|
@@ -1,8 +1,10 @@
|
|
|
|
+.. _codingstyle:
|
|
|
|
|
|
- Linux kernel coding style
|
|
|
|
|
|
+Linux kernel coding style
|
|
|
|
+=========================
|
|
|
|
|
|
This is a short document describing the preferred coding style for the
|
|
This is a short document describing the preferred coding style for the
|
|
-linux kernel. Coding style is very personal, and I won't _force_ my
|
|
|
|
|
|
+linux kernel. Coding style is very personal, and I won't **force** my
|
|
views on anybody, but this is what goes for anything that I have to be
|
|
views on anybody, but this is what goes for anything that I have to be
|
|
able to maintain, and I'd prefer it for most other things too. Please
|
|
able to maintain, and I'd prefer it for most other things too. Please
|
|
at least consider the points made here.
|
|
at least consider the points made here.
|
|
@@ -13,7 +15,8 @@ and NOT read it. Burn them, it's a great symbolic gesture.
|
|
Anyway, here goes:
|
|
Anyway, here goes:
|
|
|
|
|
|
|
|
|
|
- Chapter 1: Indentation
|
|
|
|
|
|
+1) Indentation
|
|
|
|
+--------------
|
|
|
|
|
|
Tabs are 8 characters, and thus indentations are also 8 characters.
|
|
Tabs are 8 characters, and thus indentations are also 8 characters.
|
|
There are heretic movements that try to make indentations 4 (or even 2!)
|
|
There are heretic movements that try to make indentations 4 (or even 2!)
|
|
@@ -36,8 +39,10 @@ benefit of warning you when you're nesting your functions too deep.
|
|
Heed that warning.
|
|
Heed that warning.
|
|
|
|
|
|
The preferred way to ease multiple indentation levels in a switch statement is
|
|
The preferred way to ease multiple indentation levels in a switch statement is
|
|
-to align the "switch" and its subordinate "case" labels in the same column
|
|
|
|
-instead of "double-indenting" the "case" labels. E.g.:
|
|
|
|
|
|
+to align the ``switch`` and its subordinate ``case`` labels in the same column
|
|
|
|
+instead of ``double-indenting`` the ``case`` labels. E.g.:
|
|
|
|
+
|
|
|
|
+.. code-block:: c
|
|
|
|
|
|
switch (suffix) {
|
|
switch (suffix) {
|
|
case 'G':
|
|
case 'G':
|
|
@@ -59,6 +64,8 @@ instead of "double-indenting" the "case" labels. E.g.:
|
|
Don't put multiple statements on a single line unless you have
|
|
Don't put multiple statements on a single line unless you have
|
|
something to hide:
|
|
something to hide:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
if (condition) do_this;
|
|
if (condition) do_this;
|
|
do_something_everytime;
|
|
do_something_everytime;
|
|
|
|
|
|
@@ -71,7 +78,8 @@ used for indentation, and the above example is deliberately broken.
|
|
Get a decent editor and don't leave whitespace at the end of lines.
|
|
Get a decent editor and don't leave whitespace at the end of lines.
|
|
|
|
|
|
|
|
|
|
- Chapter 2: Breaking long lines and strings
|
|
|
|
|
|
+2) Breaking long lines and strings
|
|
|
|
+----------------------------------
|
|
|
|
|
|
Coding style is all about readability and maintainability using commonly
|
|
Coding style is all about readability and maintainability using commonly
|
|
available tools.
|
|
available tools.
|
|
@@ -87,7 +95,8 @@ with a long argument list. However, never break user-visible strings such as
|
|
printk messages, because that breaks the ability to grep for them.
|
|
printk messages, because that breaks the ability to grep for them.
|
|
|
|
|
|
|
|
|
|
- Chapter 3: Placing Braces and Spaces
|
|
|
|
|
|
+3) Placing Braces and Spaces
|
|
|
|
+----------------------------
|
|
|
|
|
|
The other issue that always comes up in C styling is the placement of
|
|
The other issue that always comes up in C styling is the placement of
|
|
braces. Unlike the indent size, there are few technical reasons to
|
|
braces. Unlike the indent size, there are few technical reasons to
|
|
@@ -95,6 +104,8 @@ choose one placement strategy over the other, but the preferred way, as
|
|
shown to us by the prophets Kernighan and Ritchie, is to put the opening
|
|
shown to us by the prophets Kernighan and Ritchie, is to put the opening
|
|
brace last on the line, and put the closing brace first, thusly:
|
|
brace last on the line, and put the closing brace first, thusly:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
if (x is true) {
|
|
if (x is true) {
|
|
we do y
|
|
we do y
|
|
}
|
|
}
|
|
@@ -102,6 +113,8 @@ brace last on the line, and put the closing brace first, thusly:
|
|
This applies to all non-function statement blocks (if, switch, for,
|
|
This applies to all non-function statement blocks (if, switch, for,
|
|
while, do). E.g.:
|
|
while, do). E.g.:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
switch (action) {
|
|
switch (action) {
|
|
case KOBJ_ADD:
|
|
case KOBJ_ADD:
|
|
return "add";
|
|
return "add";
|
|
@@ -116,6 +129,8 @@ while, do). E.g.:
|
|
However, there is one special case, namely functions: they have the
|
|
However, there is one special case, namely functions: they have the
|
|
opening brace at the beginning of the next line, thus:
|
|
opening brace at the beginning of the next line, thus:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
int function(int x)
|
|
int function(int x)
|
|
{
|
|
{
|
|
body of function
|
|
body of function
|
|
@@ -123,20 +138,24 @@ opening brace at the beginning of the next line, thus:
|
|
|
|
|
|
Heretic people all over the world have claimed that this inconsistency
|
|
Heretic people all over the world have claimed that this inconsistency
|
|
is ... well ... inconsistent, but all right-thinking people know that
|
|
is ... well ... inconsistent, but all right-thinking people know that
|
|
-(a) K&R are _right_ and (b) K&R are right. Besides, functions are
|
|
|
|
|
|
+(a) K&R are **right** and (b) K&R are right. Besides, functions are
|
|
special anyway (you can't nest them in C).
|
|
special anyway (you can't nest them in C).
|
|
|
|
|
|
-Note that the closing brace is empty on a line of its own, _except_ in
|
|
|
|
|
|
+Note that the closing brace is empty on a line of its own, **except** in
|
|
the cases where it is followed by a continuation of the same statement,
|
|
the cases where it is followed by a continuation of the same statement,
|
|
-ie a "while" in a do-statement or an "else" in an if-statement, like
|
|
|
|
|
|
+ie a ``while`` in a do-statement or an ``else`` in an if-statement, like
|
|
this:
|
|
this:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
do {
|
|
do {
|
|
body of do-loop
|
|
body of do-loop
|
|
} while (condition);
|
|
} while (condition);
|
|
|
|
|
|
and
|
|
and
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
if (x == y) {
|
|
if (x == y) {
|
|
..
|
|
..
|
|
} else if (x > y) {
|
|
} else if (x > y) {
|
|
@@ -155,11 +174,15 @@ comments on.
|
|
|
|
|
|
Do not unnecessarily use braces where a single statement will do.
|
|
Do not unnecessarily use braces where a single statement will do.
