.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "AIO_READ" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" aio_read 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
aio_read \- asynchronous read from a file (\fBREALTIME\fP)
.SH SYNOPSIS
.LP
\fB#include <aio.h>
.br
.sp
int aio_read(struct aiocb *\fP\fIaiocbp\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIaio_read\fP() function shall read \fIaiocbp\fP->\fIaio_nbytes\fP
from the file associated with
\fIaiocbp\fP->\fIaio_fildes\fP into the buffer pointed to by \fIaiocbp\fP->\fIaio_buf\fP.
The function call shall return
when the read request has been initiated or queued to the file or
device (even when the data cannot be delivered immediately).
.LP
If prioritized I/O is supported for this file, then the asynchronous
operation shall be submitted at a priority equal to the
scheduling priority of the process minus \fIaiocbp\fP->\fIaio_reqprio\fP.
.LP
The \fIaiocbp\fP value may be used as an argument to \fIaio_error\fP()
and \fIaio_return\fP() in order to determine the error status and
return status, respectively, of
the asynchronous operation while it is proceeding. If an error condition
is encountered during queuing, the function call shall
return without having initiated or queued the request. The requested
operation takes place at the absolute position in the file as
given by \fIaio_offset\fP, as if \fIlseek\fP() were called immediately
prior to the
operation with an \fIoffset\fP equal to \fIaio_offset\fP and a \fIwhence\fP
equal to SEEK_SET. After a successful call to
enqueue an asynchronous I/O operation, the value of the file offset
for the file is unspecified.
.LP
The \fIaiocbp\fP->\fIaio_lio_opcode\fP field shall be ignored by \fIaio_read\fP().
.LP
The \fIaiocbp\fP argument points to an \fBaiocb\fP structure. If the
buffer pointed to by \fIaiocbp\fP->\fIaio_buf\fP or
the control block pointed to by \fIaiocbp\fP becomes an illegal address
prior to asynchronous I/O completion, then the behavior is
undefined.
.LP
Simultaneous asynchronous operations using the same \fIaiocbp\fP produce
undefined results.
.LP
If synchronized I/O is enabled on the file associated with \fIaiocbp\fP->\fIaio_fildes\fP,
the behavior of this function shall
be according to the definitions of synchronized I/O data integrity
completion and synchronized I/O file integrity completion. 
.LP
For any system action that changes the process memory space while
an asynchronous I/O is outstanding to the address range being
changed, the result of that action is undefined.
.LP
For regular files, no data transfer shall occur past the offset maximum
established in the open file description associated with
\fIaiocbp\fP->\fIaio_fildes\fP.
.SH RETURN VALUE
.LP
The \fIaio_read\fP() function shall return the value zero to the calling
process if the I/O operation is successfully queued;
otherwise, the function shall return the value -1 and set \fIerrno\fP
to indicate the error.
.SH ERRORS
.LP
The \fIaio_read\fP() function shall fail if:
.TP 7
.B EAGAIN
The requested asynchronous I/O operation was not queued due to system
resource limitations.
.sp
.LP
Each of the following conditions may be detected synchronously at
the time of the call to \fIaio_read\fP(), or asynchronously.
If any of the conditions below are detected synchronously, the \fIaio_read\fP()
function shall return -1 and set \fIerrno\fP to
the corresponding value. If any of the conditions below are detected
asynchronously, the return status of the asynchronous
operation is set to -1, and the error status of the asynchronous operation
is set to the corresponding value.
.TP 7
.B EBADF
The \fIaiocbp\fP->\fIaio_fildes\fP argument is not a valid file descriptor
open for reading.
.TP 7
.B EINVAL
The file offset value implied by \fIaiocbp\fP->\fIaio_offset\fP would
be invalid, \fIaiocbp\fP->\fIaio_reqprio\fP is
not a valid value, or \fIaiocbp\fP->\fIaio_nbytes\fP is an invalid
value.
.sp
.LP
In the case that the \fIaio_read\fP() successfully queues the I/O
operation but the operation is subsequently canceled or
encounters an error, the return status of the asynchronous operation
is one of the values normally returned by the \fIread\fP() function
call. In addition, the error status of the asynchronous operation
is set to one
of the error statuses normally set by the \fIread\fP() function call,
or one of the following
values:
.TP 7
.B EBADF
The \fIaiocbp\fP->\fIaio_fildes\fP argument is not a valid file descriptor
open for reading.
.TP 7
.B ECANCELED
The requested I/O was canceled before the I/O completed due to an
explicit \fIaio_cancel\fP() request.
.TP 7
.B EINVAL
The file offset value implied by \fIaiocbp\fP->\fIaio_offset\fP would
be invalid.
.sp
.LP
The following condition may be detected synchronously or asynchronously:
.TP 7
.B EOVERFLOW
The file is a regular file, \fIaiobcp\fP->\fIaio_nbytes\fP is greater
than 0, and the starting offset in
\fIaiobcp\fP->\fIaio_offset\fP is before the end-of-file and is at
or beyond the offset maximum in the open file description
associated with \fIaiocbp\fP->\fIaio_fildes\fP.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
The \fIaio_read\fP() function is part of the Asynchronous Input and
Output option and need not be available on all
implementations.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIaio_cancel\fP(), \fIaio_error\fP(), \fIlio_listio\fP(), \fIaio_return\fP(),
\fIaio_write\fP(), \fIclose\fP(), \fIexec\fP(), \fIexit\fP(),
\fIfork\fP(), \fIlseek\fP(), \fIread\fP(), the Base Definitions
volume of
IEEE\ Std\ 1003.1-2001, \fI<aio.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .