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

[Michal Sekletar]

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
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.

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

Michal