On Sun, 2008-05-04 at 23:24 +0200, Johannes Berg wrote:
quoted text
> This assigns the netdev's needed_headroom/tailroom members
> to take advantage of pre-allocated space for 802.11 headers.
>=20
> Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
> ---
> Builds on my other patch to add those fields, of course!
>=20
>  net/mac80211/iface.c |    8 ++++++++
>  net/mac80211/tx.c    |   14 +++++++++-----
>  2 files changed, 17 insertions(+), 5 deletions(-)
>=20
> --- everything.orig/net/mac80211/iface.c	2008-05-04 15:40:53.000000000 +0=
200
quoted text
> +++ 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;
> =20
> +	ndev->needed_headroom =3D 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;

Although this seems to have worked for me, that was most likely
coincidence because I had two bytes extra headroom and no fourth MAC
address, I actually forgot 8 bytes here (rfc1042/bridge tunnel
encapsulation)

johannes