Archipelago » qemu

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 have 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.

2. Line width

Lines are 80 characters; not longer.

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.

 - 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.