112 lines
3.0 KiB
Groff
112 lines
3.0 KiB
Groff
.\" 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)
|