mac80211: let the driver reserve extra tailroom in beacons

Can be used to add extra IEs (such as P2P NoA) without having to
reallocate the buffer.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -1613,6 +1613,9 @@ enum ieee80211_hw_flags {
  * @extra_tx_headroom: headroom to reserve in each transmit skb
  *	for use by the driver (e.g. for transmit headers.)
  *
+ * @extra_beacon_tailroom: tailroom to reserve in each beacon tx skb.
+ *	Can be used by drivers to add extra IEs.
+ *
  * @channel_change_time: time (in microseconds) it takes to change channels.
  *
  * @max_signal: Maximum value for signal (rssi) in RX information, used
@@ -1695,6 +1698,7 @@ struct ieee80211_hw {
 	void *priv;
 	u32 flags;
 	unsigned int extra_tx_headroom;
+	unsigned int extra_beacon_tailroom;
 	int channel_change_time;
 	int vif_data_size;
 	int sta_data_size;

net/mac80211/tx.c

@@ -2549,7 +2549,8 @@ struct sk_buff *ieee80211_beacon_get_tim(struct ieee80211_hw *hw,
 			 */
 			skb = dev_alloc_skb(local->tx_headroom +
 					    beacon->head_len +
-					    beacon->tail_len + 256);
+					    beacon->tail_len + 256 +
+					    local->hw.extra_beacon_tailroom);
 			if (!skb)
 				goto out;
 
@@ -2581,7 +2582,8 @@ struct sk_buff *ieee80211_beacon_get_tim(struct ieee80211_hw *hw,
 			ieee80211_update_csa(sdata, presp);
 
 
-		skb = dev_alloc_skb(local->tx_headroom + presp->head_len);
+		skb = dev_alloc_skb(local->tx_headroom + presp->head_len +
+				    local->hw.extra_beacon_tailroom);
 		if (!skb)
 			goto out;
 		skb_reserve(skb, local->tx_headroom);
@@ -2608,7 +2610,8 @@ struct sk_buff *ieee80211_beacon_get_tim(struct ieee80211_hw *hw,
 		skb = dev_alloc_skb(local->tx_headroom +
 				    bcn->head_len +
 				    256 + /* TIM IE */
-				    bcn->tail_len);
+				    bcn->tail_len +
+				    local->hw.extra_beacon_tailroom);
 		if (!skb)
 			goto out;
 		skb_reserve(skb, local->tx_headroom);