[PATCH] CodingStyle: add typedefs chapter
Add a chapter on typedefs, copied from an email from Linus to lkml on Feb. 3, 2006. (Subject: Re: [RFC][PATCH 1/5] Virtualization/containers: startup) Signed-off-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Randy Dunlap
Linus Torvalds
parent
3439dd86e3
commit
226a6b84aa
1 changed files with 88 additions and 12 deletions
|
|
@ -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.
|
||||
|
|
|
|||
Loading…
Reference in a new issue