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Launchpad Entry: hardy-lts-upgrades
Packages affected: update-manager
Summary
This spec describes what is required to implement 8.04 LTS to LTS+1 upgrades and some of the high level problems that need to be overcome for it.
Release Note
This makes it possible to do release upgrades from one long-term support release to the next in one step.
Rationale
Our LTS releases are supported for 3 years on the desktop and 5 on the server. This means that with the regular upgrades (that can't skip versions) the user will have to perform up a lot of them (and waste a lot of time/bandwidth).
Use Cases
Anne is using hardy on her desktop and she does not intend to upgrade to any other version than a LTS. When the new LTS comes out she gets a button telling her about the new LTS release and she happily upgrades.
Scope
This spec affects update-manager.
Design
Python problems
The changes in the python policy are challenging for the upgrader because it is written in python. The new policy allows only packages called "python-foo" that then contain the binary libs build against the currently supported python versions. The python-apt package currently contains:
/usr/lib/python2.5/site-packages/apt_pkg.so /usr/lib/python2.4/site-packages/apt_pkg.so
The old policy had packages for each python version (e.g. python2.4-apt). This means that during the upgrade from hardy that uses python2.5 by default some binary libs may go away because the python packages get upgraded and do no longer contain the libs for python2.5. Examples are python-apt, python-gtk, python-vte and python-qt3.
There are some ways around the problem, no one is very elegant:
- provide debs/udebs with the required libs and install them into location that the upgrader is unpacked. The disadvantage is that those need to go onto the alternative CD too
- rewrite the upgrader in C++ where propper shared libraries are available
- copy the required python libs into the upgrader place (how to find the information?)
- perform the upgrade from a special chroot environment and/or boot into special upgrade mode and/or provide a upgrade mode on the live-cd so that we have a stable environment while performing the upgrade
Notification
The update-manager in hardy has a configuration file /etc/update-manager/release-upgrades that can be used to specify what upgrade options are displayed. It defaults to "lts" upgrades only and can be changed with the gnome-software-properties tool.
Release-upgrader
The release upgrader supports two different upgrade configurations. If DistUpgrade.cfg.$fromDist is present, that will be used instead of the regular DistUpgrade.cfg. This means that a additional DistUpgrade.cfg.hardy needs to be created. If backports of apt/dpkg/python-apt are required we can use prereq.hardy.list.
CDROM upgrades
The pre-requisites for the upgrade need to go onto the CD. Build once for the previous LTS (e.g. dapper) and once for the previous regular version (e.g. gutsy). The upgrader needs to figure which one to use.
Future
Finding a way to test the upgrade in a fully revertable way would offer us a great many more testers. It should be investigated if it is feasible to implement a test-mode. With a test-mode like this it would be possible to find out in advance if all packages upgrade cleanly and if not to send a problem report.
A possible way to do this is a qemu/kvm based upgrade. It would require booting into a special test-mode where the main filesystem is mounted ro and a device-mapper COW device is created over the real root filesystem that is used for the upgrade test. The following steps are required:
- reboot into special test-mode
- create dm COW for the upgrade tester
- run script in COW target that will modify /etc/X11/xorg.conf to use "vesa" and modify /etc/fstab so that "/" is mounted from "/dev/hda" (and possibly other FS mount points have to change too)
- run qemu/kvm with that COW as rootfs and run the upgrade test in it
- when it finished, reboot again into the real system
- copy the upgrade logs from the COW device
The dm-snapshot documentation is available at: http://lxr.linux.no/source/Documentation/device-mapper/snapshot.txt
All the required features are available in dapper's 2.6.15 kernel.