[Mesa-dev] [RFC] Compatibility between old dri modules and new loaders, and vice verse

[Ian Romanick]

On 06/22/2015 11:54 AM, Dave Airlie wrote:
>>
>> As kindly hinted by Marek, currently we do have a wide selection of
>> supported dri <> loader combinations.
>>
>> Although we like to think that things never break, we have to admit
>> that not many of us test every possible combinations of dri modules
>> and loaders. With the chances getting smaller as the time gap (age)
>> between the two increases. As such I would like to ask if we're
>> interested in gradually depreciating as the gap grows beyond X years.
>>
>> The rough idea that I have in my mind is:
>> - Check for obsolete extensions (requirements for such) - both in the
>> dri modules and the loaders (including the xserver).
>> - Add some WARN messages ("You're using an old loader/DRI module.
>> Update to XXX or later") when such code path is hit.
>> - After X mesa releases, we remove the dri extension from the
>> module(s) and bump the requirement(s) in the loader(s).
>>
>> And now the more important question why ?
>>  - Very rarely tested and not actively supported - if it works it
>> works, we only cover one stable branch.
>>  - Having a quick look at the the "if extension && extension.version
>>> = y" maze does leave most of us speechless.
>>  - Will allow us to start removing a few of the nasty quirks/hacks
>> that we currently have laying around.
>>
>> Worth mentioning:
>>  - Depreciation period will be based on the longest time frame set by
>> LTS versions of distros. For example if Debian A ships X and mesa 3
>> years apart, while Ubuntu does is ~2.5 and RedHat ~2.8, we'll stick
>> with 3 years.
>>  - libGL dri1 support... it's been almost four years since the removal
>> of the dri1 modules. Since then the only activity that I've noticed by
>> Connor Behan on the r128 front. Although it seems that he has covered
>> the ddx and is just looking at the kernel side of things. Should we
>> consider mesa X (10.6 ?) as the last one that supports such old
>> modules in it's libGL and give it a much needed cleanup ?
>>
>>
>> How would people feel about this - do we have any strong ack/nack
>> about the idea ? Are there many people/companies that support distros
>> where the xserver <> mesa gap is over, say 2 years ?
> 
> We still ship 7.11 based dri1 drivers in RHEL6, and there is still a
> chance of us rebasing to newer Mesa in that depending on schedules.
> 
> ajax might have a different opinion, on how likely that is, but
> that would be at least another year from now where we'd want DRI1
> to work.

A time line would be good.  I think it will take a fair amount of time
to get a new loader<>driver interface in order.  If we can't change
anything for two years, then there's not a lot of point to thinking
about it now.  If it's a year or less away, that's a different story.

The other possibility would be for RHEL to ship more than one libGL...
one for DRI1 drivers and one for everything else.  I don't know how
horrible that would be.

> Dave.
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