int cluster_push(vnode_t, int);
int cluster_push_ext(vnode_t, int, int (*)(buf_t, void *), void *);
+int cluster_push_err(vnode_t, int, int (*)(buf_t, void *), void *, int *);
int cluster_bp(buf_t);
int cluster_bp_ext(buf_t, int (*)(buf_t, void *), void *);