stages/selinux: add an selinux stage

This stage labels the target tree based on an SELinux policy already
installed in the target.

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

samples/base-with-selinux.json

@@ -0,0 +1,23 @@
+{
+  "name": "base-with-selinux",
+  "stages": [
+    {
+      "name": "io.weldr.untree",
+      "options": {
+        "tree": "base"
+      }
+    },
+    {
+      "name": "io.weldr.selinux",
+      "options": {
+        "file_contexts": "etc/selinux/targeted/contexts/files/file_contexts"
+      }
+    }
+  ],
+  "assembler": {
+    "name": "io.weldr.tree",
+    "options": {
+      "tree": "base-with-selinux"
+    }
+  }
+}

samples/base.json

@@ -14,7 +14,8 @@
           }
         },
         "packages": [
-          "@Core"
+          "@Core",
+          "selinux-policy-targeted"
         ]
       }
     }

stages/io.weldr.selinux

@@ -0,0 +1,16 @@
+#!/usr/bin/python3
+
+import json
+import os
+import subprocess
+import sys
+
+def main(tree, options):
+    file_contexts = os.path.join(f"{tree}", options["file_contexts"])
+
+    subprocess.run(["setfiles", "-F", "-r", f"{tree}", f"{file_contexts}", f"{tree}"], check=True)
+
+if __name__ == '__main__':
+    args = json.load(sys.stdin)
+    r = main(args["tree"], args["options"])
+    sys.exit(r)