Re: [PATCH v6 05/10] KVM: selftests: Read binary stat data in lib

[Peter Xu <peterx@redhat.com>]

On Wed, Apr 20, 2022 at 10:35:08AM -0700, Ben Gardon wrote:
> Move the code to read the binary stats data to the KVM selftests
> library. It will be re-used by other tests to check KVM behavior.
> 
> No functional change intended.

I think there's a very trivial functional change...

> 
> Reviewed-by: David Matlack <dmatlack@google.com>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
>  .../selftests/kvm/include/kvm_util_base.h     |  3 ++
>  .../selftests/kvm/kvm_binary_stats_test.c     |  7 ++--
>  tools/testing/selftests/kvm/lib/kvm_util.c    | 36 +++++++++++++++++++
>  3 files changed, 41 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index fabe46ddc1b2..2a3a4d9ed8e3 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -403,6 +403,9 @@ int vcpu_get_stats_fd(struct kvm_vm *vm, uint32_t vcpuid);
>  void read_stats_header(int stats_fd, struct kvm_stats_header *header);
>  struct kvm_stats_desc *read_stats_desc(int stats_fd,
>  				       struct kvm_stats_header *header);
> +int read_stat_data(int stats_fd, struct kvm_stats_header *header,
> +		   struct kvm_stats_desc *desc, uint64_t *data,
> +		   ssize_t max_elements);
>  
>  uint32_t guest_get_vcpuid(void);
>  
> diff --git a/tools/testing/selftests/kvm/kvm_binary_stats_test.c b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> index 8b31f8fc7e08..59677fae26e5 100644
> --- a/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> +++ b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> @@ -160,11 +160,8 @@ static void stats_test(int stats_fd)
>  	size_data = 0;
>  	for (i = 0; i < header.num_desc; ++i) {
>  		pdesc = (void *)stats_desc + i * size_desc;
> -		ret = pread(stats_fd, stats_data,
> -				pdesc->size * sizeof(*stats_data),
> -				header.data_offset + size_data);
> -		TEST_ASSERT(ret == pdesc->size * sizeof(*stats_data),
> -				"Read data of KVM stats: %s", pdesc->name);
> +		read_stat_data(stats_fd, &header, pdesc, stats_data,
> +			       pdesc->size);
>  		size_data += pdesc->size * sizeof(*stats_data);
>  	}
>  
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 12fa8cc88043..ea4ab64e5997 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -2615,3 +2615,39 @@ struct kvm_stats_desc *read_stats_desc(int stats_fd,
>  
>  	return stats_desc;
>  }
> +
> +/*
> + * Read stat data for a particular stat
> + *
> + * Input Args:
> + *   stats_fd - the file descriptor for the binary stats file from which to read
> + *   header - the binary stats metadata header corresponding to the given FD
> + *   desc - the binary stat metadata for the particular stat to be read
> + *   max_elements - the maximum number of 8-byte values to read into data
> + *
> + * Output Args:
> + *   data - the buffer into which stat data should be read
> + *
> + * Return:
> + *   The number of data elements read into data or -ERRNO on error.
> + *
> + * Read the data values of a specified stat from the binary stats interface.
> + */
> +int read_stat_data(int stats_fd, struct kvm_stats_header *header,
> +		   struct kvm_stats_desc *desc, uint64_t *data,
> +		   ssize_t max_elements)
> +{
> +	ssize_t size = min_t(ssize_t, desc->size, max_elements);
> +	ssize_t ret;
> +
> +	ret = pread(stats_fd, data, size * sizeof(*data),
> +		    header->data_offset + desc->offset);
> +
> +	/* ret from pread is in bytes. */
> +	ret = ret / sizeof(*data);
> +
> +	TEST_ASSERT(ret == size,
> +		    "Read data of KVM stats: %s", desc->name);

... where we do the check with 8-bytes aligned now, so we'll stop failing
the case e.g. when pread() didn't get multiples of 8 bytes.

But not a big deal I guess.

Reviewed-by: Peter Xu <peterx@redhat.com>

Thanks,

-- 
Peter Xu