DRI3SetDRMDeviceInUse is a hint that lets a client tell the server what DRM device it is currently using. This lets the server make more informed decisions for what modifiers to return to the client.
This is needed for proper linux dmabuf feedback with Xwayland. Xwayland needs to return a set of modifiers for a particular window for the device that window is using. i.e. if linux_dmabuf feedback advertises a scanout tranche on a device, we need a way to check which device a window is using so we know if we should add that tranche to the window modifiers in the GetSupportedModifiers request.
Xwayland change: xorg/xserver!818 (merged)