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Re: STP and vlan_hard_start

To: Gleb Natapov <gleb@xxxxxxxxxxx>
Subject: Re: STP and vlan_hard_start
From: jamal <hadi@xxxxxxxxxx>
Date: Tue, 24 Oct 2000 06:52:59 -0400 (EDT)
Cc: Ben Greear <greearb@xxxxxxxxxxxxxxx>, Matti Aarnio <matti.aarnio@xxxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <20001024115332.B8243@xxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx

On Tue, 24 Oct 2000, Gleb Natapov wrote:

>  The problem is that you not always know how much is "adequate space" and if 
> you didn't guess
> correct you must allocate new buffer and copy all data from old one.

This is a common problem in a lot protocols which insert headers
in between at the lower layers. It becomes even more sexy when this
inserted layer is variable (eg an MPLS label-stack).
The brute force way is to ofcourse always allocate a size equal to the
path MTU.  
How about using some of the route flags to indicate that a particular
path has a requirement like this? so then you know apriori what the extra
gap is and can allocate for it. Add to this a generic call:
skb_add_to_header(skb,offset,length,value) and you are almost set.

cheers,
jamal


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