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
if (condition)
|
|
if (condition)
|
|
action();
|
|
action();
|
|
|
|
|
|
and
|
|
and
|
|
|
|
|
|
|
|
+.. code-block:: none
|
|
|
|
+
|
|
if (condition)
|
|
if (condition)
|
|
do_this();
|
|
do_this();
|
|
else
|
|
else
|
|
@@ -168,6 +191,8 @@ and
|
|
This does not apply if only one branch of a conditional statement is a single
|
|
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:
|
|
statement; in the latter case use braces in both branches:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
if (condition) {
|
|
if (condition) {
|
|
do_this();
|
|
do_this();
|
|
do_that();
|
|
do_that();
|
|
@@ -175,57 +200,67 @@ statement; in the latter case use braces in both branches:
|
|
otherwise();
|
|
otherwise();
|
|
}
|
|
}
|
|
|
|
|
|
- 3.1: Spaces
|
|
|
|
|
|
+3.1) Spaces
|
|
|
|
+***********
|
|
|
|
|
|
Linux kernel style for use of spaces depends (mostly) on
|
|
Linux kernel style for use of spaces depends (mostly) on
|
|
function-versus-keyword usage. Use a space after (most) keywords. The
|
|
function-versus-keyword usage. Use a space after (most) keywords. The
|
|
notable exceptions are sizeof, typeof, alignof, and __attribute__, which look
|
|
notable exceptions are sizeof, typeof, alignof, and __attribute__, which look
|
|
somewhat like functions (and are usually used with parentheses in Linux,
|
|
somewhat like functions (and are usually used with parentheses in Linux,
|
|
-although they are not required in the language, as in: "sizeof info" after
|
|
|
|
-"struct fileinfo info;" is declared).
|
|
|
|
|
|
+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:
|
|
|
|
|
|
+So use a space after these keywords::
|
|
|
|
|
|
if, switch, case, for, do, while
|
|
if, switch, case, for, do, while
|
|
|
|
|
|
but not with sizeof, typeof, alignof, or __attribute__. E.g.,
|
|
but not with sizeof, typeof, alignof, or __attribute__. E.g.,
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
|
|
+
|
|
s = sizeof(struct file);
|
|
s = sizeof(struct file);
|
|
|
|
|
|
Do not add spaces around (inside) parenthesized expressions. This example is
|
|
Do not add spaces around (inside) parenthesized expressions. This example is
|
|
-*bad*:
|
|
|
|
|
|
+**bad**:
|
|
|
|
+
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
|
|
|
|
s = sizeof( struct file );
|
|
s = sizeof( struct file );
|
|
|
|
|
|
When declaring pointer data or a function that returns a pointer type, the
|
|
When declaring pointer data or a function that returns a pointer type, the
|
|
-preferred use of '*' is adjacent to the data name or function name and not
|
|
|
|
|
|
+preferred use of ``*`` is adjacent to the data name or function name and not
|
|
adjacent to the type name. Examples:
|
|
adjacent to the type name. Examples:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
|
|
+
|
|
char *linux_banner;
|
|
char *linux_banner;
|
|
unsigned long long memparse(char *ptr, char **retptr);
|
|
unsigned long long memparse(char *ptr, char **retptr);
|
|
char *match_strdup(substring_t *s);
|
|
char *match_strdup(substring_t *s);
|
|
|
|
|
|
Use one space around (on each side of) most binary and ternary operators,
|
|
Use one space around (on each side of) most binary and ternary operators,
|
|
-such as any of these:
|
|
|
|
|
|
+such as any of these::
|
|
|
|
|
|
= + - < > * / % | & ^ <= >= == != ? :
|
|
= + - < > * / % | & ^ <= >= == != ? :
|
|
|
|
|
|
-but no space after unary operators:
|
|
|
|
|
|
+but no space after unary operators::
|
|
|
|
|
|
& * + - ~ ! sizeof typeof alignof __attribute__ defined
|
|
& * + - ~ ! sizeof typeof alignof __attribute__ defined
|
|
|
|
|
|
-no space before the postfix increment & decrement unary operators:
|
|
|
|
|
|
+no space before the postfix increment & decrement unary operators::
|
|
|
|
|
|
++ --
|
|
++ --
|
|
|
|
|
|
-no space after the prefix increment & decrement unary operators:
|
|
|
|
|
|
+no space after the prefix increment & decrement unary operators::
|
|
|
|
|
|
++ --
|
|
++ --
|
|
|
|
|
|
-and no space around the '.' and "->" structure member operators.
|
|
|
|
|
|
+and no space around the ``.`` and ``->`` structure member operators.
|
|
|
|
|
|
Do not leave trailing whitespace at the ends of lines. Some editors with
|
|
Do not leave trailing whitespace at the ends of lines. Some editors with
|
|
-"smart" indentation will insert whitespace at the beginning of new lines as
|
|
|
|
|
|
+``smart`` indentation will insert whitespace at the beginning of new lines as
|
|
appropriate, so you can start typing the next line of code right away.
|
|
appropriate, so you can start typing the next line of code right away.
|
|
However, some such editors do not remove the whitespace if you end up not
|
|
However, some such editors do not remove the whitespace if you end up not
|
|
putting a line of code there, such as if you leave a blank line. As a result,
|
|
putting a line of code there, such as if you leave a blank line. As a result,
|
|
@@ -237,22 +272,23 @@ of patches, this may make later patches in the series fail by changing their
|
|
context lines.
|
|
context lines.
|
|
|
|
|
|
|
|
|
|
- Chapter 4: Naming
|
|
|
|
|
|
+4) Naming
|
|
|
|
+---------
|
|
|
|
|
|
C is a Spartan language, and so should your naming be. Unlike Modula-2
|
|
C is a Spartan language, and so should your naming be. Unlike Modula-2
|
|
and Pascal programmers, C programmers do not use cute names like
|
|
and Pascal programmers, C programmers do not use cute names like
|
|
ThisVariableIsATemporaryCounter. A C programmer would call that
|
|
ThisVariableIsATemporaryCounter. A C programmer would call that
|
|
-variable "tmp", which is much easier to write, and not the least more
|
|
|
|
|
|
+variable ``tmp``, which is much easier to write, and not the least more
|
|
difficult to understand.
|
|
difficult to understand.
