+static inline struct vfsmount *first_slave(struct vfsmount *p)
+{
+ return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
+}
+
+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;
+ struct vfsmount *slave_mnt;
+
+ /*
+ * slave 'mnt' to a peer mount that has the
+ * same root dentry. If none is available than
+ * slave it to anything that is available.
+ */
+ while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
+ peer_mnt->mnt_root != mnt->mnt_root) ;
+
+ if (peer_mnt == mnt) {
+ peer_mnt = next_peer(mnt);
+ if (peer_mnt == mnt)
+ peer_mnt = NULL;
+ }
+ if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
+ mnt_release_group_id(mnt);
+
+ list_del_init(&mnt->mnt_share);
+ mnt->mnt_group_id = 0;
+
+ if (peer_mnt)
+ master = peer_mnt;
+
+ if (master) {
+ list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
+ slave_mnt->mnt_master = master;
+ list_move(&mnt->mnt_slave, &master->mnt_slave_list);
+ list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
+ INIT_LIST_HEAD(&mnt->mnt_slave_list);
+ } else {
+ struct list_head *p = &mnt->mnt_slave_list;
+ while (!list_empty(p)) {
+ slave_mnt = list_first_entry(p,
+ struct vfsmount, mnt_slave);
+ list_del_init(&slave_mnt->mnt_slave);
+ slave_mnt->mnt_master = NULL;
+ }
+ }
+ mnt->mnt_master = master;
+ CLEAR_MNT_SHARED(mnt);
+ return 0;
+}
+