KVM: selftests: Read binary stats desc in lib

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.
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220613212523.3436117-4-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/include/kvm_util_base.h

@@ -316,6 +316,31 @@ static inline void read_stats_header(int stats_fd, struct kvm_stats_header *head
 	TEST_ASSERT(ret == sizeof(*header), "Read stats header");
 }
 
+struct kvm_stats_desc *read_stats_descriptors(int stats_fd,
+					      struct kvm_stats_header *header);
+
+static inline ssize_t get_stats_descriptor_size(struct kvm_stats_header *header)
+{
+	 /*
+	  * The base size of the descriptor is defined by KVM's ABI, but the
+	  * size of the name field is variable, as far as KVM's ABI is
+	  * concerned. For a given instance of KVM, the name field is the same
+	  * size for all stats and is provided in the overall stats header.
+	  */
+	return sizeof(struct kvm_stats_desc) + header->name_size;
+}
+
+static inline struct kvm_stats_desc *get_stats_descriptor(struct kvm_stats_desc *stats,
+							  int index,
+							  struct kvm_stats_header *header)
+{
+	/*
+	 * Note, size_desc includes the size of the name field, which is
+	 * variable. i.e. this is NOT equivalent to &stats_desc[i].
+	 */
+	return (void *)stats + index * get_stats_descriptor_size(header);
+}
+
 void vm_create_irqchip(struct kvm_vm *vm);
 
 void vm_set_user_memory_region(struct kvm_vm *vm, uint32_t slot, uint32_t flags,

tools/testing/selftests/kvm/kvm_binary_stats_test.c

@@ -35,7 +35,7 @@ static void stats_test(int stats_fd)
 	/* Read kvm stats header */
 	read_stats_header(stats_fd, &header);
 
-	size_desc = sizeof(*stats_desc) + header.name_size;
+	size_desc = get_stats_descriptor_size(&header);
 
 	/* Read kvm stats id string */
 	id = malloc(header.name_size);
@@ -62,18 +62,12 @@ 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 = read_stats_descriptors(stats_fd, &header);
 
 	/* Sanity check for fields in descriptors */
 	for (i = 0; i < header.num_desc; ++i) {
-		pdesc = (void *)stats_desc + i * size_desc;
+		pdesc = get_stats_descriptor(stats_desc, i, &header);
 		/* Check type,unit,base boundaries */
 		TEST_ASSERT((pdesc->flags & KVM_STATS_TYPE_MASK)
 				<= KVM_STATS_TYPE_MAX, "Unknown KVM stats type");
@@ -129,7 +123,7 @@ static void stats_test(int stats_fd)
 			"Data size is not correct");
 	/* Check stats offset */
 	for (i = 0; i < header.num_desc; ++i) {
-		pdesc = (void *)stats_desc + i * size_desc;
+		pdesc = get_stats_descriptor(stats_desc, i, &header);
 		TEST_ASSERT(pdesc->offset < size_data,
 			"Invalid offset (%u) for stats: %s",
 			pdesc->offset, pdesc->name);
@@ -144,7 +138,7 @@ static void stats_test(int stats_fd)
 	/* Read kvm stats data one by one */
 	size_data = 0;
 	for (i = 0; i < header.num_desc; ++i) {
-		pdesc = (void *)stats_desc + i * size_desc;
+		pdesc = get_stats_descriptor(stats_desc, i, &header);
 		ret = pread(stats_fd, stats_data,
 				pdesc->size * sizeof(*stats_data),
 				header.data_offset + size_data);

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -1850,3 +1850,36 @@ unsigned int vm_calc_num_guest_pages(enum vm_guest_mode mode, size_t size)
 	n = DIV_ROUND_UP(size, vm_guest_mode_params[mode].page_size);
 	return vm_adjust_num_guest_pages(mode, n);
 }
+
+/*
+ * Read binary stats descriptors
+ *
+ * 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
+ *
+ * Output Args: None
+ *
+ * Return:
+ *   A pointer to a newly allocated series of stat descriptors.
+ *   Caller is responsible for freeing the returned kvm_stats_desc.
+ *
+ * Read the stats descriptors from the binary stats interface.
+ */
+struct kvm_stats_desc *read_stats_descriptors(int stats_fd,
+					      struct kvm_stats_header *header)
+{
+	struct kvm_stats_desc *stats_desc;
+	ssize_t desc_size, total_size, ret;
+
+	desc_size = get_stats_descriptor_size(header);
+	total_size = header->num_desc * desc_size;
+
+	stats_desc = calloc(header->num_desc, desc_size);
+	TEST_ASSERT(stats_desc, "Allocate memory for stats descriptors");
+
+	ret = pread(stats_fd, stats_desc, total_size, header->desc_offset);
+	TEST_ASSERT(ret == total_size, "Read KVM stats descriptors");
+
+	return stats_desc;
+}