Merge ~raharper/curtin:fix/no-by-id-grub-debconf into curtin:master

[Ryan Harper]

block: disk_to_byid_path handle missing /dev/disk/by-id directory

If a system has disks without any persistent indentifier (like serial)
then udev won't create any /dev/disk/by-id symlinks. This can happen
in VMs which do not provide serial numbers by default (e.g. virtio).

If /dev/disk/by-id did not exist then os.listdir on that path would
raise a FileNotFoundException and prevented disk_to_byid_path from
returning None (or the correct path).

This is fixed by checking if the target prefix exists and if not
return an empty dict.

LP: #1876258

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:56361669c20a0002b68390f2b2b8a11e1dd563ad
https://jenkins.ubuntu.com/server/job/curtin-ci/175/
Executed test runs:
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-amd64/175/
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-arm64/175/
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-ppc64el/175/
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-s390x/175/

Click here to trigger a rebuild:
https://jenkins.ubuntu.com/server/job/curtin-ci/175//rebuild

review: Approve (continuous-integration)

[Chad Smith (chad.smith)]

+1! LGTM!

review: Approve

diff --git a/curtin/block/__init__.py b/curtin/block/__init__.py
index a422264..10b8b9e 100644
--- a/curtin/block/__init__.py
+++ b/curtin/block/__init__.py
@@ -853,6 +853,8 @@ def _get_dev_disk_by_prefix(prefix):
      '/dev/sda1': '/dev/disk/<prefix>/virtio-aaaa-part1',
     }
     """
+    if not os.path.exists(prefix):
+        return {}
     return {
         os.path.realpath(bypfx): bypfx
         for bypfx in [os.path.join(prefix, path)
diff --git a/tests/unittests/test_block.py b/tests/unittests/test_block.py
index c62c153..78e331d 100644
--- a/tests/unittests/test_block.py
+++ b/tests/unittests/test_block.py
@@ -179,6 +179,18 @@ class TestBlock(CiTestCase):
         byid_path = block.disk_to_byid_path('/dev/sdb')
         self.assertEqual(mapping.get('/dev/sdb'), byid_path)
 
+    @mock.patch("curtin.block.os.path.exists")
+    def test__get_dev_disk_by_prefix_returns_empty_dict(self, m_exists):
+        """ _get_disk_by_prefix returns empty dict prefix dir does not exit """
+        m_exists.return_value = False
+        self.assertEqual({}, block._get_dev_disk_by_prefix("/dev/disk/by-id"))
+
+    @mock.patch("curtin.block.os.path.exists")
+    def test_disk_to_byid_returns_none_if_disk_byid_missing(self, m_exists):
+        """ disk_to_byid path returns None if /dev/disk/by-id is missing """
+        m_exists.return_value = False
+        self.assertEqual(None, block.disk_to_byid_path('/dev/sdb'))
+
 
 class TestSysBlockPath(CiTestCase):
     @mock.patch("curtin.block.get_blockdev_for_partition")