> Are there calls in rdma_cm that allow me to do this? For the life of
> me I can't figure out how, for instance, I would write an app that has
> a single QP that recieves UD datagrams from anyone. How do potential
> clients find the QP number, qkey and ah without using listen/accept
> which will create a brand new QP every time?
Yeah, the UD sample was based on an RC sample and isn't all that instructive...
When you call rdma_accept(), you can specify the qp_num as part of the
conn_param. So, once you call rdma_create_qp(), you can just reference that
QPN for other lookup requests. The code could look something like this in the
thread that listens:
/* create QP */
rdma_create_id(&qp_id)
rdma_bind_addr()
rdma_create_qp()
/* listen for QPN lookup */
rdma_getaddrinfo(... use RAI_PASSIVE flag)
rdma_create_ep(&listen_id) /* or rdma_create_id + rdma_bind_addr */
rdma_listen()
/* get lookup requests, reply, then discard */
conn_param.qp_num = qp_id->qp->qp_num;
while (1) {
rdma_get_request(listen_id, new_id)
rdma_accept(new_id)
rdma_destroy_id(new_id)
}
If you use async operation, it requires a little more work to retrieve the
events from the kernel, but this is the basic idea. You can also create the QP
on the first request that you receive, as long as you don't destroy that id
until you're done with the QP. I think you can even call rdma_create_qp() on
the listen_id as long as it's been bound to a device first.
- Sean
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