[Cake] SCE/CAKE coding curiosities

[Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>]

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.

1) https://github.com/dtaht/sch_cake/blob/47d821f89f39c1b2216d6f65b014f609e46fc57c/sce.h#L50  Curious as to why htons isn’t used here as per other instances in CAKE?

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 ??

Curious of Basingstoke, England :-)

Cheers,

Kevin D-B

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