Wayland in Plasma 5.7

Last week we released the beta version of Plasma 5.7 which means we know what this release will have for better Wayland support. First of all I need to mention what didn’t make it: unfortunately I missed the freeze of Frameworks 5.23 to land support for xdg-shell. I have a working implementation, but was not yet satisfied with the API. This is a difficult interface to provide an API for due to the unstable nature of the interface. Due to lack of xdg-shell support GTK applications are still going to use X11 on Wayland (like the Firefox window I’m just typing this blog post in).

In the past I already blogged about a few new features in 5.7 like the improved task manager for Wayland, the virtual keyboard support, sub-surface support and improved input device support. So in this blog post I want to focus on a different topic: quality.

For Plasma 5.7 my aim was to get the Plasma session into a state that I can use it as my primary system. And since last week I have not started into an X11 session any more. This means that we needed to get the whole system stable enough to have neither KWin nor applications crash due to Wayland. Given that our Wayland code is quite a fair amount of new code, changing lots of assumptions there are of course bugs to be expected. We still have code which calls into X11 unconditionally, we have things which are not implemented correctly and of course we do stupid mistakes. So for Plasma 5.7 the task was to find these issues and fix one for one.

For Wayland it’s much easier for us to test. KWayland – our framework for Wayland support – is developed in a test driven approach making it possible to create test cases for every problem. They expose the problems and verify that they are fixed and as regression tests ensure that they won’t hit us again. Over the last release cycle we added several thousand lines of test code in KWayland alone.

Finding those issues is not always easy. If KWin crashes we don’t have DrKonqi like normally, it doesn’t work for Wayland (tries to connect to a display server, but that just crashed). What I saw on my Wayland test device was that KWin sometimes randomly crashed – more often when I interacted with X11 windows. But when attaching gdb to KWin it didn’t crash. But once I caught it: it turned out to be an error in KWin in the handling of Xwayland windows. There are two possible code paths it can take and one was with a mistake. Due to running through a debugger it was more likely to take the correct one. So yeah it’s not always easy.

With that problem gone we were able to find a few more and fix also some bugs which caused windows to quit. Unfortunately some of this fixes had to go into KWayland after the 5.23 release. This means the frameworks version used with Plasma 5.7 is not going to have all fixes. If you want to give Plasma/Wayland a try I recommend to not just wait for Plasma 5.7 but also for frameworks 5.24.

This week I will be at the openSUSE conference in Nuremberg, where I will also give a talk about how Wayland helps us to improve our quality and our workflows. I’ll do another blog post about the content of that presentation – don’t want to spoil 😉 Though if you follow our development you are already aware of it. Thanks to openSUSE to give me the possibility to present at the conference and thanks to KDE e.V. for the support to go there.

I can hear you asking now the question of all questions: “When will it be ready?” I think that I am not objective enough to answer the question or to say that it is ready. I’m too close to the code and might just omit important problems because I don’t see them. Thus I cannot say that it is ready. It depends on your workflow and whether that workflow is already fully implemented. This is something only you can know.

Last week KDE had a very important developer sprint (where I did not participate) and is currently running a fundraising campaign for this sprint. We need the money to send our developers to such meetings or to a conference like openSUSE conf where I will be this week. At the moment just 107 people have participated and donated. This is something which makes me sad. I see the statistics for my blog posts and know that this one will have at least 1000 direct hits. In addition there are people reading planetkde and not directly my blog. We are trying to raise 24000 EUR and please do the math yourself to see how close we would be to it if everybody would donate just 10 EUR.

Why planetkde needs to have political posts

Johnathan’s blog post about the EU triggered quite some noise about that there should not be political posts on planetkde. I think it’s important that we have political posts on planetkde. KDE is a political movement, let’s look at our vision:

A world in which everyone has control over their digital life and enjoys freedom and privacy.

This is a political statement. We want to change the world! We are political! We need to be able to discuss political topics like the Snowden-documents, we need to be able to lobby on planetkde for Free Software in our governments, we need to be able to report about such efforts.

This means politics belong to KDE and belong to planetkde.

This means we need to also tolerate political opinion posts on topics which are not directly KDE related, like Johnathan’s. If we start to remove such posts or start to censor us, we run the risk of not having the relevant posts on planetkde anymore because people don’t post political articles at all anymore.

Please remember that planetkde is for the KDE community by the KDE community. Any political opinion expressed on planetkde does not represent the opinion of KDE or KDE e.V.

A task manager for the Plasma Wayland session

Plasma 5.7 will ship with a new taskmanager library. One of the reasons to implement a new taskmanager library is the port to Wayland. Our old code base was heavily relying on X11 and didn’t support the concept of multiple windowing systems. You can read more on that in Eike’s blog post about the new task manager. In this blog post I want to focus a little bit on the Wayland side of a task manager.

Architectural difference to X11

On X11 every application is able to read every aspect of every other window. This allows to implement a task manager. The task manager can get notified when a window is added, when a window is removed and install event filters for the changes of the window properties. That’s the basics for a task manager.

On Wayland the world is different. An application is not able to see the windows of other applications. This means by default Plasma is not able to see what windows exists, the taskmanager would be empty. The only application which knows about the existing windows is the Wayland compositor.

