diff options
Diffstat (limited to 'man/io_uring_prep_readv2.3')
-rw-r--r-- | man/io_uring_prep_readv2.3 | 111 |
1 files changed, 111 insertions, 0 deletions
diff --git a/man/io_uring_prep_readv2.3 b/man/io_uring_prep_readv2.3 new file mode 100644 index 0000000..171a699 --- /dev/null +++ b/man/io_uring_prep_readv2.3 @@ -0,0 +1,111 @@ +.\" Copyright (C) 2021 Stefan Roesch <shr@fb.com> +.\" +.\" SPDX-License-Identifier: LGPL-2.0-or-later +.\" +.TH io_uring_prep_readv2 3 "November 15, 2021" "liburing-2.1" "liburing Manual" +.SH NAME +io_uring_prep_readv2 \- prepare vector I/O read request with flags +.SH SYNOPSIS +.nf +.B #include <sys/uio.h> +.B #include <liburing.h> +.PP +.BI "void io_uring_prep_readv2(struct io_uring_sqe *" sqe "," +.BI " int " fd "," +.BI " const struct iovec *" iovecs "," +.BI " unsigned " nr_vecs "," +.BI " __u64 " offset "," +.BI " int " flags ");" +.fi +.SH DESCRIPTION +.PP +The +.BR io_uring_prep_readv2 (3) +prepares a vectored IO read request. The submission queue entry +.I sqe +is setup to use the file descriptor +.I fd +to start reading +.I nr_vecs +into the +.I iovecs +array at the specified +.IR offset . +The behavior of the function can be controlled with the +.I flags +parameter. + +Supported values for +.I flags +are: +.TP +.B RWF_HIPRI +High priority request, poll if possible +.TP +.B RWF_DSYNC +per-IO O_DSYNC +.TP +.B RWF_SYNC +per-IO O_SYNC +.TP +.B RWF_NOWAIT +per-IO, return +.B -EAGAIN +if operation would block +.TP +.B RWF_APPEND +per-IO O_APPEND + +.P +On files that support seeking, if the offset is set to +.BR -1 , +the read operation commences at the file offset, and the file offset is +incremented by the number of bytes read. See +.BR read (2) +for more details. Note that for an async API, reading and updating the +current file offset may result in unpredictable behavior, unless access +to the file is serialized. It is not encouraged to use this feature, if it's +possible to provide the desired IO offset from the application or library. + +On files that are not capable of seeking, the offset is ignored. + +After the write has been prepared, it can be submitted with one of the submit +functions. + +.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 +Unless an application explicitly needs to pass in more than iovec, it is more +efficient to use +.BR io_uring_prep_read (3) +rather than this function, as no state has to be maintained for a +non-vectored IO request. +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_prep_read (3), +.BR io_uring_prep_readv (3), +.BR io_uring_submit (3) |