nl/cfg80211: force scan using an AP vif if requested

If the user wants to scan using a vif configured as AP,
cfg80211 must give him a chance to do it, even if this
will disrupt the stations performance due to off-channel
scanning. To do so, this patch adds a 'force' flag to the
SCAN_TRIGGER command which tells cfg80211 to perform the
scanning operation even if the vif is an AP and the
beaconing has already started.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 5739bfb..5eab132 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -1855,7 +1855,16 @@
 		 * beaconing hasn't been configured yet
 		 */
 	case NL80211_IFTYPE_AP:
-		if (sdata->u.ap.beacon)
+		/*
+		 * If the scan has been forced (and the driver supports
+		 * forcing), don't care about being beaconing already.
+		 * This will create problems to the attached stations (e.g. all
+		 * the  frames sent while scanning on other channel will be
+		 * lost)
+		 */
+		if (sdata->u.ap.beacon &&
+		    (!(wiphy->features & NL80211_FEATURE_AP_SCAN) ||
+		     !(req->flags & NL80211_SCAN_FLAG_AP)))
 			return -EOPNOTSUPP;
 		break;
 	default: