Re: [Qemu-devel] [PATCH] Document Qemu coding style

[malc]

On Mon, 30 Mar 2009, Avi Kivity wrote:

> With the help of some Limoncino I noted several aspects of the Qemu coding

QEMU

> style, particularly where it differs from the Linux coding style as many
> contributors work on both projects.
> 
> Signed-off-by: Avi Kivity <address@hidden>
> ---
>  CODING_STYLE |   77 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 77 insertions(+), 0 deletions(-)
>  create mode 100644 CODING_STYLE
> 
> diff --git a/CODING_STYLE b/CODING_STYLE
> new file mode 100644
> index 0000000..54fdeff
> --- /dev/null
> +++ b/CODING_STYLE
> @@ -0,0 +1,77 @@
> +Qemu Coding Style
> +=================
> +
> +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 by some moron.
> +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.
> +
> +2. Line width
> +
> +Lines are 80 characters wide plus some slop.  Try to fit your code into
> +eighty characters, but if it makes a snippet particularly ugly, allow
> +yourself some slack.  Don't overdo it though.
> +
> +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.  Scalar type
> +names are lower_case_with_underscores_ending_with_a_t, like the Posix
> +uint64_t and family.

POSIX

anything_than_ends_with_a_t is reserved
(http://www.opengroup.org/pubs/online/7908799/xns/namespace.html)

QEMU does use quite a few of types ending with a _t and this should
be fixed.

> +
> +Typedefs are used to eliminate the redundant 'struct' keyword.  It is the
> +Qemu coding style.
> +
> +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");
> +    }
> +
> +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.
> 

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