Re: [Xen-devel] qemu and xl semantics

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On Friday 17 December 2010 10:15:14 Ian Campbell wrote:
> On Fri, 2010-12-17 at 09:00 +0000, Christoph Egger wrote:
> > Hi!
> >
> > When I start a guest with xm  the disk startup script assigns a loopback
> > device for qemu to open it.
> >
> > Now it seems that qemu opens the disk image directly. Then when
> > the loopback device wants to open the disk image then that fails
> > with EBUSY.
>
> By "Now..." you mean "With xl..." ?

no, I mean with xm.

>
> > How is the disk startup script supposed to work with the new
> > semantic for
> > a) HVM guests
> > b) PV guests
> > ?
>
> I think this is all very specific to the precise disk type you have in
> your config, i.e. tap: vs file: vs phy: etc. Which are you using?

I use 'file'.

> > The network startup script adds the tap device to the bridge
> > or assigns an ip address.
> > With xl neither the disk nor the network script runs.
> > So when I start the guest with xl then I have
> > the tap device assigned to the guest but the
> > tap device is not configured in the dom0.
> >
> > How does the 'xl' way work in respect to the network script
> > used with 'xm' ?
>
> On Linux these are run from the hotplug event, via the udev rules. I
> presume you are talking about on NetBSD though?

Yes.

> Under Linux I think it was always the same under xm too although there
> have been some tweaks recently, e.g. the vif script is now always
> /etc/xen/scripts/vif-setup which handles the indirection to the script
> in the domain config or the default. Previously xend the hotplug rules
> called the configured script directly. This change was
> 21549:8bcaec29574e and was common to xm and xl I think.

On NetBSD a xenbackendd starts along with xenstored.
xenbackendd watches on /local/domain/0/backend
and invokes the corresponding scripts when something changes
beneath that.

'xend' is doing that in DevController.py. Since 'xl' is not interacting
with 'xend' the scripts don't get launched at all.

Christoph


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