Re: Hotplugged devices in Xen 4.5 and domain reboot

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2015-12-01 at 15:29 +0000, Wei Liu wrote:
> On Tue, Dec 01, 2015 at 04:58:55PM +0200, Iurii Mykhalskyi wrote:
> > Our real usb mass-storage device are located at driver domain (DomD).
> > So we
> > setup second block-device backend there.
> > 
> > To hotplug usb mass-storage from DomD we use follow command:
> > 
> > xl block-attach domU_id phy:/bla-bla,xvda10,w,backend="DomD"
> > 
> 
> What happens if you run this in Dom0? I guess DomD doesn't respond to
> the request?
> 
> > There was no support of attaching block-device in runtime from domain
> > other
> > to Domain-0, so we have made some hacks to allow call block-attach
> > command
> > from non-dom0 privileged domain.
> 
> So this is a special use case. This is the first time I know people
> actually run xl block-attach in driver domain.

Toolstack commands (xl *) should be run in the toolstack domain, not in the
driver domain.

I don't think it should be expected that the latter work (at least not
without a large amount of development work).

In general a driver domain would not be expected to have sufficient
privilege over e.g. a guest domain's /local/domain/domU/devices to create
the f.e. dirs.

> There is a daemon "xl devd" in driver domain. We might be able to teach
> it to response to Dom0 toostack request. I'm a bit surprised if it
> doesn't do that already. Did you forget to start that daemon?

That's the entire purpose of that daemon, isn't it?

> 
> Roger, Ian and Ian, any thought?
> 
> Wei.