multiarch library support in Natty and Oneiric

[Steve Langasek]

Dear developers,

Well, it's been a long time coming, but it's finally here.  As of today, it
is possible to install library packages of other architectures on your natty
system through multiarch.

That means that commands like this one can now be configured to work in an
amd64 chroot:

 $ sudo apt-get install flashplugin-installer:i386

Thanks to everyone who's helped get us to this stage!

We're still some way away from being able to do this on the desktop,
however, since this command currently wants to remove lots of amd64
libraries and replace them with the i386 ones!  Which is, in fact, the point
of this mail.  There's a core set of libraries that have now been
bootstrapped for multiarch in natty, but there are obviously a lot more
libraries that will need to be transitioned for multiarch before we can even
begin to think about dropping ia32-libs from the archive.

Many more, in fact, than we will have a chance to get to during the natty
cycle, since we are well past feature freeze already and there are almost 50
libraries yet to be converted before we can even run the above apt-get
command on a desktop, let alone address /all/ the use cases of ia32-libs.

Still, with a freeze exception granted by the release team and most of the
tricky dependencies already dealt with, I'm going to try to hit that target
in time for the beta freeze.  This would be a lot easier if it weren't a
one-man operation, so if anyone would like to help converting a stack of
libraries, please grab me on IRC to coordinate.

This is *not* an open invitation to convert arbitrary libraries to use the
multiarch paths; freeze exception or not, moving libraries around on the
system carries some significant risk of breakage, and needs to be done with
care and a clear understanding of the consequences - and a committment to
fix any of the fallout in order to not jeopardize the beta coming up next
week.  If there are other (small, self-contained) library sets that you
think are important to convert over for multiarch in natty, please talk to
me and we can try to coordinate this.

With the caveats out of the way, here's a link to some documentation
describing step-by-step how to convert a library package to the multiarch
paths:

  http://wiki.debian.org/Multiarch/Implementation

This documentation is written with both Debian and Ubuntu in mind.  Before
11.04 is released, I expect we'll see dpkg 1.16.0 landing in Debian
unstable, so even if we don't get everything into natty that we want we can
still help move this transition along in Debian so that oneiric opens with
as complete of multiarch support as possible.  So if you're interested in
helping with multiarch, please have a look at that page.  And please help
extend the documentation with anything I've missed!

And tune in next week for the documentation on how to configure your system
to use multiarch packages now that we have them. :-)

Thanks,
-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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