Always fall back from hard linking to copying filesbugfix/21.3

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
(cherry picked from commit 59c6ad96ce35c9deecfedb5698c5806f3883a8af)

1 files changed, 14 insertions, 21 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))