nsfs: move root inode number to uapi

Userspace relies on the root inode numbers to identify the initial
namespaces. That's already a hard dependency. So we cannot change that
anymore. Move the initial inode numbers to a public header.

Link: systemd/systemd@d293fad
Link: https://lore.kernel.org/20250606-work-nsfs-v1-1-b8749c9a8844@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

include/linux/proc_ns.h

@@ -6,6 +6,7 @@
 #define _LINUX_PROC_NS_H
 
 #include <linux/ns_common.h>
+#include <uapi/linux/nsfs.h>
 
 struct pid_namespace;
 struct nsset;
@@ -40,12 +41,12 @@ extern const struct proc_ns_operations timens_for_children_operations;
  */
 enum {
 	PROC_ROOT_INO		= 1,
-	PROC_IPC_INIT_INO	= 0xEFFFFFFFU,
-	PROC_UTS_INIT_INO	= 0xEFFFFFFEU,
-	PROC_USER_INIT_INO	= 0xEFFFFFFDU,
-	PROC_PID_INIT_INO	= 0xEFFFFFFCU,
-	PROC_CGROUP_INIT_INO	= 0xEFFFFFFBU,
-	PROC_TIME_INIT_INO	= 0xEFFFFFFAU,
+	PROC_IPC_INIT_INO	= IPC_NS_INIT_INO,
+	PROC_UTS_INIT_INO	= UTS_NS_INIT_INO,
+	PROC_USER_INIT_INO	= USER_NS_INIT_INO,
+	PROC_PID_INIT_INO	= PID_NS_INIT_INO,
+	PROC_CGROUP_INIT_INO	= CGROUP_NS_INIT_INO,
+	PROC_TIME_INIT_INO	= TIME_NS_INIT_INO,
 };
 
 #ifdef CONFIG_PROC_FS

include/uapi/linux/nsfs.h

@@ -42,4 +42,13 @@ struct mnt_ns_info {
 /* Get previous namespace. */
 #define NS_MNT_GET_PREV		_IOR(NSIO, 12, struct mnt_ns_info)
 
+enum init_ns_ino {
+	IPC_NS_INIT_INO		= 0xEFFFFFFFU,
+	UTS_NS_INIT_INO		= 0xEFFFFFFEU,
+	USER_NS_INIT_INO	= 0xEFFFFFFDU,
+	PID_NS_INIT_INO		= 0xEFFFFFFCU,
+	CGROUP_NS_INIT_INO	= 0xEFFFFFFBU,
+	TIME_NS_INIT_INO	= 0xEFFFFFFAU,
+};
+
 #endif /* __LINUX_NSFS_H */