Hi! I've been tasked with edicating some new hires on linux kernel coding style. While we have Documentation/CodingStyle, it skips detail that is supposed to be learned by example.
Since I've been burned by this a couple of times myself till I learned, I've put together a short list of rules complementing Documentation/CodingStyle. This list is attached, below. Please cc me directly with comments, if any. Thanks, MST --- kernel guide to space AKA a boring list of rules http://www.mellanox.com/mst/boring.txt This text deals mostly with whitespace issues, hence the name. Whitespace -- In computer science, a whitespace (or a whitespace character) is any character which does not display itself but does take up space. From Wikipedia, the free encyclopedia. 1. Read Documentation/CodingStyle. Yes, it applies to you. When working on a specific driver/subsystem, try to follow the style of the surrounding codebase. 2. The last character on a line is never a whitespace Get a decent editor and don't leave whitespace at the end of lines. Documentation/CodingStyle Whitespace issues: 3. Space rules for C 3a. Binary operators + - / * % == != > < >= <= && || & | ^ << >> = *= /= %= += -= <<= >>= &= ^= |= spaces around the operator a + b 3b. Unary operators ! ~ + - * & no space between operator and operand *a 3c. * in types Leave space between name and * in types. Multiple * dont need additional space between them. struct foo **bar; 3d. Conditional ?: spaces around both ? and : a ? b : c 3e. sizeof space after the operator sizeof a 3f. Braces etc () [] -> . no space around any of these (but see 3h) foo(bar) 3g. Comma , space after comma, no space before comma foo, bar 3h. Semicolon ; no space before semicolon foo; 3i. if/else/do/while/for/switch space between if/else/do/while and following/preceeding statements/expressions, if any: if (a) { } else { } do { } while (b); 3j. Labels goto and case labels should have a line of their own (possibly with a comment). No space before colon in labels. int foobar() { ... foolabel: /* short comment */ foo(); } 4. Indentation rules for C Use tabs, not spaces, for indentation. Tabs should be 8 characters wide. 4a. Labels case labels should be indented same as the switch statement. statements occurring after a case label are indented by one level. switch (foo) { case foo: bar(); default: break; } 4b. Global scope Functions, type definitions/declarations, defines, global variables etc are global scope. Start them at the first character in a line (indent level 0). static struct foo *foo_bar(struct foo *first, struct bar *second, struct foobar* thirsd); 4c. Breaking long lines Descendants are always substantially shorter than the parent and are placed substantially to the right. Documentation/CodingStyle Descendant must be indented at least to the level of the innermost compound expression in the parent. All descendants at the same level are indented the same. if (foobar(.................................) + barbar * foobar(bar + foo * oof)) { } 5. Blank lines One blank line between functions. void foo() { } /* comment */ void bar() { } No more than one blank line in a row. Last (or first) line in a file is never blank. Non-whitespace issues: 6. One-line statement does not need a {} block, so dont put it into one if (foo) bar; 7. Comments Dont use C99 // comments. 8. Return codes Functions that return success/failure status, should use 0 for success, a negative value for failure. Error codes are in linux/errno.h . if (do_something()) { handle_error(); return -EINVAL; } Functions that test a condition return 1 if condition is satisfied, 0 if its not. if (is_condition()) condition_true(); 9. Data types Standard linux types are in linux/types.h . See also Linux Device Drivers, Third Edition, Chapter 11: Data Types in the Kernel. http://lwn.net/images/pdf/LDD3/ 9a. Integer types int is the default integer type. Use unsigned type if you perform bit operations (<<,>>,&,|,~). Use unsigned long if you have to fit a pointer into integer. long long is at least 64 bit wide on all platforms. char is for ASCII characters and strings. Use u8,u16,u32,u64 if you need an integer of a specific size. 9b. typedef Using typedefs to hide the data type is generally discouraged. typedefs to function types are ok, since these can get very long. typedef struct foo *(foo_bar_handler)(struct foo *first, struct bar *second, struct foobar* thirsd); Editor configuration: 9. The following is helpful with VIM set cinoptions=(0:0 Michael S. Tsirkin -- MST - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
