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January 2009
February 2009

2009-01-21 »

Tracking an entire Windows sytem inside Git

I am often accused, sometimes by myself, of being a complete nutcase. This is one of those times.

"But wait!" I say to myself. "Sure, I might look crazy, and I might be crazy, but don't you at least agree that there might be a point to all this?"

I look back at myself suspiciously. "And if there is?"

"Well, that would mean..."

"Never! Don't even say it! It's all nonsense! You're just trying to make me go along with another one of your insane schemes!"



Anyway, yes, I did it. I put all of Windows under git version control.

You see, I installed Windows 98 inside Win4lin Terminal Server (the old Win4lin, before the useless qemu-based "Win4lin Pro" came out). To do it, I had to downgrade my Linux kernel to, the last one that Win4lin ever made a patch for. But that's no big deal; it's an old machine anyway. It works fine with the old kernel, even in Debian Etch.

Now, Win4lin (the old one, the only one that matters) has the little-known but extremely useful property that it shares its filesystem directly with the Linux host system. That is, unlike VMware and other "pure" virtualization systems that use "disk images," the files in your Win4lin system map exactly to files in a subdirectory on your Linux system, usually ~/win. So there are files like ~/win/autoexec.bat, ~/win/windows/explorer.exe, and so on.

In the olden days, this was nice primarily because it meant the virtual Windows system didn't need to have its own disk cache. Also because Linux's disk cache and filesystem are fantastically more efficient than anything in Windows, by a very large margin. (Trust me, I've done comparisons. I'm sure other people have too. Maybe they just don't publish the results because they don't look believable enough.) Oh, and of course, you can access files on your Linux system without using Samba, which means things go way faster.

So those are all reason enough to use Win4lin. Or were, in the olden days. Nowadays, Windows 98 is looking a bit old, and the old Win4lin doesn't support Windows NT-based systems (like 2000, XP, and Vista). So to tolerate the limitations of Windows 98, you need a pretty good reason.

This week I found that reason: git!

I've been working on a project that requires me to develop plugins that are backwards compatible with old versions of MS Office, perhaps as far back as Office 97. I also need to test with all the newer versions: 2000, XP, 2003, and 2007. So here's the thing: all those versions, except 2007, work just fine on Windows 98, and Microsoft is really good at backward compatibility. So if I make a plugin for Office 97 on Windows 98, it should run with (close to) no problems on newer platforms. I should be able to just do a cursory check every now and then to make sure.

So, I thought, win4lin should be a good system to check all the old versions on. Then if I throw in a VMware with XP and one with Vista, I should be all set.

After setting it all up (which was admittedly a bit painful), I realized just how efficient Windows 98 is... at least compared to later versions. Did you know a base install of Win98 is less than 100 megs? Why, I have bigger source trees than that lying around nowadays.

...source trees... hmmm...

I had to try it, of course. I went into ~/win, typed "git init", and "git add .", and "git commit". Ta da, a working git repository with my fresh Win98 install.

Then I created separate branches, one for each version of Office, and installed them one by one. And now I can easily test new versions of my plugin: "git checkout office2000; win" or "git checkout office97sr2; win".

Now, the final trick will be to get this whole system running inside VMware. If that works, then the major limitation on this setup - the old kernel that will surely be missing a necessary driver eventually - goes away. I'll be able to use this setup forever to test Office plugins up to Office 2003.

Unfortunately, I can't advise you to try to duplicate my setup. I happened to have a valid Windows 98 license and a valid Win4lin license, neither of which you can buy anymore, and a collection of valid MS Office licenses acquired over time (including the most recent ones via MSDN).

In fact, the rarer Windows 98 licenses become, the more distinctive my amazing setup will make me. Bow down to my power, lowly normal people!


And all this makes me think of something I should add to my thresholds list: the day when a Windows XP install is "small enough" to put under version control.

In other news, ReactOS is looking surprisingly promising lately.

If I get a virus, I can 'git revert' it.


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