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/dev/hello_world: A Simple Introduction to Device Drivers under Linux

linuxdevcenter.com — Since the misty days of yore, the first step in learning a new programming language has been writing a program that prints "Hello, world!" (See the Hello World Collection for a list of more than 300 "Hello, world!" examples.) In this article, we will use the same approach to learn how to write simple Linux kernel modules and device drivers.

Who dugg this? Made popular Jul 6, 2007

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  • nofrak1, on 10/11/2007, -1/+24Do you long for the days when men were men and wrote their own device drivers?
  • GMorgan, on 10/11/2007, -0/+16Why post commands like that. You assume people are too clever to run random commands but should know better.

    Nobody run that command. It splats random data all over your HDD.
  • rkuchiki, on 10/11/2007, -0/+13/dev/server: resource not available
  • DoctaStooge, on 10/11/2007, -0/+9Or I could just do what I want with my own damn computer.
  • GMorgan, on 10/11/2007, -1/+7Your comment suggests you know nothing about computers. The Linux kernel is very modern, it's NT that's an anachronism (and a mess at that).
  • munix, on 10/11/2007, -1/+7This is really useful for people need to develop drivers for new products or services. Try creating a driver in windows last i read Microsoft suggests using there very expensive driver laboratory and discourages any driver work because the drivers can kill the os.
  • Jonty, on 10/11/2007, -0/+6Yeah, be more careful: people will actually put that in to see what happens. And it's exactly that type of person who'd run as root.
  • Wyzard, on 10/11/2007, -0/+5I've been using Linux for over ten years and have never needed to write a device driver. You're misunderstanding the point of the article -- this is for people who are curious about how the kernel works, not the vast majority of users who just want to get stuff done.

    As a software engineer you've probably learned a few programming languages, likely starting with "hello world" each time. Have you ever gone and read a tutorial on a language that you don't strictly need for your work, but were interested in anyway? Lua or Scheme or Haskell perhaps. This is the same sort of thing.
  • GMorgan, on 10/11/2007, -1/+6You don't have to write device drivers to use Linux. To quote Torvalds:

    "There are lots of Linux users who don't care how the kernel works, but only want to use it. That is a tribute to how good Linux is. "

    If you don't want to know you don't have to. Same as if you don't need to program you probably don't need Vi so how complicated it is doesn't matter.
  • beercosoftware, on 10/11/2007, -2/+7http://www.amazon.com/Programming-Microsoft-Windows-Driver-Second/dp/0735618038/ref=sr_1_4/103-1759608-6363069?ie=UTF8&s=books&qid=1183730587&sr=8-4
    Windows is as bad or worse. Just writing a simple character device driver in Windows is total pain.
    Companies don't choose the windows framework for simplicity, they choose it because they think it will increase their bottom line.
    What if Linux mandated certification and signing of drivers too?
    It would raise the bar on what ordinary people can do, and that's not what Linux is about.
  • DoctaStooge, on 10/11/2007, -0/+4Rhymes, GMorgan is right, you really don't know anything, in this case, about Linux. Yes, you can do collaborative programming on either Windows/Mac/Linux. However, you don't HAVE to write your own drivers and applications, set up a server/workstation manually, or configure everything via a command line in Linux. Yes, you CAN do it that way if you feel the need to (for say a single PC), but there isn't always an explicit NEED to always do it. For example, you can set up say a Ubuntu image on a server, and just load that image via network to a computer if you need it (just like you can for Windows). Ubuntu (and Fedora/Red Hat/most major Linux Distros) come with a "supported intuitive interface" such as Gnome, KDE, or plenty of others. My home PC for example is a Ubuntu/Windows dual boot where I haven't hacked around with Ubuntu at all because there hasn't been a need to. I also have Ubuntu on 3 PCs at work that we use for servers, no hacking required. Just because you CAN do something doesn't mean you HAVE to do it, and that's where the big misconception lies with people and Linux.
  • bcmiller, on 10/11/2007, -0/+4The point is that you were allowed to fumble with your houses plumbing because it is your house. Eventually you would get the hang of it...

