"Incidentally i was thinking about using KVM for automated testing. Important pieces of hardware should get an in-KVM simulator/emulator, that way developers who do not own that hardware can do functionality testing too,"Ingo Molnar suggested during a thread discussing a SCSI driver bug fix. Linus Torvalds was originally unimpressed by the idea:
"Using emulators to test device drivers is almost certain to be pointless. The problem with device drivers tends to be timing issues, odd hardware interactions, and lots of strange (and sometimes undocumented) behaviour and dependencies (eg things like 'you have to wait 50us after setting the reset bit until the hardware has actually reset'). These are all things that you'd generally not catch in emulation - because the emulation by necessity is only going to be a very weak picture of the real thing."
Alan Cox countered, "for some things. I do it a bit because you can use it to fake failures that are tricky to do in the real world. It won't tell you the driver works but its surprisingly good for testing for races (forcing IRQ delivery at specific points), buggy hardware you don't posses, and things like media failures and timeouts your real hardware refuses to do." Linus acquiesced conditionally, "I do agree that you likely find bugs, even if quite often it's exactly because the behaviour is something that will never happen on real hardware," then acknowledged previous debugging efforts by Alan, "but failure testing is very useful - I forget who it was who debugged some driver by taking a CD and just scratching it mercilessly to induce read errors ;)" Ingo added, "something like that wont enable 100% coverage (or even reasonable coverage for most hardware), so it's no replacement for actual hard testing, but it could push out the domain of minimally tested code quite a bit and increase the quality of the kernel."
