Xen, New VM wizard, paravirt vs full virt

[Craig Miskell]

Hi,
   I'm running virt-manager 0.7.0 on Ubuntu, connecting using SSH to libvirt
running on Debian Lenny Xen-3.2.1 (please, no flames :))

The trouble is, when I go to create a new VM using the wizard, no install
options are available because:
1) "Network install" is not available unless the connection is local, and
2) Local install media and  Network boot (PXE) are not available because of the
following line in create.py (around line 340):
is_pv = (self.capsguest.os_type == "xen")

I changed that line to:
is_pv = False
because Xen can do Full Virtualisation these days.  And I'm then able to create
local CD install of a full virtualisation VM, which boots and works perfectly.

Three questions:

1) Am I missing something, or is the is_pv definition just historical?
2) What's wrong with doing a "Network install" when you're not local; I thought
(please correct me if wrong) that a Network Install involved passing a URL to
some sort of install repository; why would that need local access.
3) Why is it not possible to do a Local Install media or PXE boot with a
para-virtualised guest?

Thanks,

--
Craig Miskell
Senior Systems Administrator - Linux
Opus International Consultants
O: Do you have one in the Cadillac? TW: No, I have a little band in there.
It's an old car, so I have a little old string band in the glove compartment.
It's grumpy.
        -- Tom Waits, on car CD players

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[Cole Robinson]

On 06/25/2009 07:52 PM, Craig Miskell wrote:

> Hi,
>   I'm running virt-manager 0.7.0 on Ubuntu, connecting using SSH to
> libvirt running on Debian Lenny Xen-3.2.1 (please, no flames :))
>
> The trouble is, when I go to create a new VM using the wizard, no
> install options are available because:
> 1) "Network install" is not available unless the connection is local, and
> 2) Local install media and  Network boot (PXE) are not available because
> of the following line in create.py (around line 340):
> is_pv = (self.capsguest.os_type == "xen")
>
> I changed that line to:
> is_pv = False
> because Xen can do Full Virtualisation these days.  And I'm then able to
> create local CD install of a full virtualisation VM, which boots and
> works perfectly.
>

This was a bug that should now be fixed upstream. I'd recommend you file a bug
with debian, with a link to the following commit:

http://hg.et.redhat.com/cgi-bin/hg-virt.cgi/applications/virt-manager--devel/rev/6374136c6247

> Three questions:
>
> 1) Am I missing something, or is the is_pv definition just historical?

Nope, it serves a use in the code: if the host machine doesn't support
fullyvirt (possibly due to hardware restrictions), we need to limit the
install options.

> 2) What's wrong with doing a "Network install" when you're not local; I
> thought (please correct me if wrong) that a Network Install involved
> passing a URL to some sort of install repository; why would that need
> local access.

Because a network install has to fetch a boot kernel and initrd from the URL,
and we have no way to tell the remote machine to fetch these locations.

> 3) Why is it not possible to do a Local Install media or PXE boot with a
> para-virtualised guest?
>

Because AFAIK xen PV guests on linux do not support CD or PXE booting.

HTH,
Cole

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