Add "install hotplug" module (SC-476) (#1069)

This commit removes automatically installing udev rules for hotplug
and adds a module to install them instead.

Automatically including the udev rules and checking if hotplug was
enabled consumed too many resources in certain circumstances. Moving the
rules to a module ensures we don't spend extra extra cycles on hotplug
if hotplug functionality isn't desired.

LP: #1946003

1 files changed, 136 insertions, 0 deletions

diff --git a/cloudinit/config/cc_install_hotplug.py b/cloudinit/config/cc_install_hotplug.py
new file mode 100644
index 00000000..d6b2a2df
--- /dev/null
+++ b/cloudinit/config/cc_install_hotplug.py
@@ -0,0 +1,136 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+"""Install hotplug udev rules if supported and enabled"""
+import os
+from textwrap import dedent
+
+from cloudinit import util
+from cloudinit import subp
+from cloudinit import stages
+from cloudinit.config.schema import get_schema_doc, validate_cloudconfig_schema
+from cloudinit.distros import ALL_DISTROS
+from cloudinit.event import EventType, EventScope
+from cloudinit.settings import PER_INSTANCE
+
+
+frequency = PER_INSTANCE
+distros = [ALL_DISTROS]
+
+schema = {
+    "id": "cc_install_hotplug",
+    "name": "Install Hotplug",
+    "title": "Install hotplug if supported and enabled",
+    "description": dedent("""\
+        This module will install the udev rules to enable hotplug if
+        supported by the datasource and enabled in the userdata. The udev
+        rules will be installed as
+        ``/etc/udev/rules.d/10-cloud-init-hook-hotplug.rules``.
+
+        When hotplug is enabled, newly added network devices will be added
+        to the system by cloud-init. After udev detects the event,
+        cloud-init will referesh the instance metadata from the datasource,
+        detect the device in the updated metadata, then apply the updated
+        network configuration.
+
+        Currently supported datasources: Openstack, EC2
+    """),
+    "distros": distros,
+    "examples": [
+        dedent("""\
+            # Enable hotplug of network devices
+            updates:
+              network:
+                when: ["hotplug"]
+        """),
+        dedent("""\
+            # Enable network hotplug alongside boot event
+            updates:
+              network:
+                when: ["boot", "hotplug"]
+        """),
+    ],
+    "frequency": frequency,
+    "type": "object",
+    "properties": {
+        "updates": {
+            "type": "object",
+            "additionalProperties": False,
+            "properties": {
+                "network": {
+                    "type": "object",
+                    "required": ["when"],
+                    "additionalProperties": False,
+                    "properties": {
+                        "when": {
+                            "type": "array",
+                            "additionalProperties": False,
+                            "items": {
+                                "type": "string",
+                                "additionalProperties": False,
+                                "enum": [
+                                    "boot-new-instance",
+                                    "boot-legacy",
+                                    "boot",
+                                    "hotplug",
+                                ]
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+__doc__ = get_schema_doc(schema)
+
+
+HOTPLUG_UDEV_PATH = "/etc/udev/rules.d/10-cloud-init-hook-hotplug.rules"
+HOTPLUG_UDEV_RULES = """\
+# Installed by cloud-init due to network hotplug userdata
+ACTION!="add|remove", GOTO="cloudinit_end"
+LABEL="cloudinit_hook"
+SUBSYSTEM=="net", RUN+="/usr/lib/cloud-init/hook-hotplug"
+LABEL="cloudinit_end"
+"""
+
+
+def handle(_name, cfg, cloud, log, _args):
+    validate_cloudconfig_schema(cfg, schema)
+    network_hotplug_enabled = (
+        'updates' in cfg and
+        'network' in cfg['updates'] and
+        'when' in cfg['updates']['network'] and
+        'hotplug' in cfg['updates']['network']['when']
+    )
+    hotplug_supported = EventType.HOTPLUG in (
+        cloud.datasource.get_supported_events(
+            [EventType.HOTPLUG]).get(EventScope.NETWORK, set())
+    )
+    hotplug_enabled = stages.update_event_enabled(
+        datasource=cloud.datasource,
+        cfg=cfg,
+        event_source_type=EventType.HOTPLUG,
+        scope=EventScope.NETWORK,
+    )
+    if not (hotplug_supported and hotplug_enabled):
+        if os.path.exists(HOTPLUG_UDEV_PATH):
+            log.debug("Uninstalling hotplug, not enabled")
+            util.del_file(HOTPLUG_UDEV_PATH)
+            subp.subp(["udevadm", "control", "--reload-rules"])
+        elif network_hotplug_enabled:
+            log.warning(
+                "Hotplug is unsupported by current datasource. "
+                "Udev rules will NOT be installed."
+            )
+        else:
+            log.debug("Skipping hotplug install, not enabled")
+        return
+    if not subp.which("udevadm"):
+        log.debug("Skipping hotplug install, udevadm not found")
+        return
+
+    util.write_file(
+        filename=HOTPLUG_UDEV_PATH,
+        content=HOTPLUG_UDEV_RULES,
+    )
+    subp.subp(["udevadm", "control", "--reload-rules"])