Function _io_uring_get_sqe

src/include/liburing.h:1964–1978

* Return an sqe to fill. Application must later call io_uring_submit() * when it's ready to tell the kernel about it. The caller may call this * function multiple times before calling io_uring_submit(). * * Returns a vacant sqe, or NULL if we're full. */

 * Returns a vacant sqe, or NULL if we're full.
 */
IOURINGINLINE struct io_uring_sqe *_io_uring_get_sqe(struct io_uring *ring)
	LIBURING_NOEXCEPT
{
	struct io_uring_sq *sq = &ring->sq;
	unsigned head = io_uring_load_sq_head(ring), tail = sq->sqe_tail;
	struct io_uring_sqe *sqe;

	if (tail - head >= sq->ring_entries)
		return NULL;

	sqe = &sq->sqes[(tail & sq->ring_mask) << io_uring_sqe_shift(ring)];
	sq->sqe_tail = tail + 1;
	io_uring_initialize_sqe(sqe);
	return sqe;
}

/*
 * Return the appropriate mask for a buffer ring of size 'ring_entries'