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Re: [bug-inetutils] Telnetd fails to handle some of TIOCPKT control byte

From: Takashi Yano
Subject: Re: [bug-inetutils] Telnetd fails to handle some of TIOCPKT control bytes.
Date: Wed, 25 Mar 2015 07:12:31 +0900

Thank you for your detailed explanations.

I understood why your patch works without problem.

Best regards,
Takashi Yano

On Sun, 22 Mar 2015 10:37:37 +0100
Mats Erik Andersson <address@hidden> wrote:

> Dear Takashi Yano!
> Den 22 March 2015 klockan 14:32 skrev Takashi Yano detta:
> > Thank you for your reply.
> > 
> > With your patch, I have confirmed the problem has disappeared.
> > 
> > However, I am a little bit concerned about calling pty_get_char(0)
> > twice in the case of TIOCPKT_FLUSHWRITE or TIOCPKT_IOCTL.
> > 
> > Is it intentional behaviour?
> A relevant observation. When acting on TIOCPKT_IOCTL the call sequence
>      pty_get_char (0);
>      copy_termbuf ();   /* Pty buffer is now emtied.  */
>      localstat ();
> discards the packet preamble, then copies payload and resets the
> buffer. This will make sure that any following pty_get_char(0)
> becomes a no-op as no data is left. The remark above was introduced
> to the development head to record this observation, but I left it
> out in my comment to the list as is has no effect on the program.
> The case of TIOCPKT_FLUSHWRITE is different, as only the network
> buffer is touched, apart from the single pty_get_char(0). Now it
> seems that your worry is justified. According to pty(7D) on Solaris
>    When a pseudo-terminal is in packet mode, the controller
>    device will return data preceded by TIOCPKT_DATA (= 0),
>    or a single byte reflecting control status information.
> This means that TIOCPKT_FLUSHWRITE arrives isolated, so also in this
> case the pty buffer is empty after the first pty_get_char(0) and the
> second becomes a no-op again. However, even though the control byte
> was flushed, is is still preserved in the variable 'c', so the
> next test is still correct even if (TIOCPKT_FLUSHWRITE | TIOCPKT_STOP)
> had been received. Neither of TIOCPKT_NOSTOP and TIOCPKT_STOP touches
> the pty buffer, so no harmful side effect is possible. The code would
> look better without this first pty_get_char(0), so I might remove it
> for better understanding and quality.
> I thank you for your interest and care in this matter.
> Best regards,
>   Mats Erik Andersson

Takashi Yano <address@hidden>

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