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 .