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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 2025-02-02. (At that time,
the date of the most recent commit that was found in the
repository was 2025-01-22.) 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_queue_init(3), io_uring_queue_init_mem(3), io_uring_queue_init_params(3)
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HTML rendering created 2025-02-02 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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