[linux-dvb] unique IDs for struct dvb_demux_feed

Patrick Boettcher patrick.boettcher at desy.de
Mon Feb 14 20:30:16 CET 2005

On Mon, 14 Feb 2005, Johannes Stezenbach wrote:

> Patrick Boettcher wrote:
>> When rewriting the skystar2 driver I saw something, which maybe can be put
>> into an upper layer:
>> Every driver, which's hardware supports PID filtering (in the demod or
>> anywhere else), implements a similar mechanism: They hold a table or a
>> static list with at least an unique ID, a pid value and an active-switch.
>> Each time the start_feed-callback is called they look for a free entry in
>> this list and reserve it until it is freed by the stop_feed-callback. The
>> unique ID can be understood as the position in the pid-filter-table of the
>> hardware, just incrementing the feed_count is of course not enough and ID
>> can be reused. For examples, see dvb-dibusb-pid, skystar2, ttusb-budget.
>> The easiest solution would be to add a unique ID to struct dvb_demux_feed.
>> Some ugly code duplicates can then be removed.
>> Please have a look at the attached patch. Does this small change in
>> dvb_demux.[ch] is sufficient, or did I miss anything?
> I guess dvb_demux.[ch] was written with devices like the Nova cards
> in mind. If your tiny patch lets us drop unnecessary code from
> dvb-dibusb-pid, skystar2, ttusb-budget then it can't be wrong ;-)

I'm not sure at all, but could it be, that adding another field to this 
struct, breaks compatibility with binary-only drivers? At least when they 
access dvb_demux_feed passed to start_feed. If so, is adding the new field 
at the end of the struct a solution?

Please enlighten me about the secrets of breaking binary compatibility. :)


   Mail: patrick.boettcher at desy.de
   WWW:  http://www.wi-bw.tfh-wildau.de/~pboettch/

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