10) {
                        wpa_printf(MSG_DEBUG, "bgscan simple: Trigger "
                                   "immediate scan");
                        eloop_cancel_timeout(bgscan_simple_timeout, data,
                                             NULL);
                        eloop_register_timeout(0, 0, bgscan_simple_timeout,
                                               data, NULL);
                }
        }
}


const struct bgscan_ops bgscan_simple_ops = {
        .name = "simple",
        .init = bgscan_simple_init,
        .deinit = bgscan_simple_deinit,
        .notify_scan = bgscan_simple_notify_scan,
        .notify_beacon_loss = bgscan_simple_notify_beacon_loss,
        .notify_signal_change = bgscan_simple_notify_signal_change,
};