[Bloat] emulating non-duplex media in linux qdiscs

[Dave Taht <dave.taht@gmail.com>]

I have been hacking away at netem for a while now in the hope that
eventually - with a great deal more hacking - it could be used to more
accurately emulate shared media like wifi and lte.

(Some people try to describe these as simplex (which is not true
because you can have multiple destinations), and they certainly are
not duplex, so I tend to say non-duplex and still hope some better
word emerges)

So... one sticking point for me has been wanting to emulate the fact
that on shared media, that you cannot transmit and receive at the same
time; that these are "coupled" events, and what I'd like to be able to
express might be something like:

tc qdisc add dev eth0 root netem rate 100mbit coupled some_identifier
... some tc mirred magic for ifb here ...
tc qdisc add dev ifb0 root netem rate 10mbit coupled the_same_identifier

"some_identifier" would be a mutex of some sort, and I confess to
not having much grip on the kernel outside of the net/sched directory.

What facility would be best to try and leverage? It would be created
(globally) on first use, ref-counted (thus destroyed when it goes to
zero), atomically updated... posix shared memory seems too heavyweight
to use....

-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619