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

On Wed, Nov 10, 2010 at 2:57 PM, Goswin von Brederlow <goswin-v-b@web.de> wrote:
> 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.

Another solution is to create a Sources file and use the 'build-dep'
command from apt-get or aptitude.

>>> 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:
>> • we could keep packages out of the archive until built on all
>>   architectures.
>> • 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.
>> • 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.

This use of alternatives will fail on non-i386 machines using sbuild's
internal build-dep resolver. It will succeed using apt or aptitude

Here's an example for anyone willing to try. It doesn't matter if the
architecture restrictions are there or not.
Build-Depends: linux-headers-2.6-i386 [i386] | linux-headers [!i386]

>> 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.
> MfG
>        Goswin
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Andres Mejia

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