io_uring_get_sqe - get the next vacant event from the submission queue
struct io_uring_sqe *io_uring_get_sqe(struct io_uring *ring);
The io_uring_get_sqe() function gets the next vacant event from the submission
queue belonging to the ring param.
On success io_uring_get_sqe() returns a pointer to the submission
queue event. On failure NULL is returned.
If a submission queue event is returned, it should be filled out
via one of the prep functions such as io_uring_prep_read(3) and
submitted via io_uring_submit(3).
io_uring_get_sqe(3) returns a pointer to the next submission queue event
on success and NULL on failure.