mac80211: Copy tx'ed beacons to monitor mode

When debugging wireless powersave issues on the AP side it's quite helpful
to see our own beacons that are transmitted by the hardware/driver. However,
this is not that easy since beacons don't pass through the regular TX queues.

Preferably drivers would call ieee80211_tx_status also for tx'ed beacons
but that's not always possible. Hence, just send a copy of each beacon
generated by ieee80211_beacon_get_tim to monitor devices when they are
getting fetched by the driver.

Also add a HW flag IEEE80211_HW_BEACON_TX_STATUS that can be used by
drivers to indicate that they report TX status for beacons.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
(with a fix from Christian Lamparted rolled in)
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -1898,6 +1898,9 @@ struct ieee80211_txq {
  * @IEEE80211_HW_SUPPORTS_AMSDU_IN_AMPDU: The driver supports receiving A-MSDUs
  *	within A-MPDU.
  *
+ * @IEEE80211_HW_BEACON_TX_STATUS: The device/driver provides TX status
+ *	for sent beacons.
+ *
  * @NUM_IEEE80211_HW_FLAGS: number of hardware flags, used for sizing arrays
  */
 enum ieee80211_hw_flags {
@@ -1932,6 +1935,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_SINGLE_SCAN_ON_ALL_BANDS,
 	IEEE80211_HW_TDLS_WIDER_BW,
 	IEEE80211_HW_SUPPORTS_AMSDU_IN_AMPDU,
+	IEEE80211_HW_BEACON_TX_STATUS,
 
 	/* keep last, obviously */
 	NUM_IEEE80211_HW_FLAGS

net/mac80211/debugfs.c

@@ -124,6 +124,7 @@ static const char *hw_flag_names[NUM_IEEE80211_HW_FLAGS + 1] = {
 	FLAG(SINGLE_SCAN_ON_ALL_BANDS),
 	FLAG(TDLS_WIDER_BW),
 	FLAG(SUPPORTS_AMSDU_IN_AMPDU),
+	FLAG(BEACON_TX_STATUS),
 
 	/* keep last for the build bug below */
 	(void *)0x1

net/mac80211/tx.c

@@ -3512,6 +3512,12 @@ struct sk_buff *ieee80211_beacon_get_tim(struct ieee80211_hw *hw,
 {
 	struct ieee80211_mutable_offsets offs = {};
 	struct sk_buff *bcn = __ieee80211_beacon_get(hw, vif, &offs, false);
+	struct sk_buff *copy;
+	struct ieee80211_supported_band *sband;
+	int shift;
+
+	if (!bcn)
+		return bcn;
 
 	if (tim_offset)
 		*tim_offset = offs.tim_offset;
@@ -3519,6 +3525,19 @@ struct sk_buff *ieee80211_beacon_get_tim(struct ieee80211_hw *hw,
 	if (tim_length)
 		*tim_length = offs.tim_length;
 
+	if (ieee80211_hw_check(hw, BEACON_TX_STATUS) ||
+	    !hw_to_local(hw)->monitors)
+		return bcn;
+
+	/* send a copy to monitor interfaces */
+	copy = skb_copy(bcn, GFP_ATOMIC);
+	if (!copy)
+		return bcn;
+
+	shift = ieee80211_vif_get_shift(vif);
+	sband = hw->wiphy->bands[ieee80211_get_sdata_band(vif_to_sdata(vif))];
+	ieee80211_tx_monitor(hw_to_local(hw), copy, sband, 1, shift, false);
+
 	return bcn;
 }
 EXPORT_SYMBOL(ieee80211_beacon_get_tim);