Wednesday, March 19, 2014

Qt 5.2.1 in Ubuntu

Ubuntu running Qt 5.2.1
Ubuntu running Qt 5.2.1
Qt 5.2.1 landed in Ubuntu 14.04 LTS last Friday, hooray! Making it into a drop-in replacement for Qt 5.0.2 was not trivial. Because of the qreal change, it was decided to rebuild everything against the new Qt, so it was an all at once approach involving roughly 130 source packages while the parts were moving constantly. The landing last week meant pushing to archives around three thousand binary packages - counting all six architectures - with the total size of closer to 10 gigabytes.

The new Qt brings performance and features to base future work on, and is a solid base for the future of Ubuntu. You may be interested in the release notes for Qt 5.2.0 and 5.2.1. The Ubuntu SDK got updated to Qt Creator 3.0.1 + new Ubuntu plugin at the same time, although updates for the older Ubuntu releases is a work in progress by the SDK Team.

How We Got Here

Throughout the last few months before the last joint push, I filed tens of tagged bugs. For most of that time I was interested only in build and unit test results, since even tracking those was quite a task. I offered simple fixes here and there myself, if I found out a fix.

I created automated Launchpad recipe builds for over 80 packages that rely on Qt 5 in Ubuntu. Meanwhile I also kept on updating the Qt packaging for its 20+ source packages and tried to stay on top of Debian's and upstream's changes.

Parallel to this work, some like the Unity 8 and UI Toolkit developers started experimenting with my Qt 5.2 PPA. It turned out the rewritten QML engine in Qt 5.2 - V4 - was not entirely stable when 5.2.0 was released, so they worked together with upstream on fixes. It was only after 5.2.1 release that it could be said that V4 worked well enough for Unity 8. Known issues like these slowed down the start of full-blown testing.

Then everything built, unit tests passed, most integration tests passed and things seemed mostly to work. We had automated autopilot integration testing runs. The apps team tested through all of the app store to find out whether some needed fixes - most were fine without changes. On top of the found autopilot test failures and other app issues, manual testing found a few more bugs

Sudoku
Some critical pieces of software
like Sudoku needed small fixing
Finally last Thursday it was decided to push Qt in, with a belief that the remaining issues had fixes in branches or not blockers. It turned out the real deployment of Qt revealed a couple of more problems, and some new issues were raised to be blockers, and not all of the believed fixes were really fixing the bugs. So it was not a complete success. Considering the complexity of the landing, it was an adequate accomplishment however.

Specific Issues

Throughout this exercise I bumped into more obstacles that I can remember, but those included:
  • Not all of the packages had seen updates for months or for example since last summer, and since I needed to rebuild everything I found out various problems that were not related to Qt 5.2
  • Unrelated changes during 14.04 development broke packages - like one wouldn't immediately think a gtkdoc update would break a package using Qt
  • Syncing packaging with Debian is GOOD, and the fixes from Debian were likewise excellent and needed, but some changes there had effects on our wide-spread Qt 5 usage, like the mkspecs directory move
  • xvfb used to run unit tests needed parameters updated in most packages because of OpenGL changes in Qt
  • arm64 and ppc64el were late to be added to the landing PPA. Fixing those archs up was quite a last minute effort and needed to continue after landing by the porters. On the plus side, with Qt 5.2's V4 working on those archs unlike Qt 5.0's V8 based Qt Declarative, a majority of Unity 8 dependencies are now already available for 64-bit ARM and PowerPC!
  • While Qt was being prepared the 100 other packages kept on changing, and I needed to keep on top of all of it, especially during the final landing phase that lasted for two weeks. During it, there was no total control of "locking" packages into Qt 5.2 transition, so for the 20+ manual uploads I simply needed to keep track of whether something changed in the distribution and accommodate.
One issue related to the last one was that some things needed were in progress at the time. There was no support for automated AP test running using a PPA. There was also no support on building images. If migration to Ubuntu Touch landing process (CI Train, a middle point on the way to CI Airlines) had been completed for all the packages earlier, handling the locking would have been clearer, and the "trunk passes all integration tests too" would have prevented "trunk seemingly got broken" situations I ended up since I was using bzr trunks everywhere.

Qt 5.3?

We are near to having a promoted Ubuntu image for the mobile users using Qt 5.2, if no new issues pop up. Ubuntu 14.04 LTS will be released in a month to the joy of desktop and mobile users alike.

It was discussed during the vUDS that Qt 5.3.x would be likely Qt version for the next cycle, to be on the more conservative side this time. It's not entirely wrong to say we should have migrated to Qt 5.1 in the beginning of this cycle and only consider 5.2. With 5.0 in use with known issues, we almost had to switch to 5.2.

Kubuntu will join the Qt 5 users next cycle, so it's no longer only Ubuntu deciding the version of Qt. Hopefully there can be a joint agreement, but in the worst case Ubuntu will need a separate Qt version packaged.
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