73 lines
1.8 KiB
Groff
73 lines
1.8 KiB
Groff
.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
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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 "February 13, 2022" "liburing-2.1" "liburing Manual"
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.SH NAME
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io_uring_prep_read_fixed \- prepare I/O read request with registered buffer
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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_fixed(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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.BI " int " buf_index ");"
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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_fixed (3)
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prepares an IO read request with a previously registered IO buffer. The
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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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and with the buffer matching the registered index of
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.IR buf_index .
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This works just like
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.BR io_uring_prep_read (3)
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except it requires the use of buffers that have been registered with
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.BR io_uring_register_buffers (3).
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The
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.I buf
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and
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.I nbytes
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arguments must fall within a region specificed by
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.I buf_index
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in the previously registered buffer. The buffer need not be aligned with
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the start of the registered buffer.
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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_prep_read (3),
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.BR io_uring_register_buffers (3)
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