The user is responsible for ensuring that a receive buffer is posted
and large enough to contain all sent data before the peer posts the
corresponding send message. The message buffer must have been registered
before being posted, with the mr parameter referencing the registration.
The buffer must remain registered until the receive completes.
Messages may be posted to an rdma_cm_id only after a queue pair has
been associated with it. A queue pair is bound to an rdma_cm_id after
calling rdma_create_ep or rdma_create_qp, if the rdma_cm_id is allocated
using rdma_create_id.
The user-defined context associated with the receive request will be
returned to the user through the work completion wr_id, work request
identifier, field.