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Re: [buildd-tools-devel] testers wanted: sbuild and build-dependencies

Roger Leigh <rleigh@codelibre.net> writes:

> On Wed, Nov 10, 2010 at 01:00:29PM +0100, Goswin von Brederlow wrote:
>> Roger Leigh <rleigh@debian.org> writes:
>> > A new "aptitude" resolver has been written by Marc 'HE' Brockschmidt.
>> > This creates a dummy "dependency package" which is installed and
>> > contains Depends and Conflicts for all the appropriate Build-Depends
>> > and Build-Conflicts, and uses aptitude to install and remove the
>> > appropriate packages to satisfy them.  This has been in use on our
>> > experimental buildds for about a year, and we now want to look towards
>> > making it the default.  However, we need some more widespread testing
>> > to make sure the dependency resolving doesn't result in inconsistent
>> > installation of packages and hence inconsistent library dependencies
>> > or break building of any packages etc.
>> Yet another or did he take the one from pbuilder?
> It's new, but based upon the ideas in pbuilder.
> Just to mention in passing, I also wrote an additional "apt"
> resolver last night, based on the aptitude resolver, which works
> in exactly the same way.  Not usable under all circumstances yet,
> but also available (in git only at present) for testing.  The
> main issue with apt is getting "apt-get -yf install" to not choose
> to remove the dependency package as a solution!  Currently looking
> at the possibilities here--any thoughts welcome!

Does that actually happen in cases where another solution would keep it?

There is a solution to this actually. Create a Packages, Release and
Release.gpg file for the pseudo package and add them as file:// url to
sources.list.d/. Then just apt-get install pseudo-package.

>> This destroys the determinicity of build dependencies. So if I say
>>   Build-Depends: lib-new-name | lib-old-name
>> so the package builds (for users) in both stable/testing and unstable it
>> is no longer given which library is used by the unstable buildds. Some
>> will pick lib-new-name and some, where the new lib isn't compiled yet,
>> lib-old-name. And so on.
>> I always heard determinicity was a wanted feature for the buildds.
> It is, and this is something to look at carefully.  In the example
> above, this is a very real problem (which could be rectified by
> having stricter build-deps).
> The root problem here is that at any given moment in time, unstable
> is not in a consistent state--packages may be outdated on several
> architectures, and so a package build may use (and depend on)
> different versions in different architectures.  There are several
> places this could be fixed:
> â?¢ we could keep packages out of the archive until built on all
>   architectures.
> â?¢ we could dep-wait a package until all its deps are the same
>   across all architectures

That is called testing. And for anything doing a library transition that
obviously won't work or migration to testing wouldn't be such big
problem all around.

Don't forget this not only happens when a package itself differs between
arch. This can also happen if any of the recursive depends differs. On
one arch lib-new-name can exist but be uninstallable while on another it
is installable.

> â?¢ we could keep the current approach of banning alternatives
>   entirely (but note that this does not solve the entire problem,
>   it's still easy to get inconsistency anyway)
> The existing approach to determinism is not to support alternatives
> at all, which is clearly not ideal.  While I don't think we should
> be encouraging the use of alternative build-deps, this is one of the
> most commonly reported bugs in sbuild--there are valid use cases for
> them.

Actually alternatives are supported. Most notably in A [i386] | B
[!i386]. Sbuild fixates on the first alternative that should be
installable. That makes it 100% perdictable to the uploader which
package he gets.

> All the modern buildds are based around snapshotting the build chroot,
> which gives us a clean slate at the start of each build.  Providing we
> have a common base environment across all our buildds, this should
> provide a measure of stability--I don't think any of the existing
> resolvers choose packages randomly--so the resolver should pick the
> same package sets across architectures so long as the available
> packages are the same.  Now, this might not always be true, but this
> also affects the existing resolver as well.  Not letting binary
> packages enter unstable until built on all architectures would be a
> solution to this.  I'd have to say, solving the problem at its root,
> and giving our tools more flexibility would be the ideal outcome.

Problem is packages aren't the same and enforcing sameness causes too
much delay and deadlocks. Just look at testing.


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