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       aio_read - asynchronous read


       #include <aio.h>

       int aio_read(struct aiocb *aiocbp);

       Link with -lrt.


       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.


       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).


       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.

              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.




       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.


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


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