|
|
|
|
|
|
HOWEVER, while mixed-case names are frowned upon, descriptive names for
|
|
HOWEVER, while mixed-case names are frowned upon, descriptive names for
|
|
-global variables are a must. To call a global function "foo" is a
|
|
|
|
|
|
+global variables are a must. To call a global function ``foo`` is a
|
|
shooting offense.
|
|
shooting offense.
|
|
|
|
|
|
-GLOBAL variables (to be used only if you _really_ need them) need to
|
|
|
|
|
|
+GLOBAL variables (to be used only if you **really** need them) need to
|
|
have descriptive names, as do global functions. If you have a function
|
|
have descriptive names, as do global functions. If you have a function
|
|
that counts the number of active users, you should call that
|
|
that counts the number of active users, you should call that
|
|
-"count_active_users()" or similar, you should _not_ call it "cntusr()".
|
|
|
|
|
|
+``count_active_users()`` or similar, you should **not** call it ``cntusr()``.
|
|
|
|
|
|
Encoding the type of a function into the name (so-called Hungarian
|
|
Encoding the type of a function into the name (so-called Hungarian
|
|
notation) is brain damaged - the compiler knows the types anyway and can
|
|
notation) is brain damaged - the compiler knows the types anyway and can
|
|
@@ -260,9 +296,9 @@ check those, and it only confuses the programmer. No wonder MicroSoft
|
|
makes buggy programs.
|
|
makes buggy programs.
|
|
|
|
|
|
LOCAL variable names should be short, and to the point. If you have
|
|
LOCAL variable names should be short, and to the point. If you have
|
|
-some random integer loop counter, it should probably be called "i".
|
|
|
|
-Calling it "loop_counter" is non-productive, if there is no chance of it
|
|
|
|
-being mis-understood. Similarly, "tmp" can be just about any type of
|
|
|
|
|
|
+some random integer loop counter, it should probably be called ``i``.
|
|
|
|
+Calling it ``loop_counter`` is non-productive, if there is no chance of it
|
|
|
|
+being mis-understood. Similarly, ``tmp`` can be just about any type of
|
|
variable that is used to hold a temporary value.
|
|
variable that is used to hold a temporary value.
|
|
|
|
|
|
If you are afraid to mix up your local variable names, you have another
|
|
If you are afraid to mix up your local variable names, you have another
|
|
@@ -270,59 +306,69 @@ problem, which is called the function-growth-hormone-imbalance syndrome.
|
|
See chapter 6 (Functions).
|
|
See chapter 6 (Functions).
|
|
|
|
|
|
|
|
|
|
- Chapter 5: Typedefs
|
|
|
|
|
|
+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
|
|
|
|
+
|
|
|
|
+.. code-block:: c
|
|
|
|
|
|
-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;
|
|
vps_t a;
|
|
|
|
|
|
in the source, what does it mean?
|
|
in the source, what does it mean?
|
|
In contrast, if it says
|
|
In contrast, if it says
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
struct virtual_container *a;
|
|
struct virtual_container *a;
|
|
|
|
|
|
-you can actually tell what "a" is.
|
|
|
|
|
|
+you can actually tell what ``a`` is.
|
|
|
|
|
|
-Lots of people think that typedefs "help readability". Not so. They are
|
|
|
|
|
|
+Lots of people think that typedefs ``help readability``. Not so. They are
|
|
useful only for:
|
|
useful only for:
|
|
|
|
|
|
- (a) totally opaque objects (where the typedef is actively used to _hide_
|
|
|
|
|
|
+ (a) totally opaque objects (where the typedef is actively used to **hide**
|
|
what the object is).
|
|
what the object is).
|
|
|
|
|
|
- Example: "pte_t" etc. opaque objects that you can only access using
|
|
|
|
|
|
+ Example: ``pte_t`` etc. opaque objects that you can only access using
|
|
the proper accessor functions.
|
|
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.
|
|
|
|
|
|
+ .. 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".
|
|
|
|
|
|
+ (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
|
|
u8/u16/u32 are perfectly fine typedefs, although they fit into
|
|
category (d) better than here.
|
|
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
|
|
|
|
|
|
+ .. 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;
|
|
typedef unsigned long myflags_t;
|
|
|
|
|
|
but if there is a clear reason for why it under certain circumstances
|
|
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.
|
|
|
|
|
|
+ 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
|
|
|
|
|
|
+ (c) when you use sparse to literally create a **new** type for
|
|
type-checking.
|
|
type-checking.
|
|
|
|
|
|
(d) New types which are identical to standard C99 types, in certain
|
|
(d) New types which are identical to standard C99 types, in certain
|
|
exceptional circumstances.
|
|
exceptional circumstances.
|
|
|
|
|
|
Although it would only take a short amount of time for the eyes and
|
|
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',
|
|
|
|
|
|
+ brain to become accustomed to the standard types like ``uint32_t``,
|
|
some people object to their use anyway.
|
|
some people object to their use anyway.
|
|
|
|
|
|
- Therefore, the Linux-specific 'u8/u16/u32/u64' types and their
|
|
|
|
|
|
+ Therefore, the Linux-specific ``u8/u16/u32/u64`` types and their
|
|
signed equivalents which are identical to standard types are
|
|
signed equivalents which are identical to standard types are
|
|
permitted -- although they are not mandatory in new code of your
|
|
permitted -- although they are not mandatory in new code of your
|
|
own.
|
|
own.
|
|
@@ -333,7 +379,7 @@ useful only for:
|
|
(e) Types safe for use in userspace.
|
|
(e) Types safe for use in userspace.
|
|
|
|
|
|
In certain structures which are visible to userspace, we cannot
|
|
In certain structures which are visible to userspace, we cannot
|
|
- require C99 types and cannot use the 'u32' form above. Thus, we
|
|
|
|
|
|
+ require C99 types and cannot use the ``u32`` form above. Thus, we
|
|
use __u32 and similar types in all structures which are shared
|
|
use __u32 and similar types in all structures which are shared
|
|
with userspace.
|
|
with userspace.
|
|
|
|
|
|
@@ -341,10 +387,11 @@ 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.
|
|
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
|
|
In general, a pointer, or a struct that has elements that can reasonably
|
|
-be directly accessed should _never_ be a typedef.
|
|
|
|
|
|
+be directly accessed should **never** be a typedef.
|
|
|
|
|
|
|
|
|
|
- Chapter 6: Functions
|
|
|
|
|
|
+6) Functions
|
|
|
|
+------------
|
|
|
|
|
|
Functions should be short and sweet, and do just one thing. They should
|
|
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,
|
|
fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24,
|
|
@@ -372,8 +419,10 @@ and it gets confused. You know you're brilliant, but maybe you'd like
|
|
to understand what you did 2 weeks from now.
|
|
to understand what you did 2 weeks from now.
