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AIO_READ(P) AIO_READ(P)
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 asyn-
chronous 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 corre-
sponding 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 oper-
ation is subsequently canceled or encounters an error, the return status of the
asynchronous operation is one of the values normally returned by the read() func-
tion 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 .
POSIX 2003 AIO_READ(P)
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