[openib-general] Re: [RFC] userspace CM/verbs QP

[Libor Michalek]

On Thu, Mar 03, 2005 at 04:37:45PM -0800, Roland Dreier wrote:
>     Libor> Roland, As it currently stands, the userspace CM needs to
>     Libor> pass a QP from userspace to kernel space in order to pass
>     Libor> it on to the kernel CM.  I'm thinking that the best way to
>     Libor> handle this is for the uCM library to pass uCM kernel the
>     Libor> uverbs QP handle, and then have the kernel uCM lookup the
>     Libor> QP from ib_uverbs. Unfortunetly this means ib_uverbs would
>     Libor> need to export a lookup function.
> 
>     Libor> Would you like a patch, or do you have some other idea?
> 
> Hmm, I guess that would be OK.  It does mean you have to hold a mutex
> to avoid another userspace thread killing the QP out from under you,
> which is a little ugly to expose...

 I was thinking of maybe ref counting the access, either in ib_qp or
ib_uobject. Adding a pair of functions, lookup and return, to manage 
the ref count... 

> What do you really need to do with the QP?  Can you just have
> userspace pass the information like QP number that you need?

I thought about that, here's the current list, but we would need to
lookup the pd anyway:

        qp->pd,
        qp->qp_num
        qp->qp_type
        qp->srq
        qp->device

-Libor