[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)
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.



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