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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | SEE ALSO | COLOPHON |
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io_uring_prep_openat2(3) liburing Manual io_uring_prep_openat2(3)
io_uring_prep_openat2 - prepare an openat2 request
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/openat2.h>
#include <liburing.h>
void io_uring_prep_openat2(struct io_uring_sqe *sqe,
int dfd,
const char *path,
struct open_how *how);
void io_uring_prep_openat2_direct(struct io_uring_sqe *sqe,
int dfd,
const char *path,
struct open_how *how,
unsigned file_index);
The io_uring_prep_openat2(3) function prepares an openat2 request.
The submission queue entry sqe is setup to use the directory file
descriptor dfd to start opening a file described by path and using
the instructions on how to open the file given in how.
If the direct variant is used, the application must first have
registered a file table using io_uring_register_files(3) of the
appropriate size. Once registered, a direct request may use any
entry in that table and is specified in file_index , as long as it
is within the size of the registered table. If the specified
entry already contains a file, the file will first be removed from
the table and closed. It's consistent with the behavior of
updating an existing file with io_uring_register_files_update(3).
If IORING_FILE_INDEX_ALLOC is used as the file_index for a direct
open, then io_uring will allocate a free direct descriptor in the
existing table. The allocated descriptor is returned in the CQE
res field just like it would be for a non-direct open request. If
no more entries are available in the direct descriptor table,
-ENFILE is returned instead.
Direct descriptors are io_uring private file descriptors. They
avoid some of the overhead associated with thread shared file
tables, and can be used in any subsequent io_uring request that
takes a file descriptor. To do so, IOSQE_FIXED_FILE must be set in
the SQE flags member, and the SQE fd field should use the direct
descriptor value rather than the regular file descriptor. Direct
descriptors are managed like registered files.
The directory file descriptor dfd is always a regular file
descriptor.
Note that old kernels don't check the SQE file_index field, which
is not a problem for liburing helpers, but users of the raw
io_uring interface need to zero SQEs to avoid unexpected behavior.
These functions prepare an async openat2(2) request. See that man
page for details.
None
The CQE res field will contain the result of the operation. See
the related man page for details on possible values. Note that
where synchronous system calls will return -1 on failure and set
errno to the actual error value, io_uring never uses errno.
Instead it returns the negated errno directly in the CQE res
field.
As with any request that passes in data in a struct, that data
must remain valid until the request has been successfully
submitted. It need not remain valid until completion. Once a
request has been submitted, the in-kernel state is stable. Very
early kernels (5.4 and earlier) required state to be stable until
the completion occurred. Applications can test for this behavior
by inspecting the IORING_FEAT_SUBMIT_STABLE flag passed back from
io_uring_queue_init_params(3).
io_uring_get_sqe(3), io_uring_submit(3), io_uring_register(2),
openat2(2)
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-2.2 March 13, 2022 io_uring_prep_openat2(3)
Pages that refer to this page: io_uring_prep_openat2(3), io_uring_prep_openat2_direct(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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