xwayland: Add glamor egl_backend for EGLStreams

Graphics / X.Org / X.Org Server - Lyude Paul [redhat.com] - 24 April 2018 20:51 EDT

This adds initial support for displaying Xwayland applications through the use of EGLStreams and nvidia's custom wayland protocol by adding another egl_backend driver. This also adds some additional egl_backend hooks that are required to make things work properly.

EGLStreams work a lot differently then the traditional way of handling buffers with wayland. Unfortunately, there are also a LOT of various pitfalls baked into it's design that need to be explained.

This has a very large and unfortunate implication: direct rendering is, for the time being at least, impossible to do through EGLStreams. The main reason being that the EGLStream spec mandates that we lose the entire color buffer contents with each eglSwapBuffers(), which goes against X's requirement of not losing data with pixmaps. no way to use an allocated EGLSurface as the storage for glamor rendering like we do with GBM, we have to rely on blitting each pixmap to it's respective EGLSurface producer each frame. In order to pull this off, we add two different additional egl_backend hooks that GBM opts out of implementing:

- egl_backend.allow_commits for holding off displaying any EGLStream backed pixmaps until the point where it's stream is completely initialized and ready for use- egl_backend.post_damage for blitting the content of the EGLStream surface producer before Xwayland actually damages and commits the wl_surface to the screen.

The other big pitfall here is that using nvidia's wayland-eglstreams helper library is also not possible for the most part. All of it's API for creating and destroying streams rely on being able to perform a roundtrip in order to bring each stream to completion since the wayland compositor must perform it's job of connecting a consumer to each EGLstream. Because Xwayland has to potentially handle both responding to the wayland compositor and it's own X clients, the situation of the wayland compositor being one of our X clients must be considered. If we perform a roundtrip with the Wayland compositor, it's possible that the wayland compositor might currently be connected to us as an X client and thus hang while both Xwayland and the wayland compositor await responses from eachother. To avoid this, we work directly with the wayland protocol and use wl_display_sync() events along with release() events to set up and destroy EGLStreams asynchronously alongside handling X clients.

Additionally, since setting up EGLStreams is not an atomic operation we have to take into consideration the fact that an EGLStream can potentially be created in response to a window resize, then immediately deleted due to another pending window resize in the same X client's pending reqests before Xwayland hits the part of it's event loop where we read from the wayland compositor. To make this even more painful, we also have to take into consideration that since EGLStreams are not atomic that it's possible we could delete wayland resources for an EGLStream before the compositor even finishes using them and thus run into errors. So, we use quite a bit of tracking logic to keep EGLStream objects alive until we know the compositor isn't using them (even if this means the stream outlives the pixmap it backed).

While the default backend for glamor remains GBM, this patch exists for users who have had to deal with the reprecussion of their GPU manufacturers ignoring the advice of upstream and the standardization of GBM across most major GPU manufacturers. It is not intended to be a final solution to the GBM debate, but merely a baindaid so our users don't have to suffer from the consequences of companies avoiding working upstream. New drivers are strongly encouraged not to use this as a backend, and use GBM like everyone else. We even spit this out as an error from Xwayland when using the eglstream backend.

54ac09717 xwayland: Add glamor egl_backend for EGLStreams
configure.ac | 24 +
hw/xwayland/Makefile.am | 24 +-
hw/xwayland/meson.build | 25 +-
hw/xwayland/xwayland-glamor-eglstream.c | 830 ++++++++++++++++++++++++++++++++
hw/xwayland/xwayland-glamor-gbm.c | 6 +-
hw/xwayland/xwayland-glamor.c | 113 ++++-
hw/xwayland/xwayland-present.c | 9 +
hw/xwayland/xwayland.c | 34 ++
hw/xwayland/xwayland.h | 39 ++
include/meson.build | 7 +-
include/xwayland-config.h.in | 3 +
include/xwayland-config.h.meson.in | 3 +
meson.build | 15 +
meson_options.txt | 2 +
14 files changed, 1117 insertions(+), 17 deletions(-)

Upstream: cgit.freedesktop.org


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