Mir graphics drivers don't automatically upgrade when libmir* is manually upgraded, resulting in broken system

[Michał Sawicz]

While investigating bug #1528279 I've noticed there's some missing dependency somewhere, I'm able to get a broken device by upgrading unity-system-compositor (which pulls in libmir*). Only after upgrading mir-graphics-drivers-android did my system come back to normal.

Excerpt from apt history.log:
Start-Date: 2015-12-21 17:59:29
Commandline: apt install unity-system-compositor
Install: libmirserver36:armhf (0.18.0+15.04.20151216.1-0ubuntu1, automatic)
Upgrade: libmircookie1:armhf (0.17.1+15.04.20151105.1-0ubuntu1, 0.18.0+15.04.20151216.1-0ubuntu1), libmirplatform11:armhf (0.17.1+15.04.20151105.1-0ubuntu1, 0.18.0+15.04.20151216.1-0ubuntu1), libmirclient9:armhf (0.17.1+15.04.20151105.1-0ubuntu1, 0.18.0+15.04.20151216.1-0ubuntu1), unity-system-compositor:armhf (0.2.0+15.04.20151008.1-0ubuntu1, 0.2.0+15.04.20151216.1-0ubuntu1), libmircommon5:armhf (0.17.1+15.04.20151105.1-0ubuntu1, 0.18.0+15.04.20151216.1-0ubuntu1), libmirprotobuf3:armhf (0.17.1+15.04.20151105.1-0ubuntu1, 0.18.0+15.04.20151216.1-0ubuntu1)
End-Date: 2015-12-21 17:59:34

→ Broken

Start-Date: 2015-12-21 18:28:00
Commandline: apt install mir-graphics-drivers-android
Install: libinput10:armhf (1.1.0-1ubuntu2~vivid1, automatic), mir-platform-input-evdev4:armhf (0.18.0+15.04.20151216.1-0ubuntu1, automatic), mir-platform-graphics-android7:armhf (0.18.0+15.04.20151216.1-0ubuntu1, automatic)
Upgrade: mir-graphics-drivers-android:armhf (0.17.1+15.04.20151105.1-0ubuntu1, 0.18.0+15.04.20151216.1-0ubuntu1)
End-Date: 2015-12-21 18:28:02

→ Fixed

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: mir-graphics-drivers-android 0.18.0+15.04.20151216.1-0ubuntu1 [origin: LP-PPA-ci-train-ppa-service-stable-phone-overlay]
Uname: Linux 3.4.67 armv7l
ApportVersion: 2.17.2-0ubuntu1.3touch1
Architecture: armhf
Date: Mon Dec 21 18:30:50 2015
InstallationDate: Installed on 2015-12-18 (3 days ago)
InstallationMedia: Ubuntu 15.04 - armhf (20151218-161516)
SourcePackage: mir
UpgradeStatus: No upgrade log present (probably fresh install)

[Daniel van Vugt (vanvugt)]

IIRC, this is by design. Mir can't possibly know which driver package is the right one for you at build time. And although we do have probing, installing all driver packages bloats the dependency tree unnecessarily. So our solution (IIRC) was to put a seed in the phone image such that the android drivers package was always included.

I'm not sure if there's something in our packaging that might have made it easier for your system to become broken...?

[Daniel van Vugt (vanvugt)]

It appears our dependencies are correct. mir-graphics-drivers-android depends on mir-platform-graphics-android7. If you install either then the problem is solved. But yeah I can see how upgrading libmir* would fail to upgrade the required drivers (although there's no evidence that an older android driver was previously installed, I assume it was).

[Daniel van Vugt (vanvugt)]

I think a virtual package ("Provides") might be the right answer here. That is mir-platform-graphics-android8 (and mesa etc) would then "Provide" a virtual "mir-server-graphics-8". And libmirserverN would depend on virtual package "mir-server-graphics-8" that is only supplied by installing one or more driver packages.

[https://www.debian.org/doc/debian-policy/ch-relationships.html]