Slashdot Mirror
Breaking Into The World Of Kernel Hacking?
crow_t_robot asks: "In
the past couple of months I have become increasingly interested in
kernel programming and have finally decided to take the leap and
'get my hands dirty.' I have searched around the web and read a few
docs and FAQs on getting started with the kernel but I was wondering
what kind of personal experiences those in the Slashdot crowd have
had that are so bold as to start goofing with the kernel code. For
those that have become competent kernel programmers, how did you
'break in' and what advice would you give beginners?"
...www.kernelnewbies.org is supposed to have a lot for the aspiring kernel hacker.
...RTFM! ;-)
Seriously, though. Try and find FRIENDLY help. Once you have that, you should be good to go. A lot of kernel hackers are very elitest, and don't take too kindly to newbies, so find yourself a good support group and go from there.
Good quote, too many chars. Seriously, the slashdot 120 char limit sucks!
(Now taking bets on whether this first hits -1 Troll or +5 Funny).
I think the kernel docs would be a good starting point.
/usr/src
2 .4.17.tar.bz2
cd
wget ftp://ftp.kernel.org/pub/linux/kernel/v2.4/linux-
tar -jxvf linux-2.4.17.tar.bz2
cd linux/Documentation
ls |more
and start reading all the documentation in there. It would probably make a good starting point.
Plus you should read Kernel Traffic and get on the Linux Kernel Mailling List.
Does the name Pavlov ring a bell?
One of the best sources of information is the O'Reilly book on Linux Device Drivers. It contains a lot of good information to get a kernel hacker up and running.
Three-thirty AM
I - tears! - grok. Now, reimage,
(7th time) -- ditch my drive.
oh, wait, did you mean the Linux kernel?
Index of Documentation for People Interested in Writing and/or Understanding the Linux Kernel >>c kers-docs.html
http://jungla.dit.upm.es/~jmseyas/linux/kernel/ha
The info was compiled by Juan-Mariano de Goyeneche after folks on the kernel list asked the same questions time & time again.
If you celebrate Xmas, befriend me (538
what are your credentials. Just feeling like doing it is not enough. What is your programming experience, education, work experience etc concerning system programming?
If you don't have that much of experience, I would start making a device driver for a relatively simple device. That way you'll learn what it's about and whether you're ready for it.
I would think that anyone really going into kernel programming would have interests/ideas developed on his own on which to work.
From Alan Cox's interview posted to slashdot a couple days ago:
"Ignore everyone who tells you kernel hacking is hard, special or different. It's a large program, and bug fixing or driver tweaking can be a best starting point. It is however not magic, nor written in a secret language that only deep initiates with beards can read.
Play with it, try things, break it horribly and enjoy yourself. I started on the networking code because it didn't work very well. Everything I knew about TCP/IP I had downloaded the same day I started hacking the net code. My first attempts were not pretty but it was *fun*."
25% Funny, 25% Insightful, 25% Informative, 25% Troll
To protect against modern DNA evidence collection, wrap youself completely in saran wrap except for breathing holes also.
If you get desperate, cut yourself with something sharp lying around the house and sue the owners. Works every time. Good luck on your new career!
--KingPrad
Two fish are in a tank. One says to the other, "I'll drive. You man the guns."
Stop the Slashdot Effect! Don't read the articles!
There isn't much tricky stuff in terms of programming. (Write good, efficient C code for example)
1: You need to have a clear goal of what you want to accomplish,
2: Understand the important concept of Operating Systems,
3: Know a bit of basic algorithms.
Then you are good to go.
Linux Magazine's Gearheads Only is a great column to read for this, especially the mouse driver and Alan Cox's articles.
Their web site should have archives.
Sumner
rage, rage against the dying of the light
1. Learn to code.
2. Learn to code in C.
3. Figure out what YOU want to add to the source.
4. Read the kernel source.
5. Understand what you read.
6. Make changes/additions to the source, per step #3.
7. Test out the changes/additions on your own system.
8. Make it work for you.
9. Send in your contribution.
10. Have it accepted/rejected.
Connect remotely to a debug build of the OS on a seperate machine than your host machine and step through the code. Set breakpoints at places that look interesting, and just skip over things that don't do much. Watch the registers and keep an eye out for error codes, these will tell you what's going on with the OS.
Oh wait, you need a kernel debugger...
Nevermind.
Take a knife and start hacking a cherry kernel. When you become good it at, you can try hacking a peach kernel with an axe, then a mango kernel with a chainsaw, and so on...
It also means that when you screw things up (if you don't, I'd be surprised; I bet even Alan Cox screws up now and again), you won't lose anything. And don't give me anything about ext3; if you screw up enough in the wrong place, your filesystem is hosed.
Have a look at the Kernel Janitors Project and perhaps KernelNewbies.org .
Buy the O'Reilly book on device drivers mentioned above, and pick a driver you use. Try to understand it, and then tweak it a bit. Since they can be loaded and unloaded, device drivers are a little easier/quicker to play with. And there is a good book on them. ;)
/. a bit ago - Have Fun!
