Add preliminary background scan and roaming module design

This allows background scanning and roaming decisions to be contained in
a single place based on a defined set of notification events which will
hopefully make it easier to experiment with roaming improvements. In
addition, this allows multiple intra-ESS roaming policies to be used
(each network configuration block can configure its own bgscan module).

The beacon loss and signal strength notifications are implemented for
the bgscan API, but the actual events are not yet available from the
driver.

The included sample bgscan module ("simple") is an example of what can
be done with the new bgscan mechanism. It requests periodic background
scans when the device remains associated with an ESS and has couple of
notes on what a more advanced bgscan module could do to optimize
background scanning and roaming. The periodic scans will cause the scan
result handler to pick a better AP if one becomes available. This bgscan
module can be taken into use by adding bgscan="simple" (or
bgscan="simple:<bgscan interval in seconds>") into the network
configuration block.

wpa_supplicant/Makefile

@@ -1037,6 +1037,17 @@ OBJS_p += ../src/crypto/aes-internal-dec.o
 OBJS_p += ../src/crypto/aes-internal-enc.o
 endif
 
+ifdef CONFIG_BGSCAN_SIMPLE
+CFLAGS += -DCONFIG_BGSCAN_SIMPLE
+OBJS += bgscan_simple.o
+NEED_BGSCAN=y
+endif
+
+ifdef NEED_BGSCAN
+CFLAGS += -DCONFIG_BGSCAN
+OBJS += bgscan.o
+endif
+
 OBJS_wpa_rm := ctrl_iface.o mlme.o ctrl_iface_unix.o
 OBJS_wpa := $(filter-out $(OBJS_wpa_rm),$(OBJS)) $(OBJS_h) tests/test_wpa.o
 ifdef CONFIG_AUTHENTICATOR

wpa_supplicant/bgscan.c

@@ -0,0 +1,110 @@
+/*
+ * WPA Supplicant - background scan and roaming interface
+ * Copyright (c) 2009, 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 "wpa_supplicant_i.h"
+#include "config_ssid.h"
+#include "bgscan.h"
+
+#ifdef CONFIG_BGSCAN_SIMPLE
+extern const struct bgscan_ops bgscan_simple_ops;
+#endif /* CONFIG_BGSCAN_SIMPLE */
+
+static const struct bgscan_ops * bgscan_modules[] = {
+#ifdef CONFIG_BGSCAN_SIMPLE
+	&bgscan_simple_ops,
+#endif /* CONFIG_BGSCAN_SIMPLE */
+	NULL
+};
+
+
+int bgscan_init(struct wpa_supplicant *wpa_s, struct wpa_ssid *ssid)
+{
+	const char *name = ssid->bgscan;
+	const char *params;
+	size_t nlen;
+	int i;
+	const struct bgscan_ops *ops = NULL;
+
+	bgscan_deinit(wpa_s);
+	if (name == NULL)
+		return 0;
+
+	params = os_strchr(name, ':');
+	if (params == NULL) {
+		params = "";
+		nlen = os_strlen(name);
+	} else {
+		nlen = params - name;
+		params++;
+	}
+
+	for (i = 0; bgscan_modules[i]; i++) {
+		if (os_strncmp(name, bgscan_modules[i]->name, nlen) == 0) {
+			ops = bgscan_modules[i];
+			break;
+		}
+	}
+
+	if (ops == NULL) {
+		wpa_printf(MSG_ERROR, "bgscan: Could not find module "
+			   "matching the parameter '%s'", name);
+		return -1;
+	}
+
+	wpa_s->bgscan_priv = ops->init(wpa_s, params, ssid);
+	if (wpa_s->bgscan_priv == NULL)
+		return -1;
+	wpa_s->bgscan = ops;
+	wpa_printf(MSG_DEBUG, "bgscan: Initialized module '%s' with "
+		   "parameters '%s'", ops->name, params);
+
+	return 0;
+}
+
+
+void bgscan_deinit(struct wpa_supplicant *wpa_s)
+{
+	if (wpa_s->bgscan && wpa_s->bgscan_priv) {
+		wpa_printf(MSG_DEBUG, "bgscan: Deinitializing module '%s'",
+			   wpa_s->bgscan->name);
+		wpa_s->bgscan->deinit(wpa_s->bgscan_priv);
+		wpa_s->bgscan = NULL;
+		wpa_s->bgscan_priv = NULL;
+	}
+}
+
+
+int bgscan_notify_scan(struct wpa_supplicant *wpa_s)
+{
+	if (wpa_s->bgscan && wpa_s->bgscan_priv)
+		return wpa_s->bgscan->notify_scan(wpa_s->bgscan_priv);
+	return 0;
+}
+
+
+void bgscan_notify_beacon_loss(struct wpa_supplicant *wpa_s)
+{
+	if (wpa_s->bgscan && wpa_s->bgscan_priv)
+		wpa_s->bgscan->notify_beacon_loss(wpa_s->bgscan_priv);
+}
+
+
+void bgscan_notify_signal_change(struct wpa_supplicant *wpa_s)
+{
+	if (wpa_s->bgscan && wpa_s->bgscan_priv)
+		wpa_s->bgscan->notify_signal_change(wpa_s->bgscan_priv);
+}

