Proposal to improve package configuration upgrades

Dominique Dumont · External Since: Feb 01, 2007 Posts: 29

Hello

The other day, I was upgrading cups and dpkg did ask me the usual way
if I wanted to keep my cups config file or take the upstream version.

Like always, I asked for a diff and was quite puzzled because I did
not remember anything about editing this file. Then I remembered that
I did a modification through cups admin web interface.

Previous common story you might say. But for a casual user (like my
mother-in-law which now use Debian Lenny Wink

), this can be
frustrating:
- I did modify the config through a nice web interface
- during the upgrade, I either have to look at all the gory details of
the config file or I have to loose my configuration.

So I was thinking that this is a typical case where the upgrade could
be smoothly handled by Config::Model.

Either in automatic mode where user data and upstream modifications
are merged (*) or in manual mode where the graphical (or curses)
interface is fired up so the user can check what's going on.

Of course, I (ou we) would need to integrate Config::Model in debconf
for this to work.

What do you think about this ?

All the best

(*) If you want I can go more in details on how an upgrade can be done

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Dominique Dumont
"Delivering successful solutions requires giving people what they
need, not what they want." Kurt Bittner

irc:
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Guy Hulbert · External Since: Jun 01, 2005 Posts: 16

On Tue, 2009-24-02 at 13:53 +0100, Dominique Dumont wrote:
> Of course, I (ou we) would need to integrate Config::Model in debconf
> for this to work.

Have you read debconf-devel(7) ?

Debconf has a well defined protocol to talk to a front-end and it looks
as if you just want a nicer front-end.

>
> What do you think about this ?

I don't think 'integrate' makes sense. To me, Config::Model looks like
it tries to do the same job as debconf.

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Jonas Smedegaard · External Since: Nov 18, 2004 Posts: 382

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On Tue, Feb 24, 2009 at 01:53:02PM +0100, Dominique Dumont wrote:

>The other day, I was upgrading cups and dpkg did ask me the usual way
>if I wanted to keep my cups config file or take the upstream version.
>
>Like always, I asked for a diff and was quite puzzled because I did
>not remember anything about editing this file. Then I remembered that
>I did a modification through cups admin web interface.
>
>Previous common story you might say. But for a casual user (like my
>mother-in-law which now use Debian Lenny Wink

), this can be
>frustrating:
>- I did modify the config through a nice web interface
>- during the upgrade, I either have to look at all the gory details of
> the config file or I have to loose my configuration.
>
>So I was thinking that this is a typical case where the upgrade could
>be smoothly handled by Config::Model.
>
>Either in automatic mode where user data and upstream modifications
>are merged (*) or in manual mode where the graphical (or curses)
>interface is fired up so the user can check what's going on.
>
>Of course, I (ou we) would need to integrate Config::Model in debconf
>for this to work.
>
>What do you think about this ?

Excellent proposal!

Augeas seems to gain momentum.

- Jonas

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* Tlf.: +45 40843136 Website: http://dr.jones.dk/

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Ansgar Burchardt · External Since: Feb 25, 2009 Posts: 11

Hi,

Dominique Dumont <dominique.dumont.TakeThisOut@hp.com> writes:

> Of course, I (ou we) would need to integrate Config::Model in debconf
> for this to work.
>
> What do you think about this ?

The recent discussion[1] on debian-devel about the interaction of ucf
and etcgit also touched the problems of merging changes to configuration
in an automatic way: one concern was that merging could produce an
invalid configuration. There was also the idea to add hooks to ucf to
enable other tools to handle merging the files.

I think the thread might be worth reading.

Regards,
Ansgar

Footnotes:
[1] http://lists.debian.org/debian-devel/2009/02/msg00596.html

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Russ Allbery · External Since: Nov 17, 2005 Posts: 897

Jonas Smedegaard <dr.DeleteThis@jones.dk> writes:

> Augeas seems to gain momentum.

Augeas, if I understand it correctly, requires modeling every
configuration file that you want to handle using it. That's going to make
it rather hard to use as a distribution-wide solution, although it may be
an improvement that's available in some specific cases where a model is
available.

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Jonas Smedegaard · External Since: Nov 18, 2004 Posts: 382

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On Tue, Feb 24, 2009 at 04:19:42PM -0800, Russ Allbery wrote:
>Jonas Smedegaard <dr DeleteThis @jones.dk> writes:
>
>> Augeas seems to gain momentum.
>
>Augeas, if I understand it correctly, requires modeling every
>configuration file that you want to handle using it. That's going to
>make it rather hard to use as a distribution-wide solution, although it
>may be an improvement that's available in some specific cases where a
>model is available.