Working on it during part of an 8 hour work day, in about 1 month I was able to hack tab support into the s390 vm console driver with nothing more than reading code, searching the net, and using that book. And that was probably a little on the slow side. (see here http://www.eagle7.org/ibmlinux.html
And like Alan Cox said in the interview posted to
_sig_ is away
Read this: http://www.xml.com/ldd/chapter/book/index.html
Lurk on this for a little while (be prepared for 200+ messages per day):
http://www.tux.org/lkml/
Watch for to do lists or bug reports to go flying by on the list and start there. Its probably best if you don't try to implement something from scratch your first time out. Start slow and learn the inner workings first.
If you want to get yelled at because you suck, try OpenBSD? At least you won't be a communist, then. ;)
just because it says "news for nerds" doesn't mean "news for l33t kernel hackers only." It also doesn't even say "news for hackers." Each of us lays his or her own claim to nerdishness... programming, fantasies about sci-fi characters, melting down Pentiums, or putting $4000 worth of computer equipment into a $200 car to make it "state-of-the-art."
:)
I think slashdot is particularly well suited to "shepherding naive kernel-hacker wannabees," simply for the fact that each of us brings unique viewpoints to each subject. (For instance, I've never even seen the kernel code for Linux, and yet I'm responding to this post.
This Linux Journal article gives a really quick introduction into writing kernel modules.
It doesn't go into all that much detail, but I found it a good starting point for messing around on my linux machine at home.
Hth =)
Okay, the question had been asked million times before and could probably be answered with a bit serious RTFM and googleing, but I wouldn't call it a newbie question.
Boycot? Blackout? Subscriptions?
I don't care!
Well I think you just dont go into the kernel to be wandering and looking for inspiration. Think about something specific you want to do and get in to it, you'll allways find you have to mess around with several modules or at least get to know 'Where the hell iz thiz thing going??' ;-).
There are some books at amazon which can helps, I like 'Linux Kernel Internals' by Michael Beck
"May the force be with you" Jorge Ivan Suarez Murillo Medellin, Colombia
Nothing taught me more about kernel modding than spending a few dollars less on the hardware I used on a linux box - and then try to get it to work.
You become very familiar with code that might be close, get to pour over specs that may or may not help, and find a small comunity of others who saved a buck or two.
The best part - when it breaks, you get to keep both peices. When if finally works, ahhhh....
+++ UGUCAUCGUAUUUCU
The assignment was to add a system call that would return the number of processes created and killed up to that point. The only difficult thing was to grok the system call table. Please look at this option as a good introduction to the kernel.
"Drug related crime" is a misnomer, "prohibition related crime" is the more accurate and correct phrase.
Its not like youre going to break anything, real, or permanent, this is all hocus pocus digital alchemy anyhow. If you kernel flies or not, it information, either on what you did right or did wrong. Have fun break some shit. Its no fun it works right all the time anyhow.
....uncomfortable to say the least.
....what are you going to hack, or just patch and compile, Look through the tree for stuff you know, see how they do it , see if you think you can do better and try it, start small....... Me, ive never personally done anything that need make it into the tree on a permanent basis. but hey its been 8 years of all kinds of fun.....
I also highly suggest the IRC channel
#kernelnewbies
I went there today for the first time looking for Rik van Riel I had some qustions about the rmap 11b patch and Guess what he was there and told me the 11c is coming today , REAL time info from people that really know their stuff.....
Kernel hacking can be fun if youre not in a rush IMHO, doing it against a dealine can be
Im assuming you know huw to extract the source tree and apply a patch , if not start there. Im also assuming you know C if you dont
One last point DO IT OFTEN !, Dont let yourself get rusty, Set a goal, a kernel hack a month, or at least a patch and compile a week if youre not cutting code....
Sig went tro...aahemmm.....fishing........
Back when I first wanted to start, I had no idea what to expect. I just dove in (not on the Linux kernel, but other Unix kernels).
Know what? It's just code. It's not that big of a mystery.
You're going to screw shit up. Have a crash machine to hack/test the kernel on before you hack your main system.
Job? I don't have time to get a job! Who will sit around and bitch about being broke and unemployed then?
First stop for a total newbie is download an early kernel (try 0.01!): _much_ less intimidating than the current monster. This should help start you in the right direction. KernelNewbies channel and site are both useful
.. is recommended. It's a medium-low level view of the entire kernel, following the source code but making it more readable. If you've taken an Operating Systems or Unix class you should be fine.
Linux Journal reviewed it.
- j
Try to do something simple, like finally adding module parameters to the framebuffer (sorry, personal irritation, but still haven't had the time to do it myself). Then keep enhancing and bug fixing small things, and move on from there to bigger changes... Post your patches on the LKML, and listen to their comments (and 'flame' them if you disagree)...
:))
That's how I rolled into the business..
(And if you get me those module parameters, I'll big you the best hug you've ever had
xer.xes -- 4181
did the mads put you up to this?
What are your credentials? Or you just some doofus calling somebody else a doofus? From his post he's above the average slashdot reader, he's actually interested in hacking code. This doesn't mean he'll be successful hacking the kernel, but even the attempt puts him above "the average". I'll worry about slashdot and the "respect" it gives the average slasdhot reader when they start posting Ask Slashdots about crochet.
