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
       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)