mac80211: add ieee80211_tx_prepare_skb() helper function

This can be used by a driver to prepare skbs for transmission, which were
obtained via functions such as ieee80211_probereq_get or
ieee80211_nullfunc_get.

This is useful for drivers that want to send those frames directly, but
need rate control information to be prepared first.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -4571,4 +4571,18 @@ void ieee80211_report_wowlan_wakeup(struct ieee80211_vif *vif,
 				    struct cfg80211_wowlan_wakeup *wakeup,
 				    gfp_t gfp);
 
+/**
+ * ieee80211_tx_prepare_skb - prepare an 802.11 skb for transmission
+ * @hw: pointer as obtained from ieee80211_alloc_hw()
+ * @vif: virtual interface
+ * @skb: frame to be sent from within the driver
+ * @band: the band to transmit on
+ * @sta: optional pointer to get the station to send the frame to
+ *
+ * Note: must be called under RCU lock
+ */
+bool ieee80211_tx_prepare_skb(struct ieee80211_hw *hw,
+			      struct ieee80211_vif *vif, struct sk_buff *skb,
+			      int band, struct ieee80211_sta **sta);
+
 #endif /* MAC80211_H */

net/mac80211/tx.c

@@ -1366,6 +1366,35 @@ static int invoke_tx_handlers(struct ieee80211_tx_data *tx)
 	return 0;
 }
 
+bool ieee80211_tx_prepare_skb(struct ieee80211_hw *hw,
+			      struct ieee80211_vif *vif, struct sk_buff *skb,
+			      int band, struct ieee80211_sta **sta)
+{
+	struct ieee80211_sub_if_data *sdata = vif_to_sdata(vif);
+	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+	struct ieee80211_tx_data tx;
+
+	if (ieee80211_tx_prepare(sdata, &tx, skb) == TX_DROP)
+		return false;
+
+	info->band = band;
+	info->control.vif = vif;
+	info->hw_queue = vif->hw_queue[skb_get_queue_mapping(skb)];
+
+	if (invoke_tx_handlers(&tx))
+		return false;
+
+	if (sta) {
+		if (tx.sta)
+			*sta = &tx.sta->sta;
+		else
+			*sta = NULL;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(ieee80211_tx_prepare_skb);
+
 /*
  * Returns false if the frame couldn't be transmitted but was queued instead.
  */