creates a completion event channel for the RDMA device context
destroys the completion event channel
returns a pointer to the created completion event channel, or NULL if the request fails.
returns 0 on success, or the value of errno on failure (which indicates the failure reason).
A "completion channel" is an abstraction introduced by libibverbs that
does not exist in the InfiniBand Architecture verbs specification or
RDMA Protocol Verbs Specification. A completion channel is
essentially file descriptor that is used to deliver completion
notifications to a userspace process. When a completion event is
generated for a completion queue (CQ), the event is delivered via the
completion channel attached to that CQ. This may be useful to steer
completion events to different threads by using multiple completion
fails if any CQs are still associated with the completion event
channel being destroyed.