Calculate UUID grain for Xen PV guests

Author: ycedres

changelog/99999.added.md

@@ -0,0 +1 @@
+Added UUID detection for Xen paravirtualized guests from `/sys/hypervisor/uuid`

salt/grains/core.py

@@ -3258,6 +3258,23 @@ def _hw_data(osdata):
         return {}
 
     grains = {}
+
+    # For Xen para-virtualized guests read UUID from /sys/hypervisor/uuid
+    if osdata["kernel"] == "Linux" and os.path.exists("/sys/hypervisor/uuid"):
+        try:
+            with salt.utils.files.fopen("/sys/hypervisor/uuid", "r") as ifile:
+                hypervisor_uuid = salt.utils.stringutils.to_unicode(
+                    ifile.read().strip(), errors="replace"
+                )
+                # Normalize to lowercase to match DMI format
+                grains["uuid"] = hypervisor_uuid.lower()
+                log.debug(
+                    "Read UUID from /sys/hypervisor/uuid for para-virtualized guest: %s",
+                    grains["uuid"],
+                )
+        except OSError as err:
+            log.debug("Unable to read /sys/hypervisor/uuid: %s", err)
+
     if osdata["kernel"] == "Linux" and os.path.exists("/sys/class/dmi/id"):
         # On many Linux distributions basic firmware information is available via sysfs
         # requires CONFIG_DMIID to be enabled in the Linux kernel configuration
@@ -3272,6 +3289,9 @@ def _hw_data(osdata):
             "serialnumber": "product_serial",
         }
         for key, fw_file in sysfs_firmware_info.items():
+            # Skip UUID if already read from /sys/hypervisor/uuid (Xen PV guests)
+            if key == "uuid" and "uuid" in grains:
+                continue
             contents_file = os.path.join("/sys/class/dmi/id", fw_file)
             if os.path.exists(contents_file):
                 try:

tests/pytests/unit/grains/test_core.py

@@ -3560,6 +3560,26 @@ def read(self):
         assert core._hw_data({"kernel": "Linux"}) == {}
 
 
+@pytest.mark.skip_unless_on_linux
+def test__hw_data_xen_pv_uuid():
+    hypervisor_uuid = "12345678-1234-1234-1234-123456789ABC"
+    expected_uuid = "12345678-1234-1234-1234-123456789abc"
+
+    def _exists_side_effect(path):
+        if path == "/sys/hypervisor/uuid":
+            return True
+        return False
+
+    with patch("os.path.exists", side_effect=_exists_side_effect), patch(
+        "salt.utils.platform.is_proxy", return_value=False
+    ), patch("salt.utils.path.which_bin", return_value=None), patch(
+        "salt.utils.files.fopen",
+        mock_open(read_data=hypervisor_uuid),
+    ):
+        result = core._hw_data({"kernel": "Linux"})
+        assert result.get("uuid") == expected_uuid
+
+
 @pytest.mark.skip_unless_on_windows
 def test_kernelparams_return_windows():
     """