Re: [Xen-devel] Restore PVHVM DomU with a different MAC

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Sep 13, 2017 at 04:25:17PM +0800, Kangjie Xi wrote:
> Hi,
> 
> I created a Ubuntu-17.04-x64 PVHVM DomU, so I can use "xl
> network-attach/detach" to add/delete network interfaces, it works
> well.
> 
> However I wanted to restore the DomU with a different MAC address, so
> before saving the checkpoit file, I deleted the network interface with
> "xl netwrok-detach", and assigned a different MAC in the configuration
> file and restored the DomU:
> 
> # xl network-detach ubuntu 0
> # xl save ubuntu ubuntu.checkpoint
> # xl restore ubuntu.cfg ubuntu.checkpoint
> 

Doing this causes xl to ignore the saved state and use the provided
config file to construct the new guest iirc. I haven't checked the code
in detail though.

The end result seems to be what you wanted.

>  But the DomU didn't detect the new network interface. In Dom0, could
> see the DomU has new MAC.
> 
> # xl network-list ubuntu
> Idx BE Mac Addr.         handle state evt-ch   tx-/rx-ring-ref BE-path
> 0   0  00:16:3e:eb:ca:67     0     1     -1    -1/-1
> /local/domain/0/backend/vif/139/0
> 

A vif is created but DomU can't find it. It is possible DomU kernel
doesn't go through the whole cycle of device probing and simply ignores
a vif that it doesn't know about during restore. As far as it is
concerned, the vif originally provided is already gone. The new vif
shows up out of nowhere.

You may be able to manually generate a udev event to make the kernel
probe the new vif. I don't know.

> If I add network interface manually after restoring, the DomU can
> detect new network interface automatically.
> 
> # xl network-attach ubuntu type=vif mac=00:16:3e:eb:ca:68 bridge=virbr0
> 
> # xl network-list ubuntu
> Idx BE Mac Addr.         handle state evt-ch   tx-/rx-ring-ref BE-path
> 0   0  00:16:3e:eb:ca:67     0     1     -1    -1/-1
> /local/domain/0/backend/vif/139/0
> 1   0  00:16:3e:eb:ca:68     1     4     -1   529/528
> /local/domain/0/backend/vif/139/1
> 
> Is it a bug?
> 

Can't say for sure at this stage.

> Thanks
> 
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