Originální popis anglicky:
aio_read - asynchronous read from a file (
REALTIME)
Návod, kniha: POSIX Programmer's Manual
#include <aio.h>
int aio_read(struct aiocb *
aiocbp);
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.
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.
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.
None.
The
aio_read() function is part of the Asynchronous Input and Output
option and need not be available on all implementations.
None.
None.
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>
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
.
