nl80211: report age of scan results

Linux keeps scan results up to 15 seconds. This can be a problem for fast
moving clients: they get back stale data. But if the kernel reports the age
of the BSS items, then user-space can simply weed out old entries by itself.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/linux/nl80211.h

@@ -1277,6 +1277,7 @@ enum nl80211_channel_type {
  * @NL80211_BSS_SIGNAL_UNSPEC: signal strength of the probe response/beacon
  *	in unspecified units, scaled to 0..100 (u8)
  * @NL80211_BSS_STATUS: status, if this BSS is "used"
+ * @NL80211_BSS_SEEN_MS_AGO: age of this BSS entry in ms
  * @__NL80211_BSS_AFTER_LAST: internal
  * @NL80211_BSS_MAX: highest BSS attribute
  */
@@ -1291,6 +1292,7 @@ enum nl80211_bss {
 	NL80211_BSS_SIGNAL_MBM,
 	NL80211_BSS_SIGNAL_UNSPEC,
 	NL80211_BSS_STATUS,
+	NL80211_BSS_SEEN_MS_AGO,
 
 	/* keep last */
 	__NL80211_BSS_AFTER_LAST,

net/wireless/nl80211.c

@@ -3105,6 +3105,8 @@ static int nl80211_send_bss(struct sk_buff *msg, u32 pid, u32 seq, int flags,
 		NLA_PUT_U16(msg, NL80211_BSS_BEACON_INTERVAL, res->beacon_interval);
 	NLA_PUT_U16(msg, NL80211_BSS_CAPABILITY, res->capability);
 	NLA_PUT_U32(msg, NL80211_BSS_FREQUENCY, res->channel->center_freq);
+	NLA_PUT_U32(msg, NL80211_BSS_SEEN_MS_AGO,
+		jiffies_to_msecs(jiffies - intbss->ts));
 
 	switch (rdev->wiphy.signal_type) {
 	case CFG80211_SIGNAL_TYPE_MBM: