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NAME

       aio_read - asynchronous read

SYNOPSIS

       #include <aio.h>

       int aio_read(struct aiocb *aiocbp);

       Link with -lrt.

DESCRIPTION

       The  aio_read()  function  requests  an asynchronous "n = read(fd, buf,
       count)"   with   fd,   buf,   count   given   by    aiocbp->aio_fildes,
       aiocbp->aio_buf, aiocbp->aio_nbytes, respectively.  The return status n
       can be retrieved upon completion using aio_return(3).

       The   data   is   read   starting   at   the   absolute   file   offset
       aiocbp->aio_offset,  regardless  of  the  current file position.  After
       this request, the value of the current file position is unspecified.

       The "asynchronous" means that this call returns as soon as the  request
       has been enqueued; the read may or may not have completed when the call
       returns.  One tests for completion using aio_error(3).

       If _POSIX_PRIORITIZED_IO is defined, and this file  supports  it,  then
       the  asynchronous operation is submitted at a priority equal to that of
       the calling process minus aiocbp->aio_reqprio.

       The field aiocbp->aio_lio_opcode is ignored.

       No data is read from a regular file beyond its maximum offset.

RETURN VALUE

       On success, 0 is returned.  On error the request is not enqueued, -1 is
       returned,  and  errno  is  set  appropriately.   If  an  error is first
       detected later, it will be reported via aio_return(3)  (returns  status
       -1)  and  aio_error(3)  (error status whatever one would have gotten in
       errno, such as EBADF).

ERRORS

       EAGAIN Out of resources.

       EBADF  aio_fildes is not a valid file descriptor open for reading.

       EINVAL One or more of aio_offset, aio_reqprio, aio_nbytes are invalid.

       ENOSYS This function is not supported.

       EOVERFLOW
              The file is a regular file, we start reading before  end-of-file
              and  want  at  least one byte, but the starting position is past
              the maximum offset for this file.

CONFORMING TO

       POSIX.1-2001.

NOTES

       It is a good idea to zero out  the  control  block  before  use.   This
       control  block  must  not  be  changed  while  the read operation is in
       progress.  The buffer area being read into must not be accessed  during
       the  operation  or  undefined  results  may  occur.   The  memory areas
       involved must remain valid.

SEE ALSO

       aio_cancel(3),     aio_error(3),      aio_fsync(3),      aio_return(3),
       aio_suspend(3), aio_write(3)

COLOPHON

       This  page  is  part of release 3.27 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

                                  2003-11-14                       AIO_READ(3)