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[Xen-devel] Re: [RFC] Switching store to use domain id's for keys

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: [Xen-devel] Re: [RFC] Switching store to use domain id's for keys
From: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Date: Wed, 31 Aug 2005 10:28:46 +0100
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Tue, Aug 30, 2005 at 03:32:46PM -0500, Anthony Liguori wrote:
> As I go through the console code, I notice that the domain console 
> information is being stored in /console/%d/domain instead of within the 
> /domain tree as one would expect.

We were wondering about this yesterday.

> The reasoning seems obvious to me, there's no easy way to get the UUID 
> for a domain so constructing a UUID based path outside of Xend is very 
> difficult.

Hmm, it's less than 40 lines of C code to iterate over the /domain entries
and find a domain with a matching name or id.  It would be convenient
to have library functions which does this...

> Perhaps now is a good time to reconsider just using domain ids instead 
> of UUIDs for the paths?  In a cluster we could just use 
> <nodeid>/domain/<domid> for unique identification.

We'd like the identifier for a domain to remain the same after
relocating the domain to a different physical machine.[1]

If we consider changing this, I'd go for /domain/<nodeid>-<domid>.  It
would make it easy to find the path for a domain on its home node but
it wouldn't work anymore once you move the domain to a new host.

> Or, if we really want to use UUIDs in the node path, perhaps we can add 
> UUIDs to the domain structure in the hypervisor so that we can actually 
> query it through getdomaininfo?

We've considered this but everytime we've found that the reason why
we wanted it was invalid.

In any case, it seems reasonable to move the console entries to the
domain tree then...


[1] this is currently broken since we create a new uuid on restore.
The issue is that device configuration is local to the host where the
domain is running and there's a short period of time where we want
device information for two hosts present at the same time.

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