Add a reattach command for fast reassociate-back-to-same-BSS

Add "reattach" command to perform single-channel single-ssid scan
instead of full scan when trying to reconnect to the currently
"connected" network (assuming old scan results are not current enough to
skip the scan completely). This allows the scan result to come back in
much faster time. In ath9k, the scan took around 12 seconds with full
background scan, and only 0.1 second with the single-channel single-ssid
scan. Thus, take much less time for the client to re-establish
connection with the currently "connected" network.

Signed-hostap: Peter Qiu <zqiu@chromium.org>

wpa_supplicant/ctrl_iface.c

@@ -5963,6 +5963,14 @@ char * wpa_supplicant_ctrl_iface_process(struct wpa_supplicant *wpa_s,
 			reply_len = -1;
 		else
 			wpas_request_connection(wpa_s);
+	} else if (os_strcmp(buf, "REATTACH") == 0) {
+		if (wpa_s->wpa_state == WPA_INTERFACE_DISABLED ||
+		    !wpa_s->current_ssid)
+			reply_len = -1;
+		else {
+			wpa_s->reattach = 1;
+			wpas_request_connection(wpa_s);
+		}
 	} else if (os_strcmp(buf, "RECONNECT") == 0) {
 		if (wpa_s->wpa_state == WPA_INTERFACE_DISABLED)
 			reply_len = -1;

wpa_supplicant/dbus/dbus_new.c

@@ -2462,6 +2462,12 @@ static const struct wpa_dbus_method_desc wpas_dbus_interface_methods[] = {
 		  END_ARGS
 	  }
 	},
+	{ "Reattach", WPAS_DBUS_NEW_IFACE_INTERFACE,
+	  (WPADBusMethodHandler) &wpas_dbus_handler_reattach,
+	  {
+		  END_ARGS
+	  }
+	},
 	{ "RemoveNetwork", WPAS_DBUS_NEW_IFACE_INTERFACE,
 	  (WPADBusMethodHandler) &wpas_dbus_handler_remove_network,
 	  {

wpa_supplicant/dbus/dbus_new_handlers.c

@@ -1486,6 +1486,29 @@ DBusMessage * wpas_dbus_handler_reassociate(DBusMessage *message,
 }
 
 
+/**
+ * wpas_dbus_handler_reattach - Reattach to current AP
+ * @message: Pointer to incoming dbus message
+ * @wpa_s: wpa_supplicant structure for a network interface
+ * Returns: NotConnected DBus error message if not connected
+ * or NULL otherwise.
+ *
+ * Handler function for "Reattach" method call of network interface.
+ */
+DBusMessage * wpas_dbus_handler_reattach(DBusMessage *message,
+					 struct wpa_supplicant *wpa_s)
+{
+	if (wpa_s->current_ssid != NULL) {
+		wpa_s->reattach = 1;
+		wpas_request_connection(wpa_s);
+		return NULL;
+	}
+
+	return dbus_message_new_error(message, WPAS_DBUS_ERROR_NOT_CONNECTED,
+				      "This interface is not connected");
+}
+
+
 /**
  * wpas_dbus_handler_remove_network - Remove a configured network
  * @message: Pointer to incoming dbus message

wpa_supplicant/dbus/dbus_new_handlers.h

@@ -101,6 +101,9 @@ DBusMessage * wpas_dbus_handler_add_network(DBusMessage *message,
 DBusMessage * wpas_dbus_handler_reassociate(DBusMessage *message,
 					    struct wpa_supplicant *wpa_s);
 
+DBusMessage * wpas_dbus_handler_reattach(DBusMessage *message,
+					 struct wpa_supplicant *wpa_s);
+
 DBusMessage * wpas_dbus_handler_remove_network(DBusMessage *message,
 					       struct wpa_supplicant *wpa_s);
 

wpa_supplicant/scan.c

@@ -665,6 +665,36 @@ static void wpa_supplicant_scan(void *eloop_ctx, void *timeout_ctx)
 		 * wildcard SSID.
 		 */
 		ssid = NULL;
+	} else if (wpa_s->reattach && wpa_s->current_ssid != NULL) {
+		/*
+		 * Perform single-channel single-SSID scan for
+		 * reassociate-to-same-BSS operation.
+		 */
+		/* Setup SSID */
+		ssid = wpa_s->current_ssid;
+		wpa_hexdump_ascii(MSG_DEBUG, "Scan SSID",
+				  ssid->ssid, ssid->ssid_len);
+		params.ssids[0].ssid = ssid->ssid;
+		params.ssids[0].ssid_len = ssid->ssid_len;
+		params.num_ssids = 1;
+
+		/*
+		 * Allocate memory for frequency array, allocate one extra
+		 * slot for the zero-terminator.
+		 */
+		params.freqs = os_malloc(sizeof(int) * 2);
+		if (params.freqs == NULL) {
+			wpa_dbg(wpa_s, MSG_ERROR, "Memory allocation failed");
+			return;
+		}
+		params.freqs[0] = wpa_s->assoc_freq;
+		params.freqs[1] = 0;
+
+		/*
+		 * Reset the reattach flag so that we fall back to full scan if
+		 * this scan fails.
+		 */
+		wpa_s->reattach = 0;
 	} else {
 		struct wpa_ssid *start = ssid, *tssid;
 		int freqs_set = 0;

wpa_supplicant/wpa_cli.c

@@ -676,6 +676,12 @@ static int wpa_cli_cmd_reassociate(struct wpa_ctrl *ctrl, int argc,
 }
 
 
+static int wpa_cli_cmd_reattach(struct wpa_ctrl *ctrl, int argc, char *argv[])
+{
+	return wpa_ctrl_command(ctrl, "REATTACH");
+}
+
+
 static int wpa_cli_cmd_preauthenticate(struct wpa_ctrl *ctrl, int argc,
 				       char *argv[])
 {
@@ -2510,6 +2516,9 @@ static struct wpa_cli_cmd wpa_cli_commands[] = {
 	{ "reassociate", wpa_cli_cmd_reassociate, NULL,
 	  cli_cmd_flag_none,
 	  "= force reassociation" },
+	{ "reattach", wpa_cli_cmd_reattach, NULL,
+	  cli_cmd_flag_none,
+	  "= force reassociation back to the same BSS" },
 	{ "preauthenticate", wpa_cli_cmd_preauthenticate, wpa_cli_complete_bss,
 	  cli_cmd_flag_none,
 	  "<BSSID> = force preauthentication" },

wpa_supplicant/wpa_supplicant_i.h

@@ -594,6 +594,7 @@ struct wpa_supplicant {
 	u8 pending_eapol_rx_src[ETH_ALEN];
 	unsigned int last_eapol_matches_bssid:1;
 	unsigned int eap_expected_failure:1;
+	unsigned int reattach:1; /* reassociation to the same BSS requested */
 
 	struct ibss_rsn *ibss_rsn;