[packagekit] preupgrade on Fedora and other distros

[Richard Hughes]

First, an explanation of the differences between update and upgrade,
in PackageKit parlance:

update: a simple remove and install that can be done on a running
system, e.g. update from totem 2.26.1 to totem 2.26.2
upgrade: updating all the packages at once, with transactions that can
not be done on the running system, e.g. update from Fedora 8 to Fedora
9.

Now, in Fedora we advise upgrading rather than updating in most
instances, as things like the update from static-dev -> udev and the
new rpm hash support need to be done with the _new_ versions of the
packages, with nothing else running.

At the moment, the upgrade framework for Fedora is:

1. session calls GetDistroUpgrades
2. system packagekitd responds with a list
3. session pops up bubble, with the latest upgrade shown
4. user clicks "upgrade" and the pk-upgrade-distro.sh file is run (as
the user, not as root)
5. If we're debian, we execute do-release-upgrade, if we're opensuse
we use wagon, and fedora we use preupgrade

now for fedora we have:

6. ask root password using consolehelper
7. run preupgrade application as root
8. download new anaconda and packages using yum
9. create kickstart file and add entry in grub.conf

Now, this is suboptimal for three reasons:

* We have a fedora specific UI which is not integrated with PolicyKit,
gnome/kde or the desktop.
* We are running a python application as root and using consolehelper.
* It's completely separate from PackageKit, and so preupgrade takes
the yum lock and blocks out all actions on the daemon until it's
completed.

Now, I'm guessing the problems we have with preupgrade are common to
other distros, and we probably need to look at PackageKit to help us
solve these properly. One very easy thing to do would be to add new
method UpgradeDistro(distro_id) which was protected by a PolicyKit
action, which actually did the mechanism. All we would then need to do
is either port the frontend parts of
preupgrade/wagon/do-release-upgrade to using PackageKit, or to sit
down with other interested parties (OpenSUSE?) and design a nice UI,
and ship it in the kpackagekit and gnome-packagekit projects.

To contend with MacOSX and Windows Vista, I do believe we need to have
a working online upgrade. I know for Fedora (but probably holds true
for other non-enterprise distros) that the frequency of releases
requires us even more-so to have a coherent stack for managing this.

I would appreciate anyone from other distros to tell us what they
think, and if they are interested in working together on this. Thanks.

Richard.