1 files changed, 51 insertions, 0 deletions

diff --git a/fs/pnode.c b/fs/pnode.c
index d18d66491a01..8d5f392ec3d3 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -28,6 +28,57 @@ static inline struct vfsmount *next_slave(struct vfsmount *p)
         return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
 }
 
+/*
+ * Return true if path is reachable from root
+ *
+ * namespace_sem is held, and mnt is attached
+ */
+static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
+                         const struct path *root)
+{
+        while (mnt != root->mnt && mnt->mnt_parent != mnt) {
+                dentry = mnt->mnt_mountpoint;
+                mnt = mnt->mnt_parent;
+        }
+        return mnt == root->mnt && is_subdir(dentry, root->dentry);
+}
+
+static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
+                                            struct mnt_namespace *ns,
+                                            const struct path *root)
+{
+        struct vfsmount *m = mnt;
+
+        do {
+                /* Check the namespace first for optimization */
+                if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
+                        return m;
+
+                m = next_peer(m);
+        } while (m != mnt);
+
+        return NULL;
+}
+
+/*
+ * Get ID of closest dominating peer group having a representative
+ * under the given root.
+ *
+ * Caller must hold namespace_sem
+ */
+int get_dominating_id(struct vfsmount *mnt, const struct path *root)
+{
+        struct vfsmount *m;
+
+        for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
+                struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root);
+                if (d)
+                        return d->mnt_group_id;
+        }
+
+        return 0;
+}
+
 static int do_make_slave(struct vfsmount *mnt)
 {
         struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;