KVM: selftests: Extract guts of THP accessor to standalone sysfs helpers

Extract the guts of thp_configured() and get_trans_hugepagesz() to
standalone helpers so that the core logic can be reused for other sysfs
files, e.g. to query numa_balancing.

Opportunistically assert that the initial fscanf() read at least one byte,
and add a comment explaining the second call to fscanf().

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: James Houghton <jthoughton@google.com>
Link: https://lore.kernel.org/r/20250508184649.2576210-2-jthoughton@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
index 8ed0b74ae8373316906c313e7adb5d609a500bcd..3dc8538f5d69648e792b91507bba8b3d311c87e7 100644 (file)
--- a/tools/testing/selftests/kvm/lib/test_util.c
+++ b/tools/testing/selftests/kvm/lib/test_util.c
@@ -132,37 +132,50 @@ void print_skip(const char *fmt, ...)
        puts(", skipping test");
 }
 
-bool thp_configured(void)
+static bool test_sysfs_path(const char *path)
 {
-       int ret;
        struct stat statbuf;
+       int ret;
 
-       ret = stat("/sys/kernel/mm/transparent_hugepage", &statbuf);
+       ret = stat(path, &statbuf);
        TEST_ASSERT(ret == 0 || (ret == -1 && errno == ENOENT),
-                   "Error in stating /sys/kernel/mm/transparent_hugepage");
+                   "Error in stat()ing '%s'", path);
 
        return ret == 0;
 }
 
-size_t get_trans_hugepagesz(void)
+bool thp_configured(void)
+{
+       return test_sysfs_path("/sys/kernel/mm/transparent_hugepage");
+}
+
+static size_t get_sysfs_val(const char *path)
 {
        size_t size;
        FILE *f;
        int ret;
 
-       TEST_ASSERT(thp_configured(), "THP is not configured in host kernel");
-
-       f = fopen("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", "r");
-       TEST_ASSERT(f != NULL, "Error in opening transparent_hugepage/hpage_pmd_size");
+       f = fopen(path, "r");
+       TEST_ASSERT(f, "Error opening '%s'", path);
 
        ret = fscanf(f, "%ld", &size);
+       TEST_ASSERT(ret > 0, "Error reading '%s'", path);
+
+       /* Re-scan the input stream to verify the entire file was read. */
        ret = fscanf(f, "%ld", &size);
-       TEST_ASSERT(ret < 1, "Error reading transparent_hugepage/hpage_pmd_size");
-       fclose(f);
+       TEST_ASSERT(ret < 1, "Error reading '%s'", path);
 
+       fclose(f);
        return size;
 }
 
+size_t get_trans_hugepagesz(void)
+{
+       TEST_ASSERT(thp_configured(), "THP is not configured in host kernel");
+
+       return get_sysfs_val("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size");
+}
+
 size_t get_def_hugetlb_pagesz(void)
 {
        char buf[64];