Re: [kvm-unit-tests PATCH v4 9/9] s390x: sclp: Add CPU entry offset comment

[Thomas Huth <thuth@redhat.com>]

On 13/01/2021 11.25, David Hildenbrand wrote:
> On 12.01.21 14:20, Janosch Frank wrote:
>> Let's make it clear that there is something at the end of the
>> struct. The exact offset is reported by the cpu_offset member.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>   lib/s390x/sclp.h | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/s390x/sclp.h b/lib/s390x/sclp.h
>> index dccbaa8..395895f 100644
>> --- a/lib/s390x/sclp.h
>> +++ b/lib/s390x/sclp.h
>> @@ -134,7 +134,10 @@ typedef struct ReadInfo {
>>   	uint8_t reserved7[134 - 128];
>>   	uint8_t byte_134_diag318 : 1;
>>   	uint8_t : 7;
>> -	struct CPUEntry entries[0];
>> +	/*
>> +	 * The cpu entries follow, they start at the offset specified
>> +	 * in offset_cpu.
>> +	 */
> 
> I mean, that's just best practice. At least when I spot "[0];" and the
> end of a struct, I know what's happening.
> 
> No strong opinion about the comment, I wouldn't need it to understand it.

The problem is that the "CPUEntry" entries either might be at this location, 
or later, so the entries[0] can be misleading. You always have to go via the 
offset_cpu field to find the right location.

  Thomas