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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 (consult 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 pri-
       ority 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 opera-
       tion, 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 syn-
       chronized 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  con-
       ditions below are detected synchronously, the aio_read() function shall
       return -1 and set errno to the corresponding value. If any of the  con-
       ditions  below  are  detected  asynchronously, the return status of the
       asynchronous operation is set to -1, and the error status of the  asyn-
       chronous 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  nor-
       mally returned by the read() function call. In addition, the error sta-
       tus of the asynchronous operation is set to one of the  error  statuses
       normally  set by the read() function call, or one of the following val-
       ues:
       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  asyn-
       chronously:
       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(3P)