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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)