On 7 Mar 2014, at 20:24, Lennart Poettering <mzerqung@0pointer.de> wrote:

> On Fri, 07.03.14 19:45, Lukasz Pawelczyk (havner@gmail.com) wrote:
>
>> Problem:
>> Has anyone thought about a mechanism to limit/remove an access to a
>> device during an application runtime? Meaning we have an application
>> that has an open file descriptor to some /dev/node and depending on
>> *something* it gains or looses the access to it gracefully (with or
>> without a notification, but without any fatal consequences).
>
> logind can mute input devices as sessions are switched, to enable
> unpriviliged X11 and wayland compositors.

Would you please elaborate on this? Where is this mechanism? How does it work without kernel space support? Is there some kernel space support I’m not aware of?

>> Example:
>> LXC. Imagine we have 2 separate containers. Both running full operating
>> systems. Specifically with 2 X servers. Both running concurrently of
>
> Well, devices are not namespaced on Linux (with the single exception of
> network devices). An X server needs device access, hence this doesn't
> fly at all.
>
> When you enumerate devices with libudev in a container they will never
> be marked as "initialized" and you do not get any udev hotplug events in
> containers, and you don#t have the host's udev db around, nor would it
> make any sense to you if you had. X11 and friends rely on udev
> however...
>
> Before you think about doing something like this, you need to fix the
> kernel to provide namespaced devices (good luck!)

Precisly! That’s the generic idea. I’m not for implementing it though at this moment. I just wanted to know whether anybody actually though about it or maybe someone is interested in starting such a work, etc.