[PATCH 1/3] libcsupport: Add and use rtems_libio_iovec_eval()

[Chris Johns]

On 17/12/2013 12:29 am, Sebastian Huber wrote:
> Pass also zero-size buffers to the write handler since they may have
> side-effects for non-regular files, e.g. sending of an empty message.

I agree regular files should follow the standard with others being 
unspecified. I do not think this patch does this.

> @@ -31,95 +29,31 @@ ssize_t writev(
>   {
>     ssize_t        total;
>     int            v;
> -  int            bytes;
>     rtems_libio_t *iop;
> -  ssize_t        old;
> -  bool           all_zeros;
>
> -  rtems_libio_check_fd( fd );
> -  iop = rtems_libio_iop( fd );
> -  rtems_libio_check_is_open( iop );
> -  rtems_libio_check_permissions_with_error( iop, LIBIO_FLAGS_WRITE, EBADF );
> -
> -  /*
> -   *  Argument validation on IO vector
> -   */
> -  if ( !iov )
> -    rtems_set_errno_and_return_minus_one( EINVAL );
> -
> -  if ( iovcnt <= 0 )
> -    rtems_set_errno_and_return_minus_one( EINVAL );
> -
> -  if ( iovcnt > IOV_MAX )
> -    rtems_set_errno_and_return_minus_one( EINVAL );
> -
> -  /*
> -   *  OpenGroup says that you are supposed to return EINVAL if the
> -   *  sum of the iov_len values in the iov array would overflow a
> -   *  ssize_t.
> -   *
> -   *  Also we would like to ensure that no IO is performed if there
> -   *  are obvious errors in the iovec.  So this extra loop ensures
> -   *  that we do not do anything if there is an argument error.
> -   *
> -   *  In addition,the OpenGroup specification says that if all the
> -   *  iov_len entries are zero, then the call has no effect.  So
> -   *  this loop does that check as well and sets "all-zero" appropriately.
> -   *  The variable "all_zero" is used as an early exit point before
> -   *  entering the write loop.
> -   */
> -  all_zeros = true;
> -  for ( old=0, total=0, v=0 ; v < iovcnt ; v++ ) {
> +  total = rtems_libio_iovec_eval( fd, iov, iovcnt, LIBIO_FLAGS_WRITE, &iop );
>
> +  if ( total >= 0 ) {

I am not sure about this...

> -  /*
> -   * A writev with all zeros is supposed to have no effect per OpenGroup.
> -   */
> -  if ( all_zeros == true ) {
> -    return 0;
> -  }

... as this statement is correct if the file is a regular file. I think 
a check for a regular file is needed if the total is 0.

Chris