ath9k/mac80211: disallow fragmentation in ath9k, report to userspace

As I've reported, ath9k currently fails utterly when fragmentation
is enabled. This makes ath9k "support" hardware fragmentation by
not supporting fragmentation at all to avoid the double-free issue.
The patch also changes mac80211 to report errors from the driver
operation to userspace.

That hack in ath9k should be removed once the rate control algorithm
it has is fixed, and we can at that time consider removing the hw
fragmentation support entirely since it's not used by any driver.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: stable@kernel.org
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath9k/main.c

@@ -1640,6 +1640,11 @@ static int ath9k_ampdu_action(struct ieee80211_hw *hw,
 	return ret;
 }
 
+static int ath9k_no_fragmentation(struct ieee80211_hw *hw, u32 value)
+{
+	return -EOPNOTSUPP;
+}
+
 static struct ieee80211_ops ath9k_ops = {
 	.tx 		    = ath9k_tx,
 	.start 		    = ath9k_start,
@@ -1664,7 +1669,8 @@ static struct ieee80211_ops ath9k_ops = {
 	.get_tsf 	    = ath9k_get_tsf,
 	.reset_tsf 	    = ath9k_reset_tsf,
 	.tx_last_beacon     = NULL,
-	.ampdu_action       = ath9k_ampdu_action
+	.ampdu_action       = ath9k_ampdu_action,
+	.set_frag_threshold = ath9k_no_fragmentation,
 };
 
 static int ath_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)

net/mac80211/wext.c

@@ -775,7 +775,7 @@ static int ieee80211_ioctl_siwfrag(struct net_device *dev,
 	 * configure it here */
 
 	if (local->ops->set_frag_threshold)
-		local->ops->set_frag_threshold(
+		return local->ops->set_frag_threshold(
 			local_to_hw(local),
 			local->fragmentation_threshold);