linux-kernel - [PATCH 2/9] mnt: expose pointer to init_mnt

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Message-Id: <20250917-work-namespace-ns_common-v1-2-1b3bda8ef8f2@kernel.org>
Date: Wed, 17 Sep 2025 12:28:01 +0200
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org
Cc: Amir Goldstein <amir73il@...il.com>, Josef Bacik <josef@...icpanda.com>, 
 Jeff Layton <jlayton@...nel.org>, Mike Yuan <me@...dnzj.com>, 
 Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>, 
 Lennart Poettering <mzxreary@...inter.de>, 
 Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>, 
 Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
 Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
 Michal Koutný <mkoutny@...e.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>, cgroups@...r.kernel.org, 
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH 2/9] mnt: expose pointer to init_mnt_ns

There's various scenarios where we need to know whether we are in the
initial set of namespaces or not to e.g., shortcut permission checking.
All namespaces expose that information. Let's do that too.

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 fs/namespace.c                | 2 ++
 include/linux/mnt_namespace.h | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index a68998449698..c8251545d57e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -81,6 +81,7 @@ static DECLARE_RWSEM(namespace_sem);
 static HLIST_HEAD(unmounted);	/* protected by namespace_sem */
 static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
 static struct mnt_namespace *emptied_ns; /* protected by namespace_sem */
+struct mnt_namespace *init_mnt_ns;
 
 #ifdef CONFIG_FSNOTIFY
 LIST_HEAD(notify_list); /* protected by namespace_sem */
@@ -6037,6 +6038,7 @@ static void __init init_mount_tree(void)
 	set_fs_root(current->fs, &root);
 
 	ns_tree_add(ns);
+	init_mnt_ns = ns;
 }
 
 void __init mnt_init(void)
diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
index 70b366b64816..7e23c8364a9c 100644
--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h
@@ -11,6 +11,8 @@ struct fs_struct;
 struct user_namespace;
 struct ns_common;
 
+extern struct mnt_namespace *init_mnt_ns;
+
 extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *,
 		struct user_namespace *, struct fs_struct *);
 extern void put_mnt_ns(struct mnt_namespace *ns);

-- 
2.47.3