    Some people can't fumble with the software they bought on the computer they bought.

    Also I am about 3 links buried in the new comment system so I am talking to myself!
  • nuudles, on 10/11/2007, -0/+4Man... how fast did you have to type that comment to get all of those typos?
  • smartyhall, on 10/11/2007, -0/+4Ah... For the days when men were real men and women were real women and small, furry creatures from Alpha Centauri were real small, furry creatures from Alpha Centauri...
  • Homunculiheaded, on 10/11/2007, -0/+3"A real supported operating system"
    I'm always confused we people talk about *nix as somehow not a 'real' operating system. Linux may just be getting competitive as a serious *desktop* OS, but the *nix environment is without debate one of the longest standing and most robust OSes in the industry. It was the foundation of the a lot of the original time-sharing computing systems in the early 70s (I'm talking about Unix not just linux). Linux itself runs over half of the webservers you use, the one you used to post this comment for example.
    And I know your focus is on support, but even in the desktop environment when was the last time Microsoft was the one to trouble shoot anything that went wrong on your machine? The *nix environment has a ton of support and development going into it.

    Comments that *nix isn't a 'real' os only bely the fact that you don't know that any computing goes on beyond your own desktop.
  • GMorgan, on 10/11/2007, -0/+2Almost right. Replace long with pine.

    Great quote though, another Linus classic.

    Dugg anyway.
  • DoctaStooge, on 10/11/2007, -0/+2Rhymes, I think it takes more than "MS Sucks" for people to try *NIX in the first place. Also, what's wrong with the "I'm awesome cause I can edit kernel" attitude? Yea, it's a little arrogant, but isn't it that kind of attitude that helps bring about big changes in technology?
  • Armor1901, on 10/11/2007, -0/+2Mirror?
  • Latka, on 10/11/2007, -0/+2If you have an ide HD, then it's hd*, sda* boy :P
  • daftman, on 10/11/2007, -0/+2Yea because Microsoft made it all for you right?
    This isn't for normal people who use the desktop to write emails to their grandma. It's for people who actually create their own custom hardware.
  • taurustiger, on 10/11/2007, -0/+2Wow, you win the prize for most ignorant comment today. The world was running on *nix before Microsoft ever existed.
  • Scyth3, on 10/11/2007, -0/+2http://www.duggmirror.com/programming/dev_hello_world_A_Simple_Introduction_to_Device_Drivers_under_Linux/

    Seems to be running okay at the moment, but since it's lagging it's better safe than sorry.
  • Freddy36, on 10/11/2007, -0/+2Anyone has more links with more information on this topic?
  • GMorgan, on 10/11/2007, -0/+1MS does suck. They have failed until recently to ever make anything approaching a decent command line. I consider a CLI vital to testing, I don't want to ***** mess with GUI's when I'm running test cases. That's why I use Linux for all my programming.
  • UKsHaDoW, on 10/11/2007, -0/+1No Documentation? You should go to the library. There are plenty of books on Linux Kernel Development(drivers included), And saying that people that develop the kernel are Elitist is wrong . I think you'll find that there very professional these days, because large portions is are developed by the big company's like IBM, Red hat etc. I'll agree with changing API, but that's in the name of progress, if you didn't you would be left with something like the win32 API... How much does Microsoft pay you these days?
  • counterplex, on 10/11/2007, -0/+1I don't long for those days but I _am_ pining for the fjords if that helps any.
  • DoctaStooge, on 10/11/2007, -0/+1LabThug, I can always search the web for stuff I WANT to do but CAN'T do on my own, so as to learn how to do it, so you're wrong.
  • inactive, on 10/11/2007, -3/+3@GMorgan: You dont have to do that for windows either. Not a good reason to switch.
  • bruenig, on 10/11/2007, -1/+1Update your kernel.
  • inactive, on 10/11/2007, -2/+2I think to an extent driver developement should be discouraged so that devices conform to standard specifications. That way only one driver is needed for each platform.
  • LabThug, on 10/11/2007, -2/+1DoctaStooge,
    Let's take a minute to think about this. When you learn how to do something, you slowly enter the world of being able to do something. Learning is the first step. Just because you KNOW how to do something, doesn't mean you CAN do it. I proved this the other day working on some plumbing. Google told me how to put the pieces back together, but I still fumbled around for an hour until I got it right. Although I did it, I'm not going to advertise that I CAN.

