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>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 8116d1a96a4a..0d2d94881f1f 100644
--- 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));