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RE: [Xen-devel] [PATCH 2/2] netfront skb padding

To: "Jon Mason" <jdmason@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH 2/2] netfront skb padding
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Wed, 9 Feb 2005 19:24:34 -0000
Cc: <ian.pratt@xxxxxxxxxxxx>, <ian.pratt@xxxxxxxxxxxx>
Delivery-date: Wed, 09 Feb 2005 19:26:02 +0000
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Thread-index: AcUO3FzWdmhKjp6iQRqPILTTddytNQAAEgDg
Thread-topic: [Xen-devel] [PATCH 2/2] netfront skb padding
 > How could their be more than one layer of encapsulation 
> greater than MTU?  
> When the packet comes into dom0, it is already <= MTU.  It 
> gets encapsulated
> with another layer of routing data, and sent to its 
> destination.  So, it is 
> at maximum size MTU+24.

Dom0 may want to put extra headers on the *front* of the packet. By
having the packet starting a fair way in to the data area of the skb it
should be possible to add them in the same data area rather than create
pre-pend another fragement.

Anyhow, the current situation doesn't really waste any memory because
skb data areas are all whole pages.

Ian


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