[systemd-devel] udev database backwards compatibility guarantees

[David Herrmann]

Hi

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).

This is not just about libudev. sd-login and friends are also
affected, as we expect libsystemd to be the same version as the binary
that generated the files in /run.

Thanks
David