Chris Kuivenhoven is a thief, beware
I'm a little offended by the notion that "nerds" represent only those who program in Linux. I'm a Mac user (now an OS X user), and I can write PHP code to interact with MySQL...and I'm proud of myself! Set against the entire gamut of the North American population, I'm on the extreme end of nerdiness. But sure, if for some sick reason I was interested in Kernel programming, I would be a "newbie", and I would expect /. to be a powerful resource for getting started. I support this topic and the goals of the poster.
You can have my one-button mouse when you pry it from my cold, dead fingers.
Dear Mr. _robot:
Hacking is illegal, and unethical. Only terrorists hack computers. If you are caught hacking computers, be it Lunix Red Hat or Microsoft Windows XP Professional 2001 NT, you will go to jail.
Remember, hackers are no better than those who seek to harm America through terrorist activities.
Signed,
Attny. General John Ashcroft
Umm, the "average /. reader" uses Windows. Of the Linux users, I'd guess 1-2% make any contribution to the free software codebase. There probably aren't more than 10 or 20 "kernel hackers" among the posters.
C'mon -- at this writing there are 33 comments at or above zero, not one of which is offering any personal experience with kernel hacking. At least it's not yet another qquestion that would do better as an Ask Google.
What I'm listening to now on Pandora...
Kernel Projects for Linux by Gary Nutt. It walks you through several areas of the Linux kernel. It's a great book. You'll especially learn a lot from discovering all the editing errors in it. :-)
And the men who hold high places must be the ones who start
To mold a new reality... closer to the heart
...or another experimental OS. VSTa in particular needs drivers (and lots of other stuff) so you can easily find something to do, and has many novel design features (being a proper microkernel design -- with almost all work, including traditionally "driver"-style code, done in userspace -- yet faster than Linux) that make it fun to learn about.
If you're decided to go with Linux, though, just pick something and do it. My first kernel driver was a network driver for a NIC (don't remember the model, it was quite a while ago; Don Becker ended up writing a better driver that was accepted into the official kernel, but it was an interesting experience anyhow). If you have access to any interesting hardware that isn't supported (which may be hard to find on x86), writing drivers or porting to new hardware (not whole new architectures, mind you -- that's a bit much) is a good starting place.
Find some small part of the kernel (like a serial port driver or something) and start fooling with it. Disect it and see how it works, maybe fix a bug or two.
If you're a Windows kernel guy wanting to break into the Linux kernel, thats even easier. Get a job doing a Windows driver for some device, then write a Linux driver for it in your spare time. That's what I did.
Please read the (free?) manual for information (if you don't mind).
Yes, I know I can say "fucking" on slashdot, but I prefer not to.
-pyrrho
1. Invest in a coffee urn. Not a pot, but one of those big chrome things that looks like a baptismal fount. Get a really big cup to go along with it.
2. Sell your Rolex. You're not going to need it anymore. Time doesn't mean a thing to a diehard kernel coder.
3. Learn to call home before you leave work, so your wife can hustle the boyfriend out the door before your arrival at two-thirty in the morning.
...to ask that question. This is slashdot - not a technical forum. You are not likely to run into any technical people here.
take a look at the linux from scratch side.
http://www.linuxfromscratch.org
i think it helps understand how the whole system works together.
good luck!
Probably the best place to start is to find some definite itch you want to scratch, and so badly that you won't stop until it's done. For me, that was getting use[ful|less] features into the kernel. As many as I could cram in, without the hard disk exploding. And then fixing all the incompatibilities, as best I could. (Phew!! There are generally a lot!! That's why many of the FOLK patches I produce are unstable.)
What you do next depends on the "itch":
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
The best way to get your hands dirty with any programming project is to get the code, study it for a while, and try to change and improve things. The kernel contains a little bit (or a lot) of everything. Try to fix bugs, improve performance or lower memory usage, if you're skilled at that kind of stuff.
The most important thing to remember is: Don't be intimidated by the kernel. Think of it as a really big program, because that's what it is. The only difference is that it doesn't get loaded by the operating system... it is the operating system!
Ive done some OpenBSD kernel programming. "The Design and Implementation of the 4.4 BSD Unix Operating System" gave me an understanding of the operation of the BSD kernel (specifically addressing in the kernel, interrupts, virtual memory (although the book details a VM system not in use by obsd)). Aside from this book the only thing that will show you how the kernel works and how to write kernel code is the source code itself.
XINU = XINU is not unix.
it is a very simple OS with multithreading and a bunch of other stuff.
the full source is available and only like 8000 lines or something. it steps you through it in the book, and it is EXTREMELY easy to read.
this was what was used to teach my OS classes in college. you can actually get in and hack the thing away and know what you are changing right from the start.
MARIJUANA, SHROOMS, X: ONLINE?! - E
Rather than just hacking in general, you should identify a particular area where kernal development has lagged. That way, you can make incremental improvements in long-neglected code rather than trying to one-up the preeminent kernel hackers.
For instance, I've noticed that there is a sad lack of resources devoted to incorporating practical jokes into the kernel. Everything is so "write to disk, read from disk, move bytes around, manage processes" boring.
