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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | SEE ALSO | COLOPHON |
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io_uring_register_files(3) liburing Manual io_uring_register_files(3)
io_uring_register_files - register file descriptors
#include <liburing.h>
int io_uring_register_files(struct io_uring *ring,
const int *files,
unsigned nr_files);
int io_uring_register_files_tags(struct io_uring *ring,
const int *files,
const __u64 *tags,
unsigned nr);
int io_uring_register_files_sparse(struct io_uring *ring,
unsigned nr_files);
int io_uring_register_files_update(struct io_uring *ring,
unsigned off,
const int *files,
unsigned nr_files);
int io_uring_register_files_update_tag(struct io_uring *ring,
unsigned off,
const int *files,
const __u64 *tags,
unsigned nr_files);
The io_uring_register_files(3) function registers nr_files number
of file descriptors defined by the array files belonging to the
ring for subsequent operations.
The io_uring_register_files_tags(3) function behaves the same as
io_uring_register_files(3) function but additionally takes tags
parameter. See IORING_REGISTER_BUFFERS2 for the resource tagging
description.
The io_uring_register_files_sparse(3) function registers an empty
file table of nr_files number of file descriptors. These files
must be updated before use, using eg
io_uring_register_files_update_tag(3). Note that if the size of
the sparse table exceeds what RLIMIT_NOFILE allows, then
io_uring_register_files_sparse(3) will attempt to raise the limit
using setrlimit(2) and retry the operation. If the registration
fails after doing that, then an error will be returned. The
sparse variant is available in kernels 5.19 and later.
Registering a file table is a prerequisite for using any request
that uses direct descriptors.
Registered files have less overhead per operation than normal
files. This is due to the kernel grabbing a reference count on a
file when an operation begins, and dropping it when it's done.
When the process file table is shared, for example if the process
has ever created any threads, then this cost goes up even more.
Using registered files reduces the overhead of file reference
management across requests that operate on a file.
The io_uring_register_files_update(3) function updates existing
registered files. The off is offset on which to start the update
nr_files number of files defined by the array files belonging to
the ring.
The io_uring_register_files_update_tag(3) function behaves the
same as io_uring_register_files_update(3) function but
additionally takes tags parameter. See IORING_REGISTER_BUFFERS2
for the resource tagging description.
On success io_uring_register_files(3),
io_uring_register_files_tags(3) and
io_uring_register_files_sparse(3) return 0.
io_uring_register_files_update(3) and
io_uring_register_files_update_tag(3) return number of files
updated. On failure they return -errno.
io_uring_register(2), io_uring_get_sqe(3),
io_uring_unregister_files(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 2025-08-11. (At that time,
the date of the most recent commit that was found in the
repository was 2025-08-02.) 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-2.1 November 15, 2021 io_uring_register_files(3)
Pages that refer to this page: io_uring_prep_accept(3), io_uring_prep_accept_direct(3), io_uring_prep_multishot_accept(3), io_uring_prep_multishot_accept_direct(3), io_uring_prep_open(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_open_direct(3), io_uring_prep_socket(3), io_uring_prep_socket_direct(3), io_uring_prep_socket_direct_alloc(3), io_uring_register_files(3), io_uring_register_files_sparse(3), io_uring_register_files_tags(3), io_uring_register_files_update(3), io_uring_register_files_update_tag(3)
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HTML rendering created 2025-09-06 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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