[PATCH 03/13] vfs-introduce-clone_private_mount

[Miklos Szeredi <miklos@szeredi.hu>]

From: Miklos Szeredi <mszeredi@suse.cz>

Overlayfs needs a private clone of the mount, so create a function for
this and export to modules.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/namespace.c        |   18 ++++++++++++++++++
 include/linux/mount.h |    3 +++
 2 files changed, 21 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 50ca17d..9791b4e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1399,6 +1399,24 @@ void drop_collected_mounts(struct vfsmount *mnt)
 	release_mounts(&umount_list);
 }
 
+struct vfsmount *clone_private_mount(struct path *path)
+{
+	struct mount *old_mnt = real_mount(path->mnt);
+	struct mount *new_mnt;
+
+	if (IS_MNT_UNBINDABLE(old_mnt))
+		return ERR_PTR(-EINVAL);
+
+	down_read(&namespace_sem);
+	new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
+	up_read(&namespace_sem);
+	if (!new_mnt)
+		return ERR_PTR(-ENOMEM);
+
+	return &new_mnt->mnt;
+}
+EXPORT_SYMBOL_GPL(clone_private_mount);
+
 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
 		   struct vfsmount *root)
 {
diff --git a/include/linux/mount.h b/include/linux/mount.h
index d7029f4..344a262 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -66,6 +66,9 @@ extern void mnt_pin(struct vfsmount *mnt);
 extern void mnt_unpin(struct vfsmount *mnt);
 extern int __mnt_is_readonly(struct vfsmount *mnt);
 
+struct path;
+extern struct vfsmount *clone_private_mount(struct path *path);
+
 struct file_system_type;
 extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 				      int flags, const char *name,
-- 
1.7.10.4