netdev - RE: skb->priority on arp packets

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Message-ID: <D5C1322C3E673F459512FB59E0DDC32902F578DE@orsmsx414.amr.corp.intel.com>
Date:	Mon, 4 Jun 2007 14:54:53 -0700
From:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
To:	"Marc Donner" <donner@...-breitband.de>, <netdev@...r.kernel.org>
Subject: RE: skb->priority on arp packets

> is it possible to set the skb->priority on arp packets 
> generated by the kernel?
> I want to to set the 802.1p priority on arp and ip packets on 
> an interface. On ip packets, this can be done by the iptables 
> CLASSIFY target and the 
> skb->priority mapping from the vlan implementation.
> 
> any ideas?

Currently unclassified ip packets have skb->priority set in ipsockglue,
by translating the IP TOS field into a Linux priority.  This is not the
same priority as 802.1p, rather, it's a Linux-based OS priority
classification for dequeuing priority in schedulers such as sch_prio.
802.1p lives in the VLAN tag, which is separate from skb->priority.  I'd
suggest reading http://lartc.org/howto/lartc.qdisc.classless.html to see
what exactly skb->priority is used for in sch_prio and pfifo_fast, and
how the ip layer determines a packet's priority.  The skb->priority
field is also used in other ways in other qdiscs I'm not completely
familiar with, but it's not directly related to priority of the packet.
I'd need to look closer at those qdiscs to be specific.

That being said, the only way I can think of manipulating skb->priority
on arp packets (and actually setting it) is modifying a qdisc to set
skb->priority if it matches a filter created using the tc command.

Cheers,
-PJ Waskiewicz
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