Re: [Qemu-devel] Guest kernel device compatability auto-detection

["Richard W.M. Jones" <rjones@redhat.com>]

On Thu, Aug 25, 2011 at 08:48:25AM +0100, Richard W.M. Jones wrote:
> On Thu, Aug 25, 2011 at 10:40:34AM +0300, Sasha Levin wrote:
> > From what I gathered libguestfs only provides access to the guests'
> > image.
> 
> Correct.
> 
> > Which part is doing the IKCONFIG or System.map probing? Or is it done in
> > a different way?
> 
> You'll have to see what Matt's doing in the virt-v2v code for the
> details, but in general we have full access to:
> 
>  - grub.conf (to determine which kernel will boot)
>  - the kernel image
>  - the corresponding System.map and config
>  - the modules directory
>  - the Xorg config
>  - boot.ini or BCD (to determine which NT kernel will boot)
>  - the Windows Registry
>  - the list of packages installed (to see if VMware-tools or some other
>    guest agent is installed)
> 
> So working out what drivers are available is just a tedious matter of
> iterating across each of these places in the filesystem.

We had some interesting discussion on IRC about this.

Detecting if a guest "supports virtio" is a tricky problem, and it
goes beyond what the guest kernel can do.  For Linux guests you also
need to check what userspace can do.  This means unpacking the initrd
and checking for virtio drivers [in the general case this is
intractable, but you can do it for specific distros].

You also need to check that udev has the correct rules and that LVM is
configured to see VGs on /dev/vd* devices.

Console and Xorg configuration may also need to be checked (for
virtio-console and Cirrus/QXL support resp.)

virt-v2v does quite a lot of work to *enable* virtio drivers
including:

 - possibly installing a new kernel and updating grub

 - rebuilding the initrd to include virtio drivers

 - adjusting many different config files

 - removing other guest tools and Xen drivers

 - reconfiguring SELinux

 - adding viostor driver to Windows and adjusting the Windows Registry
   Critical Device Database

Of course virt-v2v confines itself to specific known guests, and we
test it like crazy.

Here is the code:

http://git.fedorahosted.org/git/?p=virt-v2v.git;a=blob;f=lib/Sys/VirtConvert/Converter/RedHat.pm;hb=HEAD
http://git.fedorahosted.org/git/?p=virt-v2v.git;a=blob;f=lib/Sys/VirtConvert/Converter/Windows.pm;hb=HEAD

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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