benefit of warning you when you're nesting your functions too deep.
Heed that warning.
+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.:
+
+ switch (suffix) {
+ case 'G':
+ case 'g':
+ mem <<= 30;
+ break;
+ case 'M':
+ case 'm':
+ mem <<= 20;
+ break;
+ case 'K':
+ case 'k':
+ mem <<= 10;
+ /* fall through */
+ default:
+ break;
+ }
+
+
Don't put multiple statements on a single line unless you have
something to hide:
if (condition) do_this;
do_something_everytime;
+Don't put multiple assignments on a single line either. Kernel coding style
+is super simple. Avoid tricky expressions.
+
Outside of comments, documentation and except in Kconfig, spaces are never
used for indentation, and the above example is deliberately broken.
next_statement;
}
- Chapter 3: Placing Braces
+ Chapter 3: Placing Braces and Spaces
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
we do y
}
+This applies to all non-function statement blocks (if, switch, for,
+while, do). E.g.:
+
+ switch (action) {
+ case KOBJ_ADD:
+ return "add";
+ case KOBJ_REMOVE:
+ return "remove";
+ case KOBJ_CHANGE:
+ return "change";
+ default:
+ return NULL;
+ }
+
However, there is one special case, namely functions: they have the
opening brace at the beginning of the next line, thus:
25-line terminal screens here), you have more empty lines to put
comments on.
+Do not unnecessarily use braces where a single statement will do.
+
+if (condition)
+ action();
+
+This does not apply if one branch of a conditional statement is a single
+statement. Use braces in both branches.
+
+if (condition) {
+ do_this();
+ do_that();
+} else {
+ otherwise();
+}
+
+ 3.1: Spaces
+
+Linux kernel style for use of spaces depends (mostly) on
+function-versus-keyword usage. Use a space after (most) keywords. The
+notable exceptions are sizeof, typeof, alignof, and __attribute__, which look
+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).
+
+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
+*bad*:
+
+ s = sizeof( struct file );
+
+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
+adjacent to the type name. Examples:
+
+ char *linux_banner;
+ unsigned long long memparse(char *ptr, char **retptr);
+ char *match_strdup(substring_t *s);
+
+Use one space around (on each side of) most binary and ternary operators,
+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.
+
Chapter 4: Naming
If you are afraid to mix up your local variable names, you have another
problem, which is called the function-growth-hormone-imbalance syndrome.
-See next chapter.
+See chapter 6 (Functions).
Chapter 5: Typedefs
and it gets confused. You know you're brilliant, but maybe you'd like
to understand what you did 2 weeks from now.
+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);
+
+In function prototypes, include parameter names with their data types.
+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.
+
Chapter 7: Centralized exiting of functions
Generally, you want your comments to tell WHAT your code does, not HOW.
Also, try to avoid putting comments inside a function body: if the
function is so complex that you need to separately comment parts of it,
-you should probably go back to chapter 5 for a while. You can make
+you should probably go back to chapter 6 for a while. You can make
small comments to note or warn about something particularly clever (or
ugly), but try to avoid excess. Instead, put the comments at the head
of the function, telling people what it does, and possibly WHY it does
it.
-When commenting the kernel API functions, please use the kerneldoc format.
+When commenting the kernel API functions, please use the kernel-doc format.
See the files Documentation/kernel-doc-nano-HOWTO.txt and scripts/kernel-doc
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:
+
+ /*
+ * This is the preferred style for multi-line
+ * comments in the Linux kernel source code.
+ * Please use it consistently.
+ *
+ * Description: A column of asterisks on the left side,
+ * with beginning and ending almost-blank lines.
+ */
+
+It's also important to comment data, whether they are basic types or derived
+types. To this end, use just one data declaration per line (no commas for
+multiple data declarations). This leaves you room for a small comment on each
+item, explaining its use.
+
+
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
remember: "indent" is not a fix for bad programming.
- Chapter 10: Configuration-files
-
-For configuration options (arch/xxx/Kconfig, and all the Kconfig files),
-somewhat different indentation is used.
+ Chapter 10: Kconfig configuration files
-Help text is indented with 2 spaces.
+For all of the Kconfig* configuration files throughout the source tree,
+the indentation is somewhat different. Lines under a "config" definition
+are indented with one tab, while help text is indented an additional two
+spaces. Example:
-if CONFIG_EXPERIMENTAL
- tristate CONFIG_BOOM
- default n
- help
- Apply nitroglycerine inside the keyboard (DANGEROUS)
- bool CONFIG_CHEER
- depends on CONFIG_BOOM
- default y
+config AUDIT
+ bool "Auditing support"
+ depends on NET
help
- Output nice messages when you explode
-endif
+ Enable auditing infrastructure that can be used with another
+ kernel subsystem, such as SELinux (which requires this for
+ logging of avc messages output). Does not do system-call
+ auditing without CONFIG_AUDITSYSCALL.
-Generally, CONFIG_EXPERIMENTAL should surround all options not considered
-stable. All options that are known to trash data (experimental write-
-support for file-systems, for instance) should be denoted (DANGEROUS), other
-experimental options should be denoted (EXPERIMENTAL).
+Features that might still be considered unstable should be defined as
+dependent on "EXPERIMENTAL":
+
+config SLUB
+ depends on EXPERIMENTAL && !ARCH_USES_SLAB_PAGE_STRUCT
+ bool "SLUB (Unqueued Allocator)"
+ ...
+
+while seriously dangerous features (such as write support for certain
+filesystems) should advertise this prominently in their prompt string:
+
+config ADFS_FS_RW
+ bool "ADFS write support (DANGEROUS)"
+ depends on ADFS_FS
+ ...
+
+For full documentation on the configuration files, see the file
+Documentation/kbuild/kconfig-language.txt.
Chapter 11: Data structures
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
-appropriate (for example as a means of replacing macros, see Chapter 11), 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
kernel, which in turn slows the system as a whole down, due to a bigger
icache footprint for the CPU and simply because there is less memory
something it would have done anyway.
+ Chapter 16: Function return values and names
+
+Functions can return values of many different kinds, and one of the
+most common is a value indicating whether the function succeeded or
+failed. Such a value can be represented as an error-code integer
+(-Exxx = failure, 0 = success) or a "succeeded" boolean (0 = failure,
+non-zero = success).
+
+Mixing up these two sorts of representations is a fertile source of
+difficult-to-find bugs. If the C language included a strong distinction
+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
+convention:
+
+ If the name of a function is an action or an imperative command,
+ the function should return an error-code integer. If the name
+ 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
+a predicate, and the pci_dev_present() function returns 1 if it succeeds in
+finding a matching device or 0 if it doesn't.
+
+All EXPORTed functions must respect this convention, and so should all
+public functions. Private (static) functions need not, but it is
+recommended that they do.
+
+Functions whose return value is the actual result of a computation, rather
+than an indication of whether the computation succeeded, are not subject to
+this rule. Generally they indicate failure by returning some out-of-range
+result. Typical examples would be functions that return pointers; they use
+NULL or the ERR_PTR mechanism to report failure.
+
+
+ Chapter 17: Don't re-invent the kernel macros
+
+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.
+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]))
+
+Similarly, if you need to calculate the size of some structure member, use
+
+ #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
+defined that you shouldn't reproduce in your code.
+
+
Appendix I: References
http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/
--
-Last updated on 30 April 2006.
+Last updated on 2006-December-06.
git.samba.org / sfrench / cifs-2.6.git / blobdiff