💻 Style9 Indent Rules on Linux/OpenBSD 🐧 🐡 👩‍💻

Get that lovely Plan9 source feel in your C code on Linux or OpenBSD

Kernel Normal Form

Kernel normal form ¹, or KNF, is the coding style used in the development of code for the BSD operating systems. According to the OpenBSD man pages ²:

This file specifies the preferred style for kernel source files in the OpenBSD source tree. It is also a guide for preferred userspace code style.

KNF is based on the original KNF concept from the Computer Systems Research Group and it dictates a programming style to which contributed code should adhere prior to its inclusion into the codebase. KNF started out as a codification of how Ken Thompson and Dennis Ritchie formatted the original UNIX C source code. It describes such things as how to name variables, use indents and the use of ANSI C or K&R C code styles. Each BSD variant has its own KNF rules, which have evolved over time to differ from each other in small ways.

The SunOS kernel and userland also uses a similar indentation style that was derived from AT&T style documents and that is sometimes known as Bill Joy Normal Form. The correctness of the indentation of a list of source files can be verified by a style checker program written by Bill Shannon. This style checker program is called cstyle.

Linux: Basically do this

From my own Debian 10 install:

$ cat /home/jas/.indent.pro 
-bap
-br
-ce
-ci4
-cli0
-d0
-di0
-i8
-ip4
-l79
-nbc
-ncdb
-ndj
-nfc1
-nlp
-npcs
-psl
-sc
-sob

Now just run indent main.c against any untidy c source file to have it indented correctly.

BSD: Options vary slightly

According to Reddit ³: “Here is mine, which tries to mimic OpenBSD KNF”

-bap
-br
-ce
-ci4
-cli0
-d0
-di0
-i8
-ip
-l79
-nbc
-ncdb
-ndj
-ei
-nfc1
-nlp
-npcs
-psl
-sc
-sob

Similarly, run indent *.c against groups of untidy c source files to tidy up :)

References