IORING_OFF_CQ_RING: mmap offset for completion queue ring
IORING_OFF_SQES: mmap offset for submission entries
IORING_OFF_SQ_RING: mmap offset for submission queue ring
(output) allocated entries in completion queue
(output) allocated entries in submission queue (both ring index array and separate entry array at SUBMISSION_QUEUE_ENTRIES_OFFSET).
(input) used if SQ_AFF and SQPOLL flags are active to pin poll thread to specific cpu. right now always checked in kernel for "possible cpu".
(input) used if SQPOLL flag is active; timeout in milliseconds until kernel poll thread goes to sleep.
Passed in for io_uring_setup(2). Copied back with updated info on success.
C API: struct io_uring_params