aio_read – asynchronous read

USAGE
       #include <aio.h>

       int aio_read(struct aiocb *aiocbp);

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_off-
       set,  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.

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

CONFORMING TO
       POSIX.1-2001