TestNode: Fix failure to start in nested VMs

ceph_devstack/resources/ceph/containers.py

@@ -218,19 +218,7 @@ def create_cmd(self):
             "/dev/fuse:/dev/fuse",
             "-v",
             "/dev/disk:/dev/disk",
-            # cephadm tries to access these DMI-related files, and by default they
-            # have 600 permissions on the host. It appears to be ok if they are
-            # empty, though.
-            # The below was bizarrely causing this error message:
-            # No such file or directory: OCI runtime attempted to invoke a command that was
-            # not found
-            # That was causing the container to fail to start up.
-            "-v",
-            "/dev/null:/sys/class/dmi/id/board_serial",
-            "-v",
-            "/dev/null:/sys/class/dmi/id/chassis_serial",
-            "-v",
-            "/dev/null:/sys/class/dmi/id/product_serial",
+            *self._get_available_dmi_mounts(),
             *self.additional_volumes,
             "--device",
             "/dev/net/tun",
@@ -329,6 +317,26 @@ def device_name(self, index: int):
     def device_image(self, device: str):
         return f"{self.name}-{device.removeprefix('/dev/loop')}"
 
+    def _get_available_dmi_mounts(self) -> List[str]:
+        """Return volume mount args for DMI files that exist on the host.
+
+        cephadm tries to access DMI-related files, and by default they have 600
+        permissions on the host. We mount /dev/null to make them accessible but empty.
+        However, in nested virtualization these files may not exist at all, so we
+        only mount them if they're present on the host.
+        """
+        dmi_files = [
+            "board_serial",
+            "chassis_serial",
+            "product_serial",
+        ]
+        mounts = []
+        for dmi_file in dmi_files:
+            dmi_path = f"/sys/class/dmi/id/{dmi_file}"
+            if host.path_exists(dmi_path):
+                mounts.extend(["-v", f"/dev/null:{dmi_path}"])
+        return mounts
+
 
 class Teuthology(Container):
     cmd_vars: List[str] = ["name", "image", "image_tag", "archive_dir"]

tests/resources/ceph/test_testnode.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
 
@@ -35,3 +36,66 @@ def test_testnode_devices_is_based_on_loop_device_count_config(self, cls):
             "/dev/loop6",
             "/dev/loop7",
         ]
+
+    def test_get_available_dmi_mounts_with_all_files_present(self, cls):
+        testnode = cls("testnode_1")
+        with patch(
+            "ceph_devstack.resources.ceph.containers.host.path_exists"
+        ) as mock_exists:
+            mock_exists.return_value = True
+            mounts = testnode._get_available_dmi_mounts()
+            assert mounts == [
+                "-v",
+                "/dev/null:/sys/class/dmi/id/board_serial",
+                "-v",
+                "/dev/null:/sys/class/dmi/id/chassis_serial",
+                "-v",
+                "/dev/null:/sys/class/dmi/id/product_serial",
+            ]
+
+    def test_get_available_dmi_mounts_with_no_files_present(self, cls):
+        testnode = cls("testnode_1")
+        with patch(
+            "ceph_devstack.resources.ceph.containers.host.path_exists"
+        ) as mock_exists:
+            mock_exists.return_value = False
+            mounts = testnode._get_available_dmi_mounts()
+            assert mounts == []
+
+    def test_get_available_dmi_mounts_with_partial_files_present(self, cls):
+        testnode = cls("testnode_1")
+        with patch(
+            "ceph_devstack.resources.ceph.containers.host.path_exists"
+        ) as mock_exists:
+            # Only board_serial exists
+            mock_exists.side_effect = lambda path: "board_serial" in path
+            mounts = testnode._get_available_dmi_mounts()
+            assert mounts == [
+                "-v",
+                "/dev/null:/sys/class/dmi/id/board_serial",
+            ]
+
+    def test_create_cmd_includes_dmi_mounts_when_available(self, cls):
+        config.load(Path(__file__).parent.joinpath("fixtures", "testnode-config.toml"))
+        testnode = cls("testnode_1")
+        with patch(
+            "ceph_devstack.resources.ceph.containers.host.path_exists"
+        ) as mock_exists:
+            mock_exists.return_value = True
+            create_cmd = testnode.create_cmd
+            assert "/dev/null:/sys/class/dmi/id/board_serial" in " ".join(create_cmd)
+            assert "/dev/null:/sys/class/dmi/id/chassis_serial" in " ".join(create_cmd)
+            assert "/dev/null:/sys/class/dmi/id/product_serial" in " ".join(create_cmd)
+
+    def test_create_cmd_excludes_dmi_mounts_when_unavailable(self, cls):
+        config.load(Path(__file__).parent.joinpath("fixtures", "testnode-config.toml"))
+        testnode = cls("testnode_1")
+        with patch(
+            "ceph_devstack.resources.ceph.containers.host.path_exists"
+        ) as mock_exists:
+            mock_exists.return_value = False
+            create_cmd = testnode.create_cmd
+            cmd_str = " ".join(create_cmd)
+            assert "/sys/class/dmi/id/board_serial" not in cmd_str
+            assert "/sys/class/dmi/id/chassis_serial" not in cmd_str
+            assert "/sys/class/dmi/id/product_serial" not in cmd_str