skb->priority

From: Matei Conovici (cmatei@profis.ro)
Date: Thu Apr 20 2000 - 12:11:24 EST

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Hi!

When forwarding a packet, skb->priority is set to a logical packet
priority, based on IP TOS, like this:

ip_forward()...

skb->priority = rt_tos2priority(iph->tos);

rt_tos2priority is defined in include/net/route.h:

extern __inline__ char rt_tos2priority(u8 tos)
{
return ip_tos2prio[IPTOS_TOS(tos)>>1];
}

The IPTOS_TOS macro masks tos with 0x1E. This means we keep delay,
throughput, reliability and bit 6 (in RFC791 notation, where bit 0 is
MSb). Bit 7 is discarded by the shift.

Can anyone please enlighten me and show me the significance of bit 6
(bits 6-7 are reserved and set to 0 in RFC791). Does it have any
significance in diffserv context, or what is it used for ?

I can only see that when bit 6 is set, skb->priority is always
TC_PRIO_FILLER ... What is TC_PRIO_FILLER's significance ?

-- Matei CONOVICI, cmatei@profis.ro

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