I've got some ideas you might want to consider for your first project. Implement these babies, and I'm sure you'll garner a great deal of attention.
- Fake "blue screen" crashes: When "root" is logged on locally, intermittently go to a blue screen with memory dump info for a few seconds, then switch back to console mode as if nothing happened.
- "Ha! Just Kidding!" memory manager: when an app requests a memory allocation, periodically claim that it has failed for no reason at all. That'll keep 'em laughing forever!
- Unionized thread scheduling: implement the concepts of lunch breas, smoke breaks, and overtime into thread scheduling. Union threads should refuse to work with non-union threads. Periodic strikes for better working conditions, and so on.
Do a good job with this stuff, and I'd be shocked if it wasn't included in the main tree!
Cheers
-b
If I wanted a sig I would have filled in that stupid box.
Give the FreeBSD or OpenBSD kernel a try. I jumped right in with these. They have tons of documentation, are friendly and relatively forgiving (if you can call a kernel 'forgiving'). My first attempts involved a simple "undelete" feature. This is a nice starting point as it requires not only knowledge of the kernel, but of the file system as well. A great learning tool. But BEWARE: you first attempts shouldn't be on a machine with your PhD thesis or 36 GB mp3 collection. Set up a new, raw machine and start hacking away. Have fun!
Here's a good place to start, the web page and the irc channel on irc.openprojects.org #kernelnewbies.
Happy Hacking!
A good starter project is a device driver for something simple. Even easier is if you find a device Net/Free/OpenBSD supports and Linux doesn't, port the driver, that way there is somewhat less code to write.
That could be harder for you then me since Linux has so many drivers now (I started with 386BSD 0.0, so there were maybe 15 supported devices...my friend and I ported the MACH SoundBlaster driver). If all else fails, write a driver for something that already has a driver.
After that you can wonder off into the kernel proper and do some "real" stuff. I did IP traffic shaping, but someone seems to have done that to Linux already...
The publisher has a sample chapter online (though their HTML looks weird to me; I hope it looks better in your browser). Also, you can read a little more about the book, find links to online reviews, get errata listings, and so on, at its support site.
Oh, and I, er, happen to know the author. :-)
``Life results from the non-random survival of randomly varying replicators.'' -- Richard Dawkins
This might not be the sort of answer you're looking for because it's expensive and will take a few months (at least) but if you haven't already, look at taking a formal course in operating systems. At my university it's a 300 level course and has some heavy pre-reqs but I've seen it offered at other universities with only the requirement of prior programming experience.
The course I took in opiples that make an operating system "go" -- scheduling, physical and virtual memory management, we touched on sockets and pipes (it was a *nix-centric course but we discussed other operating systems including Windows, as well).
If you dont want to spend the time or money on a formal course, I'd at least reccomend the dinosaur book. While lacking in code examples (it doesn't try to show you how to write a *nix-like OS in C, it tries to explain concepts that can be applied to any platform, any language, etc.), it is extremely thorough and makes hard concepts easier to learn.
While I haven't actually read it (yet), I hear Tanenbaum's Modern Operating Systems is also excellent.
We were given a problem to solve: build a kernel patch to any version of the linux kernel that allowed a third party who is writing is driver to have the driver interact with a software emulator instead of real hardware. The end goal was to enable people to write drivers based only on the hardware specs and an emulator. The emulator would instruct the kernel to route certain hardware calls to it. After the driver was written the real hardware could be dropped in place and the driver would not have to be re-written, it could be used out of the box. Essentially it was hardware abstraction without knowing what hardware to abstract before hand.
Personally, if you are just looking at getting into it just find yourself a problem and solve it. It doesn't matter what problem it is, any problem, useful to the world or not. Remember that the end result of this step is to learn, not solve 2.4 VM problems, or to build a better SMP design. (That's the next step!)
If you like to see how things work, the best way is usually to write some code that tries it out. With a little extra work, you can create a small test case. Then submit the test program to the Linux Test Project.
Linux desperately needs more serious testers.
LTP - http://ltp.sf.net/
...A lot of kernel hackers are very elitest...
:)
Shouldn't that be "most elite", or simply "best"?
And no, I couldn't hack a kernel if it "grokked" me in the ass, so I'm not one of them either way...
(Ok, sorry, I was bored).
I had an algorithms class in college and we rewrote parts of the kernel using various algorithms and benchmarked the results. Of course, we usually made things slower, but I learned a lot.
I was just about to get into some kernal hacking, and I've only ever glanced at some source. Probably a bit daunting, but I'm looking for fun!
My first project? Finish my compression and use that for a virtual compressed drive module. Of course, I'll do others before hand as practice, tweaking little things.
