netdev - Re: [RFC] mac80211: assign needed_headroom/tailroom for netdevs

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Date:	Sun, 04 May 2008 23:31:18 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	John Linville <linville@...driver.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: [RFC] mac80211: assign needed_headroom/tailroom for netdevs

On Sun, 2008-05-04 at 23:24 +0200, Johannes Berg wrote:
> 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@...solutions.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;

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

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