Draw9p.readdrawrefresh = function(dd, offset, callback){	cons.log("readdrawrefresh"); 	var conn = this.conns[dd.drawdir];	if(conn == undefined){		return callback.error("invalid draw connection");	} 	/* XXX This breaks if multiple reads are outstanding on the */	/* refresh file!  Should we permit this and use some sort of */	/* array of refreshcallbacks, or should we be setting (and */	/* obeying!) the exclusive-use bit on the relevant [qf]id? */	if(conn.refreshcallback != undefined){ 		return callback.error("multiple reads are not allowed");	} 	conn.refreshcallback = callback;}