mirror of https://github.com/mkerrisk/man-pages
177 lines
4.2 KiB
Groff
177 lines
4.2 KiB
Groff
.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
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.\"
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.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, see
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.\" <http://www.gnu.org/licenses/>.
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.\" %%%LICENSE_END
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.\"
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.TH AIO_READ 3 2021-03-22 "" "Linux Programmer's Manual"
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.SH NAME
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aio_read \- asynchronous read
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.SH SYNOPSIS
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.nf
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.B "#include <aio.h>"
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.PP
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.BI "int aio_read(struct aiocb *" aiocbp );
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.PP
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Link with \fI\-lrt\fP.
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.fi
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.SH DESCRIPTION
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The
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.BR aio_read ()
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function queues the I/O request described by the buffer pointed to by
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.IR aiocbp .
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This function is the asynchronous analog of
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.BR read (2).
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The arguments of the call
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.PP
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read(fd, buf, count)
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.PP
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correspond (in order) to the fields
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.IR aio_fildes ,
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.IR aio_buf ,
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and
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.IR aio_nbytes
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of the structure pointed to by
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.IR aiocbp .
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(See
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.BR aio (7)
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for a description of the
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.I aiocb
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structure.)
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.PP
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The data is read starting at the absolute position
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.IR aiocbp\->aio_offset ,
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regardless of the file offset.
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After the call,
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the value of the file offset is unspecified.
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.PP
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The "asynchronous" means that this call returns as soon as the
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request has been enqueued; the read may or may not have completed
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when the call returns.
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One tests for completion using
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.BR aio_error (3).
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The return status of a completed I/O operation can be obtained by
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.BR aio_return (3).
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Asynchronous notification of I/O completion can be obtained by setting
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.IR aiocbp\->aio_sigevent
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appropriately; see
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.BR sigevent (7)
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for details.
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.PP
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If
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.B _POSIX_PRIORITIZED_IO
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is defined, and this file supports it,
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then the asynchronous operation is submitted at a priority equal
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to that of the calling process minus
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.IR aiocbp\->aio_reqprio .
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.PP
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The field
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.I aiocbp\->aio_lio_opcode
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is ignored.
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.PP
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No data is read from a regular file beyond its maximum offset.
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.SH RETURN VALUE
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On success, 0 is returned.
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On error, the request is not enqueued, \-1
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is returned, and
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.I errno
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is set to indicate the error.
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If an error is detected only later, it will
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be reported via
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.BR aio_return (3)
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(returns status \-1) and
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.BR aio_error (3)
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(error status\(emwhatever one would have gotten in
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.IR errno ,
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such as
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.BR EBADF ).
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.SH ERRORS
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.TP
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.B EAGAIN
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Out of resources.
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.TP
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.B EBADF
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.I aio_fildes
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is not a valid file descriptor open for reading.
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.TP
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.B EINVAL
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One or more of
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.IR aio_offset ,
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.IR aio_reqprio ,
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or
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.I aio_nbytes
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are invalid.
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.TP
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.B ENOSYS
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.BR aio_read ()
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is not implemented.
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.TP
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.B EOVERFLOW
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The file is a regular file, we start reading before end-of-file
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and want at least one byte, but the starting position is past
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the maximum offset for this file.
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.SH VERSIONS
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The
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.BR aio_read ()
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function is available since glibc 2.1.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.ad l
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.nh
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.TS
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allbox;
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lbx lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR aio_read ()
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T} Thread safety MT-Safe
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.TE
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.hy
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.ad
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.sp 1
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008.
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.SH NOTES
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It is a good idea to zero out the control block before use.
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The control block must not be changed while the read operation
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is in progress.
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The buffer area being read into
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.\" or the control block of the operation
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must not be accessed during the operation or undefined results may occur.
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The memory areas involved must remain valid.
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.PP
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Simultaneous I/O operations specifying the same
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.I aiocb
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structure produce undefined results.
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.SH EXAMPLES
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See
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.BR aio (7).
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.SH SEE ALSO
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.BR aio_cancel (3),
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.BR aio_error (3),
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.BR aio_fsync (3),
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.BR aio_return (3),
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.BR aio_suspend (3),
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.BR aio_write (3),
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.BR lio_listio (3),
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.BR aio (7)
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