[RFC] mac80211: assign needed_headroom/tailroom for netdevs

[Johannes Berg <johannes@sipsolutions.net>]

This assigns the netdev's needed_headroom/tailroom members
to take advantage of pre-allocated space for 802.11 headers.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
---
Builds on my other patch to add those fields, of course!

 net/mac80211/iface.c |    8 ++++++++
 net/mac80211/tx.c    |   14 +++++++++-----
 2 files changed, 17 insertions(+), 5 deletions(-)

--- everything.orig/net/mac80211/iface.c	2008-05-04 15:40:53.000000000 +0200
+++ everything/net/mac80211/iface.c	2008-05-04 16:08:45.000000000 +0200
@@ -53,6 +53,14 @@ int ieee80211_if_add(struct net_device *
 	if (!ndev)
 		return -ENOMEM;
 
+	ndev->needed_headroom = local->tx_headroom +
+				4*6 /* four MAC addresses */
+				+ 2 + 2 + 2 + 2 /* ctl, dur, seq, qos */
+				+ 6 /* mesh */
+				- ETH_HLEN /* ethernet hard_header_len */
+				+ IEEE80211_ENCRYPT_HEADROOM;
+	ndev->needed_tailroom = IEEE80211_ENCRYPT_TAILROOM;
+
 	ret = dev_alloc_name(ndev, ndev->name);
 	if (ret < 0)
 		goto fail;