wpa_supplicant/bgscan.h

@@ -0,0 +1,68 @@
+/*
+ * WPA Supplicant - background scan and roaming interface
+ * Copyright (c) 2009, 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.
+ */
+
+#ifndef BGSCAN_H
+#define BGSCAN_H
+
+struct wpa_supplicant;
+struct wpa_ssid;
+
+struct bgscan_ops {
+	const char *name;
+
+	void * (*init)(struct wpa_supplicant *wpa_s, const char *params,
+		       const struct wpa_ssid *ssid);
+	void (*deinit)(void *priv);
+
+	int (*notify_scan)(void *priv);
+	void (*notify_beacon_loss)(void *priv);
+	void (*notify_signal_change)(void *priv);
+};
+
+#ifdef CONFIG_BGSCAN
+
+int bgscan_init(struct wpa_supplicant *wpa_s, struct wpa_ssid *ssid);
+void bgscan_deinit(struct wpa_supplicant *wpa_s);
+int bgscan_notify_scan(struct wpa_supplicant *wpa_s);
+void bgscan_notify_beacon_loss(struct wpa_supplicant *wpa_s);
+void bgscan_notify_signal_change(struct wpa_supplicant *wpa_s);
+
+#else /* CONFIG_BGSCAN */
+
+static inline int bgscan_init(struct wpa_supplicant *wpa_s,
+			      struct wpa_ssid *ssid)
+{
+	return 0;
+}
+
+static inline void bgscan_deinit(struct wpa_supplicant *wpa_s)
+{
+}
+
+static inline int bgscan_notify_scan(struct wpa_supplicant *wpa_s)
+{
+	return 0;
+}
+
+static inline void bgscan_notify_beacon_loss(struct wpa_supplicant *wpa_s)
+{
+}
+
+static inline void bgscan_notify_signal_change(struct wpa_supplicant *wpa_s)
+{
+}
+
+#endif /* CONFIG_BGSCAN */
+
+#endif /* BGSCAN_H */

wpa_supplicant/bgscan_simple.c

@@ -0,0 +1,130 @@
+/*
+ * WPA Supplicant - background scan and roaming module: simple
+ * Copyright (c) 2009, 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 "bgscan.h"
+
+struct bgscan_simple_data {
+	struct wpa_supplicant *wpa_s;
+	const struct wpa_ssid *ssid;
+	int scan_interval;
+};
+
+
+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);
+	}
+}
+
+
+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 (params)
+		data->scan_interval = atoi(params);
+	if (data->scan_interval <= 0)
+		data->scan_interval = 30;
+	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);
+	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)
+{
+	wpa_printf(MSG_DEBUG, "bgscan simple: signal level changed");
+	/* TODO: if signal strength dropped enough, speed up background
+	 * scanning */
+}
+
+
+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,
+};

wpa_supplicant/config.c

@@ -1458,7 +1458,8 @@ static const struct parse_data ssid_fields[] = {
 	{ INT_RANGE(peerkey, 0, 1) },
 	{ INT_RANGE(mixed_cell, 0, 1) },
 	{ INT_RANGE(frequency, 0, 10000) },
-	{ INT(wpa_ptk_rekey) }
+	{ INT(wpa_ptk_rekey) },
+	{ STR(bgscan) },
 };
 
