From 5bedb5e44757ba83dba9d618f5b951416cf44345 Mon Sep 17 00:00:00 2001
From: Olivier Certner <olce@FreeBSD.org>
Date: Wed, 29 Apr 2026 19:11:34 +0200
Subject: [PATCH] MAC/do: Comment to explain the main invariant for
 configurations

Once visible, configuration structures must *never* change.

Spell that out in a comment to help future readers/contributors
understand the design.

Reviewed by:    bapt
MFC after:      1 month
Sponsored by:   The FreeBSD Foundation
Pull Request:   https://ron-dev.freebsd.org/FreeBSD/src/pulls/38
---
 sys/security/mac_do/mac_do.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sys/security/mac_do/mac_do.c b/sys/security/mac_do/mac_do.c
index 125054d1542..4e7a65ae2ca 100644
--- a/sys/security/mac_do/mac_do.c
+++ b/sys/security/mac_do/mac_do.c
@@ -210,6 +210,11 @@ struct exec_paths {
 	int exec_path_count;
 };
 
+/*
+ * Once in use, i.e., being pointed to by a jail, a configuration structure MUST
+ * NEVER CHANGE (except for the 'use_count' field).  This invariant is
+ * fundamental to correctness!
+ */
 struct conf {
 	struct rules rules;
 	struct exec_paths exec_paths;