Re: [RFC PATCH 1/2] KVM: selftests: Add a macro to get string of vm_mem_backing_src_type

[wangyanan (Y)]

Hi Sean,

On 2021/2/9 1:43, Sean Christopherson wrote:
> On Mon, Feb 08, 2021, Yanan Wang wrote:
> > Add a macro to get string of the backing source memory type, so that
> > application can add choices for source types in the help() function,
> > and users can specify which type to use for testing.
> >
> > Signed-off-by: Yanan Wang <wangyanan55@xxxxxxxxxx>
> > ---
> >   tools/testing/selftests/kvm/include/kvm_util.h | 3 +++
> >   tools/testing/selftests/kvm/lib/kvm_util.c     | 8 ++++++++
> >   2 files changed, 11 insertions(+)
> >
> > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> > index 5cbb861525ed..f5fc29dc9ee6 100644
> > --- a/tools/testing/selftests/kvm/include/kvm_util.h
> > +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> > @@ -69,7 +69,9 @@ enum vm_guest_mode {
> >   #define PTES_PER_MIN_PAGE	ptes_per_page(MIN_PAGE_SIZE)
> >   
> >   #define vm_guest_mode_string(m) vm_guest_mode_string[m]
> > +#define vm_mem_backing_src_type_string(s) vm_mem_backing_src_type_string[s]
> Oof, I see this is just following vm_guest_mode_string.  IMO, defining the
> string to look like a function is unnecessary and rather mean.
>
> >   extern const char * const vm_guest_mode_string[];
> > +extern const char * const vm_mem_backing_src_type_string[];
> >   
> >   struct vm_guest_mode_params {
> >   	unsigned int pa_bits;
> > @@ -83,6 +85,7 @@ enum vm_mem_backing_src_type {
> >   	VM_MEM_SRC_ANONYMOUS,
> >   	VM_MEM_SRC_ANONYMOUS_THP,
> >   	VM_MEM_SRC_ANONYMOUS_HUGETLB,
> > +	NUM_VM_BACKING_SRC_TYPES,
> >   };
> >   
> >   int kvm_check_cap(long cap);
> > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> > index fa5a90e6c6f0..a9b651c7f866 100644
> > --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > @@ -165,6 +165,14 @@ const struct vm_guest_mode_params vm_guest_mode_params[] = {
> >   _Static_assert(sizeof(vm_guest_mode_params)/sizeof(struct vm_guest_mode_params) == NUM_VM_MODES,
> >   	       "Missing new mode params?");
> >   
> > +const char * const vm_mem_backing_src_type_string[] = {
> A shorter name would be nice, though I don't have a good suggestion.
>
> > +	"VM_MEM_SRC_ANONYMOUS        ",
> > +	"VM_MEM_SRC_ANONYMOUS_THP    ",
> > +	"VM_MEM_SRC_ANONYMOUS_HUGETLB",
> It'd be more robust to explicitly assign indices, that way tweaks to
> vm_mem_backing_src_type won't cause silent breakage.  Ditto for the existing
> vm_guest_mode_string.
>
> E.g. I think something like this would work (completely untested)
>
> const char *vm_guest_mode_string(int i)
> {
> 	static const char *const strings[] = {
> 		[VM_MODE_P52V48_4K]	= "PA-bits:52,  VA-bits:48,  4K pages",
> 		[VM_MODE_P52V48_64K]	= "PA-bits:52,  VA-bits:48, 64K pages",
> 		[VM_MODE_P48V48_4K]	= "PA-bits:48,  VA-bits:48,  4K pages",
> 		[VM_MODE_P48V48_64K]	= "PA-bits:48,  VA-bits:48, 64K pages",
> 		[VM_MODE_P40V48_4K]	= "PA-bits:40,  VA-bits:48,  4K pages",
> 		[VM_MODE_P40V48_64K]	= "PA-bits:40,  VA-bits:48, 64K pages",
> 		[VM_MODE_PXXV48_4K]	= "PA-bits:ANY, VA-bits:48,  4K pages",
> 	};
>
> 	_Static_assert(sizeof(strings)/sizeof(char *) == NUM_VM_MODES,
> 		       "Missing new mode strings?");
>
> 	TEST_ASSERT(i < NUM_VM_MODES);
>
> 	return strings[i];
> }

I think this is better. Moving these three staffs together into a single 
function and check the indices here is more reasonable.

Thanks,

Yanan.

> > +};
> > +_Static_assert(sizeof(vm_mem_backing_src_type_string)/sizeof(char *) == NUM_VM_BACKING_SRC_TYPES,
> > +	       "Missing new source type strings?");
> > +
> >   /*
> >    * VM Create
> >    *
> > --
> > 2.23.0
> .