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Diffstat (limited to 'Documentation/CodingStyle')
| -rw-r--r-- | Documentation/CodingStyle | 70 |
1 files changed, 65 insertions, 5 deletions
diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 3171822c22a5..618a33c940df 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -392,7 +392,12 @@ The goto statement comes in handy when a function exits from multiple locations and some common work such as cleanup has to be done. If there is no cleanup needed then just return directly. -The rationale is: +Choose label names which say what the goto does or why the goto exists. An +example of a good name could be "out_buffer:" if the goto frees "buffer". Avoid +using GW-BASIC names like "err1:" and "err2:". Also don't name them after the +goto location like "err_kmalloc_failed:" + +The rationale for using gotos is: - unconditional statements are easier to understand and follow - nesting is reduced @@ -403,9 +408,10 @@ The rationale is: int fun(int a) { int result = 0; - char *buffer = kmalloc(SIZE); + char *buffer; - if (buffer == NULL) + buffer = kmalloc(SIZE, GFP_KERNEL); + if (!buffer) return -ENOMEM; if (condition1) { @@ -413,14 +419,25 @@ int fun(int a) ... } result = 1; - goto out; + goto out_buffer; } ... -out: +out_buffer: kfree(buffer); return result; } +A common type of bug to be aware of it "one err bugs" which look like this: + +err: + kfree(foo->bar); + kfree(foo); + return ret; + +The bug in this code is that on some exit paths "foo" is NULL. Normally the +fix for this is to split it up into two error labels "err_bar:" and "err_foo:". + + Chapter 8: Commenting Comments are good, but there is also a danger of over-commenting. NEVER @@ -845,6 +862,49 @@ next instruction in the assembly output: : /* outputs */ : /* inputs */ : /* clobbers */); + Chapter 20: Conditional Compilation + +Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .c +files; doing so makes code harder to read and logic harder to follow. Instead, +use such conditionals in a header file defining functions for use in those .c +files, providing no-op stub versions in the #else case, and then call those +functions unconditionally from .c files. The compiler will avoid generating +any code for the stub calls, producing identical results, but the logic will +remain easy to follow. + +Prefer to compile out entire functions, rather than portions of functions or +portions of expressions. Rather than putting an ifdef in an expression, factor +out part or all of the expression into a separate helper function and apply the +conditional to that function. + +If you have a function or variable which may potentially go unused in a +particular configuration, and the compiler would warn about its definition +going unused, mark the definition as __maybe_unused rather than wrapping it in +a preprocessor conditional. (However, if a function or variable *always* goes +unused, delete it.) + +Within code, where possible, use the IS_ENABLED macro to convert a Kconfig +symbol into a C boolean expression, and use it in a normal C conditional: + + if (IS_ENABLED(CONFIG_SOMETHING)) { + ... + } + +The compiler will constant-fold the conditional away, and include or exclude +the block of code just as with an #ifdef, so this will not add any runtime +overhead. However, this approach still allows the C compiler to see the code +inside the block, and check it for correctness (syntax, types, symbol +references, etc). Thus, you still have to use an #ifdef if the code inside the +block references symbols that will not exist if the condition is not met. + +At the end of any non-trivial #if or #ifdef block (more than a few lines), +place a comment after the #endif on the same line, noting the conditional +expression used. For instance: + +#ifdef CONFIG_SOMETHING +... +#endif /* CONFIG_SOMETHING */ + Appendix I: References |