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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |NOTES |SEE ALSO |COLOPHON | |
io_uring_prep_openat(3) liburing Manualio_uring_prep_openat(3)io_uring_prep_openat - prepare an openat request
#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <liburing.h>void io_uring_prep_open(struct io_uring_sqe *sqe,const char *path,intflags,mode_tmode);void io_uring_prep_open_direct(struct io_uring_sqe *sqe,const char *path,intflags,mode_tmode,unsignedfile_index);void io_uring_prep_openat(struct io_uring_sqe *sqe,intdfd,const char *path,intflags,mode_tmode);void io_uring_prep_openat_direct(struct io_uring_sqe *sqe,intdfd,const char *path,intflags,mode_tmode,unsignedfile_index);
Theio_uring_prep_openat(3) function prepares an openat request. The submission queue entrysqe is setup to use the directory file descriptordfd to start opening a file described bypath and using the open flags inflags and using the file mode bits specified inmode. Similarlyio_uring_prep_open(3) prepares an open request. If the direct variant is used, the application must first have registered a file table usingio_uring_register_files(3) of the appropriate size. Once registered, a direct accept request may use any entry in that table and is specified infile_index , as long as it is within the size of the registered table. If a 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 withio_uring_register_files_update(3). IfIORING_FILE_INDEX_ALLOCis used as thefile_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 CQEres field just like it would be for a non-direct open request. If no more entries are available in the direct descriptor table,-ENFILEis 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_FILEmust be set in the SQEflags member, and the SQEfd field should use the direct descriptor value rather than the regular file descriptor. Direct descriptors are managed like registered files. The directory file descriptordfd is always a regular file descriptor. Note that old kernels don't check the SQEfile_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 asyncopenat(2) oropen(2) request. See that man page for details.
None
The CQEres 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-1on failure and seterrno to the actual error value, io_uring never useserrno. Instead it returns the negatederrno directly in the CQEres 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 theIORING_FEAT_SUBMIT_STABLEflag passed back fromio_uring_queue_init_params(3).
io_uring_get_sqe(3),io_uring_submit(3),io_uring_register(2),openat(2)
This page is part of theliburing (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 isnot part of the original manual page), send a mail to man-pages@man7.orgliburing-2.2 March 13, 2022io_uring_prep_openat(3)Pages that refer to this page:io_uring_prep_fixed_fd_install(3), io_uring_register_file_alloc_range(3)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |