Device Namespaces

Serge Hallyn serge.hallyn at ubuntu.com
Tue Oct 1 20:46:05 UTC 2013


Quoting Eric W. Biederman (ebiederm at xmission.com):
> "Serge E. Hallyn" <serge at hallyn.com> writes:
> 
> > Quoting Andy Lutomirski (luto at amacapital.net):
> >> On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen at gmail.com> wrote:
> >> > On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> >> > <gregkh at linuxfoundation.org> wrote:
> >> >
> >> >>> - We can relay a call of /sbin/hotplug from outside of a container
> >> >>>   to inside of a container based on policy.
> >> >>>   (But no one uses /sbin/hotplug anymore).
> >> >>
> >> >> That's right, they should be listening to libudev events, so why can't
> >> >> your daemon shuffle them off to the proper container, all in userspace?
> >> >
> >> > Which reminds me, one potential reason being..
> >> > http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
> >> >
> >> 
> >> Can't the daemon live outside the container and shuffle stuff in?
> >
> > That's exactly what Michael Warfield is suggesting, fwiw.
> 
> Michael Warfields example of dynamically assigning serial ports to
> containers is a pretty good test case.  Serial ports are extremely well
> known kernel objects who evolution effectively stopped long ago.  When
> we need it we have ptys to virtual serial ports when we need it, but in
> general unprivileged users are safe to directly use a serial port
> device.
> 
> Glossing over the details.  The general problem is some policy exists
> outside of the container that deciedes if an when a container gets a
> serial port and stuffs it in.
> 
> The expectation is that system containers will then run the udev
> rules and send the libuevent event.  

I thought the suggestion was that udev on the host would be given
container-specific rules, saying "plop this device into /dev/container1/"
(with /dev/container1 being bind-mounted to $container1_rootfs/dev).

-serge


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