'\" t
.\" Copyright (c) 2003 Andries Brouwer (aeb@cwi.nl)
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.TH aio_read 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
aio_read \- asynchronous read
.SH LIBRARY
Real-time library
.RI ( librt ", " \-lrt )
.SH SYNOPSIS
.nf
.B "#include <aio.h>"
.PP
.BI "int aio_read(struct aiocb *" aiocbp );
.fi
.SH DESCRIPTION
The
.BR aio_read ()
function queues the I/O request described by the buffer pointed to by
.IR aiocbp .
This function is the asynchronous analog of
.BR read (2).
The arguments of the call
.PP
.in +4n
.EX
read(fd, buf, count)
.EE
.in
.PP
correspond (in order) to the fields
.IR aio_fildes ,
.IR aio_buf ,
and
.I aio_nbytes
of the structure pointed to by
.IR aiocbp .
(See
.BR aio (7)
for a description of the
.I aiocb
structure.)
.PP
The data is read starting at the absolute position
.IR aiocbp\->aio_offset ,
regardless of the file offset.
After the call,
the value of the file offset is unspecified.
.PP
The "asynchronous" means that this call returns as soon as the
request has been enqueued; the read may or may not have completed
when the call returns.
One tests for completion using
.BR aio_error (3).
The return status of a completed I/O operation can be obtained by
.BR aio_return (3).
Asynchronous notification of I/O completion can be obtained by setting
.I aiocbp\->aio_sigevent
appropriately; see
.BR sigevent (7)
for details.
.PP
If
.B _POSIX_PRIORITIZED_IO
is defined, and this file supports it,
then the asynchronous operation is submitted at a priority equal
to that of the calling process minus
.IR aiocbp\->aio_reqprio .
.PP
The field
.I aiocbp\->aio_lio_opcode
is ignored.
.PP
No data is read from a regular file beyond its maximum offset.
.SH RETURN VALUE
On success, 0 is returned.
On error, the request is not enqueued, \-1
is returned, and
.I errno
is set to indicate the error.
If an error is detected only later, it will
be reported via
.BR aio_return (3)
(returns status \-1) and
.BR aio_error (3)
(error status\[em]whatever one would have gotten in
.IR errno ,
such as
.BR EBADF ).
.SH ERRORS
.TP
.B EAGAIN
Out of resources.
.TP
.B EBADF
.I aio_fildes
is not a valid file descriptor open for reading.
.TP
.B EINVAL
One or more of
.IR aio_offset ,
.IR aio_reqprio ,
or
.I aio_nbytes
are invalid.
.TP
.B ENOSYS
.BR aio_read ()
is not implemented.
.TP
.B EOVERFLOW
The file is a regular file, we start reading before end-of-file
and want at least one byte, but the starting position is past
the maximum offset for this file.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR aio_read ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
glibc 2.1.
POSIX.1-2001.
.SH NOTES
It is a good idea to zero out the control block before use.
The control block must not be changed while the read operation
is in progress.
The buffer area being read into
.\" or the control block of the operation
must not be accessed during the operation or undefined results may occur.
The memory areas involved must remain valid.
.PP
Simultaneous I/O operations specifying the same
.I aiocb
structure produce undefined results.
.SH EXAMPLES
See
.BR aio (7).
.SH SEE ALSO
.BR aio_cancel (3),
.BR aio_error (3),
.BR aio_fsync (3),
.BR aio_return (3),
.BR aio_suspend (3),
.BR aio_write (3),
.BR lio_listio (3),
.BR aio (7)