KVM: selftests: Add a helper to get system default hugetlb page size

If HUGETLB is configured in the host kernel, then we can know the system
default hugetlb page size through *cat /proc/meminfo*. Otherwise, we will
not see the information of hugetlb pages in file /proc/meminfo if it's not
configured. So add a helper to determine whether HUGETLB is configured and
then get the default page size by reading /proc/meminfo.

This helper can be useful when a program wants to use the default hugetlb
pages of the system and doesn't know the default page size.
Signed-off-by: NYanan Wang <wangyanan55@huawei.com>
Reviewed-by: NAndrew Jones <drjones@redhat.com>
Message-Id: <20210330080856.14940-8-wangyanan55@huawei.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

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

@@ -80,6 +80,7 @@ struct vm_mem_backing_src_alias {
 
 bool thp_configured(void);
 size_t get_trans_hugepagesz(void);
+size_t get_def_hugetlb_pagesz(void);
 void backing_src_help(void);
 enum vm_mem_backing_src_type parse_backing_src_type(const char *type_name);
 

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

@@ -146,6 +146,31 @@ size_t get_trans_hugepagesz(void)
 	return size;
 }
 
+size_t get_def_hugetlb_pagesz(void)
+{
+	char buf[64];
+	const char *tag = "Hugepagesize:";
+	FILE *f;
+
+	f = fopen("/proc/meminfo", "r");
+	TEST_ASSERT(f != NULL, "Error in opening /proc/meminfo");
+
+	while (fgets(buf, sizeof(buf), f) != NULL) {
+		if (strstr(buf, tag) == buf) {
+			fclose(f);
+			return strtoull(buf + strlen(tag), NULL, 10) << 10;
+		}
+	}
+
+	if (feof(f))
+		TEST_FAIL("HUGETLB is not configured in host kernel");
+	else
+		TEST_FAIL("Error in reading /proc/meminfo");
+
+	fclose(f);
+	return 0;
+}
+
 void backing_src_help(void)
 {
 	int i;