Re: [Engine-devel] Network Wiring

On 11/15/2012 02:33 PM, Itamar Heim wrote: >On 11/15/2012 02:29 PM, Dan Kenigsberg wrote: >>On Wed, Nov 14, 2012 at 02:12:07PM -0500, Simon Grinberg wrote: >>>> >>>>The intention is to use the new API VDSM.libvirtVm.updateVmInteface >>>>for >>>>performing the network rewire in a single command. >>> >>>What does it do? I could not find updateVmInteface in vdsm git. >>>Where is this defined? >>> >>>It's critical. >>> >>>- You can change the interface directly by moving the VM from >>>one network to another >>>- You can do that but toggle the ling state so the VM will be aware. >>> >>>Which if these two? >>>If you do only the first then it's not the common use case. In >>>most cases you must toggle the link status to the VM. >>>This will cause: >>>1. Speed negotiation + arp request that also informs the >>>switched about the change >>>2. In case it's DHCP (which most likely the case for guests) >>>it will trigger new DHCP request. >>> >>>If you don't baaad things will happen :) >> >>I think that baaaaad things are going to happen anyway. In "baaaaad >>things", I mean "stuff that require guest intervension". >> >>The guest may be moved from one subnet into another one, maybe on >>different VLAN or physical LAN. We can not expect that the applications >>running on it will be happy about these changes. A similar case appears >>if we rewire the network while the VM is down (or hibernated). When the >>VM is restarted, it is going to use mismatching IP addresses. >> >>You are right that it may make sense to request an new IP address after >>the rewiring, however, a little test I just did on my desktop >>showed that >>dhclient does not initiate a new request just because the carrier >>dropped for few seconds. So we should try harder if we want to refresh >>dhcp after rewiring: I think that it would be cool to have a >>guest agent verb >>that does it. Blame your OS if it doesn't do media sensing at all (or correctly).

> >shouldn't this simulate a link disconnect/connect event to the OS? I sincerely hope it does.