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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | SEE ALSO | COLOPHON |
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io_uring_queue_init(3) liburing Manual io_uring_queue_init(3)
io_uring_queue_init - setup io_uring submission and completion
queues
#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);
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).
io_uring_queue_init(3) returns 0 on success and -errno on
failure.
io_uring_setup(2), io_uring_register_ring_fd(3), mmap(2),
io_uring_queue_exit(3)
This page is part of the liburing (A library for io_uring)
project. Information about the project can be found at
⟨https://github.com/axboe/liburing⟩. If you have a bug report for
this manual page, send it to io-uring@vger.kernel.org. This page
was obtained from the project's upstream Git repository
⟨https://github.com/axboe/liburing⟩ 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
man-pages@man7.org
liburing-0.7 July 10, 2020 io_uring_queue_init(3)
Pages that refer to this page: io_uring_prep_accept(3), io_uring_prep_accept_direct(3), io_uring_prep_connect(3), io_uring_prep_files_update(3), io_uring_prep_link(3), io_uring_prep_linkat(3), io_uring_prep_mkdir(3), io_uring_prep_mkdirat(3), io_uring_prep_multishot_accept(3), io_uring_prep_multishot_accept_direct(3), io_uring_prep_openat2(3), io_uring_prep_openat2_direct(3), io_uring_prep_openat(3), io_uring_prep_openat_direct(3), io_uring_prep_readv2(3), io_uring_prep_readv(3), io_uring_prep_recvmsg(3), io_uring_prep_recvmsg_multishot(3), io_uring_prep_rename(3), io_uring_prep_renameat(3), io_uring_prep_sendmsg(3), io_uring_prep_statx(3), io_uring_prep_symlink(3), io_uring_prep_symlinkat(3), io_uring_prep_timeout(3), io_uring_prep_timeout_remove(3), io_uring_prep_timeout_update(3), io_uring_prep_unlink(3), io_uring_prep_unlinkat(3), io_uring_prep_writev2(3), io_uring_prep_writev(3), io_uring_queue_init(3), io_uring_queue_init_params(3), io_uring_submit(3)
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