Question
http://www.ironfroggy.com/
Learn x86 assembly language and you will rule.
well, I guess no one can accuse you of being off topic, nice work...
because of two reasons:
- module guide or howto. You have to be armed with good C knowledge, and some idea of how a computer _really_ works (understand interrupts? memory addresses?). If you want to write for a current kernel (say, 2.4.17), you _will_ have to look at the source code, and actually try to understand what is happening (told you you'd need to know C). You will also need to know, or at least have some idea of how the peripheral you're writing code for (say, if you're writing a driver module) works.
a)The elitist attitude of some, who will tell you to go RTFM. And unless you are willing to write code for a really old kernel, you won't find much documentation. And even so, the little free documentation you will find, is not that helpful for newbie kernel hackers (and I don't mean to piss on the efforts of those who have written docs, but they're complex to digest for real newbies).
b)The recipe-minded newbie. Let's face it, you won't find a connect-a-b-and-c-shake-bake-and-wham!-You-have-a
My experience: I was an absolute newbie to kernel programming, so I started reading the code for the tty driver on kernel 2.4.0, which seems to me is one of the simpler parts. After a lot of reading, I wrote my own module (it was just for fun, so don't think it was anything useful...) as a simple device you could write data to, then read it back. Try it on a machine you don't mind screwing up, though, because you will have tons of oopses and kernel panics.
No, seriously, I just come here for the articles.
I can only imagine what happens when people decide first to start hacking and only second what they're going to hack on.
Dissatisfaction -- not optimism -- is the basis of hacking.
Then fix the driver to get the app to work properly/faster/more reliably/to spec. You'll soon find yourself in kernel space, and start to wonder what all the fuss was about. Often there's several levels of drivers to contend with, e.g. PCMCIA, CardBus, 1394 -- to get, say, a progressive scan camera to talk to a laptop.
programming = nerd, in most people's minds, hell, i consider myself a nerd, proud of it, in fact.
and the way i see it, kernel hacking would be the pinnacle of programming expertise, so, yeah, dont tell me this kind of stuff doesnt belong on /.
Beer, now there's a temporary solution -- Homer Jay S.
There's a few good kernel API books here which might be a good read for anyone wanting to learn, including one specifically for anyone wanting to get into kernel hacking.
If you don't have a spare PC laying around, VMWare is a pretty spectacular way to get your hands dirty without having to worry about completely hosing your development machine on accident. The only thing you really can't do with VMWare is hardware level drivers, for obvious reasons.
/proc interface ... and it was pretty easy to get into. I started with a basic understanding of how things work (inodes, etc.), and it came pretty easily. If you're going to be working on file systems, make periodic copies (backups) of your virtual drive image (if you're using VMWare/Bochs) ... it's a life saver for the first few weeks. :)
...
If you really want to get gritty on the emulation level, I highly recommend Bochs. It's a fully functional x86 emulator, and since it's open source, it comes with some nifty options, and the source code is on hand if you really need to get tricky.
I think the key to working efficiently with an x86 emulator/virtualizer is having a significant amount of RAM, and a RAM disk to mount your virtual drives on. Since RAM is so cheap these days, there's no excuse not to have at least a gig of it in a development box. It makes rebooting the virtual machine (which happens a lot) a bearable process.
If you need to work with hardware, you can build yourself a test platform for around $300 now, including a cheap monitor - unless you need exotic hardware.
My experience kernel hacking is in on the VFS level, inserting and modifying a few core routines to report through a
The kernel is complex, but so is any major piece of software. Thankfully, lots of bits in the kernel are well engineered and compartmentalized, so chances are you won't have to worry about screwing up the TCP stack if you're in the midst of inode.c
have fun!
Get down and dirty with a kernel project. I chose Reiserfs on alpha.
This taught me a lot about lkml politics, which is probably the first skill (and some larrikins would say, the only skill you need) you must master to be a successful long term kernel hacker. First lkml hint: don't slag off anyone. Don't piss off a few people in the know until you get to know them, and then...
Then, don't talk - do. Respect is directly based upon your skills with patches, and their acceptance rate.
Patch submission. Follow the standard guidelines (found elsewhere), but know now that Linus sucks at code control. The mainline kernel development process is slow, prone to serious lossage, allows regression, and is irreparably harmed by Linus' refusal to adopt modern code control practices. So when you submit a patch, don't worry if it's not accepted. Every time the kernel is revved, re-do your patch and re-submit. It'll eventually be accepted, particularly if it helps the kernel boot. For example, it took nearly a month of my submitting a two line patch to allow the alpha to boot before it was accepted into mainline 2.4.0pre development. That's why I ditched Linux for a while - dickheads in charge. All the *BSDs have better kernel development practices, and their bleeding edge kernels are far more stable than any stable Linux kernel. However, for various reasons, I get attracted back to Linux on a regular basis, like a fly to a pus-filled boil.
Anyway, the things that need desperate attention are:
the kernel janitor project (clean out the cruft!)
the linux kernel testing project
These are far more important than any single feature you might want to add, and in particular the kernel janitor project will help you get familiarized with the kernel the quickest.
http://sourceforge.net/projects/ltp/
http://sourceforge.net/projects/kernel-janitor/
Andrew van der Stock
Let me say that, at least for me, this was not like debugging any of the userspace programs that I had done before. If you're like me, when your program crashes, you first up gdb, load the core, and backtrace/step from there. First of all, there's no core dump. In this case I didn't even have the luxury of an oops readout; as I would find out later this particular bug was locking the computer even before the kernel could flush its output buffers and print to the screen.
