On Sun, May 21, 2006, Trent Piepho wrote:
> On Sun, 21 May 2006, Johannes Stezenbach wrote:
> >
> > For binary compatibility it isn't sufficient to just add new
> > fields to struct dvbs2_params. There must also be an indicator
> > which the kernel can use to see if struct dvb_frontend_params
> > was prepared by old or new userspace, i.e. if the new fields
> > are valid or contain uninitialized data.
>
> Would this work:
>
> Userspace programs must memset the entire dvbfe_params struct to zero. This
> in effect sets every field to XXXX_IGNORE.
You can't rely on that, and for some fields 0 is a valid value.
> Then userspace programs set the fields they know about to their (non-zero)
> values.
>
> If the kernel gets DVBFE_SET_PARAMS and a field is zero, that means the
> userspace program was using an old api before that field existed. The
> driver should do whatever it would do before the field was there.
Some people may like to write code like this:
int dvbs2_tune(int f, int sr, enum dvbfe_modulation mod, enum dvbfe_fec fec)
{
struct dvbfe_params foo = {
.frequency = f,
{
.dvbs2 = {
.symbol_rate = sr,
.modulation = mod,
.fec = fec
}
}
};
return ioctl(fefd, DVBFE_SET_PARAMS, &foo) == 0;
}
Johannes
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