Re: [Qemu-devel] [PATCH 4/3] checkpatch: Enforce proper do/while (0) style

[Eric Blake <eblake@redhat.com>]

On 11/30/2017 08:01 AM, Eric Blake wrote:
> while (0) is only idiomatic in a macro definition, where the caller
> will be supplying the trailing ';'.  Warn if the macro has a duplicate.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>   scripts/checkpatch.pl | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 34df753571..acb66bff34 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -1622,6 +1622,11 @@ sub process {
>   			}
>   		}
> 
> +# 'while (0);' is odd; only macros should use while (0), without trailing ;
> +		if ($line =~ /while\s*\(0\);/) {

Should this also check for uses of 'while (false);' ?

Interestingly enough, we have an instance of 'do/while (false);' in 
tests/vhost-user-bridge.c that is NOT in a macro, but is used for the 
convenience of being able to 'break;' out early rather than using a 
goto.  Similarly for chardev/char-serial.c using 'while (0);' outside of 
a macro.  Those may be worth rewriting to use goto as separate patches 
if we want to restrict ALL use of 'while \((0|false)\);'

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org