So I had to start meticulously reconstructing the function call stack using printk(). It took me awhile before I figured out why none of these were getting printed (for the reason I just mentioned.) So that didn't work either.
I searched high and low but never did find a way to debug the kernel that was as easy as using gdb to debug a userspace program, and that's not saying much. No stepping, no backtraces, nada. The "bug" in my particular driver consisted of a single offending line which wrote an 8-bit register and was not to spec. I would have never ferreted it out if I hadn't "stumbled" across the NDA'd specs myself.
Anyways, moral of the story: kernel debugging sucks for really hard bugs. If anyone knows of better tools to use kindly inform me of them.
I think there is a world market for maybe five personal web logs.
...and try to understand the driver, or write your own.
It is essential to have a good spec. For comodity microcontrollers, the manufacturer will usually make the spec available. Read the spec. Understand the spec. Then think about your driver, or read through the existing driver and figure out how what the code does twiddles the control lines just right.
There's a kind of art to understanding these hardware specs, and it takes a bit of practice. Try starting with something like a serial bus controller, or something else that's well understood.
And get yourself a copy of the Linux Device Drivers book, it's worth the cost. Or read it online from oreilley.com. For many devices, you can find information about that device in linux/Documentation about how the driver works and/or how to write clients for the driver.
As you come to understand the driver, comment the bits that drove you nuts. Submit the commented driver to the driver's maintainer. If you watch on the lkml, you'll ocassionally see somebody submit a comments-only patch. YOU COULD BE THAT SOMEBODY!
Andrew
Working in the Linux kernel is like riding a bicycle. You can read about it till the cows come home, but you just have to dig in and do it. You'll fall off , pick yourself up, dust yourself off and climb that saddle again. Do it a few times, and you're on! Practice configuring and building kernels first without making changes till you get the hang of it. I had to dig in when the driver for my network card, which used to work in 2.2 stopped working in 2.4, and I had to go fix it -- it would have been faster to buy another network card I suppose, but I was born stubborn. (I still have to patch every kernel with that fix, because no one seems interested in applying the fix permanently to the source code tree...)
You can find a half baked kernelhacking-HOWTO at http://www.kernelhacking.org
Start reading the MBR, then follow the chain of execution until you are deep into the kernel...
That's how I started on the FreeBSD kernel and the Linux kernel.
Sure at the first there's some dependencies - and you are sent on a journey through about 20 H files just to find one #define ition, and to know A you need to know B, which requires C, but it worked for me.
--jq
A book I found good is the Linux Core Kernal Commentary. It's by Scott Maxwell and published by CoriolisOpen Press. It comes with in-depth code annotation and a CD full of useful tools.
If you're interested the ISBN is 1-57610-469-9
-AlPhAbEt
It's called XP
--
The Cap is nigh. Time to get a fresh new account.
You'll have linux up and running on the thing in no time, and you'll be able to play around with writing device drivers and fixing kernel scheduler bugs and stuff. All on the SH4 processor, which is much simpler than the x86 you're probably using.
Cryptnotic
My other first post is car post.
Ok, now you can go back to read all these good advices that other
When I had time, I went and fixed the old keyboard, and rearranged the keys as a Devorak keyboard while I was at it. Unfortunately, the USB-PS/2 dongle that came with my IBM keyboard doesn't work with my Dell PS2 keyboard. However, I currently have the IBM keyboard hooked up to my USB port and my old Dell keyboard (with rearranged keys) as my PS/2 keyboard.
Luckily, keybdev.c (both the one in drivers/input and the one in drivers/usb) is astonishingly short. There's all of about 5 functions in there and most of the complexity is hidden in other modules.
The USB keyboard driver interfaces the PS/2 subsystem IIRC (don't know where I read this, maybe the hid.c documentation on linux-usb) so you can't have seperate keyboard mappings, unless you munge the keycodes inside the USBdriver. As long as you don't lock up your USB keyboard driver or have a buffer overun, you should always be able to restart.
I have LILO (GRUB, actually) setup to boot me into either a 2.2.20 kernel or a 2.4.17 kernel. That way, I can ensure that my hacked module won't be loaded by hotplug if I screw it up.
The Steps I took /usr/src/linux (after untarring the 2.4.17 source) and changed the line near the to from "EXTRAVERSION = " to "EXTRAVERSION = -maxmodular"
this changes the name of the kernel from vmlinuz-2.4.17 to vmlinuz-2.4.17-maxmodular and
makesa seperate directory in /lib/modules for your hacked modules. (I called it maxmodular because I even made the "misc binary support", "a.out binary support" and "floppy drive support" as modules.) Potential Gottcha: IDE support is no enabled by default, and comes after the IDE-parport questions in the config menu, so I must have recompiled 10 times trying to figure out why it couldn't mount the root partition.
Downloads I downloaded the 2.4.17 source code and used apt-get to install kernel-package (makes Debian kernel packages, so your nightly apt-get upgrades won't destroy your work).
Renaming I went into
Snooping arroundI poked around the drivers/usb/ kernel source and documentation some to try and figure out what needed to be hacked. I incorreclty identified drivers/usb/keybdev.c and after none of my printk's worked, I tried drivers/input/keybdev.c (this does not affect the PS/2 keyboard).
