On 30/11/09 10:52, Matthew Booth wrote:
One of the things we would really like to be able to do for V2V is to install a new driver in a Windows guest. There are a couple of reasons for this:
* The guest may not be bootable without the driver installed, for example because the underlying virtual hardware has changed from vmscsi to virtio.
* If the guest can boot, the alternative is to modify the guest to run a script on next boot. This requires making assumptions about supporting software being installed and working correctly on the guest. Certain environments, particularly heavily locked-down environments, make this an unsafe assumption.
The Windows PE environment looks perfect for this task. It gives you a very lightweight Windows OS which can be customised with additional tools. It is specifically for doing installations. I spent Friday trying to use it to install a driver in a guest. Here's what I tried and why it didn't work.
Installing a driver in Windows is 'driven' by a .inf file. From my (admittedly limited) understanding, this broadly describes:
* The files which need to be installed * The hardware the driver is compatible with
The files, including the .inf file itself must be copied in to the correct places. In addition, information from the .inf file must be written to the registry. It is this last part which causes problems.
From reading documentation, it appears that a driver would normally be installed using the SetupCopyOEMInf() library call. I wrote a simple wrapper round this and installed it in the Windows PE image, along with the VirtIO drivers. I booted into Windows PE and attempted to install the driver. As you might expect, the drivers were installed into the Windows PE image rather than the guest. I then tried setting %systemdrive% and %systemroot% to the guest image. This appears to have no effect. This is what makes me suspect that the process is primarily registry driven.
I started looking around for ways of using a different registry. I discovered the Registry Editor PE plugin to BartPE (https://sourceforge.net/projects/regeditpe/) which allows editing the registry of a guest. Looking at how it does this, it uses reg.exe to load the guests's hives. I confirmed that you can do this. Unfortunately you don't seem to be able to replace the default hives. The new hives are loaded in a different part of the tree, and are therefore ignored.
This is as far as I've got. Still on my list are:
* Ask on various Windows mailing lists how to do this * Investigate if the packaged .msi containing the drivers is more flexible. * Look for other, possibly lower level, ways of replacing making a process use a different registry.
Any and all suggestions are gratefully received,
An update on this as promised: I have now made it work with Windows 2008 R2! The short version: 1. Create a Windows PE image containing VirtIO drivers * Install WAIK for Windows 7 on your build system * Create a stock amd64 Windows PE image * Use DISM to mount the image * Use DISM to install the amd64 viostor driver for Win2008 in the image * Use DISM to unmount the image * Copy the image to sources\boot.wim in the ISO tree * Copy the complete contents of the virtio driver floppy into ISO tree * Create a bootable ISO image from the ISO tree 2. Use Windows PE image to install driver in guest * Ensure guest is configured to use VirtIO for storage * Add Windows PE image as boot image for guest * Boot guest with Windows PE image Guest system drive is D: Mounted ISO image is E: * Run: dism /image:d:\ /add-driver /driver:e:\virtio\amd64\win2008\viostor.inf * exit * Configure guest to boot from HD The guest will now boot normally using VirtIO. The biggest gotcha in the above is that if you google 'WAIK' it will send you to a download page for Windows Automated Installation Kit. Unless you're extremely eagle-eyed (I wasn't) you won't notice that this was released in 2007, and it doesn't support Windows 2008 R2. However, if you search for WAIK in the search box (not the Bing one, the useful one below that), you'll find it. DISM is new in the latest WAIK. Compared to pkgmgr it's a doddle to install a driver as you don't need an obtuse unattend.xml. I'm about to test the same image against 32bit Windows 2003. I'll report back on how that goes. Matt -- Matthew Booth, RHCA, RHCSS Red Hat Engineering, Virtualisation Team M: +44 (0)7977 267231 GPG ID: D33C3490 GPG FPR: 3733 612D 2D05 5458 8A8A 1600 3441 EA19 D33C 3490