Always fall back from hard linking to copying files

The current check is insufficient: it passes for Kubernetes shared
volumes, although hard-linking between them is not possible.
This patch changes the approach to trying a hard link and falling
back to copyfile instead.

The patch relies on optimizations in Python 3.8 and thus should not
be backported beyond the Zed series to avoid performance regression.

Change-Id: I929944685b3ac61b2f63d2549198a2d8a1c8fe35

3 files changed, 40 insertions, 107 deletions

diff --git a/ironic/common/image_service.py b/ironic/common/image_service.py
index 5280ee6bc..4b95b5152 100644
--- a/ironic/common/image_service.py
+++ b/ironic/common/image_service.py
@@ -34,10 +34,6 @@ from ironic.common import utils
 from ironic.conf import CONF
 
 IMAGE_CHUNK_SIZE = 1024 * 1024  # 1mb
-# NOTE(kaifeng) Image will be truncated to 2GiB by sendfile,
-# we use a large chunk size here for a better performance
-# while keep the chunk size less than the size limit.
-SENDFILE_CHUNK_SIZE = 1024 * 1024 * 1024  # 1Gb
 LOG = log.getLogger(__name__)
 
 
@@ -264,26 +260,23 @@ class FileImageService(BaseImageService):
         """
         source_image_path = self.validate_href(image_href)
         dest_image_path = image_file.name
-        local_device = os.stat(dest_image_path).st_dev
         try:
-            # We should have read and write access to source file to create
-            # hard link to it.
-            if (local_device == os.stat(source_image_path).st_dev
-                    and os.access(source_image_path, os.R_OK | os.W_OK)):
-                image_file.close()
-                os.remove(dest_image_path)
+            image_file.close()
+            os.remove(dest_image_path)
+
+            try:
                 os.link(source_image_path, dest_image_path)
+            except OSError as exc:
+                LOG.debug('Could not create a link from %(src)s to %(dest)s, '
+                          'will copy the content instead. Error: %(exc)s.',
+                          {'src': source_image_path, 'dest': dest_image_path,
+                           'exc': exc})
             else:
-                filesize = os.path.getsize(source_image_path)
-                offset = 0
-                with open(source_image_path, 'rb') as input_img:
-                    while offset < filesize:
-                        count = min(SENDFILE_CHUNK_SIZE, filesize - offset)
-                        nbytes_out = os.sendfile(image_file.fileno(),
-                                                 input_img.fileno(),
-                                                 offset,
-                                                 count)
-                        offset += nbytes_out
+                return
+
+            # NOTE(dtantsur): starting with Python 3.8, copyfile() uses
+            # efficient copying (i.e. sendfile) under the hood.
+            shutil.copyfile(source_image_path, dest_image_path)
         except Exception as e:
             raise exception.ImageDownloadFailed(image_href=image_href,
                                                 reason=str(e))
diff --git a/ironic/tests/unit/common/test_image_service.py b/ironic/tests/unit/common/test_image_service.py
index 197518e1a..297a1b4b9 100644
--- a/ironic/tests/unit/common/test_image_service.py
+++ b/ironic/tests/unit/common/test_image_service.py
@@ -10,7 +10,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import builtins
 import datetime
 from http import client as http_client
 import io
@@ -483,119 +482,55 @@ class FileImageServiceTestCase(base.TestCase):
                           'properties': {},
                           'no_cache': True}, result)
 