Printk() is your friend. Add printk()s (printk() works just like printf(). Make sure to do your kernel module insertion from a non-X virtual terminal to minimize the time it takes prints to get to you in the case of an impending crash.) to the beginning of every function in the driver, letting you know that it's being called (and optionally the arguments). Then recompile and load your module. This gives you a feel for how the driver works and confirms that you have the right driver.
Trim prink()s to only print out the information you need. In my case, I got rid of the printks from everything but the keyboard event handling function and the emulate_raw function kalled by the event handler. I printed out every keycode that was pressed (but not it's release) so that I could write down the keycode for each key I needed to remap. (And some of the neat colorful buttons IBM added above the funtion keys. I later used these to turn on and off the devorak remapping and turn on and off the printks in my module.
After that, what you do is pretty specific to your module. For keyboards, they send a 16-number, called a scancode that is one of the arguments to the keyboard event hadler function. All of the normal keys have scancodes less than 256, so I just made an unsigned char[256] usb_key_remap_table and did something like
if (code < 256 && code >= 0) {code = usb_key_remap_table[code];}
The more astute amoung you will remeber that I'm only remapping the USB keyboard, which is my good keyboard and therefore unmodified. Oh well, I figure having the incorrect letters written on the keys discourages me from looking down.
Anyway, the USB subsystem seems very readable for the higher level drvers and USB keeps getting more and more devices, so I'd recomed starting with a USB subsystem... too bad RadioShack is out of USB cue:cats :-D
Copyright Violation:"theft, piracy"::Anti-Trust Violation:"thermonuclear price terrorism"<-Overly dramatic language.
I actually wrote something up that was recently posted online at the linux journal site: http://www.linuxjournal.com/article.php?sid=4715 Since I wrote it over a year ago, some of the links are a bit out of date, but the general principles are still good.
So, since I'm closing in on 30, you be the 12-year old then? ;)
:)
"Elitest" is not a word at all. But it could be a bad grammar form of "most elite" (as if that would be good grammar heh).
What the poster meants was "Elitist" which would mean that they are "on high horses", so to speak, and only speaks to other "elite" people. It was a bad joke man. Like I said, I was bored.
If I would really try to nitpick someone about grammar, I would choose my mother-tongue, which is not English. I suggest you do too. Thanks.
And no, no comment about my favourite trolls. Have a nice flaming.
I do not think it is right that whenever someone says kernel, that it automatically means the Linux kernel. Linux users are very unix ignorent and they do not know that there are many other free operating system with kenerl source code avialable. When I first saw this i thougt what kenerl they might be talking about then I rembered that when you see the world "kernel" you automatically associate it with the Linux kernel. People, please start calling it (whatever os) Kernel. Don't take this the wrong way, I have used Linux in the past but have now since moved on to the *BSDs.
An article by Michael J. DeMaria over at networkcomputing.com.
For those who don't remember their history, MINIX was a complete UNIX kernel (and environment) developed by Andrew S. Tanenbaum SPECIFICALLY to teach UNIX kernel internals. It was documented in his book Operating Systems: Design and Implementation, which includes the ENTIRE source code listing for the kernel.
MINUX was never designed as a real-world system, although it did inspire at least one person, namely Linus Torvalds, to write one...
-p.
I started programming in the linux kernel many years ago. I think the thing that helped me the most is that at first I just stuck to one thing. I didn't try to get it all at once. Kernels are very large, and there are a few tricks to kernel programming that aren't as intuitive as applications programming. After playing around in the TCP/IP stack I just branched out a bit. After a while whenever I encountered some new routines or structure, I tried to read every bit of code involved with it.
Some years later I decided to switch to *BSD. I have found their source to be much cleaner and their debugging tools are far more useful for me. After I felt comfortable enough with BSD I started contributing code back. At first small things, and then gradually larger projects. Now I do custom FreeBSD kernel code for a living. I do everything from new file systems to device drivers and custom TCP/IP code. I enjoy it much more than user space programming.. I always joke that I did it all to get away from getopt(3) though.
There are a variety of books you can read on the topic. Don't restrict yourself to linux books, please. Learn that there is more than one way to solve a problem. I'll list some of my favorite kernel books here:
"The Design and Implementation of the 4.4BSD Operating System"
"UNIX Internals: New Frontiers"
"Solaris Internals"
"UNIX Systems for Modern Architectures: Symmetric Multiprocessing and Caching for Kernel Programmers"
After you get a rough idea of how the kernel works, the only way to really learn it is to read code and research papers.
Good luck.
Were you thinking of doing some work on Darwin? That would be a much better choice than Linux, of course. Darwin is based on a free-as-in-speech license, unlike Linux. Linux is licensed under the GPL, which places all kinds of restrictions on your freedom to use the code; for instance, you can only link it to other GPL'd code. Also, Darwin is a microkernel design, so unlike Linux, it actually has a future on the desktop -- you can actually install a new device driver without recompiling the kernel.
Find free books.
The odds are better that a Linux kernel hacker would show up (and be found) here, versus a 'Windows'... eh,... ring zero hacker? Ya know, the kind that Doonesbury once labeled as having a 'minty green' complexion? ;)
I'd have a personalized plate on my car, but "toxic bachelor" won't fit into 7 letters.
