On Tuesday 2015-04-07 02:38, Alexander Duyck wrote:
>On 04/06/2015 11:05 AM, Arturo Borrero Gonzalez wrote:
>> linux_list.h:381:59: warning: right-hand operand of comma expression has no effect [-Wunused-value]
>> for (pos = list_entry((head)->next, typeof(*pos), member), \
>> ^
>> libiptc.c:552:2: note: in expansion of macro 'list_for_each_entry'
>> list_for_each_entry(c, &h->chains, list) {
>> ^
>>
>> [ Patch copied from one similar of Patrick McHardy on libnftnl ]
>>
>> Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@xxxxxxxxx>
>> ---
>> libiptc/linux_list.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/libiptc/linux_list.h b/libiptc/linux_list.h
>> index abdcf88..559e33c 100644
>> --- a/libiptc/linux_list.h
>> +++ b/libiptc/linux_list.h
>> @@ -27,7 +27,7 @@
>> 1; \
>> })
>>
>> -#define prefetch(x) 1
>> +#define prefetch(x) ((void)0)
>>
>> /* empty define to make this work in userspace -HW */
>> #define smp_wmb()
>>
>
>Why not just use "do {} while (0)"? I know that is what is used in the
>kernel for functions that don't do anything.
I may be getting the terms wrong, but:
do{}while(0) is not an expression, it is a (block) control statement.
In particular, do{}while(0) won't evaluate to an rvalue.
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