linux-kernel - Re: [PATCH v4 03/10] KVM: selftests: Read binary stats desc in lib

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Date:   Tue, 12 Apr 2022 00:54:55 +0000
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        David Dunn <daviddunn@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH v4 03/10] KVM: selftests: Read binary stats desc in lib

On Mon, Apr 11, 2022, Ben Gardon wrote:
> Move the code to read the binary stats descriptors to the KVM selftests
> library. It will be re-used by other tests to check KVM behavior.
> 
> No functional change intended.
> 
> Signed-off-by: Ben Gardon <bgardon@...gle.com>
> ---
>  .../selftests/kvm/include/kvm_util_base.h     |  4 +++
>  .../selftests/kvm/kvm_binary_stats_test.c     |  9 ++----
>  tools/testing/selftests/kvm/lib/kvm_util.c    | 29 +++++++++++++++++++
>  3 files changed, 35 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
> index 5ba3132f3110..c5f34551ff76 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util_base.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
> @@ -401,6 +401,10 @@ void assert_on_unhandled_exception(struct kvm_vm *vm, uint32_t vcpuid);
>  int vm_get_stats_fd(struct kvm_vm *vm);
>  int vcpu_get_stats_fd(struct kvm_vm *vm, uint32_t vcpuid);
>  void read_vm_stats_header(int stats_fd, struct kvm_stats_header *header);
> +struct kvm_stats_desc *alloc_vm_stats_desc(int stats_fd,
> +					  struct kvm_stats_header *header);
> +void read_vm_stats_desc(int stats_fd, struct kvm_stats_header *header,
> +			struct kvm_stats_desc *stats_desc);
>  
>  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 22c22a90f15a..e4795bad7db6 100644
> --- a/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> +++ b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
> @@ -62,14 +62,9 @@ static void stats_test(int stats_fd)
>  							header.data_offset),
>  			"Descriptor block is overlapped with data block");
>  
> -	/* Allocate memory for stats descriptors */
> -	stats_desc = calloc(header.num_desc, size_desc);
> -	TEST_ASSERT(stats_desc, "Allocate memory for stats descriptors");
>  	/* Read kvm stats descriptors */
> -	ret = pread(stats_fd, stats_desc,
> -			size_desc * header.num_desc, header.desc_offset);
> -	TEST_ASSERT(ret == size_desc * header.num_desc,
> -			"Read KVM stats descriptors");
> +	stats_desc = alloc_vm_stats_desc(stats_fd, &header);
> +	read_vm_stats_desc(stats_fd, &header, stats_desc);
>  
>  	/* Sanity check for fields in descriptors */
>  	for (i = 0; i < header.num_desc; ++i) {
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 0caf28e324ed..e3ae26fbef03 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -2564,3 +2564,32 @@ void read_vm_stats_header(int stats_fd, struct kvm_stats_header *header)
>  	ret = read(stats_fd, header, sizeof(*header));
>  	TEST_ASSERT(ret == sizeof(*header), "Read stats header");
>  }
> +
> +static ssize_t stats_descs_size(struct kvm_stats_header *header)
> +{
> +	return header->num_desc *
> +	       (sizeof(struct kvm_stats_desc) + header->name_size);
> +}
I was very confused on header->name_size. So this field means the
maximum string size of a stats name, right? Can we update the comments
in the kvm.h to specify that? By reading the comments, I don't really
feel this is how we should use this field.

hmm, if that is true, isn't this field a compile time value? Why do we
have to get it at runtime?

> +
> +/* Caller is responsible for freeing the returned kvm_stats_desc. */
> +struct kvm_stats_desc *alloc_vm_stats_desc(int stats_fd,
> +					  struct kvm_stats_header *header)
> +{
> +	struct kvm_stats_desc *stats_desc;
> +
> +	stats_desc = malloc(stats_descs_size(header));
> +	TEST_ASSERT(stats_desc, "Allocate memory for stats descriptors");
> +
> +	return stats_desc;
> +}
> +
> +void read_vm_stats_desc(int stats_fd, struct kvm_stats_header *header,
> +			struct kvm_stats_desc *stats_desc)
> +{
> +	ssize_t ret;
> +
> +	ret = pread(stats_fd, stats_desc, stats_descs_size(header),
> +		    header->desc_offset);
> +	TEST_ASSERT(ret == stats_descs_size(header),
> +		    "Read KVM stats descriptors");
> +}
> -- 
> 2.35.1.1178.g4f1659d476-goog
>