.clang-format

text · 10 lines · annotated 100% · upstream

About this file

Configuration for clang-format, a tool that rewrites C source files into a consistent layout (indentation, line breaks, brace placement). make fmt runs it on every .c and .h file in kernel/, user/ and mkfs/ (Makefile:202), and the CI job fails if that changes anything (.github/workflows/test.yml:9). So every C file you read on this site is exactly in the format these settings produce.

The file is YAML. It does not name a base style, so clang-format starts from its default, the LLVM style: indent by 2 spaces, lines at most 80 characters. The lines here change only what xv6 does differently. The file needs clang-format 20 or later: BreakAfterReturnType appeared in version 19 (replacing AlwaysBreakAfterReturnType) and the value Never for ReflowComments in 20; an older version stops with an error about the configuration.

Show notes inline

1SortIncludes: Never
2ReflowComments: Never
3
4BreakAfterReturnType: TopLevelDefinitions
5BreakBeforeBraces: Custom
6BraceWrapping:
7  AfterFunction: true
8AlignConsecutiveMacros: Consecutive
9ContinuationIndentWidth: 2
10BreakStringLiterals: false

Lines 1–2

Leave includes and comments alone

SortIncludes: Never: keep #include lines in the order written. In xv6 order matters: most headers use types such as uint without including kernel/types.h themselves, so it must come first. Sorting (which reorders each run of consecutive #include lines) would, for example, turn mkfs/mkfs.c:9–12 into fs.h, param.h, stat.h, types.h, putting types.h after the headers that need it and breaking the build.
ReflowComments: Never: do not re-wrap long comments. Many xv6 comments are laid out by hand (diagrams, lists, the disk-layout picture in kernel/fs.h:7).

Lines 4–7

Where function definitions break

BreakAfterReturnType: TopLevelDefinitions: in a function definition, put the return type on its own line, so the function name starts the next line:
```
void *
kalloc(void)
```
This is the classic Unix style, and it means a search for ^kalloc finds the definition and nothing else. Declarations (prototypes) are not affected.
BreakBeforeBraces: Custom with BraceWrapping: AfterFunction: true: the { that opens a function body goes on its own line. Because the style is Custom, all other brace positions keep the LLVM default: if (...) {, for (...) { and struct x { keep the brace on the same line.

Lines 8–10

Macros, continuation lines and strings

AlignConsecutiveMacros: Consecutive: in a run of #define lines with no blank line between them, line up the values in one column, as in kernel/param.h and kernel/fs.h.
ContinuationIndentWidth: 2: when a statement is too long and wraps, indent the continuation by 2 spaces instead of the LLVM default 4.
BreakStringLiterals: false: never split a long string constant into pieces to fit in 80 columns. The long printf format on mkfs/mkfs.c:109 stays whole, so you can still search the code for a message you saw printed.