@mmu_man Does the book say anything about how to hack a Linux kernel?

@NerdResa nope, it's more general on the usual Unix architecture.

@mmu_man

@NerdResa

In hal.inria.fr you will find some case about tcp with linux kernel (english text inside)

@XavCC Thanks, I'll check it out. I even speak French, but tech documentation in French would be a new thing for me.

@mmu_man Ok, that won't help with Linux kernel hacking. Thanks for trying though.

@NerdResa well, you didn't specify which kernel :p
Besides, still useful to read a bit about the theory as well.

@mmu_man @NerdResa Yup. The general idea from the book will probably be still there, but you will find a lot of optimisations (offloads, message-something to avoid lots of irqs under high load, async workers etc). You should also be aware that this is one of „tightly” maintained subsystems and maintainers have a very clear vision of it, if you know what I mean.

@Neil I've done low-level user space on Linux, e.g. stuff with netlink. Don't know yet how far the "jump" to the kernel is.
Thanks for the resources, I'll check them out.

@NerdResa you need to know there's no hope

@NerdResa The Linux Device Drivers book is available online under Creative Commons and works for many people as a way to get started:

https://lwn.net/Kernel/LDD3/

There are repositories on GitHub with the examples updated to newer kernel versions, e.g.

https://github.com/martinezjavier/ldd3

My advice would be to find some area that interests you or an itch to scratch and read a lot of code. I started with the crypto subsystem (Ripemd algo) and the code got merge surprisingly quickly :p

@Kensan Thanks, I'll take a look at it!
My area is Networking, specifically TCP. (Don't worry, I'm not trying to get this upstream)

@NerdResa @Kensan Unfortunately the Linux Device Drivers book covers very little of the networking stack, because it's focused on things developers need to know to write… well, device drivers. 😅 But the first eight chapters may have good context for Linux kernel hacking in general, and the network drivers chapter should at least cover some of the abstractions that are shared with the higher layers.

@NerdResa The bible there is „Understanding Linux Network Internals“ but it had aged quite a bit and is not free.

Now if you are not set in Linux and are open to consider FreeBSD or even the MirageOS TCP/IP stack then I am sure @hannesm can give you some pointers ;)

@NerdResa @Kensan for me the stevens is still a very good book on tcp/ip and how to implement it

@NerdResa @Kensan from the theory side, i suggest https://www.cl.cam.ac.uk/~pes20/Netsem/paper3.pdf and the full label transition system https://www.cl.cam.ac.uk/~pes20/Netsem/alldoc.pdf -- but this doesn't contain anything about kernel programming, just tcp/ip.. ;)

@NerdResa You probably don't need anything more to start hacking. You will see, however, a lot of kernel specific programming patterns and utilities: lists, rcu, offsetof, macros (tons of them) etc. Always look at two implementations of object of the same class like TCP and SCTP to find patterns in the interfacing code.

@steelman That sounds helpful, thanks! :)

@NerdResa if you have an idea of what you want to hack on just jump in and try to make it work. Enjoy the discovery, you can worry about doing-things-the-right-way-TM later...

Ofc things may go horribly wrong, but it's easier to find help with a practical problem later on :)

@NerdResa hm maybe https://mobile.twitter.com/alicegoldfuss can give some advice. Afaik she's starting in the topic as well.

@NerdResa The best introductory/tutorial material I'm aware of for getting started on Linux kernel hacking is the first-patch documentation for Outreachy internship applicants: https://kernelnewbies.org/OutreachyfirstpatchSetup

Most of the Linux kernel is plain C, with some caveats: 1) Linux kernel developers often use obscure corners of the language standard as well as GCC/clang-specific extensions; 2) the standard library is not available, so e.g. there's kmalloc not malloc, etc.

@NerdResa Also you may find https://www.kernel.org/doc/ helpful as reference material. Alternatively you can find a fair amount of the same material in your kernel source tree checkout under the Documentation/ directory. I often use `git grep` on either the Documentation/ or include/ directory when I see a function I don't understand.

@jamey Oooh, I was looking for something like this! Thank you *-*

@NerdResa There's some amount of material you'll need to learn but depending on what you want to do it might not be all that much. A lot of kernel stuff has analogies in userspace, just with different names.

It helps to do some reading about fundamental kernel concepts before diving into code. I have some slightly outdated linux 2.6-ish kernel development books collecting dust on my shelf which I could drop off somewhere at TU for you if you want.

@stsp Yea, I think the thing I'm planning to do isn't actually that much, but I'm not sure yet. Usually I'd read a book but I don't think I've got enough time, I'll just start hacking. :)
Thanks for the offer though, I might get back to it.

@NerdResa Sure, any time. Happy hacking 🙃

@NerdResa If you want to gather experiences in bare-metal programming (i.e. OS development), grab yourself either QEMU or Raspberry Pi or a board, which is in fact documented well, and write stuff. The really interesting part for me is putting everything together, that already works in Linux :D

@snaums TCP the transport protocol, yes. I'm not aware of any other TCP there is in the kernel ;>