netdev - Re: mac80211 truesize bugs

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Date:	Thu, 01 May 2008 02:56:35 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	johannes@...solutions.net
Cc:	mb@...sch.de, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org
Subject: Re: mac80211 truesize bugs

From: Johannes Berg <johannes@...solutions.net>
Date: Thu, 01 May 2008 11:48:19 +0200

> > Signed-off-by: David S. Miller <davem@...emloft.net>
>  
> > +	/* This is safe because the buffer has been orphaned.  */
> > +	skb->truesize += sizeof(*rthdr);
> 
> Hmm. The disconnect between truesize and skb->len+sizeof(*skb) was
> usually 17 or 19 bytes and sizeof(*rthdr) is only 11. On the other hand,
> I don't see where the other bytes should be coming from. I'll give this
> a try, thanks.

Grrr, I bet it's coming from a combination of the
skb_set_mac_header(skb, 0); call done by mac80211 and the skb_push()
calls in net/packet/af_packet.c

davem@...set:~/src/GIT/net-2.6$ egrep skb_push net/packet/af_packet.c
	skb_push(skb, skb->data - skb_mac_header(skb));
			skb_push(skb, skb->data - skb_mac_header(skb));
			skb_push(skb, skb->data - skb_mac_header(skb));
davem@...set:~/src/GIT/net-2.6$ 
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