DMARC-Filter: OpenDMARC Filter v1.4.2 delorie.com 57U3CUsa1736901
Authentication-Results: delorie.com; dmarc=pass (p=none dis=none) header.from=cygwin.com
Authentication-Results: delorie.com; spf=pass smtp.mailfrom=cygwin.com
DKIM-Filter: OpenDKIM Filter v2.11.0 delorie.com 57U3CUsa1736901
Authentication-Results: delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=x0PALR/6
X-Recipient: archive-cygwin AT delorie DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 783A43858410
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1756523548;
	bh=Ntr62pdl6JJPKBtJH50XCECGsCkZSg23LgkxkaF9Rb8=;
	h=Date:To:Subject:In-Reply-To:References:List-Id:List-Unsubscribe:
	 List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:
	 From;
	b=x0PALR/6Kh3kDU5MnMnwtRGE6EEtr6eCUOG0cJk2avQC07DArA43ROOeBoeQBER/Z
	 Ou9RfUNpNZbHjkO3VUDmkhHr6i68wjAvDJtHmOI6jmavJgh1opuTPZRr1TacliODVt
	 4RPaRgEKBqDFpmvROYNXGrBmk/8ilqr6tFcItFMg=
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org A3486385841F
ARC-Filter: OpenARC Filter v1.0.0 sourceware.org A3486385841F
ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1756523475; cv=none;
 b=f1IpJqV29HDPdsoviwvuf9+yXfcKMCcK2vAHA8immXvA1YiT1fiB4jQ2/ibsIw0gb/8DeqFrbliHMKI3KH8PFwueX6ILxeqnGMvHfosfzA9QhwNge7qjK5zZnlYx+aArs/zH6QOdxGSKkIirpGWtv8Dceow8j7iUvxlKwkhT1B4=
ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key;
 t=1756523475; c=relaxed/simple;
 bh=RLPKnlH1fET180iJ36SEwDH24hFFcdr5jmK8n98BJCE=;
 h=Date:From:To:Subject:Message-Id:Mime-Version:DKIM-Signature;
 b=sNh8c/LwN0rLJFscC7DuOqnhd7Pa8z3TUXoHvny8FtIHynxMGJ1lJZJxBAnd7fsA+jfEbvVARX8EKWr2sdvRlFe+mJqS5DXysZwUjfKDRDPvmEJn7cVqXtccRsaFdxMcuh6TLRS8aeH/VCGHBMbsc507LeNzdbHltt4c7bfJxlo=
ARC-Authentication-Results: i=1; server2.sourceware.org
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A3486385841F
Date: Sat, 30 Aug 2025 12:11:11 +0900
To: cygwin AT cygwin DOT com
Subject: Re: pty read loop losing data in wsl context
Message-Id: <20250830121111.f6eda5bcc5ff659d43a635f3@nifty.ne.jp>
In-Reply-To: <1b1e8e7f-0ee9-41b8-931f-202af6704c4d@towo.net>
References: <1b1e8e7f-0ee9-41b8-931f-202af6704c4d AT towo DOT net>
X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.30; i686-pc-mingw32)
Mime-Version: 1.0
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.30
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
Content-Type: text/plain; charset="utf-8"
Errors-To: cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from base64 to 8bit by delorie.com id 57U3CUsa1736901

On Thu, 28 Aug 2025 05:36:06 +0200
Thomas Wolff wrote:
> When running wsl.exe from mintty, typing ^O corrupts terminal display.
> This was reported in
> https://github.com/mintty/mintty/issues/1332
> and I later reported it towards Windows conpty
> https://github.com/microsoft/terminal/issues/19285
> but conpty is unlikely the cause, as testing suggests.
> 
> Test case, in mintty:
> wsl
> ls -1 /bin
> ^O # enter the control character
> ls -1 /bin # repeat
> 
> The same happens in xterm and some other terminals, but not all.
> 
> Mintty uses a loop to read terminal output from the pty and fill its buffer:
>          do {
>            int ret = read(pty_fd, buf + len, sizeof buf - len);
>            if (ret > 0)
>              len += ret;
>            else
>              break;
>          } while (len < sizeof buf);
> Tracing the loop shows that, while running wsl, after having entered ^O, 
> every subsequent read returns -1.
> Taking out the loop (by patching it, or currently by using option Baud 
> with some high value) fixes the problem.
> I suspect some very obscure interworking problem between wsl/conpty and 
> cygwin pty handling. As noted in the latter issue, it does not happen 
> with terminals running remotely, so the suspicion goes more to the 
> cygwin side.
> What’s the role of ^O in this puzzle? Does it trigger something in cygwin?
> Is there anything peculiar that would cause pty chunks not be recognised 
> and then skipped in such a loop?

Thanks for the report. I fixed the Ctrl^O (FLUSHO) handling.
Please try cygwin-3.7.0-dev-286-g7b5fb35e.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple