[systemd-devel] udev database backwards compatibility guarantees

[Kay Sievers]

On Wed, Oct 22, 2014 at 1:33 PM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Thu, 11.09.14 10:49, Alexander Larsson (alexl at redhat.com) wrote:
>
>> 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?
>
> Good question. Ideally we wouldn't expose any raw devices to apps, but
> I figure this is not going to suffice (already with video4linux and
> things).
>
> Kay, any ideas on the udev database stability?

No stability. And so far no guarantees that things will not change.

The versions of the udev daemon, libudev and the runtime data must
match. Any expectations about version mix and match would require a
promise we do not give at this moment.

It might change with an imaginary "sd-device library", but it is very
unlikely to happen with the current udev.

Kay