The user is responsible for ensuring that the receive is posted,
and the total buffer space is large enough to contain all sent data
before the peer posts the corresponding send message. The message buffers
must have been registered before being posted, and the buffers 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.