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Re: [PATCH] Move shaper control information into skb->cb

To: "David S. Miller" <davem@xxxxxxxxxx>
Subject: Re: [PATCH] Move shaper control information into skb->cb
From: Andi Kleen <ak@xxxxxx>
Date: Tue, 25 Apr 2000 01:50:08 +0200
Cc: ak@xxxxxx, kuznet@xxxxxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <200004242306.QAA02602@pizda.ninka.net>; from David S. Miller on Tue, Apr 25, 2000 at 01:12:40AM +0200
References: <20000424234623.A1446@fred.muc.de> <200004242306.QAA02602@pizda.ninka.net>
Sender: owner-netdev@xxxxxxxxxxx
On Tue, Apr 25, 2000 at 01:12:40AM +0200, David S. Miller wrote:
>    Date: Mon, 24 Apr 2000 23:46:23 +0200
>    From: Andi Kleen <ak@xxxxxx>
> 
>    This moves the shaper local data into the skb->cb struct, removing
>    ugly ifdefs from the sk_buff. I also documented the purpose of 
>    the control buffer better. For 2.3.x.
> 
> I really like this.
> 
> Just one question, did you verify that this won't clobber CB data
> used by whoever generated the packet?  Just say yes, and if I see
> no other objections I'll put this into the tree.

Actually I didn't (because I ``knew'' that only TCP/IP uses it),
but of course i was wrong: econet and decnet use it. econet does
not queue, and decnet seems to always call skb_clone() before
submitting. Other than that I cannot find any other cb users.

> 
> I know intuitively that once, for example, tcp_transmit_skb has
> built the TCP header the control block can be clobbered by any
> further usage.  We should really document this, at least in a
> comment above that function.

I documented it in skbuff.h (``is owned by whoever has the skb queued'')

BTW, the hippi private fields should be probably moved there too.
 
> Sounds like something which would be nice to audit in our tree.

Done (with grep, hopefully I didn't miss anything) 


-Andi

-- 
This is like TV. I don't like TV.

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