c++ device driver development in linux

Question

I wanted to get more details for writing Graphics device drivers and audio device drivers using c++ for Linux box. I am newbie at developing device drivers , Please provide me development/documentation details for the same.

Thanks

-Pravin

Answer 1

Coming to this page late, the question itself has been answered by Chris Stratton, but it's important to correct a couple of things Chris Becke put here that are common misconceptions with people that are not familiar with C++:

• C++ does not create implicit code or data, just what you request. Even for an average C++ programmer, there will be no extra code or data. I found it out through knowing the asm behind C++, but just read Scott Meyers books it's good enough.
• Not only are exceptions optional in C++, their entire code can be excluded in linkage for mostly every tool out there. This is in fact done in RT apps.

This is to address the misconceptions posted here. To add more however:

1) A novice C++ programmer may do nonsense, but a novice C programmer trying to implement by himself polymorphism and inheritance as done time and time again in the kernel just without calling it as such, will do lots more inefficient undebuggable nonsense.

2) Saying that, the only thing that may be created in base C++ is a virtual pointer IF YOU NEED IT and specify "virtual", and then also C programmers usually just create such a pointer manipulate it by themselves add lookup tables and get much harder bugs down the line due to it. As always in C++, if you don't mention "virtual" then you don't even get this pointer. Inheritance and encapsulation are of course completely free of overhead.

3) C++ creates the same amount of asm and memory as C if you don't EXPLICITLY request special features, but there is a common case when C++ is more efficient - when passing function pointers. If you use C++'s functors you can inline the pointed function. This is EXTREMELY useful in embedded apps.

4) If embedded RT uses C++ why linux doesn't? Just because of myths, so please do read this message carefully, and refer to scott meyers or better yet the asm itself. I am 20 years in RT and had the same disbelief in C++ when I switch 14 years ago, but the facts do not confirm any such distrust.

TL;DR - it's very easy to write as efficient and in a common case more efficient code in C++, studies, much industry experience and books are abound on this subject.

Answer 2

Linux kernel device drivers are written in C rather than C++.

Most device drivers are accessed via a special device file (/dev/yourdevice0) on which control as well as read and write operations can be performed.

User mode client programs and user mode drivers open the device file and use it as a pathway to talk to the kernel mode driver. These user mode drivers could conceivably be written in C++ or any other language.

Generally the best way to get started is to have a device which needs a driver, and learn what you need to in order to write it. And often the best way to do that is to find an existing driver for either a related device, or one with similar interface paradigms, and start by modifying that until it works for your new device instead or as well.