io_uring_queue_init_params(3) — Linux manual page


io_uring_queue_init(3)       liburing Manual      io_uring_queue_init(3)

NAME         top

       io_uring_queue_init - setup io_uring submission and completion

SYNOPSIS         top

       #include <liburing.h>

       int io_uring_queue_init(unsigned entries,
                               struct io_uring *ring,
                               unsigned flags);

       int io_uring_queue_init_params(unsigned entries,
                                      struct io_uring *ring,
                                      struct io_uring_params *params);

DESCRIPTION         top

       The io_uring_queue_init(3) function executes the
       io_uring_setup(2) system call to initialize the submission and
       completion queues in the kernel with at least entries entries in
       the submission queue and then maps the resulting file descriptor
       to memory shared between the application and the kernel.

       By default, the CQ ring will have twice the number of entries as
       specified by entries for the SQ ring. This is adequate for
       regular file or storage workloads, but may be too small networked
       workloads. The SQ ring entries do not impose a limit on the
       number of in-flight requests that the ring can support, it merely
       limits the number that can be submitted to the kernel in one go
       (batch). if the CQ ring overflows, e.g. more entries are
       generated than fits in the ring before the application can reap
       them, then the ring enters a CQ ring overflow state. This is
       indicated by IORING_SQ_CQ_OVERFLOW being set in the SQ ring
       flags. Unless the kernel runs out of available memory, entries
       are not dropped, but it is a much slower completion path and will
       slow down request processing. For that reason it should be
       avoided and the CQ ring sized appropriately for the workload.
       Setting cq_entries in struct io_uring_params will tell the kernel
       to allocate this many entries for the CQ ring, independent of the
       SQ ring size in given in entries.  If the value isn't a power of
       2, it will be rounded up to the nearest power of 2.

       On success, io_uring_queue_init(3) returns 0 and ring will point
       to the shared memory containing the io_uring queues. On failure
       -errno is returned.

       flags will be passed through to the io_uring_setup syscall (see

       If the io_uring_queue_init_params(3) variant is used, then the
       parameters indicated by params will be passed straight through to
       the io_uring_setup(2) system call.

       On success, the resources held by ring should be released via a
       corresponding call to io_uring_queue_exit(3).

RETURN VALUE         top

       io_uring_queue_init(3) returns 0 on success and -errno on

SEE ALSO         top

       io_uring_setup(2), io_uring_register_ring_fd(3), mmap(2),

COLOPHON         top

       This page is part of the liburing (A library for io_uring)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, send it to  This page
       was obtained from the project's upstream Git repository
       ⟨⟩ on 2022-12-17.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2022-12-12.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

liburing-0.7                  July 10, 2020       io_uring_queue_init(3)

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