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| -rw-r--r-- | Documentation/CodingStyle | 100 |
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diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index ce5d2c0..6d2412e 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -155,7 +155,83 @@ problem, which is called the function-growth-hormone-imbalance syndrome. See next chapter. - Chapter 5: Functions + Chapter 5: Typedefs + +Please don't use things like "vps_t". + +It's a _mistake_ to use typedef for structures and pointers. When you see a + + vps_t a; + +in the source, what does it mean? + +In contrast, if it says + + struct virtual_container *a; + +you can actually tell what "a" is. + +Lots of people think that typedefs "help readability". Not so. They are +useful only for: + + (a) totally opaque objects (where the typedef is actively used to _hide_ + what the object is). + + Example: "pte_t" etc. opaque objects that you can only access using + the proper accessor functions. + + NOTE! Opaqueness and "accessor functions" are not good in themselves. + The reason we have them for things like pte_t etc. is that there + really is absolutely _zero_ portably accessible information there. + + (b) Clear integer types, where the abstraction _helps_ avoid confusion + whether it is "int" or "long". + + u8/u16/u32 are perfectly fine typedefs, although they fit into + category (d) better than here. + + NOTE! Again - there needs to be a _reason_ for this. If something is + "unsigned long", then there's no reason to do + + typedef unsigned long myflags_t; + + but if there is a clear reason for why it under certain circumstances + might be an "unsigned int" and under other configurations might be + "unsigned long", then by all means go ahead and use a typedef. + + (c) when you use sparse to literally create a _new_ type for + type-checking. + + (d) New types which are identical to standard C99 types, in certain + exceptional circumstances. + + Although it would only take a short amount of time for the eyes and + brain to become accustomed to the standard types like 'uint32_t', + some people object to their use anyway. + + Therefore, the Linux-specific 'u8/u16/u32/u64' types and their + signed equivalents which are identical to standard types are + permitted -- although they are not mandatory in new code of your + own. + + When editing existing code which already uses one or the other set + of types, you should conform to the existing choices in that code. + + (e) Types safe for use in userspace. + + In certain structures which are visible to userspace, we cannot + require C99 types and cannot use the 'u32' form above. Thus, we + use __u32 and similar types in all structures which are shared + with userspace. + +Maybe there are other cases too, but the rule should basically be to NEVER +EVER use a typedef unless you can clearly match one of those rules. + +In general, a pointer, or a struct that has elements that can reasonably +be directly accessed should _never_ be a typedef. + + + Chapter 6: Functions Functions should be short and sweet, and do just one thing. They should fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24, @@ -183,7 +259,7 @@ and it gets confused. You know you're brilliant, but maybe you'd like to understand what you did 2 weeks from now. - Chapter 6: Centralized exiting of functions + Chapter 7: Centralized exiting of functions Albeit deprecated by some people, the equivalent of the goto statement is used frequently by compilers in form of the unconditional jump instruction. @@ -220,7 +296,7 @@ out: return result; } - Chapter 7: Commenting + Chapter 8: Commenting Comments are good, but there is also a danger of over-commenting. NEVER try to explain HOW your code works in a comment: it's much better to @@ -240,7 +316,7 @@ When commenting the kernel API functions, please use the kerneldoc format. See the files Documentation/kernel-doc-nano-HOWTO.txt and scripts/kernel-doc for details. - Chapter 8: You've made a mess of it + Chapter 9: You've made a mess of it That's OK, we all do. You've probably been told by your long-time Unix user helper that "GNU emacs" automatically formats the C sources for @@ -288,7 +364,7 @@ re-formatting you may want to take a look at the man page. But remember: "indent" is not a fix for bad programming. - Chapter 9: Configuration-files + Chapter 10: Configuration-files For configuration options (arch/xxx/Kconfig, and all the Kconfig files), somewhat different indentation is used. @@ -313,7 +389,7 @@ support for file-systems, for instance) should be denoted (DANGEROUS), other experimental options should be denoted (EXPERIMENTAL). - Chapter 10: Data structures + Chapter 11: Data structures Data structures that have visibility outside the single-threaded environment they are created and destroyed in should always have @@ -344,7 +420,7 @@ Remember: if another thread can find your data structure, and you don't have a reference count on it, you almost certainly have a bug. - Chapter 11: Macros, Enums and RTL + Chapter 12: Macros, Enums and RTL Names of macros defining constants and labels in enums are capitalized. @@ -399,7 +475,7 @@ The cpp manual deals with macros exhaustively. The gcc internals manual also covers RTL which is used frequently with assembly language in the kernel. - Chapter 12: Printing kernel messages + Chapter 13: Printing kernel messages Kernel developers like to be seen as literate. Do mind the spelling of kernel messages to make a good impression. Do not use crippled @@ -410,7 +486,7 @@ Kernel messages do not have to be terminated with a period. Printing numbers in parentheses (%d) adds no value and should be avoided. - Chapter 13: Allocating memory + Chapter 14: Allocating memory The kernel provides the following general purpose memory allocators: kmalloc(), kzalloc(), kcalloc(), and vmalloc(). Please refer to the API @@ -429,7 +505,7 @@ from void pointer to any other pointer type is guaranteed by the C programming language. - Chapter 14: The inline disease + Chapter 15: The inline disease There appears to be a common misperception that gcc has a magic "make me faster" speedup option called "inline". While the use of inlines can be @@ -457,7 +533,7 @@ something it would have done anyway. - Chapter 15: References + Appendix I: References The C Programming Language, Second Edition by Brian W. Kernighan and Dennis M. Ritchie. @@ -481,4 +557,4 @@ Kernel CodingStyle, by greg@kroah.com at OLS 2002: http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/ -- -Last updated on 30 December 2005 by a community effort on LKML. +Last updated on 30 April 2006. |
