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Subject:	Re: Incorrect behavior in TIOCINQ ioctl
To:	cygwin AT cygwin DOT com
References:	<d6a35f8b-3e4d-c8c6-4d3c-f15ccd72866d AT gmail DOT com> <20200228192330 DOT GN4045 AT calimero DOT vinschen DOT de>
From:	=?UTF-8?Q?=c3=85ke_Rehnman?= <ake DOT rehnman AT gmail DOT com>
Message-ID:	<09e4b16c-a4fb-4062-1d29-a92a916f186b@gmail.com>
Date:	Sat, 29 Feb 2020 11:37:25 +0100
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On 2020-02-28 20:23, Corinna Vinschen wrote:

> - Is it a safe bet that ClearCommError returns valid values in
>    st.cbInQue even if one of the error conditions occur?  Maybe the
>    right thing to do is to return 0 in certain error cases...?

The win32 api  documentation does not mention anything about not 
returning proper device status as long as the function succeeds...

Anyhow in my pursuit for the truth I whipped up a small test program and 
strace:d it (with some extra debug printout in fhandler_serial::ioctl)

  127 2403456 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=7
   216 3406481 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=E
    90 4409676 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=15
   141 5413027 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=1C
   129 6416204 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=23
   121 7419254 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=2A
   203 8423829 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=31
    89 9427183 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=38
   131 10431271 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=3F
   118 11435254 [main] python2.7 1662 fhandler_serial::ioctl: 0 = 
ioctl(541B, 0xFFFFBCB0) ev=C st.cbInQue=46

>
> - Did you actually try if this fixes your problem?  It's pretty
>    simple to build the Cygwin DLL
>    https://cygwin.com/faq.html#faq.programming.building-cygwin

I patched it yesterday and it solved the problem...

/Ake


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