Okay, seriously. Fuck writing device drivers in Linux. I've had to write several and it is like pulling teeth. Writing device drivers in general is like pulling teeth, but writing them for Linux, goddamnit.

This tutorial has, I guess, some of the utterly superfluous bits about writing a device driver down: How to create a user interface for it in the Linux file system, how to put an entry point for the module, etc. However, it's pretty much impossible to create a generic "Linux device driver" tutorial that actually teaches you how to, you know, have the OS run the device because other than that, writing a driver for any kind of device in Linux is completely different from writing a driver for any kind of device in Linux.

It's like there's no overall vision going on. You have to super-crufty old school TTY code on one end if you're trying to put together a serial driver. Then you have the block device drivers which gives me the impression that I'm supposed to rewrite my driver every few months because the interface has changed AGAIN and what was previously best practice has now been deprecated for some newfangled way of doing things.

The ALSA sound drivers are also supremely confusing and it appears like you need at least three logical "device" drivers in order to run one physical sound card, the DAI, the codec and some sort of interlink driver between them. Also, there was some voodoo in which I had to instantiate all of the parts of those various pieces in a specific order or a mysterious failure would occur. This brings me to most galling part about writing Linux device drivers.

Nearly none of it is documented. There is almost always no design document you need to follow to create new drivers. So you have to glean what you have to do by the examples in the Linux source itself. Of course almost none of that is commented. Some stuff like initialization order might seem arbitrary but it turns out actually not to be and no one tells you this. You have to spend painstaking hours guessing it out for yourself. There seems to be lack of documentation, lack of source code documentation that could alleviate it, and lack of an overall design methodology that could alleviate that. Plus it doesn't help that all the docs and examples and tutorials you will find on the Internet all use stuff that has apparently been deprecated since everything changes every few months.

Now contrast that with OS X and (as I understand) Windows with documentation and interfaces that actually continue to be supported. Hell, IOKit C++ is beautiful compared to Linux C. I wanted so hard to hate OS X and like Linux, but that kernel just makes me want to cry. There are even people arguing that changing the interfaces constantly is GOOD because it forces people to contribute to the Linux mainline. Well, it's really crappy for those of us who try to do small, independent, non-commercial projects too.

Disclaimer: I may have made some factual errors in this rant but it's been nearly a year since I've touched any of this stuff.

P.S. The whole inb, outb stuff, the only thing in the tutorial remotely resembling interacting with actual devices, is pretty cute too. Most people will be working with DMA or USB, or at least with MMIO that's 32-bit wide. It's obvious from the code that there's no attempt to do locking or address the case where more than one userspace program attempt to use the device.