Hi Zhenhua,

> @@ -278,6 +278,7 @@ void g_at_hdlc_unref(GAtHDLC *hdlc)
>  		hdlc->record_fd = -1;
>  	}
>  
> +	g_at_io_set_disconnect_function(hdlc->io, NULL, NULL);

Since GAtHDLC does not set the disconnect function, this really belongs
in GAtPPP.

>  	g_at_io_unref(hdlc->io);
>  	hdlc->io = NULL;
>  

However, I really question why this patch is necessary.  The only way
the disconnect function is not reset today is if the GAtIO is refed and
g_at_chat_resume is not called.

We do call g_at_io_set_disconnect function in g_at_chat_resume.

Regards,
-Denis