NAME

       io_uring_queue_init - setup io_uring submission and completion queues

SYNOPSIS

       #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

       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
       for 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 io_uring_setup(2)).

       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

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

SEE ALSO

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