[openib-general] RFC: mthca: implement timewait by tracking QPNs

[Roland Dreier]

My gut reaction is that it seems pretty ugly.  I guess we'll also need
similar patches for ipath and ehca too -- which makes me want to have
this in common code somehow.

Also timewait is really only part of the CM spec -- do we want to
limit the rate of RC QP creation in general for potential non-CM users
that know what they're doing?

I'm not sure the following is a real concern (since a hostile user can
currently just create a ton of QPs and hold onto them forever), but
this also allows someone to create a bunch of QPs with a super-long
timeout and prevent any other QPs from being created for a few hours
(until the timewait expires).

Finally one implementation comment: I think you'll want a list in
addition to QPN + timer, to allow the ib_mthca module to be unloaded
without having to wait an hour for all timers to expire.  This allows
timewait to be bypassed by unloading + reloading but that's no
different than rebooting really.

Another good prophylactic measure would probably to randomize initial
PSNs for RC connections.  SRP currently does this.

 - R.