fix:(disk_setup):handle empty disk in check_partition_gpt_layout_sfdisk

When checking GPT partition layout using sfdisk, handle the case
where a disk has no partition table yet. Previously, this would
raise an exception. Now it returns an empty list.

Add unit test to cover this empty disk scenario.

Fixes GH-6682

Signed-off-by: Amy Chen <xiachen@redhat.com>

Author: xiachen-rh

cloudinit/config/cc_disk_setup.py

@@ -805,7 +805,11 @@ def check_partition_gpt_layout_sfdisk(device, layout):
     # Use sfdisk's JSON output for reliability
     prt_cmd = ["sfdisk", "-l", "-J", device]
     try:
-        out, _err = subp.subp(prt_cmd, update_env=LANG_C_ENV)
+        out, _err = subp.subp(prt_cmd, update_env=LANG_C_ENV, rcs=[0, 1])
+        # Device has no partition table or other error, return empty list
+        if not out:
+            return []
+        # Try to parse JSON output
         ptable = json.loads(out)["partitiontable"]
         if "partitions" in ptable:
             partitions = ptable["partitions"]

tests/unittests/config/test_cc_disk_setup.py

@@ -137,6 +137,25 @@ def test_simple1_gpt(self, *args):
             "gpt", "/dev/xvdb1", [(100, Linux_GUID)]
         )
 
+    @mock.patch(
+        "cloudinit.config.cc_disk_setup.subp.subp",
+        return_value=(
+            "",
+            "/dev/sdb: does not contain a recognized partition table",
+        ),
+    )
+    def test_empty_disk_no_partition_table(self, m_subp):
+        """Test that empty disk (no partition table) returns empty list."""
+        result = cc_disk_setup.check_partition_gpt_layout_sfdisk(
+            "/dev/sdb", []
+        )
+        assert result == []
+        m_subp.assert_called_once_with(
+            ["sfdisk", "-l", "-J", "/dev/sdb"],
+            update_env={"LANG": "C"},
+            rcs=[0, 1],
+        )
+
 
 class TestUpdateFsSetupDevices:
     def test_regression_1634678(self):