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

1 files changed, 7 insertions, 0 deletions

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