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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 queues the I/O request described by the buffer
       pointed to by aiocbp.  This function  is  the  asynchronous  analog  of
       read(2).  The arguments of the call

           read(fd, buf, count)

       correspond (in order) to the fields aio_fildes, aio_buf, and aio_nbytes
       of the structure pointed to by aiocbp.  (See aio(7) for  a  description
       of the aiocb structure.)

       The   data   is   read   starting   at   the   absolute   file   offset
       aiocbp->aio_offset, regardless of the current file offset.   After  the
       call, the value of the current file offset 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).  The return
       status of a completed I/O  operation  can  be  obtained  aio_return(3).
       Asynchronous  notification of I/O completion can be obtained by setting
       aiocbp->aio_sigevent appropriately; see sigevent(7) for details.

       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 only 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,  or  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.

VERSIONS

       The aio_read() function is available since glibc 2.1.

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       It  is  a  good  idea  to  zero  out the control block before use.  The
       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.

       Simultaneous I/O operations specifying the same aiocb structure produce
       undefined results.

EXAMPLE

       See aio(7).

SEE ALSO

       aio_cancel(3),     aio_error(3),      aio_fsync(3),      aio_return(3),
       aio_suspend(3), aio_write(3), lio_listio(3), aio(7)

COLOPHON

       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.

                                  2010-10-03                       AIO_READ(3)