3 files changed, 16 insertions, 11 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cffc402c2451..be56c2192926 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2700,18 +2700,22 @@ static inline struct user_namespace *file_mnt_user_ns(struct file *file)
 	return mnt_user_ns(file->f_path.mnt);
 }
 
+static inline struct mnt_idmap *file_mnt_idmap(struct file *file)
+{
+	return mnt_idmap(file->f_path.mnt);
+}
+
 /**
  * is_idmapped_mnt - check whether a mount is mapped
  * @mnt: the mount to check
  *
- * If @mnt has an idmapping attached different from the
- * filesystem's idmapping then @mnt is mapped.
+ * If @mnt has an non @nop_mnt_idmap attached to it then @mnt is mapped.
  *
  * Return: true if mount is mapped, false if not.
  */
 static inline bool is_idmapped_mnt(const struct vfsmount *mnt)
 {
-	return mnt_user_ns(mnt) != mnt->mnt_sb->s_user_ns;
+	return mnt_idmap(mnt) != &nop_mnt_idmap;
 }
 
 extern long vfs_truncate(const struct path *, loff_t);
diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h
index c8002294a72d..092c52aa6c2c 100644
--- a/include/linux/mnt_idmapping.h
+++ b/include/linux/mnt_idmapping.h
@@ -5,12 +5,10 @@
 #include <linux/types.h>
 #include <linux/uidgid.h>
 
+struct mnt_idmap;
 struct user_namespace;
-/*
- * Carries the initial idmapping of 0:0:4294967295 which is an identity
- * mapping. This means that {g,u}id 0 is mapped to {g,u}id 0, {g,u}id 1 is
- * mapped to {g,u}id 1, [...], {g,u}id 1000 to {g,u}id 1000, [...].
- */
+
+extern struct mnt_idmap nop_mnt_idmap;
 extern struct user_namespace init_user_ns;
 
 typedef struct {
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 55a4abaf6715..62475996fac6 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -16,6 +16,7 @@
 struct super_block;
 struct dentry;
 struct user_namespace;
+struct mnt_idmap;
 struct file_system_type;
 struct fs_context;
 struct file;
@@ -70,13 +71,15 @@ struct vfsmount {
 	struct dentry *mnt_root;	/* root of the mounted tree */
 	struct super_block *mnt_sb;	/* pointer to superblock */
 	int mnt_flags;
-	struct user_namespace *mnt_userns;
+	struct mnt_idmap *mnt_idmap;
 } __randomize_layout;
 
-static inline struct user_namespace *mnt_user_ns(const struct vfsmount *mnt)
+struct user_namespace *mnt_user_ns(const struct vfsmount *mnt);
+struct user_namespace *mnt_idmap_owner(const struct mnt_idmap *idmap);
+static inline struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt)
 {
 	/* Pairs with smp_store_release() in do_idmap_mount(). */
-	return smp_load_acquire(&mnt->mnt_userns);
+	return smp_load_acquire(&mnt->mnt_idmap);
 }
 
 extern int mnt_want_write(struct vfsmount *mnt);