netdev - Re: [PATCH net-next v3 3/4] net: use skb->priority for overloading skb->dropcount and skb->reserved

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Message-ID: <1424788868.5565.81.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 24 Feb 2015 06:41:08 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eyal Birger <eyal.birger@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Shmulik Ladkani <shmulik.ladkani@...il.com>,
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 3/4] net: use skb->priority for overloading
 skb->dropcount and skb->reserved_tailroom instead of skb->mark

On Tue, 2015-02-24 at 16:07 +0200, Eyal Birger wrote:

> Well, I took a look, then I tried :)
> 
> It breaks in packet_rcv() in a BUILD_BUG_ON() assertion. The asserted size is:
> 
> sizeof(*PACKET_SKB_CB(skb)) + MAX_ADDR_LEN - 8
> 
> This was introduced in ffbc61117d32dc4e768 ("[PACKET]: Fix skb->cb
> clobbering between aux and sockaddr")
> It requires the ability to store the maximal possible address length (32).

OK this might require to move origlen elsewhere in skb.

skb->dev for example is set to NULL, same for skb dst.

We have to be a bit creative/hacky to keep skb size small.


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