|
|
|
|
|
|
In source files, separate functions with one blank line. If the function is
|
|
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.:
|
|
|
|
|
|
+exported, the **EXPORT** macro for it should follow immediately after the
|
|
|
|
+closing function brace line. E.g.:
|
|
|
|
+
|
|
|
|
+.. code-block:: c
|
|
|
|
|
|
int system_is_up(void)
|
|
int system_is_up(void)
|
|
{
|
|
{
|
|
@@ -386,7 +435,8 @@ Although this is not required by the C language, it is preferred in Linux
|
|
because it is a simple way to add valuable information for the reader.
|
|
because it is a simple way to add valuable information for the reader.
|
|
|
|
|
|
|
|
|
|
- Chapter 7: Centralized exiting of functions
|
|
|
|
|
|
+7) Centralized exiting of functions
|
|
|
|
+-----------------------------------
|
|
|
|
|
|
Albeit deprecated by some people, the equivalent of the goto statement is
|
|
Albeit deprecated by some people, the equivalent of the goto statement is
|
|
used frequently by compilers in form of the unconditional jump instruction.
|
|
used frequently by compilers in form of the unconditional jump instruction.
|
|
@@ -396,18 +446,21 @@ locations and some common work such as cleanup has to be done. If there is no
|
|
cleanup needed then just return directly.
|
|
cleanup needed then just return directly.
|
|
|
|
|
|
Choose label names which say what the goto does or why the goto exists. An
|
|
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:"
|
|
|
|
|
|
+example of a good name could be ``out_free_buffer:`` if the goto frees ``buffer``.
|
|
|
|
+Avoid using GW-BASIC names like ``err1:`` and ``err2:``, as you would have to
|
|
|
|
+renumber them if you ever add or remove exit paths, and they make correctness
|
|
|
|
+difficult to verify anyway.
|
|
|
|
|
|
The rationale for using gotos is:
|
|
The rationale for using gotos is:
|
|
|
|
|
|
- unconditional statements are easier to understand and follow
|
|
- unconditional statements are easier to understand and follow
|
|
- nesting is reduced
|
|
- nesting is reduced
|
|
- errors by not updating individual exit points when making
|
|
- errors by not updating individual exit points when making
|
|
- modifications are prevented
|
|
|
|
|
|
+ modifications are prevented
|
|
- saves the compiler work to optimize redundant code away ;)
|
|
- saves the compiler work to optimize redundant code away ;)
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
int fun(int a)
|
|
int fun(int a)
|
|
{
|
|
{
|
|
int result = 0;
|
|
int result = 0;
|
|
@@ -425,27 +478,41 @@ The rationale for using gotos is:
|
|
goto out_buffer;
|
|
goto out_buffer;
|
|
}
|
|
}
|
|
...
|
|
...
|
|
- out_buffer:
|
|
|
|
|
|
+ out_free_buffer:
|
|
kfree(buffer);
|
|
kfree(buffer);
|
|
return result;
|
|
return result;
|
|
}
|
|
}
|
|
|
|
|
|
-A common type of bug to be aware of is "one err bugs" which look like this:
|
|
|
|
|
|
+A common type of bug to be aware of is ``one err bugs`` which look like this:
|
|
|
|
+
|
|
|
|
+.. code-block:: c
|
|
|
|
|
|
err:
|
|
err:
|
|
kfree(foo->bar);
|
|
kfree(foo->bar);
|
|
kfree(foo);
|
|
kfree(foo);
|
|
return ret;
|
|
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:".
|
|
|
|
|
|
+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_free_bar:`` and
|
|
|
|
+``err_free_foo:``:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
|
|
- Chapter 8: Commenting
|
|
|
|
|
|
+ err_free_bar:
|
|
|
|
+ kfree(foo->bar);
|
|
|
|
+ err_free_foo:
|
|
|
|
+ kfree(foo);
|
|
|
|
+ return ret;
|
|
|
|
+
|
|
|
|
+Ideally you should simulate errors to test all exit paths.
|
|
|
|
+
|
|
|
|
+
|
|
|
|
+8) Commenting
|
|
|
|
+-------------
|
|
|
|
|
|
Comments are good, but there is also a danger of over-commenting. NEVER
|
|
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
|
|
try to explain HOW your code works in a comment: it's much better to
|
|
-write the code so that the _working_ is obvious, and it's a waste of
|
|
|
|
|
|
+write the code so that the **working** is obvious, and it's a waste of
|
|
time to explain badly written code.
|
|
time to explain badly written code.
|
|
|
|
|
|
Generally, you want your comments to tell WHAT your code does, not HOW.
|
|
Generally, you want your comments to tell WHAT your code does, not HOW.
|
|
@@ -461,11 +528,10 @@ When commenting the kernel API functions, please use the kernel-doc format.
|
|
See the files Documentation/kernel-documentation.rst and scripts/kernel-doc
|
|
See the files Documentation/kernel-documentation.rst and scripts/kernel-doc
|
|
for details.
|
|
for details.
|
|
|
|
|
|
-Linux style for comments is the C89 "/* ... */" style.
|
|
|
|
-Don't use C99-style "// ..." comments.
|
|
|
|
-
|
|
|
|
The preferred style for long (multi-line) comments is:
|
|
The preferred style for long (multi-line) comments is:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
/*
|
|
/*
|
|
* This is the preferred style for multi-line
|
|
* This is the preferred style for multi-line
|
|
* comments in the Linux kernel source code.
|
|
* comments in the Linux kernel source code.
|
|
@@ -478,6 +544,8 @@ The preferred style for long (multi-line) comments is:
|
|
For files in net/ and drivers/net/ the preferred style for long (multi-line)
|
|
For files in net/ and drivers/net/ the preferred style for long (multi-line)
|
|
comments is a little different.
|
|
comments is a little different.
