change return value for dmi data of all \xff to be ""

Previously we returned a string of "." the same length as the dmi field.
That seems confusing to the user as "." would seem like a valid response
when in fact this value should not be considered valid.

So now, in this case, return empty string.

2 files changed, 5 insertions, 2 deletions

diff --git a/cloudinit/util.py b/cloudinit/util.py
index 01dc7751..20916e53 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -2148,7 +2148,7 @@ def _read_dmi_syspath(key):
         # uninitialized dmi values show as all \xff and /sys appends a '\n'.
         # in that event, return a string of '.' in the same length.
         if key_data == b'\xff' * (len(key_data) - 1) + b'\n':
-            key_data = b'.' * (len(key_data) - 1) + b'\n'
+            key_data = b""
 
         str_data = key_data.decode('utf8').strip()
         LOG.debug("dmi data %s returned %s", dmi_key_path, str_data)
@@ -2168,6 +2168,9 @@ def _call_dmidecode(key, dmidecode_path):
         cmd = [dmidecode_path, "--string", key]
         (result, _err) = subp(cmd)
         LOG.debug("dmidecode returned '%s' for '%s'", result, key)
+        result = result.strip()
+        if result.replace(".", "") == "":
+            return ""
         return result
     except (IOError, OSError) as _err:
         LOG.debug('failed dmidecode cmd: %s\n%s', cmd, _err.message)
diff --git a/tests/unittests/test_util.py b/tests/unittests/test_util.py
index 0a986fec..37a984ac 100644
--- a/tests/unittests/test_util.py
+++ b/tests/unittests/test_util.py
@@ -389,7 +389,7 @@ class TestReadDMIData(helpers.FilesystemMockingTestCase):
         # uninitialized dmi values show as \xff, return those as .
         my_len = 32
         dmi_value = b'\xff' * my_len + b'\n'
-        expected = '.' * my_len
+        expected = ""
         dmi_key = 'system-product-name'
         sysfs_key = 'product_name'
         self._create_sysfs_file(sysfs_key, dmi_value)