mac80211: provide interface iterator for drivers

Sometimes drivers need to know which interfaces are associated with
their hardware. Rather than forcing those drivers to keep track of
the interfaces that were added, this adds an iteration function to
mac80211.

As it is intended to be used from the interface add/remove callbacks,
the iteration function may currently only be called under RTNL.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 17b6039..1470e1b 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1406,4 +1406,20 @@
  */
 void ieee80211_scan_completed(struct ieee80211_hw *hw);
 
+/**
+ * ieee80211_iterate_active_interfaces - iterate active interfaces
+ *
+ * This function iterates over the interfaces associated with a given
+ * hardware that are currently active and calls the callback for them.
+ * Must be called under RTNL.
+ *
+ * @hw: the hardware struct of which the interfaces should be iterated over
+ * @iterator: the iterator function to call
+ * @data: first argument of the iterator function
+ */
+void ieee80211_iterate_active_interfaces(struct ieee80211_hw *hw,
+					 void (*iterator)(void *data, u8 *mac,
+							  int if_id),
+					 void *data);
+
 #endif /* MAC80211_H */