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authorDaniel P. Berrangé <berrange@redhat.com>2019-08-23 17:09:24 +0100
committerDaniel P. Berrangé <berrange@redhat.com>2019-09-05 14:27:06 +0100
commit336a7451e8803c21a2da6e7d1eca8cfb8e8b219a (patch)
tree62b2745dc8a2549652a4aa92c157f0e1b85b8411 /CODING_STYLE
parent500efcfcf0fe2e0dae1d25637a13435ce7b6e421 (diff)
docs: convert README, CODING_STYLE and HACKING to RST syntax
Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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-QEMU Coding Style
-=================
-
-Please use the script checkpatch.pl in the scripts directory to check
-patches before submitting.
-
-1. Whitespace
-
-Of course, the most important aspect in any coding style is whitespace.
-Crusty old coders who have trouble spotting the glasses on their noses
-can tell the difference between a tab and eight spaces from a distance
-of approximately fifteen parsecs. Many a flamewar has been fought and
-lost on this issue.
-
-QEMU indents are four spaces. Tabs are never used, except in Makefiles
-where they have been irreversibly coded into the syntax.
-Spaces of course are superior to tabs because:
-
- - You have just one way to specify whitespace, not two. Ambiguity breeds
- mistakes.
- - The confusion surrounding 'use tabs to indent, spaces to justify' is gone.
- - Tab indents push your code to the right, making your screen seriously
- unbalanced.
- - Tabs will be rendered incorrectly on editors who are misconfigured not
- to use tab stops of eight positions.
- - Tabs are rendered badly in patches, causing off-by-one errors in almost
- every line.
- - It is the QEMU coding style.
-
-Do not leave whitespace dangling off the ends of lines.
-
-1.1 Multiline Indent
-
-There are several places where indent is necessary:
-
- - if/else
- - while/for
- - function definition & call
-
-When breaking up a long line to fit within line width, we need a proper indent
-for the following lines.
-
-In case of if/else, while/for, align the secondary lines just after the
-opening parenthesis of the first.
-
-For example:
-
- if (a == 1 &&
- b == 2) {
-
- while (a == 1 &&
- b == 2) {
-
-In case of function, there are several variants:
-
- * 4 spaces indent from the beginning
- * align the secondary lines just after the opening parenthesis of the
- first
-
-For example:
-
- do_something(x, y,
- z);
-
- do_something(x, y,
- z);
-
- do_something(x, do_another(y,
- z));
-
-2. Line width
-
-Lines should be 80 characters; try not to make them longer.
-
-Sometimes it is hard to do, especially when dealing with QEMU subsystems
-that use long function or symbol names. Even in that case, do not make
-lines much longer than 80 characters.
-
-Rationale:
- - Some people like to tile their 24" screens with a 6x4 matrix of 80x24
- xterms and use vi in all of them. The best way to punish them is to
- let them keep doing it.
- - Code and especially patches is much more readable if limited to a sane
- line length. Eighty is traditional.
- - The four-space indentation makes the most common excuse ("But look
- at all that white space on the left!") moot.
- - It is the QEMU coding style.
-
-3. Naming
-
-Variables are lower_case_with_underscores; easy to type and read. Structured
-type names are in CamelCase; harder to type but standing out. Enum type
-names and function type names should also be in CamelCase. Scalar type
-names are lower_case_with_underscores_ending_with_a_t, like the POSIX
-uint64_t and family. Note that this last convention contradicts POSIX
-and is therefore likely to be changed.
-
-When wrapping standard library functions, use the prefix qemu_ to alert
-readers that they are seeing a wrapped version; otherwise avoid this prefix.
-
-4. Block structure
-
-Every indented statement is braced; even if the block contains just one
-statement. The opening brace is on the line that contains the control
-flow statement that introduces the new block; the closing brace is on the
-same line as the else keyword, or on a line by itself if there is no else
-keyword. Example:
-
- if (a == 5) {
- printf("a was 5.\n");
- } else if (a == 6) {
- printf("a was 6.\n");
- } else {
- printf("a was something else entirely.\n");
- }
-
-Note that 'else if' is considered a single statement; otherwise a long if/
-else if/else if/.../else sequence would need an indent for every else
-statement.
-
-An exception is the opening brace for a function; for reasons of tradition
-and clarity it comes on a line by itself:
-
- void a_function(void)
- {
- do_something();
- }
-
-Rationale: a consistent (except for functions...) bracing style reduces
-ambiguity and avoids needless churn when lines are added or removed.
-Furthermore, it is the QEMU coding style.
-
-5. Declarations
-
-Mixed declarations (interleaving statements and declarations within
-blocks) are generally not allowed; declarations should be at the beginning
-of blocks.
-
-Every now and then, an exception is made for declarations inside a
-#ifdef or #ifndef block: if the code looks nicer, such declarations can
-be placed at the top of the block even if there are statements above.
-On the other hand, however, it's often best to move that #ifdef/#ifndef
-block to a separate function altogether.
-
-6. Conditional statements
-
-When comparing a variable for (in)equality with a constant, list the
-constant on the right, as in:
-
- if (a == 1) {
- /* Reads like: "If a equals 1" */
- do_something();
- }
-
-Rationale: Yoda conditions (as in 'if (1 == a)') are awkward to read.
-Besides, good compilers already warn users when '==' is mis-typed as '=',
-even when the constant is on the right.
-
-7. Comment style
-
-We use traditional C-style /* */ comments and avoid // comments.
-
-Rationale: The // form is valid in C99, so this is purely a matter of
-consistency of style. The checkpatch script will warn you about this.
-
-Multiline comment blocks should have a row of stars on the left,
-and the initial /* and terminating */ both on their own lines:
- /*
- * like
- * this
- */
-This is the same format required by the Linux kernel coding style.
-
-(Some of the existing comments in the codebase use the GNU Coding
-Standards form which does not have stars on the left, or other
-variations; avoid these when writing new comments, but don't worry
-about converting to the preferred form unless you're editing that
-comment anyway.)
-
-Rationale: Consistency, and ease of visually picking out a multiline
-comment from the surrounding code.
-
-8. trace-events style
-
-8.1 0x prefix
-
-In trace-events files, use a '0x' prefix to specify hex numbers, as in:
-
-some_trace(unsigned x, uint64_t y) "x 0x%x y 0x" PRIx64
-
-An exception is made for groups of numbers that are hexadecimal by
-convention and separated by the symbols '.', '/', ':', or ' ' (such as
-PCI bus id):
-
-another_trace(int cssid, int ssid, int dev_num) "bus id: %x.%x.%04x"
-
-However, you can use '0x' for such groups if you want. Anyway, be sure that
-it is obvious that numbers are in hex, ex.:
-
-data_dump(uint8_t c1, uint8_t c2, uint8_t c3) "bytes (in hex): %02x %02x %02x"
-
-Rationale: hex numbers are hard to read in logs when there is no 0x prefix,
-especially when (occasionally) the representation doesn't contain any letters
-and especially in one line with other decimal numbers. Number groups are allowed
-to not use '0x' because for some things notations like %x.%x.%x are used not
-only in Qemu. Also dumping raw data bytes with '0x' is less readable.
-
-8.2 '#' printf flag
-
-Do not use printf flag '#', like '%#x'.
-
-Rationale: there are two ways to add a '0x' prefix to printed number: '0x%...'
-and '%#...'. For consistency the only one way should be used. Arguments for
-'0x%' are:
- - it is more popular
- - '%#' omits the 0x for the value 0 which makes output inconsistent