So assuming you know what you need to know to start hacking away at the kernel, there is no sense re-inventing the wheel. What are the important features that the kernel is still lacking?
It is kind of hard to start coding without a goal.
... was mostly very small, very simple stuff. There's the old "disable the kernel's ability to use the kernel speaker" by making the first statement in linux/drivers/char/vt.c function _kd_mksound a simple return().
/proc/pcspeaker entry to which I could echo 1 in order to enable the speaker and 0 to disable it.
The next thing I did was to make a
Allright, so it's very banal and easy, but the key is that it was my first delving into the kernel and it was all possible to figure out by simply watching the existing code in there and duplicating what existed elsewhere.
I think that's the best approach if you just want to start getting your hands dirty; dive in there and look at the small bits you can easily affect while still knowing what you're doing. Then, as you grow bolder, you'll probably want to reach for those FAQs and manuals - but at least you'll have outgrown the initial fear of even touching the kernel source, and from that only good can come.
Seriously. Talk to anyone who's worked on a operating system in a serious way. From an architectural standpoint, linux is pretty primitive and pretty much wed to that architecture.
If you want to work in the kernel (and I assume that you're talking about linux's kernel), you have to remember that debugging's a hell of a lot harder. You'll do well to spend twice as long as normal making sure that it's right b/c you can easily spend 10 times as long figuring out what you screwed up.
If you want to seriously get involved with the linux kernel, my suggestion would be to try to bring some of the better architectural features from an industrial strength OS (e.g. Solaris) to linux. Personally, I'm interested in observability, and debugging. Adding something like Solaris's agent LWP would be a pretty isolated project and highly worthwhile.
If there's one thing I agree with Rik Van Riel about, it's that further kernel hacking won't help Linux be adobted further.
The real problems for Linux exist in the middle layers, all the things between the kernel and KDE/GNOME. In here there is vast amounts of work that needs to be done, and way too few people doing it.
I have difficulty understanding why it is that people focus so much on kernel development, when at this point in development gcc and glibc hacking is incredibly more important. This is the bottom of the system, controlling the performance of everything. And this layer is not good enough yet.
Now, if you really want to hack on the kernel, by all means do so. Don't let anyone tell you that it's not necessary or won't do any good. Because that's not what I'm saying here. But I am saying that you would do Linux a whole lot of good by choosing a different area than the kernel.
I know; it's difficult to choose another project when sites like Slashdot only gives any attention to Kernel hackers and KDE/GNOME releases. It's difficult to live in a meritocracy when people are not giving equal merits to the different parts of the system.
Last: Whatever you choose, stick with it. The one thing Linux really needs is a bunch of people who knows a *lot* about their topic. People like me who knows something of everything are not equally valuable.
Happy hacking,
Bo Thorsen,
SuSE Labs.
I know I might get a lot of flames for this, but to really understand how a big source code is fitted together (headers, dependencies etc) - trying out things on minix could prove very useful. Reasons:
1. It's small
2. You can test your changes (thus gain confidence in building a bigger system)
3. Your OS fundamentals get stronger
If you are new to unix, you may want to look at the lions' commentary on unix.
The book by Alessandro Rubini (Linux Device Drivers) is also very good.
It goes without saying that you need to dig into the code and get familiar with it... there is _NO_ alternative.
If someone has linux kernel documentation (like lions' commentary), _KINDLY_ mail!
v==hal if
As someone who has taken on the job of adding to a small, not often used, but personally very interesting driver, here's the advice I have:
1) Get used to rebooting a lot. You're better off if you can do this on a system that's not your main workstation, so you can, you know, still get work done.
2) Appreciate and treat very well anyone, I mean anyone, who gives you any useful advice at all. Because every little bit counts.
-Peter
== Just my opinion(s)
Didn't Al Gore also "invent" computers as well?
I mean, is there not an Al-Gore-ythm in YOUR code?
Damn irony!
Politicians now take credit for the products of others.....How old was Al G. when "the" I-net was created? Damn, he WAS good, wasn't he?
206.39.38.2, DDN-BLK-36, DOD NET INFO CENTER. 800.365.3642 206.36.0.0-206.39.255.255 NET RANGE.
Uhh I cant believe no one has said Minix.
Minix is a Unix style operating system for educational purposes.
minix.org will get you started
Which kernel are you talking about? You just think we assume you mean Linux? Somehow anything with the word 'kernel' in it, means Linux ????
The "Gearheads Only" section of Linux Magazine have a few interesting article :
http://www.linux-mag.com/depts/gear.html
:wq
AND I listen to guys in Rome with pointy hats, religiously you might say. ;-)
your suggestions are humourous and perhaps at some places _do_ reflect the evolved hacker state. But I figure that you are _preaching_ about a certain dress/lifestyle code which in my opinion is not a necessary condition to know your kernel and not sufficient either (I have a beard, but don't know the kmod details). You don't decide to get rid of all your razors or your bf/gf, sometimes they get rid of you.
You don't have to look weird, to be wired.
Linus is an example, not an exception.
v==hal if