[libvirt] RFC: API to report guest IP address(es)

Osier Yang jyang at redhat.com
Thu Feb 9 04:45:24 UTC 2012

On 2012年02月08日 19:30, Michal Privoznik wrote:
> Hi,
> Now we have qemu guest agent it is possible for us to:
> 1) extend guest agent to report IP addresses (not trivial among OSes).
> 2) Write API which will report these to mgmt application.
> One thing that I am not sure about and would like you to ask is:
> how should the API look like?
> In addition, we have this nwfilter which already learns host interfaces
> address (yeah, only one per interface).
> What scenarios are we facing here?
> 1) It is impossible (in general) to tie guest interface with the host
> interface because guest can change  MAC address of any interface and
> this change is not propagated to the outside world. Therefore vnet1 can
> be eth0 or eth1 or even hello_i_am_funky_interface99.
> 2) Guest can create virtual interfaces within itself and therefore
> create a totally different structure than observed from outside, e.g.
> bonding.
> 3) Interface can have multiple addresses or even none.
> Therefore I lean to something like:
> int virDomainGetIPAddresses(virDomainPtr dom, char **addr[], int
> *addr_size);
> That is - simply return an array of IPs in string format (yes, allocated
> by us) and leave mgmt application to decide what to do with that.
> Any thoughts?

 From a user's point of view, one will more like to ask questions
like "which's the IP of vnet0 in guest?", but not "what's the IP
of all interfaces". But as you explained in 2), the user could
play with the interfaces as he want in the guest, ask like
"what's the IP of foo in guest" doesn't work in this case. I guess
that's the mainly reason for you to choose the second way.

But in this case, we need to returns a struct instead, supposing
one will request to get other info later. (e.g. the netmask you
mentioned in later mail). And also we need the MAC address or
interface's name to associated the IP with interface, only returns
the IP address doesn't help one figure out to which interface the
IP belongs.

/me thinking if there is a good way to support both those 2 questions
in one API. (i.e. What's the IP of vnet0, What's the IP of all interfaces).


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