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
/* The preferred comment style for files in net/ and drivers/net
|
|
/* The preferred comment style for files in net/ and drivers/net
|
|
* looks like this.
|
|
* looks like this.
|
|
*
|
|
*
|
|
@@ -491,10 +559,11 @@ multiple data declarations). This leaves you room for a small comment on each
|
|
item, explaining its use.
|
|
item, explaining its use.
|
|
|
|
|
|
|
|
|
|
- Chapter 9: You've made a mess of it
|
|
|
|
|
|
+9) You've made a mess of it
|
|
|
|
+---------------------------
|
|
|
|
|
|
That's OK, we all do. You've probably been told by your long-time Unix
|
|
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
|
|
|
|
|
|
+user helper that ``GNU emacs`` automatically formats the C sources for
|
|
you, and you've noticed that yes, it does do that, but the defaults it
|
|
you, and you've noticed that yes, it does do that, but the defaults it
|
|
uses are less than desirable (in fact, they are worse than random
|
|
uses are less than desirable (in fact, they are worse than random
|
|
typing - an infinite number of monkeys typing into GNU emacs would never
|
|
typing - an infinite number of monkeys typing into GNU emacs would never
|
|
@@ -503,63 +572,66 @@ make a good program).
|
|
So, you can either get rid of GNU emacs, or change it to use saner
|
|
So, you can either get rid of GNU emacs, or change it to use saner
|
|
values. To do the latter, you can stick the following in your .emacs file:
|
|
values. To do the latter, you can stick the following in your .emacs file:
|
|
|
|
|
|
-(defun c-lineup-arglist-tabs-only (ignored)
|
|
|
|
- "Line up argument lists by tabs, not spaces"
|
|
|
|
- (let* ((anchor (c-langelem-pos c-syntactic-element))
|
|
|
|
- (column (c-langelem-2nd-pos c-syntactic-element))
|
|
|
|
- (offset (- (1+ column) anchor))
|
|
|
|
- (steps (floor offset c-basic-offset)))
|
|
|
|
- (* (max steps 1)
|
|
|
|
- c-basic-offset)))
|
|
|
|
-
|
|
|
|
-(add-hook 'c-mode-common-hook
|
|
|
|
- (lambda ()
|
|
|
|
- ;; Add kernel style
|
|
|
|
- (c-add-style
|
|
|
|
- "linux-tabs-only"
|
|
|
|
- '("linux" (c-offsets-alist
|
|
|
|
- (arglist-cont-nonempty
|
|
|
|
- c-lineup-gcc-asm-reg
|
|
|
|
- c-lineup-arglist-tabs-only))))))
|
|
|
|
-
|
|
|
|
-(add-hook 'c-mode-hook
|
|
|
|
- (lambda ()
|
|
|
|
- (let ((filename (buffer-file-name)))
|
|
|
|
- ;; Enable kernel mode for the appropriate files
|
|
|
|
- (when (and filename
|
|
|
|
- (string-match (expand-file-name "~/src/linux-trees")
|
|
|
|
- filename))
|
|
|
|
- (setq indent-tabs-mode t)
|
|
|
|
- (setq show-trailing-whitespace t)
|
|
|
|
- (c-set-style "linux-tabs-only")))))
|
|
|
|
|
|
+.. code-block:: none
|
|
|
|
+
|
|
|
|
+ (defun c-lineup-arglist-tabs-only (ignored)
|
|
|
|
+ "Line up argument lists by tabs, not spaces"
|
|
|
|
+ (let* ((anchor (c-langelem-pos c-syntactic-element))
|
|
|
|
+ (column (c-langelem-2nd-pos c-syntactic-element))
|
|
|
|
+ (offset (- (1+ column) anchor))
|
|
|
|
+ (steps (floor offset c-basic-offset)))
|
|
|
|
+ (* (max steps 1)
|
|
|
|
+ c-basic-offset)))
|
|
|
|
+
|
|
|
|
+ (add-hook 'c-mode-common-hook
|
|
|
|
+ (lambda ()
|
|
|
|
+ ;; Add kernel style
|
|
|
|
+ (c-add-style
|
|
|
|
+ "linux-tabs-only"
|
|
|
|
+ '("linux" (c-offsets-alist
|
|
|
|
+ (arglist-cont-nonempty
|
|
|
|
+ c-lineup-gcc-asm-reg
|
|
|
|
+ c-lineup-arglist-tabs-only))))))
|
|
|
|
+
|
|
|
|
+ (add-hook 'c-mode-hook
|
|
|
|
+ (lambda ()
|
|
|
|
+ (let ((filename (buffer-file-name)))
|
|
|
|
+ ;; Enable kernel mode for the appropriate files
|
|
|
|
+ (when (and filename
|
|
|
|
+ (string-match (expand-file-name "~/src/linux-trees")
|
|
|
|
+ filename))
|
|
|
|
+ (setq indent-tabs-mode t)
|
|
|
|
+ (setq show-trailing-whitespace t)
|
|
|
|
+ (c-set-style "linux-tabs-only")))))
|
|
|
|
|
|
This will make emacs go better with the kernel coding style for C
|
|
This will make emacs go better with the kernel coding style for C
|
|
-files below ~/src/linux-trees.
|
|
|
|
|
|
+files below ``~/src/linux-trees``.
|
|
|
|
|
|
But even if you fail in getting emacs to do sane formatting, not
|
|
But even if you fail in getting emacs to do sane formatting, not
|
|
-everything is lost: use "indent".
|
|
|
|
|
|
+everything is lost: use ``indent``.
|
|
|
|
|
|
Now, again, GNU indent has the same brain-dead settings that GNU emacs
|
|
Now, again, GNU indent has the same brain-dead settings that GNU emacs
|
|
has, which is why you need to give it a few command line options.
|
|
has, which is why you need to give it a few command line options.
|
|
However, that's not too bad, because even the makers of GNU indent
|
|
However, that's not too bad, because even the makers of GNU indent
|
|
recognize the authority of K&R (the GNU people aren't evil, they are
|
|
recognize the authority of K&R (the GNU people aren't evil, they are
|
|
just severely misguided in this matter), so you just give indent the
|
|
just severely misguided in this matter), so you just give indent the
|
|
-options "-kr -i8" (stands for "K&R, 8 character indents"), or use
|
|
|
|
-"scripts/Lindent", which indents in the latest style.
|
|
|
|
|
|
+options ``-kr -i8`` (stands for ``K&R, 8 character indents``), or use
|
|
|
|
+``scripts/Lindent``, which indents in the latest style.
|
|
|
|
|
|
-"indent" has a lot of options, and especially when it comes to comment
|
|
|
|
|
|
+``indent`` has a lot of options, and especially when it comes to comment
|
|
re-formatting you may want to take a look at the man page. But
|
|
re-formatting you may want to take a look at the man page. But
|
|
-remember: "indent" is not a fix for bad programming.
|
|
|
|
|
|
+remember: ``indent`` is not a fix for bad programming.
|
|
|
|
|
|
|
|
|
|
- Chapter 10: Kconfig configuration files
|
|
|
|
|
|
+10) Kconfig configuration files
|
|
|
|
+-------------------------------
|
|
|
|
|
|
For all of the Kconfig* configuration files throughout the source tree,
|
|
For all of the Kconfig* configuration files throughout the source tree,
|
|
-the indentation is somewhat different. Lines under a "config" definition
|
|
|
|
|
|
+the indentation is somewhat different. Lines under a ``config`` definition
|
|
are indented with one tab, while help text is indented an additional two
|
|
are indented with one tab, while help text is indented an additional two
|
|
-spaces. Example:
|
|
|
|
|
|
+spaces. Example::
|
|
|
|
|
|
-config AUDIT
|
|
|
|
|
|
+ config AUDIT
|
|
bool "Auditing support"
|
|
bool "Auditing support"
|
|
depends on NET
|
|
depends on NET
|
|
help
|
|
help
|
|
@@ -569,9 +641,9 @@ config AUDIT
|
|
auditing without CONFIG_AUDITSYSCALL.
