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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);
int io_uring_queue_init_mem(unsigned entries,
struct io_uring *ring,
struct io_uring_params *params,
void *buf, size_t buf_size);
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 if the kernel supports IORING_FEAT_NODROP the ring
enters a CQ ring overflow state. Otherwise it drops the CQEs and
increments cq.koverflow in struct io_uring with the number of
CQEs dropped. The overflow state 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)).
The io_uring_queue_init_params(3) and io_uring_queue_init_mem(3)
variants will pass the parameters indicated by params straight
through to the io_uring_setup(2) system call.
The io_uring_queue_init_mem(3) variant uses the provided buf with
associated size buf_size as the memory for the ring, using the
IORING_SETUP_NO_MMAP flag to io_uring_setup(2). The buffer
passed to io_uring_queue_init_mem(3) must already be zeroed.
Typically, the caller should allocate a huge page and pass that
in to io_uring_queue_init_mem(3). Pages allocated by mmap are
already zeroed. io_uring_queue_init_mem(3) returns the number of
bytes used from the provided buffer, so that the app can reuse
the buffer with the returned offset to put more rings in the same
huge page.
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) and io_uring_queue_init_params(3) return 0
on success and -errno on failure.
io_uring_queue_init_mem(3) returns the number of bytes used from
the provided buffer 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 2023-12-22. (At that
time, the date of the most recent commit that was found in the
repository was 2023-12-19.) 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_sendmsg_zc(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_mem(3), io_uring_queue_init_params(3), io_uring_submit(3)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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