mac80211: make alignment warning optional

Driver authors should be aware of the alignment requirements, but
not everybody cares about the warning. This patch makes it depend
on a new Kconfig symbol MAC80211_DEBUG_PACKET_ALIGNMENT which can
be enabled regardless of MAC80211_DEBUG and is recommended for
driver authors (only). This also restricts the warning to data
packets so other packets need not be realigned to not trigger the
warning.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/Kconfig

@@ -98,6 +98,18 @@ config MAC80211_DEBUGFS
 
 	  Say N unless you know you need this.
 
+config MAC80211_DEBUG_PACKET_ALIGNMENT
+	bool "Enable packet alignment debugging"
+	depends on MAC80211
+	help
+	  This option is recommended for driver authors and strongly
+	  discouraged for everybody else, it will trigger a warning
+	  when a driver hands mac80211 a buffer that is aligned in
+	  a way that will cause problems with the IP stack on some
+	  architectures.
+
+	  Say N unless you're writing a mac80211 based driver.
+
 config MAC80211_DEBUG
 	bool "Enable debugging output"
 	depends on MAC80211

net/mac80211/rx.c

@@ -340,11 +340,15 @@ static u32 ieee80211_rx_load_stats(struct ieee80211_local *local,
 	return load;
 }
 
+#ifdef CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT
 static ieee80211_txrx_result
 ieee80211_rx_h_verify_ip_alignment(struct ieee80211_txrx_data *rx)
 {
 	int hdrlen;
 
+	if (!WLAN_FC_DATA_PRESENT(rx->fc))
+		return TXRX_CONTINUE;
+
 	/*
 	 * Drivers are required to align the payload data in a way that
 	 * guarantees that the contained IP header is aligned to a four-
@@ -371,11 +375,14 @@ ieee80211_rx_h_verify_ip_alignment(struct ieee80211_txrx_data *rx)
 
 	return TXRX_CONTINUE;
 }
+#endif
 
 ieee80211_rx_handler ieee80211_rx_pre_handlers[] =
 {
 	ieee80211_rx_h_parse_qos,
+#ifdef CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT
 	ieee80211_rx_h_verify_ip_alignment,
+#endif
 	NULL
 };