Prepare a uring_cmd request
# DESCRIPTION
The [io_uring_prep_uring_cmd128] function prepares uring_cmd (fd
specific) request for a 128 byte submission queue entry. The submission
queue entry *sqe* is setup to use the filedescriptor *fd* to send file
descriptor specific *cmd_op*.
The reserved fields are initialized to 0. Otherwise the caller has to
set up any submission queue entry's operation specific fields.
# RETURN VALUE
None
# ERRORS
None
# SEE ALSO
[io_uring_prep_uring_cmd], [io_uring_get_sqe],
[io_uring_submit],