[systemd-devel] [libvirt] How to make udev not touch my device?

[Daniel P. Berrange]

On Fri, Nov 11, 2016 at 02:15:38PM +0100, Michal Sekletar wrote:
> On Mon, Nov 7, 2016 at 1:20 PM, Daniel P. Berrange <berrange at redhat.com> wrote:
> 
> > So if libvirt creates a private mount namespace for each QEMU and mounts
> > a custom /dev there, this is invisible to udev, and thus udev won't/can't
> > mess with permissions we set in our private /dev.
> >
> > For hotplug, the libvirt QEMU would do the same as the libvirt LXC driver
> > currently does. It would fork and setns() into the QEMU mount namespace
> > and run mknod()+chmod() there, before doing the rest of its normal hotplug
> > logic. See lxcDomainAttachDeviceMknodHelper() for what LXC does.
> 
> We try to migrate people away from using mknod and messing with /dev/
> from user-space. For example, we had to deal with non-trivial problems
> wrt. mknod and Veritas storage stack in the past (most of these issues

What kind of issues ? 

> remain unsolved to date). I don't like to hear that you plan to get
> into /dev management business in libvirt too. I am judging based on
> past experiences, nevertheless, I don't like this plan.

Libvirt is already doing this for its LXC driver, populating a private
/dev with only the devices permitted for the container in question.

> Also, managing separate mount namespace for each qemu process and
> forking helper that joins the namespace to do some work seems quite
> complex too.

Again, libvirt is already doing this for LXC so its not any great
burden.

Regards,
Daniel
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