prov/ucx: Question on event queues and connectionless endpoints

[AOA-Mohammed]

According to https://ofiwg.github.io/libfabric/v2.3.1/man/fi_setup.7.html and https://ofiwg.github.io/libfabric/v2.3.1/man/fi_endpoint.3.html, an event queue is needed for connected endpoints and passive endpoints, but not for connectionless endpoints.

However, nothing says that we can not create/bind an event queue to a connectionless endpoint. Would that be incorrect to create/bind an event queue to a connectionless endpoint?
I am asking because binding an event queue to a ucx endpoint fails with an error (invalid argument -FI_EINVAL).

If they are not required/used by a connectionless endpoint, is it better not to create them? (fewer resources)

[j-xiong]

Connectionless endpoints don't need and don't use event queues. The API doesn't explicitly define the outcome of trying to bind an event queue to a connectionless endpoint, but the common provider behavior is returning an error. Applications should avoid such kind of operations and yes, the event queue should not be created at all.