SME: Optimize recovery from common load balancing mechanisms

When authentication or association fails when trying to connect to
a BSS in an ESS that has multiple BSSes based on previous scans,
limit the first recovery scan to only the known channels that has
been seen previously. This speeds up recovery in some of the most
commonly used load balancing mechanisms in enterprise WLAN
networks.

wpa_supplicant/scan.c

@@ -448,6 +448,14 @@ static void wpa_supplicant_scan(void *eloop_ctx, void *timeout_ctx)
 	}
 #endif /* CONFIG_P2P */
 
+	if (params.freqs == NULL && wpa_s->next_scan_freqs) {
+		wpa_printf(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;
+
 	params.filter_ssids = wpa_supplicant_build_filter_ssids(
 		wpa_s->conf, &params.num_filter_ssids);
 

wpa_supplicant/sme.c

@@ -33,9 +33,30 @@
 #include "scan.h"
 #include "sme.h"
 
-static int sme_another_bss_in_ess(struct wpa_supplicant *wpa_s)
+static void add_freq(int *freqs, int *num_freqs, int freq)
+{
+	int i;
+
+	for (i = 0; i < *num_freqs; i++) {
+		if (freqs[i] == freq)
+			return;
+	}
+
+	freqs[*num_freqs] = freq;
+	(*num_freqs)++;
+}
+
+
+static int * sme_another_bss_in_ess(struct wpa_supplicant *wpa_s)
 {
 	struct wpa_bss *bss, *cbss;
+	const int max_freqs = 10;
+	int *freqs;
+	int num_freqs = 0;
+
+	freqs = os_zalloc(sizeof(int) * (max_freqs + 1));
+	if (freqs == NULL)
+		return NULL;
 
 	cbss = wpa_s->current_bss;
 
@@ -44,11 +65,19 @@ static int sme_another_bss_in_ess(struct wpa_supplicant *wpa_s)
 			continue;
 		if (bss->ssid_len == cbss->ssid_len &&
 		    os_memcmp(bss->ssid, cbss->ssid, bss->ssid_len) == 0 &&
-		    wpa_blacklist_get(wpa_s, bss->bssid) == NULL)
+		    wpa_blacklist_get(wpa_s, bss->bssid) == NULL) {
-			return 1;
+			add_freq(freqs, &num_freqs, bss->freq);
+			if (num_freqs == max_freqs)
+				break;
+		}
 	}
 
-	return 0;
+	if (num_freqs == 0) {
+		os_free(freqs);
+		freqs = NULL;
+	}
+
+	return freqs;
 }
 
 
@@ -57,6 +86,7 @@ static void sme_connection_failed(struct wpa_supplicant *wpa_s,
 {
 	int timeout;
 	int count;
+	int *freqs = NULL;
 
 	/*
 	 * Add the failed BSSID into the blacklist and speed up next scan
@@ -74,10 +104,18 @@ static void sme_connection_failed(struct wpa_supplicant *wpa_s,
 		 * next. Otherwise, we may as well try this one once more
 		 * before allowing other, likely worse, ESSes to be considered.
 		 */
-		if (sme_another_bss_in_ess(wpa_s)) {
+		freqs = sme_another_bss_in_ess(wpa_s);
+		if (freqs) {
 			wpa_printf(MSG_DEBUG, "SME: Another BSS in this ESS "
 				   "has been seen; try it next");
 			wpa_blacklist_add(wpa_s, bssid);
+			/*
+			 * On the next scan, go through only the known channels
+			 * used in this ESS based on previous scans to speed up
+			 * common load balancing use case.
+			 */
+			os_free(wpa_s->next_scan_freqs);
+			wpa_s->next_scan_freqs = freqs;
 		}
 	}
 

wpa_supplicant/wpa_supplicant.c

@@ -433,6 +433,9 @@ static void wpa_supplicant_cleanup(struct wpa_supplicant *wpa_s)
 #ifdef CONFIG_P2P
 	wpas_p2p_deinit(wpa_s);
 #endif /* CONFIG_P2P */
+
+	os_free(wpa_s->next_scan_freqs);
+	wpa_s->next_scan_freqs = NULL;
 }
 
 

wpa_supplicant/wpa_supplicant_i.h

@@ -404,6 +404,7 @@ struct wpa_supplicant {
 	int scan_req; /* manual scan request; this forces a scan even if there
 		       * are no enabled networks in the configuration */
 	int scan_runs; /* number of scan runs since WPS was started */
+	int *next_scan_freqs;
 
 	struct wpa_client_mlme mlme;
 	unsigned int drv_flags;