[Cake] passing args to bpf programs

Dave Taht dave.taht at gmail.com
Wed Aug 1 12:22:41 EDT 2018

this really isn't the right list for this... but I wanted to build on
the ack_filter bpf code I had, to create impairments, like dropping
acks every X packets, or randomly, or when a specific pattern is seen
(like timestamps or sack). This was sort of the reverse complement to
getting the cake ack-filter right, now that I know everything that can
go wrong...

I see I can return ACT_SHOT, so I can drop packets.

But what I can't quite figure out is how to pass args to an tc ebpf
program. Do I have to pass those via a file descriptor? A map
generated elsewhere? what? Sure as heck don't want to compile one
program per opt....

Simplest args would be:

max 16 - drop every 16th ack packet
random 24 - drop randomly between 0 24
match only certain flags

followed by more gnarly ones like:

miscalculate if I have a payload or not
drop sack
mangle timestamps


Dave Täht
CEO, TekLibre, LLC
Tel: 1-669-226-2619

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