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

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Tue, 11 May 2021 17:38:04 +0200
David Hildenbrand <david@redhat.com> wrote:

> 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.

as I said, I do not have a strong opinion either way :)