mac80211: Add define for TX headroom reserved by mac80211 itself.

Add a definition of the amount of TX headroom reserved by mac80211 itself
for its own purposes. Also add BUILD_BUG_ON to validate the value.
This define can then be used by drivers to request additional TX headroom
in the most efficient manner.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 2aff490..538d6b7 100644 (file)
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1737,6 +1737,12 @@ static inline void ieee80211_rx_ni(struct ieee80211_hw *hw,
        local_bh_enable();
 }
 
+/*
+ * The TX headroom reserved by mac80211 for its own tx_status functions.
+ * This is enough for the radiotap header.
+ */
+#define IEEE80211_TX_STATUS_HEADROOM   13
+
 /**
  * ieee80211_tx_status - transmit status callback
  *

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 8116d1a..0d2d948 100644 (file)
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -515,6 +515,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
         * and we need some headroom for passing the frame to monitor
         * interfaces, but never both at the same time.
         */
+       BUILD_BUG_ON(IEEE80211_TX_STATUS_HEADROOM !=
+                       sizeof(struct ieee80211_tx_status_rtap_hdr));
        local->tx_headroom = max_t(unsigned int , local->hw.extra_tx_headroom,
                                   sizeof(struct ieee80211_tx_status_rtap_hdr));