Re: [Xen-devel] xen_domain_handle_t usage

[Ewan Mellor <ewan@xxxxxxxxxxxxx>]

On Tue, Nov 15, 2005 at 11:43:49AM -0800, Cihula, Joseph wrote:

> I noticed that the changesets around 7378:bd3268de4145 introduced the
> xen_domain_handle_t param to xc_create_domain(), the struct domain, etc.
> and call it a "tool UUID".
> 
> Can someone explain how this is envisioned being used (xend sets it to
> some magic values but I don't see it get used anywhere)?

Theoretically, this value is just an opaque block of bits, usable by anyone
for any purpose.  Xen just stores it along with the domain, and gives it back
again when you ask.

Xend uses it as a unique identifier for a VM.  In this terminology, a "VM" is a
running guest.  The VM may migrate to a different machine (where it would
become a different domain) or it may be rebooted, in which case it would become
a different domain on the same machine.  However, the VM remains the same, and
is identified by its unique ID (the UUID).

It is useful for Xend to be able to store this UUID along with the domain as
it makes it easy for Xend to restart (say after a crash) and yet be able to
reconcile the contents of the store with the current running domains.

This is just what Xend uses it for.  In a world without Xend, you might use the
UUID for something else.  Of course, at the moment, no-one has a system 
that has Xen but is without Xend.  However, this explains the slightly curious
wording of the xen_domain_handle_t.

Ewan.

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