Initial hotplug support (#936)

Adds a udev script which will invoke a hotplug hook script on all net
add events. The script will write some udev arguments to a systemd FIFO
socket (to ensure we have only instance of cloud-init running at a
time), which is then read by a new service that calls a new 'cloud-init
devel hotplug-hook' command to handle the new event.

This hotplug-hook command will:
- Fetch the pickled datsource
- Verify that the hotplug event is supported/enabled
- Update the metadata for the datasource
- Ensure the hotplugged device exists within the datasource
- Apply the config change on the datasource metadata
- Bring up the new interface (or apply global network configuration)
- Save the updated metadata back to the pickle cache

Also scattered in some unrelated typing where helpful

4 files changed, 26 insertions, 5 deletions

diff --git a/cloudinit/sources/DataSourceConfigDrive.py b/cloudinit/sources/DataSourceConfigDrive.py
index 62756cf7..19c8d126 100644
--- a/cloudinit/sources/DataSourceConfigDrive.py
+++ b/cloudinit/sources/DataSourceConfigDrive.py
@@ -12,9 +12,8 @@ from cloudinit import log as logging
 from cloudinit import sources
 from cloudinit import subp
 from cloudinit import util
-
+from cloudinit.event import EventScope, EventType
 from cloudinit.net import eni
-
 from cloudinit.sources.DataSourceIBMCloud import get_ibm_platform
 from cloudinit.sources.helpers import openstack
 
@@ -37,6 +36,13 @@ class DataSourceConfigDrive(openstack.SourceMixin, sources.DataSource):
 
     dsname = 'ConfigDrive'
 
+    supported_update_events = {EventScope.NETWORK: {
+        EventType.BOOT_NEW_INSTANCE,
+        EventType.BOOT,
+        EventType.BOOT_LEGACY,
+        EventType.HOTPLUG,
+    }}
+
     def __init__(self, sys_cfg, distro, paths):
         super(DataSourceConfigDrive, self).__init__(sys_cfg, distro, paths)
         self.source = None
diff --git a/cloudinit/sources/DataSourceEc2.py b/cloudinit/sources/DataSourceEc2.py
index 8a7f7c60..700437b0 100644
--- a/cloudinit/sources/DataSourceEc2.py
+++ b/cloudinit/sources/DataSourceEc2.py
@@ -76,6 +76,13 @@ class DataSourceEc2(sources.DataSource):
     # Whether we want to get network configuration from the metadata service.
     perform_dhcp_setup = False
 
+    supported_update_events = {EventScope.NETWORK: {
+        EventType.BOOT_NEW_INSTANCE,
+        EventType.BOOT,
+        EventType.BOOT_LEGACY,
+        EventType.HOTPLUG,
+    }}
+
     def __init__(self, sys_cfg, distro, paths):
         super(DataSourceEc2, self).__init__(sys_cfg, distro, paths)
         self.metadata_address = None
diff --git a/cloudinit/sources/DataSourceOpenStack.py b/cloudinit/sources/DataSourceOpenStack.py
index 619a171e..a85b71d7 100644
--- a/cloudinit/sources/DataSourceOpenStack.py
+++ b/cloudinit/sources/DataSourceOpenStack.py
@@ -8,11 +8,11 @@ import time
 
 from cloudinit import dmi
 from cloudinit import log as logging
-from cloudinit.net.dhcp import EphemeralDHCPv4, NoDHCPLeaseError
 from cloudinit import sources
 from cloudinit import url_helper
 from cloudinit import util
-
+from cloudinit.event import EventScope, EventType
+from cloudinit.net.dhcp import EphemeralDHCPv4, NoDHCPLeaseError
 from cloudinit.sources.helpers import openstack
 from cloudinit.sources import DataSourceOracle as oracle
 
@@ -46,6 +46,13 @@ class DataSourceOpenStack(openstack.SourceMixin, sources.DataSource):
     # Whether we want to get network configuration from the metadata service.
     perform_dhcp_setup = False
 
+    supported_update_events = {EventScope.NETWORK: {
+        EventType.BOOT_NEW_INSTANCE,
+        EventType.BOOT,
+        EventType.BOOT_LEGACY,
+        EventType.HOTPLUG
+    }}
+
     def __init__(self, sys_cfg, distro, paths):
         super(DataSourceOpenStack, self).__init__(sys_cfg, distro, paths)
         self.metadata_address = None
diff --git a/cloudinit/sources/__init__.py b/cloudinit/sources/__init__.py
index 9d25b0ee..bf6bf139 100644
--- a/cloudinit/sources/__init__.py
+++ b/cloudinit/sources/__init__.py
@@ -23,6 +23,7 @@ from cloudinit import type_utils
 from cloudinit import user_data as ud
 from cloudinit import util
 from cloudinit.atomic_helper import write_json
+from cloudinit.distros import Distro
 from cloudinit.event import EventScope, EventType
 from cloudinit.filters import launch_index
 from cloudinit.persistence import CloudInitPickleMixin
@@ -215,7 +216,7 @@ class DataSource(CloudInitPickleMixin, metaclass=abc.ABCMeta):
 
     _ci_pkl_version = 1
 
-    def __init__(self, sys_cfg, distro, paths, ud_proc=None):
+    def __init__(self, sys_cfg, distro: Distro, paths, ud_proc=None):
         self.sys_cfg = sys_cfg
         self.distro = distro
         self.paths = paths