mac80211: Disable requests for new scans in AP mode

AP mode operations are seriously affected if mac80211 runs through a multi-second scan while the AP is trying to send Beacon frames on the operation channel. While this could be implemented in a way that does not cause too many problems, it is not very simple and will require synchronization with Beacon frame scheduling in the drivers (scan one channel at a time between Beacon frames). Furthermore, such scanning takes quite a bit longer time and existing userspace applications would be likely to timeout while waiting for the results.

For now, just refuse requests for new scans (SIOCSIWSCAN) when in AP mode. In practice, this moves the rejection from iwl* drivers into mac80211 to make it apply to every mac80211-based driver.

This issue shows up in associated stations getting disconnected when something (e.g., Network Manager) requests a scan while the interface is in AP mode. When doing this continuously (e.g., NM does it every 60 seconds), the network gets close to useless.

Signed-off-by Jouni Malinen <[email protected]>

Index: wireless-testing/drivers/net/wireless/iwlwifi/iwl-agn.c
===================================================================

drivers/net/wireless/iwlwifi/iwl-agn.c +0 -6

@@ -2972,12 +2972,6 @@ static int iwl_mac_hw_scan(struct ieee80
 		goto out_unlock;
 	}
 
-	if (priv->iw_mode == NL80211_IFTYPE_AP) {	/* APs don't scan */
-		ret = -EIO;
-		IWL_ERROR("ERROR: APs don't scan\n");
-		goto out_unlock;
-	}
-
 	/* We don't schedule scan within next_scan_jiffies period.
 	 * Avoid scanning during possible EAPOL exchange, return
 	 * success immediately.

Index: wireless-testing/drivers/net/wireless/iwlwifi/iwl3945-base.c
===================================================================

drivers/net/wireless/iwlwifi/iwl3945-base.c +0 -11

@@ -2105,11 +2105,6 @@ static void iwl3945_setup_rxon_timing(st
 
 static int iwl3945_scan_initiate(struct iwl3945_priv *priv)
 {
-	if (priv->iw_mode == NL80211_IFTYPE_AP) {
-		IWL_ERROR("APs don't scan.\n");
-		return 0;
-	}
-
 	if (!iwl3945_is_ready_rf(priv)) {
 		IWL_DEBUG_SCAN("Aborting scan due to not ready.\n");
 		return -EIO;

@@ -6991,12 +6986,6 @@ static int iwl3945_mac_hw_scan(struct ie
 		goto out_unlock;
 	}
 
-	if (priv->iw_mode == NL80211_IFTYPE_AP) {	/* APs don't scan */
-		rc = -EIO;
-		IWL_ERROR("ERROR: APs don't scan\n");
-		goto out_unlock;
-	}
-
 	/* we don't schedule scan within next_scan_jiffies period */
 	if (priv->next_scan_jiffies &&
 			time_after(priv->next_scan_jiffies, jiffies)) {

Index: wireless-testing/net/mac80211/wext.c
===================================================================

net/mac80211/wext.c +1 -2

@@ -418,8 +418,7 @@ static int ieee80211_ioctl_siwscan(struc
 
 	if (sdata->vif.type != NL80211_IFTYPE_STATION &&
 	    sdata->vif.type != NL80211_IFTYPE_ADHOC &&
-	    sdata->vif.type != NL80211_IFTYPE_MESH_POINT &&
-	    sdata->vif.type != NL80211_IFTYPE_AP)
+	    sdata->vif.type != NL80211_IFTYPE_MESH_POINT)
 		return -EOPNOTSUPP;
 
 	/* if SSID was specified explicitly then use that */

AP mode operations are seriously affected if mac80211 runs through a multi-second scan while the AP is trying to send Beacon frames on the operation channel. While this could be implemented in a way that does not cause too many problems, it is not very simple and will require synchronization with Beacon frame scheduling in the drivers (scan one channel at a time between Beacon frames). Furthermore, such scanning takes quite a bit longer time and existing userspace applications would be likely to timeout while waiting for the results.

For now, just refuse requests for new scans (SIOCSIWSCAN) when in AP mode. In practice, this moves the rejection from iwl* drivers into mac80211 to make it apply to every mac80211-based driver.

