Allow None for block_device_mapping_v2.boot_index

The legacy v2 API allowed None for the boot_index [1]. It
allowed this implicitly because the API code would convert
the block_device_mapping_v2 dict from the request into a
BlockDeviceMapping object, which has a boot_index field that
is nullable (allows None).

The API reference documentation [2] also says:

"To disable a device from booting, set the boot index
to a negative value or use the default boot index value,
which is None."

It appears that with the move to v2.1 and request schema
validation, the boot_index schema was erroneously set to
not allow None for a value, which is not backward compatible
with the v2 API behavior.

This change fixes the schema to allow boot_index=None again
and adds a test to show it working.

This should not require a microversion bump since it's fixing
a regression in the v2.1 API which worked in the v2 API and
is already handled throughout Nova's block device code.

Closes-Bug: #1662699

[1] https://github.com/openstack/nova/blob/13.0.0/nova/compute/api.py#L1268
[2] http://developer.openstack.org/api-ref/compute/#create-server

Change-Id: Ice78a0982bcce491f0c9690903ed2c6b6aaab1be
(cherry picked from commit e34f05edb2)
(cherry picked from commit ff1925ae47)

nova/api/openstack/compute/schemas/block_device_mapping.py

@@ -56,8 +56,10 @@ block_device_mapping_new_item = {
         'type': 'string', 'maxLength': 255,
     },
     # Defined as integer in nova/block_device.py:from_api()
+    # NOTE(mriedem): boot_index=None is also accepted for backward
+    # compatibility with the legacy v2 API.
     'boot_index': {
-        'type': ['integer', 'string'],
+        'type': ['integer', 'string', 'null'],
         'pattern': '^-?[0-9]+$',
     },
 }

nova/block_device.py

@@ -197,7 +197,13 @@ class BlockDeviceDict(dict):
                 api_dict[source_type + '_id'] = device_uuid
             if source_type == 'image' and destination_type == 'local':
                 try:
-                    boot_index = int(api_dict.get('boot_index', -1))
+                    # NOTE(mriedem): boot_index can be None so we need to
+                    # account for that to avoid a TypeError.
+                    boot_index = api_dict.get('boot_index', -1)
+                    if boot_index is None:
+                        # boot_index=None is equivalent to -1.
+                        boot_index = -1
+                    boot_index = int(boot_index)
                 except ValueError:
                     raise exception.InvalidBDMFormat(
                         details=_("Boot index is invalid."))

nova/tests/unit/api/openstack/compute/test_block_device_mapping.py

@@ -201,6 +201,51 @@ class BlockDeviceMappingTestV21(test.TestCase):
         self.assertRaises(exception.ValidationError,
                           self._test_create, params)
 
+    def test_create_instance_with_boot_index_none_ok(self):
+        """Tests creating a server with two block devices. One is the boot
+        device and the other is a non-bootable device.
+        """
+        # From the docs:
+        # To disable a device from booting, set the boot index to a negative
+        # value or use the default boot index value, which is None. The
+        # simplest usage is, set the boot index of the boot device to 0 and use
+        # the default boot index value, None, for any other devices.
+        bdms = [
+            # This is the bootable device that would create a 20GB cinder
+            # volume from the given image.
+            {
+                'source_type': 'image',
+                'destination_type': 'volume',
+                'boot_index': 0,
+                'uuid': '155d900f-4e14-4e4c-a73d-069cbf4541e6',
+                'volume_size': 20
+            },
+            # This is the non-bootable 10GB ext4 ephemeral block device.
+            {
+                'source_type': 'blank',
+                'destination_type': 'local',
+                'boot_index': None,
+                # If 'guest_format' is 'swap' then a swap device is created.
+                'guest_format': 'ext4'
+            }
+        ]
+        params = {block_device_mapping.ATTRIBUTE_NAME: bdms}
+        self._test_create(params, no_image=True)
+
+    def test_create_instance_with_boot_index_none_image_local_fails(self):
+        """Tests creating a server with a local image-based block device which
+        has a boot_index of None which is invalid.
+        """
+        bdms = [{
+            'source_type': 'image',
+            'destination_type': 'local',
+            'boot_index': None,
+            'uuid': '155d900f-4e14-4e4c-a73d-069cbf4541e6'
+        }]
+        params = {block_device_mapping.ATTRIBUTE_NAME: bdms}
+        self.assertRaises(exc.HTTPBadRequest, self._test_create,
+                          params, no_image=True)
+
     def test_create_instance_with_device_name_not_string(self):
         self.bdm[0]['device_name'] = 123
         old_create = compute_api.API.create

releasenotes/notes/bug-1662699-06203e7262e02aa6.yaml

@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    Fixes `bug 1662699`_ which was a regression in the v2.1 API from the
+    ``block_device_mapping_v2.boot_index`` validation that was performed in the
+    legacy v2 API. With this fix, requests to create a server with
+    ``boot_index=None`` will be treated as if ``boot_index`` was not specified,
+    which defaults to meaning a non-bootable block device.
+
+    .. _bug 1662699: https://bugs.launchpad.net/nova/+bug/1662699