[PATCH] Re: [linux-dvb] [PATCH] Multi protocol support (stage #1)

Trent Piepho xyzzy at speakeasy.org
Mon May 22 00:52:37 CEST 2006

On Sun, 21 May 2006, Johannes Stezenbach wrote:
> On Fri, May 19, 2006, Marcel Siegert wrote:
> > a) don't get any kind of e.g. memcopy problems with new structs and old
> > kernels after
> >    this patch went in. so the size of e.g. the tuning params for dvb-s2 can
> >    be extended
> >    without having to change the structs size. so also old kernel will
> >    perform a correct
> >    memcopy.
> 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.

Then userspace programs set the fields they know about to their (non-zero)

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.

More information about the linux-dvb mailing list