WNM: Optimize a single BSS transition management candidate scan

If the BSS Transition Management Request frame includes only a single
candidate and we need to scan for the BSS to get up-to-date information,
use a scan for the known BSSID instead of wildcard BSSID. In addition,
set the SSID in the scan if it is known based on old scan results in the
BSS table. This removes unnecessary Probe Response frames when we are
interested in results from only a single BSS.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

wpa_supplicant/scan.c

@@ -1006,6 +1006,27 @@ ssid_list_set:
 		}
 	}
 
+	if (!is_zero_ether_addr(wpa_s->next_scan_bssid)) {
+		struct wpa_bss *bss;
+
+		params.bssid = wpa_s->next_scan_bssid;
+		bss = wpa_bss_get_bssid_latest(wpa_s, params.bssid);
+		if (bss && bss->ssid_len && params.num_ssids == 1 &&
+		    params.ssids[0].ssid_len == 0) {
+			params.ssids[0].ssid = bss->ssid;
+			params.ssids[0].ssid_len = bss->ssid_len;
+			wpa_dbg(wpa_s, MSG_DEBUG,
+				"Scan a previously specified BSSID " MACSTR
+				" and SSID %s",
+				MAC2STR(params.bssid),
+				wpa_ssid_txt(bss->ssid, bss->ssid_len));
+		} else {
+			wpa_dbg(wpa_s, MSG_DEBUG,
+				"Scan a previously specified BSSID " MACSTR,
+				MAC2STR(params.bssid));
+		}
+	}
+
 	scan_params = &params;
 
 scan:
@@ -1066,6 +1087,8 @@ scan:
 #ifdef CONFIG_INTERWORKING
 		wpa_s->interworking_fast_assoc_tried = 0;
 #endif /* CONFIG_INTERWORKING */
+		if (params.bssid)
+			os_memset(wpa_s->next_scan_bssid, 0, ETH_ALEN);
 	}
 }
 

wpa_supplicant/wnm_sta.c

@@ -1148,6 +1148,14 @@ static void ieee802_11_rx_bss_trans_mgmt_req(struct wpa_supplicant *wpa_s,
 		}
 
 		wnm_set_scan_freqs(wpa_s);
+		if (wpa_s->wnm_num_neighbor_report == 1) {
+			os_memcpy(wpa_s->next_scan_bssid,
+				  wpa_s->wnm_neighbor_report_elements[0].bssid,
+				  ETH_ALEN);
+			wpa_printf(MSG_DEBUG,
+				   "WNM: Scan only for a specific BSSID since there is only a single candidate "
+				   MACSTR, MAC2STR(wpa_s->next_scan_bssid));
+		}
 		wpa_supplicant_req_scan(wpa_s, 0, 0);
 	} else if (reply) {
 		enum bss_trans_mgmt_status_code status;

wpa_supplicant/wpa_supplicant_i.h

@@ -640,6 +640,7 @@ struct wpa_supplicant {
 #define MAX_SCAN_ID 16
 	int scan_id[MAX_SCAN_ID];
 	unsigned int scan_id_count;
+	u8 next_scan_bssid[ETH_ALEN];
 
 	struct wpa_ssid_value *ssids_from_scan_req;
 	unsigned int num_ssids_from_scan_req;