[lxc-devel] Questions about lxc.autodev

[Stéphane Graber]

On Thu, Nov 27, 2014 at 11:19:18AM +0100, vivo75 at gmail.com wrote:
> Il 26/11/2014 22:35, Stéphane Graber ha scritto:
> > Hello,
> >
> > So I'm looking into how to rework lxc.autodev to apply properly to all
> > the cases we care about:
> >  - Privileged containers started by root
> >  - Unprivileged containers started by privileged root
> >  - Unprivileged containers started by unprivileged root
> >  - Unprivileged containers started by unprivileged user
> >
> > My understanding is that autodev currently creates /dev/.lxc and then
> > uses one directory per-container+lxc-path-hash under there, creates the
> > devices nodes and uses that as the container's /dev.
> >
> > My question is why the /dev/.lxc directory to begin with, wouldn't
> > it make more sense to use LXC_PATH/<container>/dev, mount a tiny
> > tmpfs on that and then use it? This would have the advantage of having
> > the same path for privileged and unprivileged containers and avoid the
> > ugly lxcpath hash.
> >
> >
> > I believe the following setup would make a bit more sense and offer a
> > consistent behaviour:
> >  - If not available or not a tmpfs, create LXC_PATH/<container>/dev and
> >    mount a tiny tmpfs on it. Chown the path to the container's root uid/gid
> >    and chmod to something sane.
> >  - For all the nodes we care about, attempt to mknod them in there, on
> >    failure, fallback to touch+bind-mount from real /dev.
> >
> > This would allow for the exact same code to be used for all 4 cases, for
> > the layout and location of the autodev tree to be entirely guessable
> > without requiring fancy hashing (making it easier for external tools to
> > interact with the autodev tree).
> >
> > As with the current implementation, the tree wouldn't be flushed on
> > container reboot but it would on container shutdown.
> >
> >
> > Does the above make sense or am I missing something about the design of
> > current autodev?
> >
> > Cheers
> >
> it make sense and avoid the case where /dev is re-mounted and lxc is
> then confused
> 
> the only potential benefit I see (w/o knowing lxc code) in using
> /dev/.lxc/ is hardlinking betweeen /dev and /dev/.lxc/container/

Which actually doesn't get you anything since nodes under /dev are
char/block devices which do not have any content :)

-- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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