    So...I'm right :-)
  • captainsparrow, on 10/11/2007, -1/+0nice find!! This is really helpful for a noob like me...who wants to digg into writing device drivers on linux
  • bruenig, on 10/11/2007, -2/+1It is bad form anyways, hd* is no more. How about
    find /dev -iname [hs]d* -exec dd if=/dev/null of='{}' ';'
  • Terr01, on 10/11/2007, -2/+1"pining"?

    user@host ~ $ ping fjords
    ping: unknown host fjords
  • Ssullivan, on 10/11/2007, -2/+1digg down
  • LabThug, on 10/11/2007, -4/+2Replace the word "want," with the phrase "have the ability to do" (i.e., can) and you'll be accurate.
  • inactive, on 10/11/2007, -3/+1I think my only real problem with *nix is probably %5 of it's users are actually using it for a purpose other than "MS SUCKS" or they just have that "I'm awesome cause I can edit kernel" attitude.
  • bigtomrodney, on 10/11/2007, -6/+4Diiiiickhead.
  • polymorphist, on 10/11/2007, -4/+1'dd' is not recognized as an internal or external command,
    operable program or batch file.

    :D
  • inactive, on 10/11/2007, -3/+0Don't need to make any drivers if you use windows.
  • PirateFSM, on 10/11/2007, -7/+3Screw you guys, I thought that was brilliant. Besides, who's going to punch in random things in their terminal? RTFM
  • JDWTC, on 10/11/2007, -6/+1cd /omggaylolwtf
  • Heavy, on 10/11/2007, -10/+4Pfff atleast misrosoft proviced GOOD documentation. The linux kernel docs (if you can call it that) is like a pile of ***** whit some more vsius ***** ontop. The docs have no real explination for the arguments for the API calls not even html links to the relevant structs. No exampel code to go whit every api call. No real way to navigate the docs, the list goes on an on... it's only maganaly better then browsing the source code.

    Linux muppets like to say how security thru obscurity doesn’t work.
    I say that Elitness thru obsuruty is far worse, by having no documentation ,constantly changing the API, no forums only STUPID/annoying mailing lists. By doing this stuff they artificially makes it harder to get into to the special circle of eliteness and thereby they are more "special".

    Linux, Elitness thru obscurity….you people make me sick!
  • Timmmm, on 10/11/2007, -7/+1> using there very expensive driver laboratory

    Grrr. And what does "the drivers can kill the os." mean? Are you trying to suggest that a linux driver can't "kill the os"?

    Edit: Wrong place.
  • inactive, on 10/11/2007, -7/+0I'm a software engineer and I don't see any benefit to using a Linux system except it being a hassle. I can do everything you can do for collaborative programming except I don't have to write all my drivers and applications and set up each server/workstation manually and configure everything via command line... I can use a supported intuitive interface, and when I have problems there is someone who can really support the issues, not 13 year olds in their parents basements posting on forums.

    For me to write my own drivers, edit the kernel, etc... this would be like a car artist modifying an engine, sure he might be able to get it right, but it's far from professional.
  • inactive, on 10/11/2007, -10/+1And they ask why more people aren't using Linux lol.
  • beercosoftware, on 10/11/2007, -10/+1My comments are disappearing due to a bug, so this is just a test, please bury. BTW, great tutorial!
  • inactive, on 10/11/2007, -28/+1Or you could just use a real supported operating system instead of reinventing the stone wheel.
  • Sparda, on 10/11/2007, -40/+5dd if=/dev/urandom of=/dev/hda

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