int vconn_open_block(const char *name, int min_version, struct vconn **);
int vconn_send_block(struct vconn *, struct ofpbuf *);
int vconn_recv_block(struct vconn *, struct ofpbuf **);
int vconn_open_block(const char *name, int min_version, struct vconn **);
int vconn_send_block(struct vconn *, struct ofpbuf *);
int vconn_recv_block(struct vconn *, struct ofpbuf **);