stages: Add org.osbuild.rhsm stage to configure RHSM

Add new org.osbuild.rhsm stage to configure to configure RHSM DNF
plugins. The stage currently supports only enabling / disabling the DNF
plugins. The stage's configuration schema allows extending it in the
future to configure other aspects of RHSM if needed.

The schema specifies each DNF plugin as an explicit object. The reason
is that although currently only setting of one common option (enabled)
is allowed, the 'subscription-manager' plugin's configuration actually
allows one additional plugin-specific option. The stage may support
setting it in the future, which will be easier with distinct objects for
each plugin.

Signed-off-by: Tomas Hozza <thozza@redhat.com>

stages/org.osbuild.rhsm

@@ -0,0 +1,95 @@
+#!/usr/bin/python3
+"""
+Configure Red Hat Subscription Management (RHSM)
+
+The stage currently supports configuring only RHSM DNF plugins,
+specifically enabling and disabling them. In the future, this
+stage may be extended to configure also other aspects of RHSM.
+
+In case the stage is configured to enable/disable specific
+DNF plugins, it expects that the appropriate configuration files
+exist in the filesystem tree. Non-existence of the configuration
+files will make the stage fail.
+"""
+
+import sys
+import iniparse
+
+import osbuild.api
+
+
+SCHEMA = """
+"additionalProperties": false,
+"properties": {
+  "dnf-plugins": {
+    "additionalProperties": false,
+    "type": "object",
+    "description": "RHSM DNF plugins configuration",
+    "properties": {
+      "product-id": {
+        "additionalProperties": false,
+        "type": "object",
+        "description": "'product-id' DNF plugin configuration",
+        "properties": {
+          "enabled": {
+            "type": "boolean",
+            "description": "enablement state of the plugin"
+          }
+        }
+      },
+      "subscription-manager": {
+        "additionalProperties": false,
+        "type": "object",
+        "description": "'subscription-manager' DNF plugin configuration",
+        "properties": {
+          "enabled": {
+            "type": "boolean",
+            "description": "enablement state of the plugin"
+          }
+        }
+      }
+    }
+  }
+}
+"""
+
+
+def configure_dnf_plugins(tree, dnf_plugins_options):
+    for plugin, plugin_options in dnf_plugins_options.items():
+        plugin_conf_path = f"{tree}/etc/dnf/plugins/{plugin}.conf"
+        plugin_conf = iniparse.SafeConfigParser()
+
+        try:
+            with open(plugin_conf_path, "r") as f:
+                plugin_conf.readfp(f)
+        except FileNotFoundError as _:
+            print(f"Error: {plugin} configuration file '{plugin_conf_path}' does not exist.")
+            return 1
+
+        for option, value in plugin_options.items():
+            # defined by the "enabled" boolean option in the "main" section
+            if option == "enabled":
+                if not plugin_conf.has_section("main"):
+                    plugin_conf.add_section("main")
+                # rhsm plugins tend to use 0/1 for boolean values
+                plugin_conf.set("main", "enabled", str(int(value)))
+            else:
+                # schema does not allow any additional properties, but keeping this for completenes
+                print(f"Error: unknown property {option} specified for {plugin} plugin.")
+                return 1
+
+        with open(plugin_conf_path, "w") as f:
+            plugin_conf.write(f)
+
+    return 0
+
+
+def main(tree, options):
+    dnf_plugins_options = options.get("dnf-plugins", {})
+    return configure_dnf_plugins(tree, dnf_plugins_options)
+
+
+if __name__ == '__main__':
+    args = osbuild.api.arguments()
+    r = main(args["tree"], args.get("options", {}))
+    sys.exit(r)