 #undef OFFSET
@@ -1623,6 +1624,7 @@ void wpa_config_free_ssid(struct wpa_ssid *ssid)
 #endif /* IEEE8021X_EAPOL */
 	os_free(ssid->id_str);
 	os_free(ssid->scan_freq);
+	os_free(ssid->bgscan);
 	os_free(ssid);
 }
 

wpa_supplicant/config_ssid.h

@@ -350,6 +350,15 @@ struct wpa_ssid {
 	 * known to not use all possible channels.
 	 */
 	int *scan_freq;
+
+	/**
+	 * bgscan - Background scan and roaming parameters or %NULL if none
+	 *
+	 * This is an optional set of parameters for background scanning and
+	 * roaming within a network (ESS) in following format:
+	 * <bgscan module name>:<module parameters>
+	 */
+	char *bgscan;
 };
 
 #endif /* CONFIG_SSID_H */

wpa_supplicant/events.c

@@ -34,6 +34,7 @@
 #include "wps_supplicant.h"
 #include "ibss_rsn.h"
 #include "sme.h"
+#include "bgscan.h"
 
 
 static int wpa_supplicant_select_config(struct wpa_supplicant *wpa_s)
@@ -658,6 +659,9 @@ static void wpa_supplicant_event_scan_results(struct wpa_supplicant *wpa_s)
 		return;
 	}
 
+	if (bgscan_notify_scan(wpa_s) == 1)
+		return;
+
 	while (selected == NULL) {
 		for (prio = 0; prio < wpa_s->conf->num_prio; prio++) {
 			selected = wpa_supplicant_select_bss(
@@ -981,6 +985,25 @@ static void wpa_supplicant_event_assoc(struct wpa_supplicant *wpa_s,
 		wpabuf_free(wpa_s->pending_eapol_rx);
 		wpa_s->pending_eapol_rx = NULL;
 	}
+
+#ifdef CONFIG_BGSCAN
+	if (wpa_s->current_ssid != wpa_s->bgscan_ssid) {
+		bgscan_deinit(wpa_s);
+		if (wpa_s->current_ssid && wpa_s->current_ssid->bgscan) {
+			if (bgscan_init(wpa_s, wpa_s->current_ssid)) {
+				wpa_printf(MSG_DEBUG, "Failed to initialize "
+					   "bgscan");
+				/*
+				 * Live without bgscan; it is only used as a
+				 * roaming optimization, so the initial
+				 * connection is not affected.
+				 */
+			} else
+				wpa_s->bgscan_ssid = wpa_s->current_ssid;
+		} else
+			wpa_s->bgscan_ssid = NULL;
+	}
+#endif /* CONFIG_BGSCAN */
 }
 
 
@@ -1018,6 +1041,7 @@ static void wpa_supplicant_event_disassoc(struct wpa_supplicant *wpa_s)
 		wpa_clear_keys(wpa_s, wpa_s->bssid);
 	}
 	wpa_supplicant_mark_disassoc(wpa_s);
+	bgscan_deinit(wpa_s);
 }
 
