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

[Sean Christopherson <seanjc@google.com>]

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@huawei.com>
> ---
>  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];
}


> +};
> +_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
>