[linux-dvb] [PATCH] Future of DVB-S2

Oliver Endriss o.endriss at gmx.de
Fri Aug 29 20:52:50 CEST 2008

Hans Werner wrote:
> > > Now, to show how simple I think all this could be, here is a PATCH
> > implementing what
> > > I think is the *minimal* API required to support DVB-S2.
> > >
> > > Notes:
> > >
> > > * same API structure, I just added some new enums and variables, nothing
> > removed
> > > * no changes required to any existing drivers (v4l-dvb still compiles)
> > > * no changes required to existing applications (just need to be
> > recompiled)
> > > * no drivers, but I think the HVR4000 MFE patch could be easily adapted
> > >
> > > I added the fe_caps2 enum because we're running out of bits in the
> > capabilities bitfield.
> > > More elegant would be to have separate bitfields for FEC capabilities
> > and modulation
> > > capabilities but that would require (easy) changes to (a lot of) drivers
> > and applications.
> > >
> > > Why should we not merge something simple like this immediately? This
> > could have been done
> > > years ago. If it takes several rounds of API upgrades to reach all the
> > feature people want then
> > > so be it, but a long journey begins with one step.
> > 
> > This will break binary compatibility with existing apps.  You're right
> > -- those apps will work with a recompile, but I believe that as a
> > whole, the linux-dvb kernel and userspace developers alike are looking
> > to avoid breaking binary compatibility.
> Michael,
> thank you for your comment.
> I understand, but I think binary compatibility *should* be broken in this case. It makes
> everything else simpler.

No way. Breaking binary compatibility is a no-go.

> I know that not breaking binary compatibility *can* be done (as in the HVR4000 SFE and
> MFE patches) but at what cost?  The resulting code is very odd. Look at multiproto which 
> bizarrely implements both the 3.2 and the 3.3 API and a compatibility layer as well, at huge cost
> in terms of development time and complexity of understanding. The wrappers used in the MFE
> patches are a neat and simple trick, but not something you would release in the kernel.

The only way to support DVB-S2 in a reasonable way is adding a new API.
Multiproto does this.

> If you take the position the binary interface cannot *ever* change then you are severely
> restricting the changes that can be made and you doom yourself to an API that is no longer
> suited to the job. And the complexity kills. As we have seen, it makes the whole process grind to a
> halt. 
> Recompilation is not a big deal. All distros recompile every application for each release (in fact much more frequently -- updates too), so most users will never even notice.  It is much better to make the right, elegant changes to the API and require a recompilation. It's better for the application developers because they get a sane evolution of the API and can more easily add new features. Anyone who
> really cannot recompile existing userspace binaries will also have plenty of other restrictions and
> should not be trying to drop a new kernel into a fixed userspace.

The linux distribution maintainers would kill you.
Applications must continue to run after a kernel update.

> I would be interested to hear your opinion on how we can move forward rapidly.

Multiproto should be merged asap.


VDR Remote Plugin 0.4.0: http://www.escape-edv.de/endriss/vdr/

More information about the linux-dvb mailing list