[linux-dvb] Re: Types and capabilites for HDTV ATSC.

[Johannes Stezenbach <js@convergence.de>]

Holger Waechtler wrote:
> Johannes Stezenbach wrote:
> >Holger Waechtler wrote:
> >
> >>struct dvb_frontend_parameters {
> >>       __u32 frequency;
> >>       fe_spectral_inversion_t inversion;
> >>       union {
> >>               struct dvb_qpsk_parameters qpsk;
> >>               struct dvb_qam_parameters  qam;
> >>               struct dvb_ofdm_parameters ofdm;
> >>               struct dvb_atsc_parameters atsc;
> >>       } u;
> >>};
> >
> >
> >But you better make sure dvb_atsc_parameters isn't larger
> >than any of the other ones; if the size of struct
> >dvb_frontend_parameters changes, you'll break binary
> >compatibility.
> 
> are you sure? It should be safe because the extended struct fields would 
> only get accessed it (fe_type == FE_ATSC), not?

The size is encoded in the ioctl number, see asm/ioctl.h. We could
work around this by providing and _OLD variant of the ioctl, as
we did for NET_ADD_IF.

> (in any case I doubt that the atsc parameter set will get larger than 
> the DVB-T monster - ;)

I hope so.

Johannes