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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 dif-
       fer (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 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 con-
       dition 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 descrip-
       tion 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 asyn-
       chronously.  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  can-
       celed  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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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)