Re: [Xen-devel] Where can I find some tutorial or manual on how to use xenstore?

[Ewan Mellor <ewan@xxxxxxxxxxxxx>]

On Thu, Jun 29, 2006 at 02:53:26PM +0100, Nick Logan wrote:

> Ewan Mellor wrote:
> 
> >On Wed, Jun 28, 2006 at 04:20:51PM +0100, Nick Logan wrote:
> >
> > 
> >
> >>Ewan Mellor wrote:
> >>
> >>   
> >>
> >>>On Wed, Jun 28, 2006 at 02:38:15PM +0100, Nick Logan wrote:
> >>>
> >>>
> >>>
> >>>     
> >>>
> >>>>The driver was started outside of xend, using a varient of Jacob's 
> >>>>buscreate program to set the necessary values in xenstore. As this a 
> >>>>3rd party driver, I'm looking for a solution that does not involve xm 
> >>>>or xend changes, if that's possible. I'll take a look at the blktap 
> >>>>patches to see if that helps.
> >>>> 
> >>>>
> >>>>       
> >>>>
> >>>Xend is explicitly bringing the devices back up on restore.  If you
> >>>deliberately bypass it, then you are going to have to do that bringup
> >>>yourself.
> >>>
> >>>Ewan.
> >>>
> >>>
> >>>     
> >>>
> >>I guessed that would be the case. The bringup for a restore would be 
> >>quite straighforward but more complex for migration. Has anyone 
> >>suggested hooks for xend to deal with 3rd party drivers so that it could 
> >>initialise and restore devices that are supported by these drivers?  
> >>This would enable new drivers to be implemented without changes to xend.
> >>   
> >>
> >
> >One would have to write a device handler that parsed generic config, and 
> >then
> >passed it through to the store unaltered, and then have hotplug scripts 
> >that
> >could cope with this unparsed config.  At the moment, the driver backends 
> >do
> >special-case things like generating a MAC address when none is supplied,
> >converting device names to their major:minor, that kind of thing.  There 
> >isn't
> >a generic device path; adding one wouldn't be hard.
> >
> >Ewan.
> > 
> >
> Can I just confirm what your proposal is:
> 
> Add a generic device config to the xm config file that would contain the 
> driver id, virtual device, physical device .....
> Add a generic device handler to xend that would pass the unparsed 
> generic config through to xenstore.
> Add a hotplug script that would parse the unparsed config in xenstore 
> and start the driver.
> When saving a domain, xend would save the generic device config.
> xend would call restore for the generic devices.
> 
> If  that's correct, I'll find some time to investigate how this could done.

Yes, that's it.  It sounds like something that would be very useful.

Cheers,

Ewan.

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