Low-level interface¶

struct io_uring_params¶

struct io_uring_params {
    __u32 sq_entries;
    __u32 cq_entries;
    __u32 flags;
    __u32 sq_thread_cpu;
    __u32 sq_thread_idle;
    __u32 features;
    __u32 wq_fd;
    __u32 resv[3];
    struct io_sqring_offsets sq_off;
    struct io_cqring_offsets cq_off;
};

Setup time flags¶

These are passed to io_uring_setup() and io_uring_queue_init().

IORING_SETUP_IOPOLL¶: io_context is polled

IORING_SETUP_SQPOLL¶: SQ poll thread

IORING_SETUP_SQ_AFF¶: sq_thread_cpu is valid

IORING_SETUP_CQSIZE¶: app defines CQ size

IORING_SETUP_CLAMP¶: clamp SQ/CQ ring sizes

IORING_SETUP_ATTACH_WQ¶: attach to existing wq

SQE Flags¶

IOSQE_FIXED_FILE
When this flag is specified, fd is an index into the files array registered with the io_uring in‐ stance (see the IORING_REGISTER_FILES section of the io_uring_register(2) man page). Available since 5.1.

IOSQE_IO_DRAIN
When this flag is specified, the SQE will not be started before previously submitted SQEs have completed, and new SQEs will not be started before this one completes. Available since 5.2.

IOSQE_IO_LINK
When this flag is specified, it forms a link with the next SQE in the submission ring. That next SQE will not be started before this one completes. This, in effect, forms a chain of SQEs, which can be arbitrarily long. The tail of the chain is denoted by the first SQE that does not have this flag set. This flag has no effect on previous SQE submissions, nor does it impact SQEs that are outside of the chain tail. This means that multiple chains can be executing in parallel, or chains and individual SQEs. Only members inside the chain are serialized. A chain of SQEs will be broken, if any request in that chain ends in error. io_uring considers any unexpected result an error. This means that, eg, a short read will also terminate the remainder of the chain. If a chain of SQE links is broken, the remaining unstarted part of the chain will be terminated and completed with -ECANCELED as the error code. Available since 5.3.

IOSQE_IO_HARDLINK
Like IOSQE_IO_LINK, but it doesn’t sever regardless of the completion result. Note that the link will still sever if we fail submitting the parent request, hard links are only resilient in the presence of completion results for requests that did submit correctly. IOSQE_IO_HARDLINK implies IOSQE_IO_LINK. Available since 5.5.

IOSQE_ASYNC
Normal operation for io_uring is to try and issue an sqe as non-blocking first, and if that fails, execute it in an async manner. To support more efficient overlapped operation of requests that the application knows/assumes will always (or most of the time) block, the application can ask for an sqe to be issued async from the start. Available since 5.6.

int io_uring_setup(unsigned entries, struct io_uring_params *p)¶