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NAME
aio_read - asynchronous read from a file (REALTIME)
SYNOPSIS
#include <aio.h> int aio_read(struct aiocb *aiocbp);
DESCRIPTION
The aio_read() function shall read aiocbp->aio_nbytes from the file associated with aiocbp->aio_fildes
into the buffer pointed to by aiocbp->aio_buf. 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).
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 aiocbp->aio_reqprio.
The aiocbp value may be used as an argument to aio_error() and aio_return() 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
aio_offset, as if lseek() were called immediately prior to the operation with an offset equal to
aio_offset and a whence 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.
The aiocbp->aio_lio_opcode field shall be ignored by aio_read().
The aiocbp argument points to an aiocb structure. If the buffer pointed to by aiocbp->aio_buf or the
control block pointed to by aiocbp becomes an illegal address prior to asynchronous I/O completion, then
the behavior is undefined.
Simultaneous asynchronous operations using the same aiocbp produce undefined results.
If synchronized I/O is enabled on the file associated with aiocbp->aio_fildes, 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.
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.
For regular files, no data transfer shall occur past the offset maximum established in the open file
description associated with aiocbp->aio_fildes.
RETURN VALUE
The aio_read() 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 errno to indicate the
error.
ERRORS
The aio_read() function shall fail if:
EAGAIN The requested asynchronous I/O operation was not queued due to system resource limitations.
Each of the following conditions may be detected synchronously at the time of the call to aio_read(), or
asynchronously. If any of the conditions below are detected synchronously, the aio_read() function shall
return -1 and set errno 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.
EBADF The aiocbp->aio_fildes argument is not a valid file descriptor open for reading.
EINVAL The file offset value implied by aiocbp->aio_offset would be invalid, aiocbp->aio_reqprio is not a
valid value, or aiocbp->aio_nbytes is an invalid value.
In the case that the aio_read() 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 read() function call. In addition, the error status of the asynchronous
operation is set to one of the error statuses normally set by the read() function call, or one of the
following values:
EBADF The aiocbp->aio_fildes argument is not a valid file descriptor open for reading.
ECANCELED
The requested I/O was canceled before the I/O completed due to an explicit aio_cancel() request.
EINVAL The file offset value implied by aiocbp->aio_offset would be invalid.
The following condition may be detected synchronously or asynchronously:
EOVERFLOW
The file is a regular file, aiobcp->aio_nbytes is greater than 0, and the starting offset in
aiobcp->aio_offset is before the end-of-file and is at or beyond the offset maximum in the open
file description associated with aiocbp->aio_fildes.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The aio_read() function is part of the Asynchronous Input and Output option and need not be available on
all implementations.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
aio_cancel() , aio_error() , lio_listio() , aio_return() , aio_write() , close() , exec() , exit() ,
fork() , lseek() , read() , the Base Definitions volume of IEEE Std 1003.1-2001, <aio.h>
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 .