70 lines
1.9 KiB
Groff
70 lines
1.9 KiB
Groff
.\" Copyright (C) 2021 Stefan Roesch <shr@fb.com>
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.\"
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.\" SPDX-License-Identifier: LGPL-2.0-or-later
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.\"
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.TH io_uring_prep_read 3 "November 15, 2021" "liburing-2.1" "liburing Manual"
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.SH NAME
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io_uring_prep_read \- prepare I/O read request
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.SH SYNOPSIS
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.nf
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.B #include <liburing.h>
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.PP
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.BI "void io_uring_prep_read(struct io_uring_sqe *" sqe ","
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.BI " int " fd ","
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.BI " void *" buf ","
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.BI " unsigned " nbytes ","
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.BI " __u64 " offset ");"
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.fi
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.SH DESCRIPTION
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.PP
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The
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.BR io_uring_prep_read (3)
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prepares an IO read request. The submission queue entry
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.I sqe
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is setup to use the file descriptor
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.I fd
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to start reading
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.I nbytes
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into the buffer
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.I buf
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at the specified
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.IR offset .
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On files that support seeking, if the offset is set to
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.BR -1 ,
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the read operation commences at the file offset, and the file offset is
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incremented by the number of bytes read. See
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.BR read (2)
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for more details. Note that for an async API, reading and updating the
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current file offset may result in unpredictable behavior, unless access
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to the file is serialized. It is not encouraged to use this feature, if it's
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possible to provide the desired IO offset from the application or library.
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On files that are not capable of seeking, the offset is ignored.
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After the read has been prepared it can be submitted with one of the submit
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functions.
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.SH RETURN VALUE
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None
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.SH ERRORS
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The CQE
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.I res
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field will contain the result of the operation. See the related man page for
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details on possible values. Note that where synchronous system calls will return
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.B -1
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on failure and set
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.I errno
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to the actual error value, io_uring never uses
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.IR errno .
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Instead it returns the negated
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.I errno
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directly in the CQE
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.I res
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field.
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.SH SEE ALSO
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.BR io_uring_get_sqe (3),
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.BR io_uring_prep_readv (3),
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.BR io_uring_prep_readv2 (3),
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.BR io_uring_submit (3)
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