Yes, it does require declaring a model.

Fuzzy 3-way non-interactive merging is evil, as seems to be the point of
others too (I have not read that thread on -devel).

I assumed that Config::Model was similarly about declaring a model, not
about guessing one. So I imagined that the suggestion to extend debconf
to use Config::Model was *exactly* about explicit models: providing
package maintainers an optional mechanism to express the model of their
configfiles for more reliable merging than ucf currently offers.

- Jonas

- --
* Jonas Smedegaard - idealist og Internet-arkitekt
* Tlf.: +45 40843136 Website: http://dr.jones.dk/

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Dominique Dumont · External Since: Feb 01, 2007 Posts: 29

Russ Allbery <rra.DeleteThis@debian.org> writes:

> Augeas, if I understand it correctly, requires modeling every
> configuration file that you want to handle using it.

Actually, Augeas requires a description of the syntax of the file (the
lens). Depending on the lens, the description may contain some
information regarding the semantics. With this description Augeas
provides a way to load configuration informations in a configuration
tree. But this configuration tree is often not able to validate
completely the content of the file.

On the other hand Config::Model require a complete description of the
semantic of the configuration file to construct a tree that will be
able to validate the content of a file. This description is
application dependant. It needs a way to load configuration file
content in the tree. This can be done with dedicated perl code (with
or without modules like Config::Ini) or with Augeas (See
Config::Model::OpenSsh for instance)

> That's going to make it rather hard to use as a distribution-wide
> solution,

It's not going to happen overnight...

> although it may be an improvement that's available in some specific
> cases where a model is available.

That's the idea.

All the best

--
Dominique Dumont
"Delivering successful solutions requires giving people what they
need, not what they want." Kurt Bittner

irc:
domidumont at irc.freenode.net
ddumont at irc.debian.org

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Dominique Dumont · External Since: Feb 01, 2007 Posts: 29

Jonas Smedegaard <dr.RemoveThis@jones.dk> writes:

> I assumed that Config::Model was similarly about declaring a model, not
> about guessing one. So I imagined that the suggestion to extend debconf
> to use Config::Model was *exactly* about explicit models: providing
> package maintainers an optional mechanism to express the model of their
> configfiles for more reliable merging than ucf currently offers.

Yes. Explicit models must be provided. See Config::Model::OpenSsh [1]
or Config::Model::Xorg[2] for instance.

An article is to be published in french magazine GNU/LinuxMag to
explain how was created the model for OpenSsh.

All the best

[1] http://cpansearch.perl.org/src/DDUMONT/Config-Model-OpenSsh-1.203/lib/...fig/Mod
[2] http://cpansearch.perl.org/src/DDUMONT/Config-Model-Xorg-0.513/lib/Con.../Model/

--
Dominique Dumont
"Delivering successful solutions requires giving people what they
need, not what they want." Kurt Bittner

irc:
domidumont at irc.freenode.net
ddumont at irc.debian.org

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Dominique Dumont · External Since: Feb 01, 2007 Posts: 29

gregor herrmann <gregoa.DeleteThis@debian.org> writes:

>> So I was thinking that this is a typical case where the upgrade could
>> be smoothly handled by Config::Model.
>
> If Config::Model could solve the merge problem (add the missing
> three-way-merge function) I'm sure many people would buy you
> $favourite_drink Smile

It won't be a walk in the park, but I'm sure we can do something
*very* useful.

> ISTR that has been discussed more than one time in the past but it
> still does not exist; I couldn't find anything on -devel or -project in 2009
>
> Ah, I was thinking of Arthur Liu's summary of last year's Google
> Summer of Code projects (summarised on his blog at
> http://www.milliways.fr/ , keyword "mergemaster")

This project looks dead.

> If I understand your idea and Config::Model's capabilities correctly
> I think this is definitively worth following. And I suggest to
> propose/discuss it on -devel (and maybe contact the people familiar
> with mergemaster or other previous efforts before).

Yes, I will propose this on -devel (and cc debian-perl) ASAP, so the
further discussions will be followed up by more people.

All the best

--
Dominique Dumont
"Delivering successful solutions requires giving people what they
need, not what they want." Kurt Bittner

irc:
domidumont at irc.freenode.net
ddumont at irc.debian.org

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