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 .

IEEE/The Open Group                                   2003                                           AIO_READ(P)