The user is responsible for ensuring that the remote peer has queued a
receive request before issuing the send operations. For a list of
supported flags, see ibv_post_send. Unless the send request is using
inline data, the message buffers must have been registered
before being posted, and the buffers must remain registered
until the send completes.
Send operations may not be posted to an rdma_cm_id or the corresponding
queue pair until it has been connected.
The user-defined context associated with the send request will be
returned to the user through the work completion wr_id, work request
identifier, field.