|
|
auditing without CONFIG_AUDITSYSCALL.
|
|
|
|
|
|
Seriously dangerous features (such as write support for certain
|
|
Seriously dangerous features (such as write support for certain
|
|
-filesystems) should advertise this prominently in their prompt string:
|
|
|
|
|
|
+filesystems) should advertise this prominently in their prompt string::
|
|
|
|
|
|
-config ADFS_FS_RW
|
|
|
|
|
|
+ config ADFS_FS_RW
|
|
bool "ADFS write support (DANGEROUS)"
|
|
bool "ADFS write support (DANGEROUS)"
|
|
depends on ADFS_FS
|
|
depends on ADFS_FS
|
|
...
|
|
...
|
|
@@ -580,41 +652,45 @@ For full documentation on the configuration files, see the file
|
|
Documentation/kbuild/kconfig-language.txt.
|
|
Documentation/kbuild/kconfig-language.txt.
|
|
|
|
|
|
|
|
|
|
- Chapter 11: Data structures
|
|
|
|
|
|
+11) Data structures
|
|
|
|
+-------------------
|
|
|
|
|
|
Data structures that have visibility outside the single-threaded
|
|
Data structures that have visibility outside the single-threaded
|
|
environment they are created and destroyed in should always have
|
|
environment they are created and destroyed in should always have
|
|
reference counts. In the kernel, garbage collection doesn't exist (and
|
|
reference counts. In the kernel, garbage collection doesn't exist (and
|
|
outside the kernel garbage collection is slow and inefficient), which
|
|
outside the kernel garbage collection is slow and inefficient), which
|
|
-means that you absolutely _have_ to reference count all your uses.
|
|
|
|
|
|
+means that you absolutely **have** to reference count all your uses.
|
|
|
|
|
|
Reference counting means that you can avoid locking, and allows multiple
|
|
Reference counting means that you can avoid locking, and allows multiple
|
|
users to have access to the data structure in parallel - and not having
|
|
users to have access to the data structure in parallel - and not having
|
|
to worry about the structure suddenly going away from under them just
|
|
to worry about the structure suddenly going away from under them just
|
|
because they slept or did something else for a while.
|
|
because they slept or did something else for a while.
|
|
|
|
|
|
-Note that locking is _not_ a replacement for reference counting.
|
|
|
|
|
|
+Note that locking is **not** a replacement for reference counting.
|
|
Locking is used to keep data structures coherent, while reference
|
|
Locking is used to keep data structures coherent, while reference
|
|
counting is a memory management technique. Usually both are needed, and
|
|
counting is a memory management technique. Usually both are needed, and
|
|
they are not to be confused with each other.
|
|
they are not to be confused with each other.
|
|
|
|
|
|
Many data structures can indeed have two levels of reference counting,
|
|
Many data structures can indeed have two levels of reference counting,
|
|
-when there are users of different "classes". The subclass count counts
|
|
|
|
|
|
+when there are users of different ``classes``. The subclass count counts
|
|
the number of subclass users, and decrements the global count just once
|
|
the number of subclass users, and decrements the global count just once
|
|
when the subclass count goes to zero.
|
|
when the subclass count goes to zero.
|
|
|
|
|
|
-Examples of this kind of "multi-level-reference-counting" can be found in
|
|
|
|
-memory management ("struct mm_struct": mm_users and mm_count), and in
|
|
|
|
-filesystem code ("struct super_block": s_count and s_active).
|
|
|
|
|
|
+Examples of this kind of ``multi-level-reference-counting`` can be found in
|
|
|
|
+memory management (``struct mm_struct``: mm_users and mm_count), and in
|
|
|
|
+filesystem code (``struct super_block``: s_count and s_active).
|
|
|
|
|
|
Remember: if another thread can find your data structure, and you don't
|
|
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.
|
|
have a reference count on it, you almost certainly have a bug.
|
|
|
|
|
|
|
|
|
|
- Chapter 12: Macros, Enums and RTL
|
|
|
|
|
|
+12) Macros, Enums and RTL
|
|
|
|
+-------------------------
|
|
|
|
|
|
Names of macros defining constants and labels in enums are capitalized.
|
|
Names of macros defining constants and labels in enums are capitalized.
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
#define CONSTANT 0x12345
|
|
#define CONSTANT 0x12345
|
|
|
|
|
|
Enums are preferred when defining several related constants.
|
|
Enums are preferred when defining several related constants.
|
|
@@ -626,7 +702,9 @@ Generally, inline functions are preferable to macros resembling functions.
|
|
|
|
|
|
Macros with multiple statements should be enclosed in a do - while block:
|
|
Macros with multiple statements should be enclosed in a do - while block:
|
|
|
|
|
|
- #define macrofun(a, b, c) \
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
|
|
+ #define macrofun(a, b, c) \
|
|
do { \
|
|
do { \
|
|
if (a == 5) \
|
|
if (a == 5) \
|
|
do_this(b, c); \
|
|
do_this(b, c); \
|
|
@@ -636,17 +714,21 @@ Things to avoid when using macros:
|
|
|
|
|
|
1) macros that affect control flow:
|
|
1) macros that affect control flow:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
#define FOO(x) \
|
|
#define FOO(x) \
|
|
do { \
|
|
do { \
|
|
if (blah(x) < 0) \
|
|
if (blah(x) < 0) \
|
|
return -EBUGGERED; \
|
|
return -EBUGGERED; \
|
|
} while (0)
|
|
} while (0)
|
|
|
|
|
|
-is a _very_ bad idea. It looks like a function call but exits the "calling"
|
|
|
|
|
|
+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.
|
|
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:
|
|
2) macros that depend on having a local variable with a magic name:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
#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
|
|
might look like a good thing, but it's confusing as hell when one reads the
|
|
@@ -659,18 +741,22 @@ bite you if somebody e.g. turns FOO into an inline function.
|
|
must enclose the expression in parentheses. Beware of similar issues with
|
|
must enclose the expression in parentheses. Beware of similar issues with
|
|
macros using parameters.
|
|
macros using parameters.
