[Cake] SCE/CAKE coding curiosities
toke at redhat.com
Tue Apr 2 13:45:08 EDT 2019
Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> writes:
> Ahoy there team Bufferboat :-)
> I’ve been looking at the new SCE related code and a few questions have fallen out of the brain cell.
> Curious as to why htons isn’t used here as per other instances in
No idea about this.
> 2) Immediately below that line we have a skb length guard before
> trying to set ECT ultimately via ipv?_change_dsfield - we have other
> places in CAKE where we play with dsfield bits that don’t have an
> (obvious) guard - should they?
> 3) And saving the most curious for last, in cake_update_flowkeys we check the protocol again (we want IPv4 packets only) but we use tc_skb_protocol(skb) https://github.com/dtaht/sch_cake/blob/47d821f89f39c1b2216d6f65b014f609e46fc57c/sch_cake.c#L628
> tc_skb_protocol says "/* We need to take extra care in case the skb came via
> * vlan accelerated path. In that case, use skb->vlan_proto
> * as the original vlan header was already stripped.
> if (skb_vlan_tag_present(skb))
> return skb->vlan_proto;
> return skb->protocol;
> What??? Should cake_handle_diffserv use tc_skb_protocol too? and
> INET_ECN_set_sce ??
Yup, I believe you are right about both of these; nice catch! I pushed
fixes for cake_handle_diffserv(); keeping my hands off the sce bits for
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