Do I need two machines to develop IOKit Mac drivers?

Question

I'm building an IOKit CFPlugin driver for OS X. I'll be working with network data coming in that will be translated to MIDI data. No hardware is involved other than the built-in Airport. I have experience with drivers on Windows machines and firmware but this is my first dip into doing it on the Mac. So far things are going pretty well, but the Apple documentation sez: "For safety reasons, you should not load your driver on your development machine."

I only have one Mac. I really don't want two Macs- sorry, Apple. Should I take this warning seriously? Are there things I need to know?

Thanks, Tom Jeffries

Answer 1

You could also consider running OS X inside a VM as your testbed. It would surely be much more convenient that having a separate boot volume.

Answer 2

The warning is rather poorly worded; what you should consider doing is using a separate boot volume (partition) for trying out your driver, since it's possible to arbitrarily hose your system with your driver. If you're doing kernel development on any OS that isn't isolated from your main system (via a VM, alternate boot disk, etc.), you're crazy!

What may be a bigger issue is that you can't do any kernel debugging, because the only option for that is to use GDB on a remote OS X system. For this, you may want to consider running OS X in virtualization.

Answer 3

you DEFINITELY want to have some way to recover a fubar kext installation: a bootable external drive or something you can quickly restore from-- this is the main reason for Apple's warning against running in-development-kernel-extensions on your production machine.

Nicholas is right that in order to debug using gdb (the only way in kernel space) you do need two machines. I've never tried using a VM as Coxy suggests: but I guess it's feasible (assuming that you run your kext on the virtual machine and use the real host machine to run gdb).

My preferred method for tracing and debugging in the kernel is kprintf() routed to firewire (aka firewire kprintf (man fwkpfv) ). for this you do need two machines with firewire ports.

finally, being an old computer musician myself, I wonder why you want to program a MIDI synthesizer (or transformer) on the network stack level. my guess is that you would have a much more gratifying experience working in userland (where you can use floating point math...)

if you need some hints or tips, feel free to get in touch...

|K<

from the ADC Kernel Programming Guide

Kernel programming is a black art that should be avoided if at all possible. Fortunately, kernel programming is usually unnecessary. You can write most software entirely in user space. Even most device drivers (FireWire and USB, for example) can be written as applications, rather than as kernel code. A few low-level drivers must be resident in the kernel's address space, however, and this document might be marginally useful if you are writing drivers that fall into this category.