 

wpa_supplicant/scan.c

@@ -178,6 +178,34 @@ static void int_array_sort_unique(int *a)
 }
 
 
+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);
+
+	if (wpa_s->drv_flags & WPA_DRIVER_FLAGS_USER_SPACE_MLME) {
+		ieee80211_sta_set_probe_req_ie(wpa_s, params->extra_ies,
+					       params->extra_ies_len);
+		ret = ieee80211_sta_req_scan(wpa_s, params->ssids[0].ssid,
+					     params->ssids[0].ssid_len);
+	} else {
+		wpa_drv_set_probe_req_ie(wpa_s, params->extra_ies,
+					 params->extra_ies_len);
+		ret = wpa_drv_scan(wpa_s, params);
+	}
+
+	if (ret) {
+		wpa_supplicant_notify_scanning(wpa_s, 0);
+		wpas_notify_scan_done(wpa_s, 0);
+	} else
+		wpa_s->scan_runs++;
+
+	return ret;
+}
+
+
 static void wpa_supplicant_scan(void *eloop_ctx, void *timeout_ctx)
 {
 	struct wpa_supplicant *wpa_s = eloop_ctx;
@@ -335,26 +363,13 @@ static void wpa_supplicant_scan(void *eloop_ctx, void *timeout_ctx)
 	}
 #endif /* CONFIG_WPS */
 
-	wpa_supplicant_notify_scanning(wpa_s, 1);
-
-	if (wpa_s->drv_flags & WPA_DRIVER_FLAGS_USER_SPACE_MLME) {
-		ieee80211_sta_set_probe_req_ie(wpa_s, params.extra_ies,
-					       params.extra_ies_len);
-		ret = ieee80211_sta_req_scan(wpa_s, params.ssids[0].ssid,
-					     params.ssids[0].ssid_len);
-	} else {
-		wpa_drv_set_probe_req_ie(wpa_s, params.extra_ies,
-					 params.extra_ies_len);
-		ret = wpa_drv_scan(wpa_s, &params);
-	}
+	ret = wpa_supplicant_trigger_scan(wpa_s, &params);
 
 	wpabuf_free(wps_ie);
 	os_free(params.freqs);
 
 	if (ret) {
 		wpa_printf(MSG_WARNING, "Failed to initiate AP scan.");
-		wpa_supplicant_notify_scanning(wpa_s, 0);
-		wpas_notify_scan_done(wpa_s, 0);
 		wpa_supplicant_req_scan(wpa_s, 10, 0);
 	} else
 		wpa_s->scan_runs++;

wpa_supplicant/wpa_supplicant.c

@@ -44,6 +44,7 @@
 #include "sme.h"
 #include "ap.h"
 #include "notify.h"
+#include "bgscan.h"
 
 const char *wpa_supplicant_version =
 "wpa_supplicant v" VERSION_STR "\n"
@@ -362,6 +363,7 @@ void wpa_supplicant_set_non_wpa_policy(struct wpa_supplicant *wpa_s,
 
 static void wpa_supplicant_cleanup(struct wpa_supplicant *wpa_s)
 {
+	bgscan_deinit(wpa_s);
 	scard_deinit(wpa_s->scard);
 	wpa_s->scard = NULL;
 	wpa_sm_set_scard_ctx(wpa_s->wpa, NULL);

wpa_supplicant/wpa_supplicant_i.h

@@ -388,6 +388,10 @@ struct wpa_supplicant {
 #ifdef CONFIG_AP
 	struct hostapd_iface *ap_iface;
 #endif /* CONFIG_AP */
+
+	struct wpa_ssid *bgscan_ssid;
+	const struct bgscan_ops *bgscan;
+	void *bgscan_priv;
 };
 
 
@@ -450,6 +454,9 @@ void wpa_supplicant_req_scan(struct wpa_supplicant *wpa_s, int sec, int usec);
 void wpa_supplicant_cancel_scan(struct wpa_supplicant *wpa_s);
 void wpa_supplicant_notify_scanning(struct wpa_supplicant *wpa_s,
 				    int scanning);
+struct wpa_driver_scan_params;
+int wpa_supplicant_trigger_scan(struct wpa_supplicant *wpa_s,
+				struct wpa_driver_scan_params *params);
 
 /* events.c */
 void wpa_supplicant_mark_disassoc(struct wpa_supplicant *wpa_s);