wext: allow returning NULL stats

Currently, wext drivers cannot return NULL for stats even though
that would make the ioctl return -EOPNOTSUPP because that would
mean they are no longer listed in /proc/net/wireless. This patch
changes the wext core's behaviour to list them if they have any
wireless_handlers, but only show their stats when available, so
that drivers can start returning NULL if stats are currently not
available, reducing confusion for e.g. IBSS.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/wext.c

@@ -610,6 +610,11 @@ static void wireless_seq_printf_stats(struct seq_file *seq,
 {
 	/* Get stats from the driver */
 	struct iw_statistics *stats = get_wireless_stats(dev);
+	static struct iw_statistics nullstats = {};
+
+	/* show device if it's wireless regardless of current stats */
+	if (!stats && dev->wireless_handlers)
+		stats = &nullstats;
 
 	if (stats) {
 		seq_printf(seq, "%6s: %04x  %3d%c  %3d%c  %3d%c  %6d %6d %6d "
@@ -628,7 +633,9 @@ static void wireless_seq_printf_stats(struct seq_file *seq,
 			   stats->discard.nwid, stats->discard.code,
 			   stats->discard.fragment, stats->discard.retries,
 			   stats->discard.misc, stats->miss.beacon);
-		stats->qual.updated &= ~IW_QUAL_ALL_UPDATED;
+
+		if (stats != &nullstats)
+			stats->qual.updated &= ~IW_QUAL_ALL_UPDATED;
 	}
 }