[linux-dvb] [PATCH] add device node locking possibility to dvbcore

Steven Toth stoth at hauppauge.com
Thu Aug 9 19:58:53 CEST 2007

Markus Rechberger wrote:
> On 8/9/07, Steven Toth <stoth at hauppauge.com> wrote:
>> Markus Rechberger wrote:
>>> Following patch adds a rather primitive way to temporary lock dvb
>>> devicenodes, this can be useful for hybrid devices which use the
>>> video4linux framework for the analogue TV part and the dvb framework for
>>> digital TV if only one mode can be accessed at a time.
>>> Signed-off-by: Markus Rechberger <markus.rechberger at amd.com>
>> Call me dumb but I don't understand how this patch helps v4l devices. :)
>> Allocation/management of a single card resource doesn't belong inside
>> the dvb framework, these answers need to come from the bridge-frameworks
>> (via callbacks from dvb-core or the analog equivalent) who are better
>> placed to make the decision about hybrid tuners, bus capacity or
>> allocation, in use devices.
>> As a working example, I added similar support in my older HVR3000 tree
>> where two frontends share a single transport bus. The code is old but it
>> demonstrates a solution, much the my earlier patches for shared
>> DVB/Blackbird boards also.
>> I understand how this patch helps the current dvb tree, it stops
>> multiple people opening a device but that's it. ... Or, maybe I've just
>> missed to point.
> Hi Steve,
> the bridge framework triggers locking these filehandles.
> http://mcentral.de/hg/~mrec/v4l-dvb-experimental/file/c0817d73a2a9/linux/drivers/media/video/em28xx/em28xx-video.c
> line 434
> this locks the dvb nodes if someone tries to open the v4l devicenode,
> it first checks if there's still something active at the DVB side.
> http://mcentral.de/hg/~mrec/v4l-dvb-experimental/file/f9f3e6bdd6fc/linux/drivers/media/video/em28xx/em2880-dvb.c
> Line 471 - 484 if this would go into the dvb core we'd have a callback
> for locking the device nodes.
Your comment about lines 471-484 make sense, but that code is not 
referenced via a callback (that I can see in the DVB patch) ... which is 
what I expected to see.

To do this cleanly in the dvb-core (or any v4l-core) I suggest requires 
callbacks into the bridge-frameworks and I didn't see those callbacks 
clearly defined in either your original patch, or your follow up 
patches. I was pretty sure I did something similar for the 
DVB/MpegEncoder shared bus support.

Have you seen this? http://linuxtv.org/hg/~stoth/hvr3000/rev/4b846f1d939b

Or more importantly this: 

Can we just re-use that?

- Steve

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