Merging Desktop Shell and Wayland compositor?

A possible solution to this problem could be to merge the desktop shell and the compositor into one process. This is the architecture used in e.g. Unity and GNOME Shell on X11.

But such an architecture has also disadvantages. It violates the concept of separating concerns and of “doing one thing and do it right”. We have an excellent task manager, an excellent window manager and an excellent desktop shell.

Also it would make code sharing between platforms more difficult. A task manager for Wayland would be very different from a task manager on X11. All the business logic and presentation should be the same. No matter which windowing system is used.

By merging the code bases together we would also make the code less reusable. One couldn’t use KWin/Wayland in another desktop environment (e.g. LXQt) nor could one use Plasma/Wayland with another compositor (e.g. sway). While we of course recommend to use KWin as the Wayland (and X11) compositor we don’t enforce it and also don’t want to enforce it.

Protocols, protocols

So a different solution is needed and that is done through a custom Wayland protocol which is called org_kde_plasma_windowmanagement. We have a few interfaces prefixed with Plasma. This does not mean that it can only be used by Plasma. It just means that the interface was first designed and developed for Plasma’s needs. We are happy to share the interface with other desktop environments.

The protocol is provided by KWin and it announces whenever a new window gets created. Once a new window gets created a bound client can bind an org_kde_plasma_window interface and get notified about all the states of the window.

The protocol exposes pretty much all the information KWin has about the window and it gets updated automatically whenever the state in KWin changes. In addition the protocol has requests the task manager needs, like “close the window”, “minimize it”, “maximize it”, etc. etc. KWin also listens to these requests and honors them.

Although the protocol is added to Wayland, it is windowing system agnostic. The created Plasma Window does not expose the actual windowing system resource (after all on Wayland another client cannot get access to it). KWin exposes a Plasma Window for both X11 managed windows and Wayland windows. By that the task manager is able to manage tasks from multiple windowing systems without knowing that it does so.

Evolution of the protocol

We added the Plasma window protocol initially for the work on the Plasma phone about a year ago. Also on the Plasma phone we had the use case of switching windows and using the X11 based task manager was just no option on a Wayland only device 😉

While the protocol worked fine for our initial needs, it was not yet sufficient for the use in the desktop task manager. So over the last weeks we introduced further support and improved the API to make it work more reliable. Also quite some changes went into KWin to ensure that only “interesting” windows are exposed. E.g. a context menu should not be shown in the task manager.

Our KWayland library of course has support for this protocol through the classes PlasmaWindowManagement and PlasmaWindow on client side. In addition there is a model exposed as PlasmaWindowModel.

Future work

The work on the interface is not done yet. There are still changes to the API needed and the upcoming KDE Frameworks 5.23 release will include new API calls in PlasmaWindow. As well we have already the first change scheduled for KDE Frameworks 5.24. And we also know that we need to expose a few more data elements in the protocol to get the task manager to the same level as on X11.

There is also an interesting idea floating around to use the – windowing system agnostic – Wayland implementation on both X11 and Wayland. For this KWin (on X11) would need to create a dummy Wayland server for the task manager to connect to. It’s an idea which we might or might not implement.

Security considerations

Currently every Wayland client is able to bind this interface, which means that some of the security improvements of Wayland are not available in Plasma/Wayland. We are fully aware of that and were also fully aware of the consequence when we added the interface. I do have ideas on how to address this and this will be implemented before we will recommend the Plasma/Wayland session for daily usage. The design allows to add security checks in these areas. Unfortunately my priority list did not allow me to implement this for Plasma 5.7, next chance 5.8.

Introducing a virtual framebuffer Wayland server in KWayland

The next KDE framework release will include a small addition in KWayland which will make it much easier to run auto tests for Wayland based applications. KWayland now installs a small virtual framebuffer test server into libexec directory.

This means it’s an application inspired by Xvfb which allows to run a graphical application with a virtual framebuffer. The new tool is the same for Wayland. KWayland makes testing already quite easy, but we noticed that we don’t have a good setup for the case that we want to test an application which uses QtWayland QPA plugin as that is not possible with the test support so far in KWayland.

The idea behind the server is that every test gets it’s own dedicated test Wayland server. The test Wayland server will start the test and terminate itself once the test finished (either successful, failure or crash). All output from the test – including exit code – is forwarded, which makes integration into a ctest based system really easy.

In fact if you use CMake as a build system to define your tests, this becomes super easy:

find_package(KF5Wayland CONFIG)
add_executable(myTest myTest.cpp)
target_link_libraries(myTest Qt5::Gui Qt5::Test)

This also allows to run the same test on X11 and on Wayland. Assuming the test is meant for build.kde.org which has an Xvfb running during the test phase, one can add the test the normal way (X11) and just add the kwaylandtest in addition. So the test will run on both windowing systems.

Now this is a really new project and the test server is still rather limited. All it does is faking rendering at 60 Hz. Otherwise it’s still limited and does not provide the functionality of e.g. a window manager on X11. In that regard it’s also inspired by Xvfb which doesn’t support that. I plan to extend this as I have need in the tests I’m going to add for it.

Speaking of that: the first test case making use of this new infrastructure is already pushed.