[systemd-devel] udev database backwards compatibility guarantees

[Alexander Larsson]

Hi, I'm looking at creating a runtime/app thing for Gnome in the style
of:
http://0pointer.net/blog/revisiting-how-we-put-together-linux-systems.html

However, I noticed that some core dependencies like mesa uses libudev.
And in fact, needs user-set additional info not in sysfs. In particular,
it reads ID_PATH_TAG on render device nodes to pick what GPU to use in
multi-gpu situations (PRIME):
http://lists.freedesktop.org/archives/mesa-dev/2014-June/061798.html

It seems to me that this means I need the host /run/udev inside the
application. I know that the udev database format changed in the past,
but can I rely on it being stable in the future, even if the host udev
is rev:ed to a later version than what is in the application runtime?

Of course, there is also the question of /dev and /sys management in
sandboxed apps in general. Clearly any "modern" app will require some
real devices for things like direct rendering. But it would be ideal to
not expose "everything". How do we see this working?