This issue shows up in associated stations getting disconnected when something (e.g., Network Manager) requests a scan while the interface is in AP mode. When doing this continuously (e.g., NM does it every 60 seconds), the network gets close to useless.

Signed-off-by Jouni Malinen <[email protected]>

Index: wireless-testing/drivers/net/wireless/iwlwifi/iwl-agn.c
===================================================================

drivers/net/wireless/iwlwifi/iwl-agn.c +0 -6

@@ -2972,12 +2972,6 @@ static int iwl_mac_hw_scan(struct ieee80
 		goto out_unlock;
 	}
 
-	if (priv->iw_mode == NL80211_IFTYPE_AP) {	/* APs don't scan */
-		ret = -EIO;
-		IWL_ERROR("ERROR: APs don't scan\n");
-		goto out_unlock;
-	}
-
 	/* We don't schedule scan within next_scan_jiffies period.
 	 * Avoid scanning during possible EAPOL exchange, return
 	 * success immediately.

Index: wireless-testing/drivers/net/wireless/iwlwifi/iwl3945-base.c
===================================================================

drivers/net/wireless/iwlwifi/iwl3945-base.c +0 -11

@@ -2105,11 +2105,6 @@ static void iwl3945_setup_rxon_timing(st
 
 static int iwl3945_scan_initiate(struct iwl3945_priv *priv)
 {
-	if (priv->iw_mode == NL80211_IFTYPE_AP) {
-		IWL_ERROR("APs don't scan.\n");
-		return 0;
-	}
-
 	if (!iwl3945_is_ready_rf(priv)) {
 		IWL_DEBUG_SCAN("Aborting scan due to not ready.\n");
 		return -EIO;

@@ -6991,12 +6986,6 @@ static int iwl3945_mac_hw_scan(struct ie
 		goto out_unlock;
 	}
 
-	if (priv->iw_mode == NL80211_IFTYPE_AP) {	/* APs don't scan */
-		rc = -EIO;
-		IWL_ERROR("ERROR: APs don't scan\n");
-		goto out_unlock;
-	}
-
 	/* we don't schedule scan within next_scan_jiffies period */
 	if (priv->next_scan_jiffies &&
 			time_after(priv->next_scan_jiffies, jiffies)) {

Index: wireless-testing/net/mac80211/wext.c
===================================================================

net/mac80211/wext.c +1 -2

@@ -418,8 +418,7 @@ static int ieee80211_ioctl_siwscan(struc
 
 	if (sdata->vif.type != NL80211_IFTYPE_STATION &&
 	    sdata->vif.type != NL80211_IFTYPE_ADHOC &&
-	    sdata->vif.type != NL80211_IFTYPE_MESH_POINT &&
-	    sdata->vif.type != NL80211_IFTYPE_AP)
+	    sdata->vif.type != NL80211_IFTYPE_MESH_POINT)
 		return -EOPNOTSUPP;
 
 	/* if SSID was specified explicitly then use that */

Every 120 seconds usually (it uses a simple backoff algorithm), but yeah, this is a good thing to do. You probably want to make NM ignore the device if you're configuring it as an AP though, since obviously NM shouldn't be driving an AP mode interface.

Quoted 4 lines · Dan Williams

Every 120 seconds usually (it uses a simple backoff algorithm), but yeah, this is a good thing to do. You probably want to make NM ignore the device if you're configuring it as an AP though, since obviously NM shouldn't be driving an AP mode interface.

Actually, I would like to be able to NM to set up a simple AP similarly to IBSS configuration.. If I'm setting up the interface manually (either for AP or even for client modes), I would like NM to ignore the device from that point on, but that is a separate point.

NM only knows about devices that NM controls, thus we can't have NM set up the device and then subsequently ignore it... However, at some point in the near future, if we can get reliable information as to whether the driver *does* in fact support AP mode, we can make NM drive the interface in AP mode instead of IBSS. The only reason it's using IBSS right now is that the driver support for AP mode was so inconsistent and buggy.

NM only knows about devices that NM controls, thus we can't have NM set up the device and then subsequently ignore it... However, at some point in the near future, if we can get reliable information as to whether the driver *does* in fact support AP mode, we can make NM drive the interface in AP mode instead of IBSS. The only reason it's using IBSS right now is that the driver support for AP mode was so inconsistent and buggy.