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

Jelle De Loecker skerit at kipdola.com
Sat Aug 30 01:46:28 CEST 2008


Wait, where are you going to merge the multiproto drivers to? Am I 
reading it correct that you'll get them in the dvb-4vl tree or.. What am 
I missing here? :)

This has been one hell of a day!

/Met vriendelijke groeten,/

*Jelle De Loecker*
Kipdola Studios - Tomberg 


Manu Abraham schreef:
> Oliver Endriss wrote:
>   
>> 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.
>>     
>
>
> True. Sorry about the long delay, just got back after quite a long
> journey. Will do so these following days.
>
> Regards,
> Manu
>
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