Fix cache image hard link between different file systems

When caching an image between different file systems, the hard link
operation would fail. This is fixed by falling back to a copy
operation.

Assisted-By: claude-4-sonnet
Change-Id: Id1eced2e0a30044b0da7dd5f4f2dedc50a5297b6
Signed-off-by: Riccardo Pittau <elfosardo@gmail.com>
(cherry picked from commit 685dbeb356)

ironic/drivers/modules/image_cache.py

@@ -19,6 +19,7 @@ Utility for caching master images.
 """
 
 import os
+import shutil
 import tempfile
 import threading
 import time
@@ -167,7 +168,17 @@ class ImageCache(object):
             if cache_up_to_date:
                 # NOTE(dtantsur): ensure we're not in the middle of clean up
                 with lockutils.lock('master_image'):
-                    os.link(master_path, dest_path)
+                    try:
+                        os.link(master_path, dest_path)
+                    except OSError as exc:
+                        LOG.debug(
+                            "Could not hardlink image file %(image)s to "
+                            "the cache location %(dest_path)s (will copy it "
+                            "over): %(error)s", {
+                                'image': master_path,
+                                'dest_path': dest_path,
+                                'error': exc})
+                        shutil.copyfile(master_path, dest_path)
                 LOG.debug("Master cache hit for image %(href)s",
                           {'href': href})
                 return

ironic/tests/unit/drivers/modules/test_image_cache.py

@@ -18,6 +18,7 @@
 
 import datetime
 import os
+import shutil
 import tempfile
 import time
 from unittest import mock
@@ -238,6 +239,34 @@ class TestImageCacheFetch(BaseTest):
         mock_clean_up.assert_not_called()
         mock_image_service.assert_not_called()
 
+    @mock.patch.object(shutil, 'copyfile', autospec=True)
+    @mock.patch.object(os, 'link', autospec=True)
+    @mock.patch.object(image_cache, '_delete_dest_path_if_stale',
+                       return_value=False, autospec=True)
+    @mock.patch.object(image_cache, '_delete_master_path_if_stale',
+                       return_value=True, autospec=True)
+    def test_fetch_image_hardlink_fails_fallback_to_copy(
+            self, mock_cache_upd, mock_dest_upd, mock_link, mock_copyfile,
+            mock_download, mock_clean_up, mock_image_service):
+        mock_link.side_effect = OSError("Invalid cross-device link")
+
+        self.cache.fetch_image(self.uuid, self.dest_path)
+
+        mock_link.assert_called_once_with(self.master_path, self.dest_path)
+
+        mock_copyfile.assert_called_once_with(self.master_path, self.dest_path)
+
+        mock_cache_upd.assert_called_once_with(
+            self.master_path, self.uuid,
+            mock_image_service.return_value.show.return_value)
+        mock_dest_upd.assert_called_once_with(self.master_path, self.dest_path)
+
+        mock_download.assert_not_called()
+        mock_clean_up.assert_not_called()
+
+        mock_image_service.assert_called_once_with(self.uuid, context=None)
+        mock_image_service.return_value.show.assert_called_once_with(self.uuid)
+
 
 @mock.patch.object(image_cache, '_fetch', autospec=True)
 class TestImageCacheDownload(BaseTest):

releasenotes/notes/fix-cache-hardlink-66a8b2302abde76d.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    When caching an image between different file systems, the hard link
+    operation would fail. This is fixed by falling back to a copy
+    operation.