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Re: [Xen-devel] XenStore management with driver domains.

To: "gibbs@xxxxxxxxxxx" <gibbs@xxxxxxxxxxx>
Subject: Re: [Xen-devel] XenStore management with driver domains.
From: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Date: Mon, 18 Jan 2010 15:39:18 -0800
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On Mon, 2010-01-18 at 17:24 -0500, Justin T. Gibbs wrote:
> I've been experimenting with serving block storage between DomUs.
> I can dynamically attach storage, transfer data to my hearts content,
> but dynamic detach is providing some trouble.  Both the front and
> backend drivers detach cleanly, but the XenStore data for the
> attachment persists, preventing the same storage object from
> being attached again.
> 
> After tracing through Xend and the hotplug scripts, it seems that
> the current framework assumes backend teardown will occur in Dom0.
> For example, xen-hotplug-cleanup, which is invoked when the backend
> device instance is removed, removes the following paths from the
> xenstore:
> 
>    /local/domain/<front domid>/device/<type>/<devid>
>    /local/domain/<back domid>/backend/<type>/<front domid>/<devid>
>    /local/domain/<back domid>/error/backend/<type>/<front domid>/<devid>
>    /vm/<front uuid>/device/<type>/<devid>

While you're cleaning up: Do you consider relative paths? 

I think fully qualified names such /local/domain/%d/device/vbd/%d/%d is
always wrong. Try using "device/vbd/%d/%d" instead.

I also think it I've seen this make an unwelcome difference in
permission checks for updates issued by domUs in the past. But this
information may be outdated.

Daniel



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