Re: [Qemu-devel] [PATCH 3/3] maint: Fix macros with broken 'do/while(0); ' usage

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Eric Blake (eblake@redhat.com) wrote:
> The point of writing a macro embedded in a 'do { ... } while (0)'
> loop is so that the macro can be used as a drop-in statement with
> the caller supplying the trailing ';'.  Although our coding style
> frowns on brace-less 'if':
>   if (cond)
>     statement;
>   else
>     something else;
> the use of do/while (0) in a macro is absolutely essential for the
> purpose of avoiding a syntax error on the 'else' - but it only works
> if there is no trailing ';' in the macro (as the ';' in the code
> calling the macro would then be a second statement and cause the
> 'else' to not pair to the 'if').
> 
> Many of the places touched in this code are examples of the ugly
> bit-rotting debug print statements; cleaning those up is left as
> a bite-sized task for another day.
> 
> Found mechanically via: $ git grep -B1 'while (0);' | grep -A1 \\\\
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---

> diff --git a/migration/rdma.c b/migration/rdma.c
> index ca56594328..9d5a424011 100644
> --- a/migration/rdma.c
> +++ b/migration/rdma.c
> @@ -88,7 +88,7 @@ static uint32_t known_capabilities = RDMA_CAPABILITY_PIN_ALL;
>              } \
>              return rdma->error_state; \
>          } \
> -    } while (0);
> +    } while (0)

Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK