1 files changed, 32 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index e5e1c7d1839b..6d3a1963879b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2483,11 +2483,43 @@ struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt)
                 __mnt_make_longterm(mnt);
                 new_ns->root = mnt;
                 list_add(&new_ns->list, &new_ns->root->mnt_list);
+        } else {
+                mntput(mnt);
         }
         return new_ns;
 }
 EXPORT_SYMBOL(create_mnt_ns);
 
+struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
+{
+        struct mnt_namespace *ns;
+        struct super_block *s;
+        struct path path;
+        int err;
+
+        ns = create_mnt_ns(mnt);
+        if (IS_ERR(ns))
+                return ERR_CAST(ns);
+
+        err = vfs_path_lookup(mnt->mnt_root, mnt,
+                        name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
+
+        put_mnt_ns(ns);
+
+        if (err)
+                return ERR_PTR(err);
+
+        /* trade a vfsmount reference for active sb one */
+        s = path.mnt->mnt_sb;
+        atomic_inc(&s->s_active);
+        mntput(path.mnt);
+        /* lock the sucker */
+        down_write(&s->s_umount);
+        /* ... and return the root of (sub)tree on it */
+        return path.dentry;
+}
+EXPORT_SYMBOL(mount_subtree);
+
 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
                 char __user *, type, unsigned long, flags, void __user *, data)
 {