proc_attach
proc = proc_attach(PROC_CLIENT, sock);
p_priv = proc_attach(PROC_PRIV, 3);
p_frontend = proc_attach(PROC_FRONTEND, fd);
p_priv = proc_attach(PROC_PRIV, 3);
p_priv = proc_attach(PROC_PRIV, 3);
p_engine = proc_attach(PROC_ENGINE, fd);
struct imsgproc *proc_attach(int, int);