56bef8511a
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
119 lines
4.3 KiB
Plaintext
119 lines
4.3 KiB
Plaintext
QEMU Coding Style
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=================
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Please use the script checkpatch.pl in the scripts directory to check
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patches before submitting.
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1. Whitespace
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Of course, the most important aspect in any coding style is whitespace.
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Crusty old coders who have trouble spotting the glasses on their noses
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can tell the difference between a tab and eight spaces from a distance
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of approximately fifteen parsecs. Many a flamewar has been fought and
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lost on this issue.
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QEMU indents are four spaces. Tabs are never used, except in Makefiles
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where they have been irreversibly coded into the syntax.
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Spaces of course are superior to tabs because:
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- You have just one way to specify whitespace, not two. Ambiguity breeds
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mistakes.
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- The confusion surrounding 'use tabs to indent, spaces to justify' is gone.
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- Tab indents push your code to the right, making your screen seriously
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unbalanced.
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- Tabs will be rendered incorrectly on editors who are misconfigured not
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to use tab stops of eight positions.
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- Tabs are rendered badly in patches, causing off-by-one errors in almost
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every line.
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- It is the QEMU coding style.
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Do not leave whitespace dangling off the ends of lines.
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2. Line width
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Lines should be 80 characters; try not to make them longer.
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Sometimes it is hard to do, especially when dealing with QEMU subsystems
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that use long function or symbol names. Even in that case, do not make
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lines much longer than 80 characters.
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Rationale:
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- Some people like to tile their 24" screens with a 6x4 matrix of 80x24
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xterms and use vi in all of them. The best way to punish them is to
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let them keep doing it.
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- Code and especially patches is much more readable if limited to a sane
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line length. Eighty is traditional.
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- The four-space indentation makes the most common excuse ("But look
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at all that white space on the left!") moot.
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- It is the QEMU coding style.
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3. Naming
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Variables are lower_case_with_underscores; easy to type and read. Structured
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type names are in CamelCase; harder to type but standing out. Enum type
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names and function type names should also be in CamelCase. Scalar type
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names are lower_case_with_underscores_ending_with_a_t, like the POSIX
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uint64_t and family. Note that this last convention contradicts POSIX
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and is therefore likely to be changed.
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When wrapping standard library functions, use the prefix qemu_ to alert
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readers that they are seeing a wrapped version; otherwise avoid this prefix.
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4. Block structure
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Every indented statement is braced; even if the block contains just one
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statement. The opening brace is on the line that contains the control
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flow statement that introduces the new block; the closing brace is on the
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same line as the else keyword, or on a line by itself if there is no else
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keyword. Example:
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if (a == 5) {
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printf("a was 5.\n");
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} else if (a == 6) {
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printf("a was 6.\n");
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} else {
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printf("a was something else entirely.\n");
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}
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Note that 'else if' is considered a single statement; otherwise a long if/
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else if/else if/.../else sequence would need an indent for every else
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statement.
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An exception is the opening brace for a function; for reasons of tradition
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and clarity it comes on a line by itself:
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void a_function(void)
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{
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do_something();
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}
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Rationale: a consistent (except for functions...) bracing style reduces
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ambiguity and avoids needless churn when lines are added or removed.
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Furthermore, it is the QEMU coding style.
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5. Declarations
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Mixed declarations (interleaving statements and declarations within
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blocks) are generally not allowed; declarations should be at the beginning
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of blocks.
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Every now and then, an exception is made for declarations inside a
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#ifdef or #ifndef block: if the code looks nicer, such declarations can
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be placed at the top of the block even if there are statements above.
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On the other hand, however, it's often best to move that #ifdef/#ifndef
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block to a separate function altogether.
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6. Conditional statements
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When comparing a variable for (in)equality with a constant, list the
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constant on the right, as in:
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if (a == 1) {
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/* Reads like: "If a equals 1" */
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do_something();
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}
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Rationale: Yoda conditions (as in 'if (1 == a)') are awkward to read.
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Besides, good compilers already warn users when '==' is mis-typed as '=',
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even when the constant is on the right.
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