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Diffstat (limited to 'man/io_uring_prep_openat2.3')
| -rw-r--r-- | man/io_uring_prep_openat2.3 | 117 |
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diff --git a/man/io_uring_prep_openat2.3 b/man/io_uring_prep_openat2.3 new file mode 100644 index 0000000..338cf7e --- /dev/null +++ b/man/io_uring_prep_openat2.3 @@ -0,0 +1,117 @@ +.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk> +.\" +.\" SPDX-License-Identifier: LGPL-2.0-or-later +.\" +.TH io_uring_prep_openat2 3 "March 13, 2022" "liburing-2.2" "liburing Manual" +.SH NAME +io_uring_prep_openat2 \- prepare an openat2 request +.SH SYNOPSIS +.nf +.B #include <sys/types.h> +.B #include <sys/stat.h> +.B #include <fcntl.h> +.B #include <linux/openat2.h> +.B #include <liburing.h> +.PP +.BI "void io_uring_prep_openat2(struct io_uring_sqe *" sqe "," +.BI " int " dfd "," +.BI " const char *" path "," +.BI " int " flags "," +.BI " struct open_how *" how ");" +.PP +.BI "void io_uring_prep_openat2_direct(struct io_uring_sqe *" sqe "," +.BI " int " dfd "," +.BI " const char *" path "," +.BI " int " flags "," +.BI " struct open_how *" how "," +.BI " unsigned " file_index ");" +.fi +.SH DESCRIPTION +.PP +The +.BR io_uring_prep_openat2 (3) +function prepares an openat2 request. The submission queue entry +.I sqe +is setup to use the directory file descriptor +.I dfd +to start opening a file described by +.I path +and using the open flags in +.I flags +and using the instructions on how to open the file given in +.IR how . + +For a direct descriptor open request, the offset is specified by the +.I file_index +argument. 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 io_uring request that takes a file descriptor. To do so, +.B IOSQE_FIXED_FILE +must be set in the SQE +.I flags +member, and the SQE +.I fd +field should use the direct descriptor value rather than the regular file +descriptor. Direct descriptors are managed like registered files. + +If the direct variant is used, the application must first have registered +a file table using +.BR io_uring_register_files (3) +of the appropriate size. Once registered, a direct accept request may use any +entry in that table, 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 with +.BR io_uring_register_files_update (3). +Note that old kernels don't check the SQE +.I 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. +If +.B IORING_FILE_INDEX_ALLOC +is used as the +.I 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 +.I res +field just like it would be for a non-direct open request. If no more entries +are available in the direct descriptor table, +.B -ENFILE +is returned instead. + +These functions prepare an async +.BR openat2 (2) +request. See that man page for details. + +.SH RETURN VALUE +None +.SH ERRORS +The CQE +.I 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 +.B -1 +on failure and set +.I errno +to the actual error value, io_uring never uses +.IR errno . +Instead it returns the negated +.I errno +directly in the CQE +.I res +field. +.SH NOTES +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 +.B IORING_FEAT_SUBMIT_STABLE +flag passed back from +.BR io_uring_queue_init_params (3). +.SH SEE ALSO +.BR io_uring_get_sqe (3), +.BR io_uring_submit (3), +.BR io_uring_register (2), +.BR openat2 (2) |