[ofw] callback support in ibv_create_cq

[Sean Hefty]

>I would like to know if  libibverbs   'ibv_create_cq'  supports
>asynchronous callback  on completion of  post send transfer or only cq
>polling is supported.

It does not support asynchronous callbacks.  This matches the behavior on Linux.

>I observe IBAL 'ib_create_cq' supports asynchronous callback. So is the
>winverbs 'ibv_create_cq' constrained to polling mechanism only due to
>user mode mailbox  access to HCA.

IBAL supports asynchronous callbacks, but to do so, it allocates a thread that
waits for CQ events, then notifies the user in a callback.  The application can
achieve the same behavior by allocating a dedicated thread to wait for CQ
events, and invoking a notification function when a CQ event occurs.

Winverbs basically pushes the application threading model entirely into the
application, rather than automatically allocating threads in order to provide a
callback event model.

- Sean