stages/waagent.conf: set WALinuxAgent configuration

This is requried to comply with Azure marketplace best
practices. The WALinuxAgent should not handle formating or
swap, as that is done by cloud-init.

Signed-off-by: Tom Gundersen <teg@jklm.no>

stages/org.osbuild.waagent.conf

@@ -0,0 +1,86 @@
+#!/usr/bin/python3
+"""
+Configure the WALinuxAgent.
+
+The tree must already include /etc/waagent.conf, and it is modified
+in place. Every attempt is made to preserve the structure of the file,
+though comments are completely ignored.
+"""
+
+import fileinput
+import sys
+
+import osbuild.api
+
+
+SCHEMA = """
+"additionalProperties": false,
+"required": ["config"],
+"properties": {
+  "config": {
+    "additionalProperties": false,
+    "description": "WALinuxAgent config options",
+    "type": "object",
+    "properties": {
+      "ResourceDisk.Format": {
+        "description": "Enable or disable disk formatting.",
+        "type": "boolean"
+      },
+      "ResourceDisk.EnableSwap": {
+        "description": "Enable or disable swap.",
+        "type": "boolean"
+      }
+    }
+  }
+}
+"""
+
+
+def bool_to_y_n(b):
+    if b:
+        return "y"
+    return "n"
+
+
+def main(tree, options):
+    sshd_config = options.get("config", {})
+    resource_disk_format = sshd_config.get("ResourceDisk.Format")
+    resource_disk_enable_swap = sshd_config.get("ResourceDisk.EnableSwap")
+    changes = {}
+    if resource_disk_format is not None:
+        changes["resourcedisk.format"] = {
+            "key": "ResourceDisk.Format",
+            "value": bool_to_y_n(resource_disk_format)
+        }
+    if resource_disk_enable_swap is not None:
+        changes["resourcedisk.enableswap"] = {
+            "key": "ResourceDisk.EnableSwap",
+            "value": bool_to_y_n(resource_disk_enable_swap)
+        }
+
+    # For each of the configured options, find the first non-commented out instance
+    # of the option and replace it (if necessary). If it does not already exist, append
+    # the option to the end of the file.
+    # Keys are case insensitive, values are not. Try to preserve the key and default to
+    # camel-case.
+    with fileinput.input(files=(f"{tree}/etc/waagent.conf"), inplace=True) as f:
+        for line in f:
+            line_list = line.split(sep='=')
+            if len(line_list) == 2:
+                key, current_value = line_list
+                entry = changes.pop(key.lower(), None)
+                if entry is not None and current_value != entry['value']:
+                    sys.stdout.write(f"{key}={entry['value']}\n")
+                    continue
+            sys.stdout.write(line)
+    with open(f"{tree}/etc/waagent.conf", mode="a") as f:
+        for entry in changes.values():
+            f.write(f"{entry['key']}={entry['value']}\n")
+
+    return 0
+
+
+if __name__ == '__main__':
+    args = osbuild.api.arguments()
+    r = main(args["tree"], args["options"])
+    sys.exit(r)