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
#define CONSTANT 0x4000
|
|
#define CONSTANT 0x4000
|
|
#define CONSTEXP (CONSTANT | 3)
|
|
#define CONSTEXP (CONSTANT | 3)
|
|
|
|
|
|
5) namespace collisions when defining local variables in macros resembling
|
|
5) namespace collisions when defining local variables in macros resembling
|
|
functions:
|
|
functions:
|
|
|
|
|
|
-#define FOO(x) \
|
|
|
|
-({ \
|
|
|
|
- typeof(x) ret; \
|
|
|
|
- ret = calc_ret(x); \
|
|
|
|
- (ret); \
|
|
|
|
-})
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
|
|
+ #define FOO(x) \
|
|
|
|
+ ({ \
|
|
|
|
+ typeof(x) ret; \
|
|
|
|
+ ret = calc_ret(x); \
|
|
|
|
+ (ret); \
|
|
|
|
+ })
|
|
|
|
|
|
ret is a common name for a local variable - __foo_ret is less likely
|
|
ret is a common name for a local variable - __foo_ret is less likely
|
|
to collide with an existing variable.
|
|
to collide with an existing variable.
|
|
@@ -679,11 +765,12 @@ The cpp manual deals with macros exhaustively. The gcc internals manual also
|
|
covers RTL which is used frequently with assembly language in the kernel.
|
|
covers RTL which is used frequently with assembly language in the kernel.
|
|
|
|
|
|
|
|
|
|
- Chapter 13: Printing kernel messages
|
|
|
|
|
|
+13) Printing kernel messages
|
|
|
|
+----------------------------
|
|
|
|
|
|
Kernel developers like to be seen as literate. Do mind the spelling
|
|
Kernel developers like to be seen as literate. Do mind the spelling
|
|
of kernel messages to make a good impression. Do not use crippled
|
|
of kernel messages to make a good impression. Do not use crippled
|
|
-words like "dont"; use "do not" or "don't" instead. Make the messages
|
|
|
|
|
|
+words like ``dont``; use ``do not`` or ``don't`` instead. Make the messages
|
|
concise, clear, and unambiguous.
|
|
concise, clear, and unambiguous.
|
|
|
|
|
|
Kernel messages do not have to be terminated with a period.
|
|
Kernel messages do not have to be terminated with a period.
|
|
@@ -713,7 +800,8 @@ already inside a debug-related #ifdef section, printk(KERN_DEBUG ...) can be
|
|
used.
|
|
used.
|
|
|
|
|
|
|
|
|
|
- Chapter 14: Allocating memory
|
|
|
|
|
|
+14) Allocating memory
|
|
|
|
+---------------------
|
|
|
|
|
|
The kernel provides the following general purpose memory allocators:
|
|
The kernel provides the following general purpose memory allocators:
|
|
kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), and
|
|
kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), and
|
|
@@ -722,6 +810,8 @@ about them.
|
|
|
|
|
|
The preferred form for passing a size of a struct is the following:
|
|
The preferred form for passing a size of a struct is the following:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
p = kmalloc(sizeof(*p), ...);
|
|
p = kmalloc(sizeof(*p), ...);
|
|
|
|
|
|
The alternative form where struct name is spelled out hurts readability and
|
|
The alternative form where struct name is spelled out hurts readability and
|
|
@@ -734,20 +824,25 @@ language.
|
|
|
|
|
|
The preferred form for allocating an array is the following:
|
|
The preferred form for allocating an array is the following:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
p = kmalloc_array(n, sizeof(...), ...);
|
|
p = kmalloc_array(n, sizeof(...), ...);
|
|
|
|
|
|
The preferred form for allocating a zeroed array is the following:
|
|
The preferred form for allocating a zeroed array is the following:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
p = kcalloc(n, sizeof(...), ...);
|
|
p = kcalloc(n, sizeof(...), ...);
|
|
|
|
|
|
Both forms check for overflow on the allocation size n * sizeof(...),
|
|
Both forms check for overflow on the allocation size n * sizeof(...),
|
|
and return NULL if that occurred.
|
|
and return NULL if that occurred.
|
|
|
|
|
|
|
|
|
|
- Chapter 15: The inline disease
|
|
|
|
|
|
+15) The inline disease
|
|
|
|
+----------------------
|
|
|
|
|
|
There appears to be a common misperception that gcc has a magic "make me
|
|
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
|
|
|
|
|
|
+faster" speedup option called ``inline``. While the use of inlines can be
|
|
appropriate (for example as a means of replacing macros, see Chapter 12), it
|
|
appropriate (for example as a means of replacing macros, see Chapter 12), it
|
|
very often is not. Abundant use of the inline keyword leads to a much bigger
|
|
very often is not. Abundant use of the inline keyword leads to a much bigger
|
|
kernel, which in turn slows the system as a whole down, due to a bigger
|
|
kernel, which in turn slows the system as a whole down, due to a bigger
|
|
@@ -771,26 +866,27 @@ appears outweighs the potential value of the hint that tells gcc to do
|
|
something it would have done anyway.
|
|
something it would have done anyway.
|
|
|
|
|
|
|
|
|
|
- Chapter 16: Function return values and names
|
|
|
|
|
|
+16) Function return values and names
|
|
|
|
+------------------------------------
|
|
|
|
|
|
Functions can return values of many different kinds, and one of the
|
|
Functions can return values of many different kinds, and one of the
|
|
most common is a value indicating whether the function succeeded or
|
|
most common is a value indicating whether the function succeeded or
|
|
failed. Such a value can be represented as an error-code integer
|
|
failed. Such a value can be represented as an error-code integer
|
|
-(-Exxx = failure, 0 = success) or a "succeeded" boolean (0 = failure,
|
|
|
|
|
|
+(-Exxx = failure, 0 = success) or a ``succeeded`` boolean (0 = failure,
|
|
non-zero = success).
|
|
non-zero = success).
|
|
|
|
|
|
Mixing up these two sorts of representations is a fertile source of
|
|
Mixing up these two sorts of representations is a fertile source of
|
|
difficult-to-find bugs. If the C language included a strong distinction
|
|
difficult-to-find bugs. If the C language included a strong distinction
|
|
between integers and booleans then the compiler would find these mistakes
|
|
between integers and booleans then the compiler would find these mistakes
|
|
for us... but it doesn't. To help prevent such bugs, always follow this
|
|
for us... but it doesn't. To help prevent such bugs, always follow this
|
|
-convention:
|
|
|
|
|
|
+convention::
|
|
|
|
|
|
If the name of a function is an action or an imperative command,
|
|
If the name of a function is an action or an imperative command,
|
|
the function should return an error-code integer. If the name
|
|
the function should return an error-code integer. If the name
|
|
is a predicate, the function should return a "succeeded" boolean.
|
|
is a predicate, the function should return a "succeeded" boolean.
|
|
|
|
|
|
-For example, "add work" is a command, and the add_work() function returns 0
|
|
|
|
-for success or -EBUSY for failure. In the same way, "PCI device present" is
|
|
|
|
|
|
+For example, ``add work`` is a command, and the add_work() function returns 0
|
|
|
|
+for success or -EBUSY for failure. In the same way, ``PCI device present`` is
|
|
a predicate, and the pci_dev_present() function returns 1 if it succeeds in
|
|
a predicate, and the pci_dev_present() function returns 1 if it succeeds in
|
|
finding a matching device or 0 if it doesn't.
