cfg80211: implement cfg80211_get_station cfg80211 API

Implement and export the new cfg80211_get_station() API.
This utility can be used by other kernel modules to obtain
detailed information about a given wireless station.

It will be in particular useful to batman-adv which will
implement a wireless rate based metric.
Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -1074,6 +1074,19 @@ struct station_info {
 	 */
 };
 
+/**
+ * cfg80211_get_station - retrieve information about a given station
+ * @dev: the device where the station is supposed to be connected to
+ * @mac_addr: the mac address of the station of interest
+ * @sinfo: pointer to the structure to fill with the information
+ *
+ * Returns 0 on success and sinfo is filled with the available information
+ * otherwise returns a negative error code and the content of sinfo has to be
+ * considered undefined.
+ */
+int cfg80211_get_station(struct net_device *dev, const u8 *mac_addr,
+			 struct station_info *sinfo);
+
 /**
  * enum monitor_flags - monitor flags
  *

net/wireless/rdev-ops.h

@@ -199,7 +199,7 @@ static inline int rdev_change_station(struct cfg80211_registered_device *rdev,
 }
 
 static inline int rdev_get_station(struct cfg80211_registered_device *rdev,
-				   struct net_device *dev, u8 *mac,
+				   struct net_device *dev, const u8 *mac,
 				   struct station_info *sinfo)
 {
 	int ret;

net/wireless/util.c

@@ -1546,6 +1546,24 @@ unsigned int ieee80211_get_num_supported_channels(struct wiphy *wiphy)
 }
 EXPORT_SYMBOL(ieee80211_get_num_supported_channels);
 
+int cfg80211_get_station(struct net_device *dev, const u8 *mac_addr,
+			 struct station_info *sinfo)
+{
+	struct cfg80211_registered_device *rdev;
+	struct wireless_dev *wdev;
+
+	wdev = dev->ieee80211_ptr;
+	if (!wdev)
+		return -EOPNOTSUPP;
+
+	rdev = wiphy_to_rdev(wdev->wiphy);
+	if (!rdev->ops->get_station)
+		return -EOPNOTSUPP;
+
+	return rdev_get_station(rdev, dev, mac_addr, sinfo);
+}
+EXPORT_SYMBOL(cfg80211_get_station);
+
 /* See IEEE 802.1H for LLC/SNAP encapsulation/decapsulation */
 /* Ethernet-II snap header (RFC1042 for most EtherTypes) */
 const unsigned char rfc1042_header[] __aligned(2) =