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, 21 insertions, 0 deletions

diff --git a/tools/hook-hotplug b/tools/hook-hotplug
new file mode 100755
index 00000000..34e95929
--- /dev/null
+++ b/tools/hook-hotplug
@@ -0,0 +1,21 @@
+#!/bin/bash
+# This file is part of cloud-init. See LICENSE file for license information.
+
+# This script checks if cloud-init has hotplug hooked and if
+# cloud-init has finished; if so invoke cloud-init hotplug-hook
+
+is_finished() {
+    [ -e /run/cloud-init/result.json ]
+}
+
+if is_finished; then
+    # open cloud-init's hotplug-hook fifo rw
+    exec 3<>/run/cloud-init/hook-hotplug-cmd
+    env_params=(
+        --devpath="${DEVPATH}"
+        --subsystem="${SUBSYSTEM}"
+        --udevaction="${ACTION}"
+    )
+    # write params to cloud-init's hotplug-hook fifo
+    echo "${env_params[@]}" >&3
+fi