Re: [kvm-unit-tests PATCH 2/4] lib: s390x: sclp: Extend feature probing

[David Hildenbrand <david@redhat.com>]

On 11.05.21 16:41, Claudio Imbrenda wrote:
> On Tue, 11 May 2021 13:43:36 +0200
> David Hildenbrand <david@redhat.com> wrote:
> 
>> On 10.05.21 17:00, Janosch Frank wrote:
>>> Lets grab more of the feature bits from SCLP read info so we can use
>>> them in the cpumodel tests.
>>>
>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
>>> ---
>>>    lib/s390x/sclp.c | 20 ++++++++++++++++++++
>>>    lib/s390x/sclp.h | 38 +++++++++++++++++++++++++++++++++++---
>>>    2 files changed, 55 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
>>> index f11c2035..f25cfdb2 100644
>>> --- a/lib/s390x/sclp.c
>>> +++ b/lib/s390x/sclp.c
>>> @@ -129,6 +129,13 @@ CPUEntry *sclp_get_cpu_entries(void)
>>>    	return (CPUEntry *)(_read_info + read_info->offset_cpu);
>>>    }
>>>    
>>> +static bool sclp_feat_check(int byte, int mask)
>>> +{
>>> +	uint8_t *rib = (uint8_t *)read_info;
>>> +
>>> +	return !!(rib[byte] & mask);
>>> +}
>>
>> Instead of a mask, I'd just check for bit (offset) numbers within the
>> byte.
>>
>> static bool sclp_feat_check(int byte, int bit)
>> {
>> 	uint8_t *rib = (uint8_t *)read_info;
>>
>> 	return !!(rib[byte] & (0x80 >> bit));
>> }
> 
> using a mask might be useful to check multiple facilities at the same
> time, but in that case the check should be

IMHO checking with a mask here multiple facilities will be very error 
prone either way ... and we only have a single byte to check for.


-- 
Thanks,

David / dhildenb