Re: [Xen-devel] Can domU config add userdefined keys to Xenstore?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-11-24 at 10:31 +0000, Florian Heigl wrote:
> 2011/11/24 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> > You could just start the VM paused, use "xl domid" to setup your keys
> > and then unpause?
> 
> This will all need wrapping around domU creation, so it would mean
> that it's not
> possible to use the normal /etc/init.d/xendomains
> For me, no problem I had to replace that anyway, but in general maybe not so
> "transparent".

Right.
> 
> > If you are using xapi then VM.xenstore_data is a list of key-value pairs
> > which is written xenstore. AFAICT The key is relative to
> > to /local/domain/<id> and must start "vm-data/..." (i.e. you can only
> > write to keys under /local/domain/<id>/vm-data/ using this mechanism).
> >
> > I suspect you aren't using xapi but the reason I mention it is that
> > someone added libxl_domain_create_info.xsdata in the early days of
> > libxl, presumably with this purpose in mind, but it appears not to be
> > hooked up into the xl configuration parser. I expect doing so would be a
> > reasonably simply job.
> 
> I'm not using Xapi, yup. But that seems a nice feature.
> 
> > Another, possibly more flexible but more complex option, would be to
> > allow for a series of hook scripts (both global and domain specific?) to
> > be called at various points in a VM lifecylce, including after building
> > but before starting.
> 
> There are already kind of hooks in the "on_reboot" "on_destroy" things.
> but thats quite in hazy future I guess. And it might be overkill.

Those options configure the behaviour of xl itself rather than calling
out to some hook script.

> It would be enough if the things you can add into a VM are configured in
> the same way, in the same place and run at start / stop!

That's what I was suggesting by exposing libxl_domain_create_info.xsdata
through xl.

> Ok. Technically the xenstore /vm/domain/XX is not IN the VM. :)
> 
> I'll poke around some more, either something using the udev xen backend
> or the easy and safe route with a small shellscripty-daemon.
> 
> Many people have looked for some way to find out the xen host's name
> from within a domU, it's pity this stuff isn't more obvious since it's quite
> nice to use (just consider stateless linux boxes)
> 
> Oh and THANKS to whomever wrote the Xenstore articles during last doc day.
> I was amazed when I found them.
> 
> Greetings,
> Florian
> 



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