[libvirt-users] exposing <actual> [was: QEMU hook on restore]

[Eric Blake]

On 02/10/2012 02:12 PM, Laine Stump wrote:
> I think if it's going to be turned on, it can just be included in any
> output of live xml.
> 
> One potential problem with this is that, as it stands, someone wanting
> to know, e.g., which ethernet device a guest interface is connected to
> with macvtap will need to look in two places - 1) if there is no
> <actual> element, then it will be in <source dev='ethX'/> under the main
> interface element, but if there *is* an <actual>, then it's <source
> dev='ethX'/> under <actual>. (In other words, if the original interface
> type isn't 'network', then <actual> won't be filled in. The question
> then is whether or not we *want* it filled in.)

Good point - making a user search two places isn't very convenient.

> 
> An alternate implementation would be to write live XML to the public API
> as if the interface config acquired from the network definition had been
> hand-configured.

>
> (basically moving everything in <actual> up to <interface>). This would
> make it easier for people trying to do report status kinds of things,
> and the loss of original config data wouldn't be a problem here, but I
> don't know if that would be an acceptable practice.

I don't like that as the default action.  Too many people do 'virsh
dumpxml' on a live machine, then use that as the template to configure a
new machine, and collapsing the <actual> into the configured portion
means that use of the XML as a template would create a different result
next time (tying the interface to one port, rather than leaving it
associated with a network pool).

But under the control of a flag, that sounds nice.

Maybe that argues for this approach:

dumpxml, flags == 0 => output <actual>, user must search two places
dumpxml, flags == DUMP_ACTUAL => rewrite XML to merge actual into the
configuration slot, so that user only has to search one place

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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