Re: [Xen-users] mount DomU root fs via. NFS

[Jeenu Viswambharan <Jeenu.Viswambharan@xxxxxxx>]

On Mon, Aug 04, 2014 at 16:36:44, Ian Campbell wrote:
> On Mon, 2014-08-04 at 15:00 +0100, Jeenu Viswambharan wrote:
> > Dom0 gets IP address using DHCP (I've ip=dhcp in Dom0 command line). Can
> > vif be configured to get IP address via. DHCP too, rather than assigning
> > a static one?
>
> Sort of, but not how you probably mean...
>
> It is possible to run a dhcpd in dom0 which serves IP addresses to the
> VMs which are behind the NAT. The vif-nat script will frob the dhcp
> config to contain the ip address which you gave in the config and
> reload the server config on the fly, so that the guest gets given that
> address.
>
> What isn't possible is to use the existing DHCP server, since it
> doesn't know about your private network. Plus you would need to be
> able to write the answer to the DHCP request into the guest cfg file,
> or do something else clever with proxy dhcp or something...
>
> If you were to setup dhcpd in dom0 you'd need to be very careful about
> which interfaces it will send replies to, otherwise you'll have your
> IT department breaking down your door ;-)
>
> Personally I don't trust that stuff much, so I would use a static IP.

OK, I don't have a static IP allocated, but I managed to use the dhtest
tool [1] to temporarily lease a dynamic IP for testing purposes on my
network. I assume, for all intent and purposes, that can be treated as a
static IP.

The wiki page [2] suggests that I can use a random MAC addresses, so
I've dhtest generate a random MAC for me: 22:1e:4e:fc:6d:be; and that
gave me an IP address 10.1.193.141.

With that, I've in my guest configuration:

  ...
  vif = [ "script=vif-nat,mac=22:1e:4e:fc:6d:be,ip=10.1.193.141" ]
  extra = "... root=/dev/nfs nfsroot=nfs.ip.add.ress:/path/to/nfs/root 
ip=192.168.1.1 ..."
  ...

What I now see that xl fails to create the guest, and it reports the
following error (verbose logs attached).

  ...
  libxl: error: libxl_device.c:1084:device_hotplug_child_death_cb: script: ip 
addr add 10.1.193.268 dev vif4.0 failed
  ...

The printed IP address 10.1.193.268 seems spurious. Does the logs give
any idea as to what's going on?

Also, I don't know if it's the MAC address is causing it to fail.
Although randomly generated, it does seem to have compatible (locally
administered, multicast etc.) bits.

FWIW, the file /var/log/xen/xen-hotplug.log has:

  Error: an inet prefix is expected rather than "10.1.193.268".

--
Jeenu

[1] https://github.com/sipwise/dhtest.git
[2] http://wiki.xen.org/wiki/Xen_Networking#MAC_addresses

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Attachment: xl.log
Description: xl.log

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