assembers/tar: add acls, selinux, xattrs options

Add the ability to opt out of preserving the ACLs, SELinux
contexts and extended attributes. It is opt out instead of
opt in since the assembler by default tries to preserve as
much as possible.

assemblers/org.osbuild.tar

@@ -13,6 +13,10 @@ Known options for `compression`: "bzip2", "xz", "lzip", "lzma", "lzop", "gzip".
 Note that using `compression` does not add an extension to `filename`, so the
 caller is responsible for making sure that `compression` and `filename` match.
 
+By default POSIX ACLs, SELinux contexts and extended attributes are included,
+in order to preserve the tree as closely as possible. It is possible to opt
+out of any of those by supplying the corresponding option.
+
 Buildhost commands used: `tar` and any named `compression` program.
 """
 
@@ -35,6 +39,21 @@ SCHEMA = """
     "description": "Name of compression program",
     "type": "string",
     "enum": ["bzip2", "xz", "lzip", "lzma", "lzop", "gzip"]
+  },
+  "acls": {
+      "description": "Enable support for POSIX ACLs",
+      "type": "boolean",
+      "default": true
+  },
+  "selinux": {
+      "description": "Enable support for SELinux contexts",
+      "type": "boolean",
+      "default": true
+  },
+  "xattrs": {
+      "description": "Enable support for extended attributes",
+      "type": "boolean",
+      "default": true
   }
 }
 """
@@ -57,11 +76,14 @@ def main(tree, output_dir, options):
     }
 
     # SELinux context, ACLs and extended attributes
-    extra_args += [
-        "--selinux",
-        "--acls",
-        "--xattrs", "--xattrs-include", "*",
-    ]
+    if options.get("acls", True):
+        extra_args += ["--acls"]
+
+    if options.get("selinux", True):
+        extra_args += ["--selinux"]
+
+    if options.get("xattrs", True):
+        extra_args += ["--xattrs", "--xattrs-include", "*"]
 
     # Set up the tar command.
     tar_cmd = [