+    @mock.patch.object(shutil, 'copyfile', autospec=True)
     @mock.patch.object(os, 'link', autospec=True)
     @mock.patch.object(os, 'remove', autospec=True)
-    @mock.patch.object(os, 'access', return_value=True, autospec=True)
-    @mock.patch.object(os, 'stat', autospec=True)
     @mock.patch.object(image_service.FileImageService, 'validate_href',
                        autospec=True)
-    def test_download_hard_link(self, _validate_mock, stat_mock, access_mock,
-                                remove_mock, link_mock):
+    def test_download_hard_link(self, _validate_mock, remove_mock, link_mock,
+                                copy_mock):
         _validate_mock.return_value = self.href_path
-        stat_mock.return_value.st_dev = 'dev1'
         file_mock = mock.Mock(spec=io.BytesIO)
         file_mock.name = 'file'
         self.service.download(self.href, file_mock)
         _validate_mock.assert_called_once_with(mock.ANY, self.href)
-        self.assertEqual(2, stat_mock.call_count)
-        access_mock.assert_called_once_with(self.href_path, os.R_OK | os.W_OK)
         remove_mock.assert_called_once_with('file')
         link_mock.assert_called_once_with(self.href_path, 'file')
+        copy_mock.assert_not_called()
 
-    @mock.patch.object(os, 'sendfile', return_value=42, autospec=True)
-    @mock.patch.object(os.path, 'getsize', return_value=42, autospec=True)
-    @mock.patch.object(builtins, 'open', autospec=True)
-    @mock.patch.object(os, 'access', return_value=False, autospec=True)
-    @mock.patch.object(os, 'stat', autospec=True)
-    @mock.patch.object(image_service.FileImageService, 'validate_href',
-                       autospec=True)
-    def test_download_copy(self, _validate_mock, stat_mock, access_mock,
-                           open_mock, size_mock, copy_mock):
-        _validate_mock.return_value = self.href_path
-        stat_mock.return_value.st_dev = 'dev1'
-        file_mock = mock.MagicMock(spec=io.BytesIO)
-        file_mock.name = 'file'
-        input_mock = mock.MagicMock(spec=io.BytesIO)
-        open_mock.return_value = input_mock
-        self.service.download(self.href, file_mock)
-        _validate_mock.assert_called_once_with(mock.ANY, self.href)
-        self.assertEqual(2, stat_mock.call_count)
-        access_mock.assert_called_once_with(self.href_path, os.R_OK | os.W_OK)
-        copy_mock.assert_called_once_with(file_mock.fileno(),
-                                          input_mock.__enter__().fileno(),
-                                          0, 42)
-
-    @mock.patch.object(os, 'sendfile', autospec=True)
-    @mock.patch.object(os.path, 'getsize', return_value=42, autospec=True)
-    @mock.patch.object(builtins, 'open', autospec=True)
-    @mock.patch.object(os, 'access', return_value=False, autospec=True)
-    @mock.patch.object(os, 'stat', autospec=True)
+    @mock.patch.object(shutil, 'copyfile', autospec=True)
+    @mock.patch.object(os, 'link', autospec=True)
+    @mock.patch.object(os, 'remove', autospec=True)
     @mock.patch.object(image_service.FileImageService, 'validate_href',
                        autospec=True)
-    def test_download_copy_segmented(self, _validate_mock, stat_mock,
-                                     access_mock, open_mock, size_mock,
-                                     copy_mock):
-        # Fake a 3G + 1k image
-        chunk_size = image_service.SENDFILE_CHUNK_SIZE
-        fake_image_size = chunk_size * 3 + 1024
-        fake_chunk_seq = [chunk_size, chunk_size, chunk_size, 1024]
+    def test_download_copy(self, _validate_mock, remove_mock, link_mock,
+                           copy_mock):
         _validate_mock.return_value = self.href_path
-        stat_mock.return_value.st_dev = 'dev1'
+        link_mock.side_effect = PermissionError
         file_mock = mock.MagicMock(spec=io.BytesIO)
         file_mock.name = 'file'
-        input_mock = mock.MagicMock(spec=io.BytesIO)
-        open_mock.return_value = input_mock
-        size_mock.return_value = fake_image_size
-        copy_mock.side_effect = fake_chunk_seq
         self.service.download(self.href, file_mock)
         _validate_mock.assert_called_once_with(mock.ANY, self.href)
-        self.assertEqual(2, stat_mock.call_count)
-        access_mock.assert_called_once_with(self.href_path, os.R_OK | os.W_OK)
-        copy_calls = [mock.call(file_mock.fileno(),
-                                input_mock.__enter__().fileno(),
-                                chunk_size * i,
-                                fake_chunk_seq[i]) for i in range(4)]
-        copy_mock.assert_has_calls(copy_calls)
-        size_mock.assert_called_once_with(self.href_path)
-
-    @mock.patch.object(os, 'remove', side_effect=OSError, autospec=True)
-    @mock.patch.object(os, 'access', return_value=True, autospec=True)
-    @mock.patch.object(os, 'stat', autospec=True)
-    @mock.patch.object(image_service.FileImageService, 'validate_href',
-                       autospec=True)
-    def test_download_hard_link_fail(self, _validate_mock, stat_mock,
-                                     access_mock, remove_mock):
-        _validate_mock.return_value = self.href_path
-        stat_mock.return_value.st_dev = 'dev1'
-        file_mock = mock.MagicMock(spec=io.BytesIO)
-        file_mock.name = 'file'
-        self.assertRaises(exception.ImageDownloadFailed,
-                          self.service.download, self.href, file_mock)
-        _validate_mock.assert_called_once_with(mock.ANY, self.href)
-        self.assertEqual(2, stat_mock.call_count)
-        access_mock.assert_called_once_with(self.href_path, os.R_OK | os.W_OK)
+        link_mock.assert_called_once_with(self.href_path, 'file')
+        copy_mock.assert_called_once_with(self.href_path, 'file')
 
