add io_uring_queue_mmap

io_uring_queue_init does not allow the caller to specify sq_thread_cpu
or sq_thread_idle.  Users that want to specify those parameters need to
call io_uring_setup(2) themselves.  Add a helper so that they don't also
have to hand-craft the code to map the submission and completion queues,
and setup the sqe ring.  This allows those applications to still make
use of io_uring_submit and get/wait_completion.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

src/liburing.h

@@ -56,6 +56,8 @@ extern int io_uring_register(int fd, unsigned int opcode, void *arg,
  */
 extern int io_uring_queue_init(unsigned entries, struct io_uring *ring,
 	unsigned flags);
+extern int io_uring_queue_mmap(int fd, struct io_uring_params *p,
+	struct io_uring *ring);
 extern void io_uring_queue_exit(struct io_uring *ring);
 extern int io_uring_get_completion(struct io_uring *ring,
 	struct io_uring_cqe **cqe_ptr);