filesystem: handle sorting disks without required metadata

If there are at least two disks and one of them is missing any metadata used
during sorting installer will crash. Issue can be reproduced using already
available machine .json file: examples/machines/existing-partitions.json
in which /dev/vda does not have serial value.

This patch makes sure that all values used in sorting are initialized

2025-01-21 15:41:33,340 ERROR root:38 finish: subiquity/apply_autoinstall_config: FAIL: '<' not supported between instances of 'str' and 'NoneType'
2025-01-21 15:41:33,340 ERROR subiquity.server.server:503 top level error
Traceback (most recent call last):
  File "/home/rmalz/repos/subiquity/subiquity/server/server.py", line 1021, in start
    await self.apply_autoinstall_config()
  File "/home/rmalz/repos/subiquity/subiquitycore/context.py", line 165, in decorated_async
    return await meth(self, **kw)
  File "/home/rmalz/repos/subiquity/subiquity/server/server.py", line 575, in apply_autoinstall_config
    await controller.apply_autoinstall_config()
  File "/home/rmalz/repos/subiquity/subiquitycore/context.py", line 165, in decorated_async
    return await meth(self, **kw)
  File "/home/rmalz/repos/subiquity/subiquity/server/controllers/filesystem.py", line 484, in apply_autoinstall_config
    await self.convert_autoinstall_config(context=context)
  File "/home/rmalz/repos/subiquity/subiquitycore/context.py", line 165, in decorated_async
    return await meth(self, **kw)
  File "/home/rmalz/repos/subiquity/subiquity/server/controllers/filesystem.py", line 1745, in convert_autoinstall_config
    await self.run_autoinstall_guided(self.ai_data["layout"])
  File "/home/rmalz/repos/subiquity/subiquity/server/controllers/filesystem.py", line 1684, in run_autoinstall_guided
    disk = self.get_bootable_matching_disk(match)
  File "/home/rmalz/repos/subiquity/subiquity/server/controllers/filesystem.py", line 1594, in get_bootable_matching_disk
    matching_disks = self.get_bootable_matching_disks(match)
  File "/home/rmalz/repos/subiquity/subiquity/server/controllers/filesystem.py", line 1582, in get_bootable_matching_disks
    matching_disks = self.model.disks_for_match(disks, match)
  File "/home/rmalz/repos/subiquity/subiquity/models/filesystem.py", line 1800, in disks_for_match
    candidates, _ = self._matching_disks(disks, match)
  File "/home/rmalz/repos/subiquity/subiquity/models/filesystem.py", line 1791, in _matching_disks
    candidates = self._sorted_matches(candidates, m)
  File "/home/rmalz/repos/subiquity/subiquity/models/filesystem.py", line 1769, in _sorted_matches
    disks.sort(key=lambda d: d.sort_key)
TypeError: '<' not supported between instances of 'str' and 'NoneType'

Fixes: #2050

subiquity/models/filesystem.py

@@ -653,10 +653,11 @@ def size(self):
     @property
     @abstractmethod
     def sort_key(self) -> Tuple:
-        """return a value that is usable for sorting.  The intent here is
-        that two runs of a specific version of subiquity must produce an
-        identical sort result for _Devices, so that while Subiquity might make
-        an arbitrary choice of disk, it's a consistent arbitrary choice.
+        """return a value that is usable for sorting and does not contain
+        any None values.  The intent here is that two runs of a specific
+        version of subiquity must produce an identical sort result for
+        _Devices, so that while Subiquity might make an arbitrary choice of
+        disk, it's a consistent arbitrary choice.
         """
         pass
 
@@ -799,8 +800,8 @@ class Disk(_Device):
     _has_in_use_partition: bool = attributes.for_api(default=False)
 
     @property
-    def sort_key(self) -> int:
-        return (self.wwn, self.serial, self.path)
+    def sort_key(self) -> Tuple:
+        return (self.wwn or "", self.serial or "", self.path or "")
 
     @property
     def available_for_partitions(self):
@@ -944,8 +945,8 @@ def __post_init__(self):
         raise Exception("Exceeded number of available partitions")
 
     @property
-    def sort_key(self) -> int:
-        return (self.device.sort_key(), self.number)
+    def sort_key(self) -> Tuple:
+        return (self.device.sort_key(), self.number or 0)
 
     def available(self):
         if self.flag in ["bios_grub", "prep"] or self.grub_device:
@@ -1039,7 +1040,7 @@ class Raid(_Device):
     _has_in_use_partition = False
 
     @property
-    def sort_key(self) -> int:
+    def sort_key(self) -> Tuple:
         return tuple([dev.sort_key for dev in raid_device_sort(self.devices)])
 
     def serialize_devices(self):
@@ -1138,7 +1139,7 @@ def size(self):
         return get_lvm_size(self.devices)
 
     @property
-    def sort_key(self) -> int:
+    def sort_key(self) -> Tuple:
         return tuple([dev.sort_key for dev in self.devices])
 
     @property
@@ -1305,8 +1306,8 @@ def size(self):
         return 0
 
     @property
-    def sort_key(self) -> int:
-        return (self.path,)
+    def sort_key(self) -> Tuple:
+        return (self.path or "",)
 
     ok_for_raid = False
     ok_for_lvm_vg = False

subiquity/models/tests/test_filesystem.py

@@ -2075,6 +2075,16 @@ def test_sort_path_wins(self, sort_criteria: str):
         self.assertEqual(d1, m.disk_for_match([d2, d1], {"size": sort_criteria}))
         self.assertEqual([d1, d2], m.disks_for_match([d2, d1], {"size": sort_criteria}))
 
+    def test_sort_disks_none_values(self):
+        m = make_model()
+        d1 = make_disk(m, wwn=None, serial="s", path="/dev/d1")
+        d2 = make_disk(m, wwn="w", serial=None, path="/dev/d2")
+        d3 = make_disk(m, wwn="w", serial="s", path=None)
+        self.assertEqual(d1, m.disk_for_match([d3, d2, d1], {"size": "largest"}))
+        self.assertEqual(
+            [d1, d2, d3], m.disks_for_match([d3, d2, d1], {"size": "largest"})
+        )
+
     def test_sort_raid(self):
         m = make_model()
         d1_1 = make_disk(m, size=100 << 30)