-    @mock.patch.object(os, 'sendfile', side_effect=OSError, autospec=True)
-    @mock.patch.object(os.path, 'getsize', return_value=42, autospec=True)
-    @mock.patch.object(builtins, 'open', autospec=True)
-    @mock.patch.object(os, 'access', return_value=False, autospec=True)
-    @mock.patch.object(os, 'stat', autospec=True)
+    @mock.patch.object(shutil, 'copyfile', autospec=True)
+    @mock.patch.object(os, 'link', autospec=True)
+    @mock.patch.object(os, 'remove', autospec=True)
     @mock.patch.object(image_service.FileImageService, 'validate_href',
                        autospec=True)
-    def test_download_copy_fail(self, _validate_mock, stat_mock, access_mock,
-                                open_mock, size_mock, copy_mock):
+    def test_download_copy_fail(self, _validate_mock, remove_mock, link_mock,
+                                copy_mock):
         _validate_mock.return_value = self.href_path
-        stat_mock.return_value.st_dev = 'dev1'
+        link_mock.side_effect = PermissionError
+        copy_mock.side_effect = PermissionError
         file_mock = mock.MagicMock(spec=io.BytesIO)
         file_mock.name = 'file'
-        input_mock = mock.MagicMock(spec=io.BytesIO)
-        open_mock.return_value = input_mock
         self.assertRaises(exception.ImageDownloadFailed,
                           self.service.download, self.href, file_mock)
         _validate_mock.assert_called_once_with(mock.ANY, self.href)
-        self.assertEqual(2, stat_mock.call_count)
-        access_mock.assert_called_once_with(self.href_path, os.R_OK | os.W_OK)
-        size_mock.assert_called_once_with(self.href_path)
+        link_mock.assert_called_once_with(self.href_path, 'file')
+        copy_mock.assert_called_once_with(self.href_path, 'file')
 
 
 class ServiceGetterTestCase(base.TestCase):
diff --git a/releasenotes/notes/cross-link-1ffd1a4958f14fd7.yaml b/releasenotes/notes/cross-link-1ffd1a4958f14fd7.yaml
new file mode 100644
index 000000000..caac13dd4
--- /dev/null
+++ b/releasenotes/notes/cross-link-1ffd1a4958f14fd7.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes ``Invalid cross-device link`` in some cases when using ``file://``
+    image URLs.