For a list of supported flags, see ibv_post_send. Unless inline
data is specified, the local data buffers must have been registered
before the write is issued, and the buffers must remain registered
until the write completes. The remote buffers must always be registered.
Write 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 write request will be
returned to the user through the work completion wr_id, work request
identifier, field.