Hardware vendor supplied modules

I see a problem with hardware (and software) vendors modules that are supplied in source code (see for instance VMWare kernel modules). If you can't compile a kernel module without the kernel source tree and on a different machine (maybe with different compiler/processor and whatnot) from the distibutor kernel, you can't use such modules.

There are a few possibilities here:

• completely disallow external modules - then, VMWare and co. would have to provide a patch to integrate their modules with the kernel source proper, and each customer would have to apply this patch and rebuild the kernel. (Or, alternatively, VMWare could ship with a custom kernel, but then they'd have to follow the GPL and open-source their module.)
• have VMWare and their ilk each track all the major vendor kernels and release modules to go with each one. Many proprietary module vendors do this today. It's a horrible hack but it does work for some people.
• freeze the kernel/module interface, somehow nullify or abstract away all differences that affect it, and maintain this situation for a given length of time (say, a stable series). That would include gcc 2.95 vs. gcc 3.2, preemptible vs. non-preemptible, UP vs. SMP, 386 vs. 586 vs. K7, highmem vs. non-highmem, and a few other details, on the x86 platform. This is the Microsoft / commercial Unix solution, and the Linux people refuse to bother with it. If you think this is the way to go, please be prepared to present your patch which does all this without affecting efficiency or maintainability of the source base. Alternately, Google for 'UDI unix linux' and see what happened the last time this was proposed.
• take some sort of snapshot of the state of the build environment when you build a kernel, and make this snapshot available somehow for when you want to build an external module. This snapshot would consist of kernel headers, .config file, exact compiler and its flags, and some sort of glue to plug the external module in to all this.

At present, we have the latter option, in the form of a live source tree. Note that if you can locate the live source tree you wish to build against, and the compiler you used to build the kernel, and any other variables you passed in when you built the kernel (like a CROSS_COMPILE variable), you can use this method just fine.

If you don't know this information, unfortunately there is no way for the computer to divine it for you. What if I build 10 different kernels on my box, destined for 10 different machines, then I try to build an external module? How is the system supposed to know which of my 10 kernels the module is for? Barring a direct DWIM neural interface (for which Linux drivers are still sadly lacking), I'm gonna have to point my module at the proper kernel tree, and re-set-up any custom variables I set the first time.