|
|
finding a matching device or 0 if it doesn't.
|
|
|
|
|
|
@@ -805,17 +901,22 @@ result. Typical examples would be functions that return pointers; they use
|
|
NULL or the ERR_PTR mechanism to report failure.
|
|
NULL or the ERR_PTR mechanism to report failure.
|
|
|
|
|
|
|
|
|
|
- Chapter 17: Don't re-invent the kernel macros
|
|
|
|
|
|
+17) Don't re-invent the kernel macros
|
|
|
|
+-------------------------------------
|
|
|
|
|
|
The header file include/linux/kernel.h contains a number of macros that
|
|
The header file include/linux/kernel.h contains a number of macros that
|
|
you should use, rather than explicitly coding some variant of them yourself.
|
|
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
|
|
For example, if you need to calculate the length of an array, take advantage
|
|
of the macro
|
|
of the macro
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
#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
|
|
Similarly, if you need to calculate the size of some structure member, use
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
#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
|
|
There are also min() and max() macros that do strict type checking if you
|
|
@@ -823,16 +924,21 @@ need them. Feel free to peruse that header file to see what else is already
|
|
defined that you shouldn't reproduce in your code.
|
|
defined that you shouldn't reproduce in your code.
|
|
|
|
|
|
|
|
|
|
- Chapter 18: Editor modelines and other cruft
|
|
|
|
|
|
+18) Editor modelines and other cruft
|
|
|
|
+------------------------------------
|
|
|
|
|
|
Some editors can interpret configuration information embedded in source files,
|
|
Some editors can interpret configuration information embedded in source files,
|
|
indicated with special markers. For example, emacs interprets lines marked
|
|
indicated with special markers. For example, emacs interprets lines marked
|
|
like this:
|
|
like this:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
-*- mode: c -*-
|
|
-*- mode: c -*-
|
|
|
|
|
|
Or like this:
|
|
Or like this:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
/*
|
|
/*
|
|
Local Variables:
|
|
Local Variables:
|
|
compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c"
|
|
compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c"
|
|
@@ -841,6 +947,8 @@ Or like this:
|
|
|
|
|
|
Vim interprets markers that look like this:
|
|
Vim interprets markers that look like this:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
/* vim:set sw=8 noet */
|
|
/* vim:set sw=8 noet */
|
|
|
|
|
|
Do not include any of these in source files. People have their own personal
|
|
Do not include any of these in source files. People have their own personal
|
|
@@ -850,7 +958,8 @@ own custom mode, or may have some other magic method for making indentation
|
|
work correctly.
|
|
work correctly.
|
|
|
|
|
|
|
|
|
|
- Chapter 19: Inline assembly
|
|
|
|
|
|
+19) Inline assembly
|
|
|
|
+-------------------
|
|
|
|
|
|
In architecture-specific code, you may need to use inline assembly to interface
|
|
In architecture-specific code, you may need to use inline assembly to interface
|
|
with CPU or platform functionality. Don't hesitate to do so when necessary.
|
|
with CPU or platform functionality. Don't hesitate to do so when necessary.
|
|
@@ -863,7 +972,7 @@ that inline assembly can use C parameters.
|
|
|
|
|
|
Large, non-trivial assembly functions should go in .S files, with corresponding
|
|
Large, non-trivial assembly functions should go in .S files, with corresponding
|
|
C prototypes defined in C header files. The C prototypes for assembly
|
|
C prototypes defined in C header files. The C prototypes for assembly
|
|
-functions should use "asmlinkage".
|
|
|
|
|
|
+functions should use ``asmlinkage``.
|
|
|
|
|
|
You may need to mark your asm statement as volatile, to prevent GCC from
|
|
You may need to mark your asm statement as volatile, to prevent GCC from
|
|
removing it if GCC doesn't notice any side effects. You don't always need to
|
|
removing it if GCC doesn't notice any side effects. You don't always need to
|
|
@@ -874,12 +983,15 @@ instructions, put each instruction on a separate line in a separate quoted
|
|
string, and end each string except the last with \n\t to properly indent the
|
|
string, and end each string except the last with \n\t to properly indent the
|
|
next instruction in the assembly output:
|
|
next instruction in the assembly output:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
asm ("magic %reg1, #42\n\t"
|
|
asm ("magic %reg1, #42\n\t"
|
|
"more_magic %reg2, %reg3"
|
|
"more_magic %reg2, %reg3"
|
|
: /* outputs */ : /* inputs */ : /* clobbers */);
|
|
: /* outputs */ : /* inputs */ : /* clobbers */);
|
|
|
|
|
|
|
|
|
|
- Chapter 20: Conditional Compilation
|
|
|
|
|
|
+20) Conditional Compilation
|
|
|
|
+---------------------------
|
|
|
|
|
|
Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .c
|
|
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,
|
|
files; doing so makes code harder to read and logic harder to follow. Instead,
|
|
@@ -903,6 +1015,8 @@ unused, delete it.)
|
|
Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
|
|
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:
|
|
symbol into a C boolean expression, and use it in a normal C conditional:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
if (IS_ENABLED(CONFIG_SOMETHING)) {
|
|
if (IS_ENABLED(CONFIG_SOMETHING)) {
|
|
...
|
|
...
|
|
}
|
|
}
|
|
@@ -918,12 +1032,15 @@ 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
|
|
place a comment after the #endif on the same line, noting the conditional
|
|
expression used. For instance:
|
|
expression used. For instance:
|
|
|
|
|
|
|
|
+.. code-block:: c
|
|
|
|
+
|
|
#ifdef CONFIG_SOMETHING
|
|
#ifdef CONFIG_SOMETHING
|
|
...
|
|
...
|
|
#endif /* CONFIG_SOMETHING */
|
|
#endif /* CONFIG_SOMETHING */
|
|
|
|
|
|
|
|
|
|
- Appendix I: References
|
|
|
|
|
|
+Appendix I) References
|
|
|
|
+----------------------
|
|
|
|
|
|
The C Programming Language, Second Edition
|
|
The C Programming Language, Second Edition
|
|
by Brian W. Kernighan and Dennis M. Ritchie.
|
|
by Brian W. Kernighan and Dennis M. Ritchie.
|
|
@@ -943,4 +1060,3 @@ language C, URL: http://www.open-std.org/JTC1/SC22/WG14/
|
|
|
|
|
|
Kernel CodingStyle, by greg@kroah.com at OLS 2002:
|
|
Kernel CodingStyle, by greg@kroah.com at OLS 2002:
|
|
http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/
|
|
http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/
|
|
-
|
|
|