[088/143] mac80211: Add define for TX headroom reserved by mac80211 itself.

[Greg KH]

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Gertjan van Wingerde <gwingerde@xxxxxxxxx>

commit d24deb2580823ab0b8425790c6f5d18e2ff749d8 upstream.

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@xxxxxxxxx>
Acked-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Signed-off-by: John W. Linville <linville@xxxxxxxxxxxxx>
[bwh: Adjust context for 2.6.32]
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 include/net/mac80211.h |    6 ++++++
 net/mac80211/main.c    |    2 ++
 2 files changed, 8 insertions(+)

--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1700,6 +1700,12 @@ void ieee80211_rx(struct ieee80211_hw *h
  */
 void ieee80211_rx_irqsafe(struct ieee80211_hw *hw, struct sk_buff *skb);
 
+/*
+ * 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
  *
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -859,6 +859,8 @@ int ieee80211_register_hw(struct ieee802
 	 * 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));
 


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