Patching gnome-flashback 3.20 to work with GNOME 3.21

I’m running Debian testing, with gnome-flashback. At present, it has installed gnome-flashback 3.20.2-1 alongside gnome-settings-daemon 3.21.90-2.

Symptoms

By default, there are some problems:

  • The “Displays” section of the config tool says only “Could not get screen information”. This prevents GUI access to a lot of functionality, including arrangement of multiple monitors.

  • The brightness adjustment keys do not work.

The root of the problem is that the DBus interface org.gnome.Mutter.DisplayConfig changed between GNOME 3.20 and GNOME 3.21; the GetResources method produces an additional result in 3.21 that is not present in 3.20’s version of the same interface.1

If you see messages similar to the following from stderr of gnome-settings-daemon at startup, you are suffering from this problem too:

(gnome-settings-daemon:7149): power-plugin-WARNING **: Could not create GnomeRRScreen: Method 'GetResources' returned type '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuud)ii)', but expected '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuudu)ii)'
(gnome-settings-daemon:7149): wacom-plugin-WARNING **: Failed to create GnomeRRScreen: Method 'GetResources' returned type '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuud)ii)', but expected '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuudu)ii)'
(gnome-settings-daemon:7149): color-plugin-WARNING **: failed to get screens: Method 'GetResources' returned type '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuud)ii)', but expected '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuudu)ii)'
(gnome-settings-daemon:7149): common-plugin-WARNING **: Failed to construct RR screen: Method 'GetResources' returned type '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuud)ii)', but expected '(ua(uxiiiiiuaua{sv})a(uxiausauaua{sv})a(uxuudu)ii)'

Fixing the problem

To fix the problem, I patched and rebuilt gnome-flashback with these commands:

sudo apt-get build-dep gnome-flashback
apt-get source gnome-flashback
wget "/files/gnome-flashback-hack-20160918.patch"
patch -p0 < gnome-flashback-hack-20160918.patch
(cd gnome-flashback-3.20.2; fakeroot ./debian/rules binary)

After these steps, you should have a new gnome-flashback binary, gnome-flashback-3.20.2/gnome-flashback/gnome-flashback. You can now move the existing one out of the way and install it:

sudo mv /usr/bin/gnome-flashback /usr/bin/gnome-flashback-AS-INSTALLED
sudo cp gnome-flashback-3.20.2/gnome-flashback/gnome-flashback /usr/bin
sudo chown root:root /usr/bin/gnome-flashback

Now restart both gnome-flashback and gnome-settings-daemon. (You should arrange for gnome-flashback to be started after gnome-settings-daemon.)

You should no longer have the stderr output complaining about the RR screen DBus signatures, and both the “Displays” section of the config tool and the brightness keys should work.

  1. It’s a shame that there’s no apparent protocol versioning in the GNOME system, or at least none that applies here. If DBus had a serialization language a little more like protobufs, it’d be possible to smoothly add fields in a backwards-compatible way.