[pulseaudio-discuss] [PATCH] module-gsettings: new module to store configuration using gsettings

[Felipe Sateler]

On 6 October 2016 at 08:28, Tanu Kaskinen <tanuk at iki.fi> wrote:
> On Wed, 2016-10-05 at 12:14 -0300, Felipe Sateler wrote:
>> On 5 October 2016 at 05:17, Sylvain Baubeau <lebauce at gmail.com> wrote:
>> >
>> >
>> >
>> > 2016-10-04 13:04 GMT+02:00 Tanu Kaskinen <tanuk at iki.fi>:
>> > >
>> > >
>> > > On Fri, 2016-09-30 at 23:21 +0200, Sylvain Baubeau wrote:
>> > > > Thanks for pointing this out. I updated my paprefs patch to apply
>> > > > paprefs.convert at startup.
>> > >
>> > > Would it be feasible for you to make it a build time option to use
>> > > gconf or gsettings in paprefs?
>> >
>> >
>> > Yes, I think it's feasible but the code would need quite a lot of rework.
>>
>> I don't think this is necessary.
>
> If it's not configurable, that will force the gsettings transition on
> all distros. But I think I agree that it's good enough if the data gets
> moved on the first run of the new paprefs version, even if paprefs
> won't necessarily work before pulseaudio gets restarted.

Distros can do the transition on their own pace by delaying the
paprefs update. Paprefs is AFAICS a mature piece of software, it is
not getting new releases frequently anyway. Delaying a couple of
months the release would not be terrible I think.

>
>> > > > > However that leaves us with another problem, as the pulseaudio daemon
>> > > > > is not restarted automatically after an upgrade, and thus gsettings
>> > > > > module might not be loaded. But, I hope paprefs can already deal with
>> > > > > such a scenario and prompt the user accordingly.
>> > > > >
>> > > >
>> > > > Unfortunately, paprefs does not deal with such a scenario. It will
>> > > > therefore be able to modify the configuration but this configuration
>> > > > will
>> > > > only take effect when pulseaudio is restarted. What do you suggest
>> > > > prompting the user with ?
>> > >
>> > > Figuring out a good message is tricky. paprefs could just say "module-
>> > > gsettings not loaded", but it would be nice to able to tell the user
>> > > what to do. However, module-gsettings not being loaded may be because
>> > > the server is too old version and doesn't support module-gsettings at
>> > > all (distributions can deal this by depending on new enough server,
>> > > though), or it has been removed from default.pa and needs to be added
>> > > there, or the server has been updated but not restarted. The last
>> > > reason is the most likely one in the beginning, but over time it
>> > > becomes less and less likely, so just saying "restart pulseaudio" or
>> > > "reboot the machine" probably isn't a good idea.
>> > >
>> > > >
>> > > > >
>> > > > > In debian there is only paprefs depending on module-gconf. I don't
>> > > > > think we'll keep module-gconf after paprefs has migrated.
>> > >
>> > > If we release a pulseaudio version with module-gsettings before we
>> > > release paprefs with gsettings support, will you run pulseaudio with
>> > > both gconf and gsettings enabled, or only with gconf? Running with both
>> > > would have the benefit that if everything goes well, the data will be
>> > > migrated without any glitch when the new paprefs version is run for the
>> > > first time, because module-gsettings will be already loaded. The risk
>> > > with that is that the migration can't be tested at the time you enable
>> > > module-gsettings, since paprefs isn't ready. If there's some unforeseen
>> > > problem when paprefs is finally updated, and module-gsettings needs to
>> > > be fixed in some way, the migration might become even more complex,
>> > > because you need to deal with detecting a situation where the server is
>> > > running with a broken version of module-gsettings.
>> > >
>> >
>> > You're right, it's probably too complicated. It's better to stick with
>> > GConf.
>>
>> FWIW, I'd rather face a one-time upgrade glitch[1] than be stuck
>> forever with an unmaintained stack. So I don't agree that it is better
>> to stick with GConf.
>>
>> From my POV, making paprefs do the migration automatically is all that
>> is missing to perform an upgrade that is as seamless as possible.
>
> (I'm not sure my nitpicking is productive, but here it goes anyway:)
> It's not as seamless as possible, because there's a chance that paprefs
> won't work before pulseaudio gets updated. Also, the data move itself
> can cause glitching, because the modules loaded by module-gconf will be
> unloaded and then reloaded by module-gsettings.

Right, my use of "as possible" was not very clear. Sorry for the
confusion. I should have added "at reasonable effort". I'll expand a
bit below

> Maybe you're arguing that it's not possible to get rid of these
> glitches, but I think it is possible. Whether it makes sense to spend
> time implementing a "perfect" solution is a different question,
> however.

I do not know if it is possible, or how much effort it takes.

I do place a relatively low cost on one-time upgrade glitches that are
solved after a login/logout cycle. Therefore, I think that it does not
make much sense to spend too much effort in making this upgrade even
better. This is how I envision the upgrade scenario for a distro like
debian:

1. Introduce the new pulseaudio with module-gsettings enabled in
parallel to module-gconf. Make it
2. Do not introduce the new paprefs for some time. A couple of months
should be sufficient.
3. Introduce the new paprefs. Ensure sufficiently strict dependencies
with a pulseaudio daemon that supports gsettings.
4. At some later version, drop the gconf module. Add a Breaks
relationship to older paprefs that do not support gsettings.

The time window in 2 is to make as few people as possible not face the
problem of having a running pulseadio daemon that does not support
module-gsettings.[1]

Note that the alternative to this less-than-perfect upgrade process is
not glitchless status quo. It is my understanding[2] that gconf will
eventually be forcefully removed from mainstream distros when
sufficiently few apps use it, so the alternative is really to drop
paprefs and module-gconf entirely in a (possibly far) future date.


[1] In fact, we are getting close to a release in Debian. Maybe I
could even wait until stretch is released before updating paprefs
(AFAIK, gconf will still be part of debian in stretch), and update
shortly after it.
[2] Based on how distros normally work, I don't have any specific
plans to quote. But maintainers of obsolete software usually don't
want to keep maintaining it forever.

-- 

Saludos,
Felipe Sateler