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How to add a system call to the Linux Kernel?

rated 0 times [ 5] [ 0] / answers: 1 / hits: 5333 / 1 Year ago, fri, april 28, 2023, 5:56:26

I'm currently reading Operating System Concepts 7th edition by Silberschartz, Galvin and Gagne. At the end of chapter 2, there is an exercise "Add a system call to the Linux Kernel". Unfortunately, I realized the directory structure that the authors used is completely different with Ubuntu's one. For example, the authors referred to "/usr/src/linux-2.x/include/asm-i386/unistd.h", but on my machine, they are:

/usr/src/linux-headers-2.6.38-10

/usr/src/linux-headers-2.6.38-10-generic

And inside this folder, I couldn't find anything called "asm-i386" :(. I wonder is there a documentation specified for Ubuntu? Any suggestion would be greatly appreciated.

Thank you,

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answered 1 Year ago alkeake · Accepted Answer

Ubuntu doesn't do anything special. Your first difficulty is that you don't have the kernel source installed, only kernel headers. The authors are describing a system with a copy of the kernel source in /usr/src/linux-2.x. If you're only compiling external modules, the headers, which are what you see on your system, are enough. Ubuntu ships kernel headers for that purpose in the linux-headers-* packages (which you would normally install via the dependency from the linux-headers-generic metapackage). If you need the whole source, get a compressed archive from the linux-source-2.6 binary package.

Another thing is that the directory structure has changed a little over time; architecture-dependent headers moved from include/asm-$ARCH to arch/$ARCH/include/asm. Furthermore the i386 and x86_64 architectures were merged into a unified x86 in 2.6.24. (More details here.) So you now need to look in arch/x86/include rather than include/asm-i386.

Here are a few useful resources for Linux kernel hackers:

Linux Device Drivers (LDD3)

LWN (news about Linux, including many technical articles about the kernel by one of the authors of LDD)

LXR to browse and search the kernel source

LKML (the Linux kernel mailing list), Stack Overflow to ask questions about the kernel and kernel development

And also read this thread on Unix & Linux, which explains how to locate the implementation of an existing syscall.