Commit 09677e0f authored by Pavel Kretov's avatar Pavel Kretov Committed by Jonathan Corbet

Documentation/CodingStyle: improve text layout

Try to make coding style documentation look a bit more readable and
consistent with the following:

 - indent every code example in C to first tab-stop;
 - surround every code example with empty lines, both top and bottom;
 - remove empty lines where text looked way too spare;
 - do not indent examples in elisp and kconfig;
 - do not do any non-whitespace changes.
Signed-off-by: default avatarPavel Kretov <firegurafiku@gmail.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 696156f0
......@@ -56,7 +56,6 @@ instead of "double-indenting" the "case" labels. E.g.:
break;
}
Don't put multiple statements on a single line unless you have
something to hide:
......@@ -156,25 +155,25 @@ comments on.
Do not unnecessarily use braces where a single statement will do.
if (condition)
action();
if (condition)
action();
and
if (condition)
do_this();
else
do_that();
if (condition)
do_this();
else
do_that();
This does not apply if only one branch of a conditional statement is a single
statement; in the latter case use braces in both branches:
if (condition) {
do_this();
do_that();
} else {
otherwise();
}
if (condition) {
do_this();
do_that();
} else {
otherwise();
}
3.1: Spaces
......@@ -186,8 +185,11 @@ although they are not required in the language, as in: "sizeof info" after
"struct fileinfo info;" is declared).
So use a space after these keywords:
if, switch, case, for, do, while
but not with sizeof, typeof, alignof, or __attribute__. E.g.,
s = sizeof(struct file);
Do not add spaces around (inside) parenthesized expressions. This example is
......@@ -209,12 +211,15 @@ such as any of these:
= + - < > * / % | & ^ <= >= == != ? :
but no space after unary operators:
& * + - ~ ! sizeof typeof alignof __attribute__ defined
no space before the postfix increment & decrement unary operators:
++ --
no space after the prefix increment & decrement unary operators:
++ --
and no space around the '.' and "->" structure member operators.
......@@ -268,13 +273,11 @@ See chapter 6 (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;
......@@ -372,11 +375,11 @@ In source files, separate functions with one blank line. If the function is
exported, the EXPORT* macro for it should follow immediately after the closing
function brace line. E.g.:
int system_is_up(void)
{
return system_state == SYSTEM_RUNNING;
}
EXPORT_SYMBOL(system_is_up);
int system_is_up(void)
{
return system_state == SYSTEM_RUNNING;
}
EXPORT_SYMBOL(system_is_up);
In function prototypes, include parameter names with their data types.
Although this is not required by the C language, it is preferred in Linux
......@@ -405,34 +408,34 @@ The rationale for using gotos is:
modifications are prevented
- saves the compiler work to optimize redundant code away ;)
int fun(int a)
{
int result = 0;
char *buffer;
buffer = kmalloc(SIZE, GFP_KERNEL);
if (!buffer)
return -ENOMEM;
if (condition1) {
while (loop1) {
...
int fun(int a)
{
int result = 0;
char *buffer;
buffer = kmalloc(SIZE, GFP_KERNEL);
if (!buffer)
return -ENOMEM;
if (condition1) {
while (loop1) {
...
}
result = 1;
goto out_buffer;
}
result = 1;
goto out_buffer;
...
out_buffer:
kfree(buffer);
return result;
}
...
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;
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:".
......@@ -612,7 +615,7 @@ have a reference count on it, you almost certainly have a bug.
Names of macros defining constants and labels in enums are capitalized.
#define CONSTANT 0x12345
#define CONSTANT 0x12345
Enums are preferred when defining several related constants.
......@@ -623,28 +626,28 @@ Generally, inline functions are preferable to macros resembling functions.
Macros with multiple statements should be enclosed in a do - while block:
#define macrofun(a, b, c) \
do { \
if (a == 5) \
do_this(b, c); \
} while (0)
#define macrofun(a, b, c) \
do { \
if (a == 5) \
do_this(b, c); \
} while (0)
Things to avoid when using macros:
1) macros that affect control flow:
#define FOO(x) \
do { \
if (blah(x) < 0) \
return -EBUGGERED; \
} while(0)
#define FOO(x) \
do { \
if (blah(x) < 0) \
return -EBUGGERED; \
} while(0)
is a _very_ bad idea. It looks like a function call but exits the "calling"
function; don't break the internal parsers of those who will read the code.
2) macros that depend on having a local variable with a magic name:
#define FOO(val) bar(index, val)
#define FOO(val) bar(index, val)
might look like a good thing, but it's confusing as hell when one reads the
code and it's prone to breakage from seemingly innocent changes.
......@@ -656,8 +659,8 @@ bite you if somebody e.g. turns FOO into an inline function.
must enclose the expression in parentheses. Beware of similar issues with
macros using parameters.
#define CONSTANT 0x4000
#define CONSTEXP (CONSTANT | 3)
#define CONSTANT 0x4000
#define CONSTEXP (CONSTANT | 3)
The cpp manual deals with macros exhaustively. The gcc internals manual also
covers RTL which is used frequently with assembly language in the kernel.
......@@ -796,11 +799,11 @@ you should use, rather than explicitly coding some variant of them yourself.
For example, if you need to calculate the length of an array, take advantage
of the macro
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
Similarly, if you need to calculate the size of some structure member, use
#define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
#define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
There are also min() and max() macros that do strict type checking if you
need them. Feel free to peruse that header file to see what else is already
......@@ -813,19 +816,19 @@ Some editors can interpret configuration information embedded in source files,
indicated with special markers. For example, emacs interprets lines marked
like this:
-*- mode: c -*-
-*- mode: c -*-
Or like this:
/*
Local Variables:
compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c"
End:
*/
/*
Local Variables:
compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c"
End:
*/
Vim interprets markers that look like this:
/* vim:set sw=8 noet */
/* vim:set sw=8 noet */
Do not include any of these in source files. People have their own personal
editor configurations, and your source files should not override them. This
......@@ -902,9 +905,9 @@ 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 */
#ifdef CONFIG_SOMETHING
...
#endif /* CONFIG_SOMETHING */
Appendix I: References
......
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