AIO_READ(3P)                                        POSIX Programmer's Manual                                       AIO_READ(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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 comple-
       tion.

       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 associ-
       ated 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  implementa-
       tions.

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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                  AIO_READ(3P)