On Thu, 2 Aug 2018 22:17:53 +0900 Toshiaki Makita <toshiaki.maki...@gmail.com> wrote:
> On 18/08/02 (木) 20:45, Jesper Dangaard Brouer wrote: > > On Thu, 2 Aug 2018 19:55:09 +0900 > > Toshiaki Makita <makita.toshi...@lab.ntt.co.jp> wrote: > > > >> + headroom = frame->data - delta - (void *)frame; > > > > Your calculation of headroom is still adding an assumption that > > xdp_frame is located in the top of data area, that is unnecessary. > > > > The headroom can be calculated as: > > > > headroom = sizeof(struct xdp_frame) + frame->headroom - delta; > > Thanks. But I'm not sure I get what you are requesting. I'm simply requesting you do not use the (void *)frame pointer address, to calculate the headroom, as it can be calculated in another way. > Supposing xdp_frame is not located in the top of data area, what ensures > that additional sizeof(struct xdp_frame) can be used? The calculation in convert_to_xdp_frame() assures this. If we later add an xdp_frame that is not located in the top of data area, and want to change the reserved headroom size, then we deal with it, and update the code. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
