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Date:	Fri, 28 Feb 2020 20:23:30 +0100
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Cc:	=?utf-8?Q?=C3=85ke?= Rehnman <ake DOT rehnman AT gmail DOT com>
Subject:	Re: Incorrect behavior in TIOCINQ ioctl
Message-ID:	<20200228192330.GN4045@calimero.vinschen.de>
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Mail-Followup-To:	cygwin AT cygwin DOT com, =?utf-8?Q?=C3=85ke?= Rehnman <ake DOT rehnman AT gmail DOT com>
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On Feb 27 22:38, =C3=85ke Rehnman wrote:
> Hi,
>=20
> I recently ran in to some troubles with the TIOCINQ ioctl. I am wondering=
 if
> the cygwin implementation is correct... It seems if there were any existi=
ng
> framing overrun errors etc etc=C2=A0 before calling the TIOCINQ ioctl it =
is
> returning an error (EINVAL). Reading through linux implmentation of TIOCI=
NQ
> does simply return number of pending chars without any clearing or checki=
ng
> for errors.
>=20
> I suggest the whole if (ev & CE_FRAME=C2=A0 ...... ) is removed.
>=20
> Excerpt from fhandler_serial.cc:
>=20
> /* ioctl: */
> int
> fhandler_serial::ioctl (unsigned int cmd, void *buf)
> {
> .
> .
> =C2=A0 if (!ClearCommError (get_handle (), &ev, &st))
> =C2=A0=C2=A0=C2=A0 {
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 __seterrno ();
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 res =3D -1;
> =C2=A0=C2=A0=C2=A0 }
> .
> .
> .
> =C2=A0=C2=A0=C2=A0=C2=A0 case TIOCINQ:
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (ev & CE_FRAME || ev & CE_IOE || =
ev & CE_OVERRUN || ev & CE_RXOVER
> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0 || ev & CE_RXPARITY)
> =C2=A0=C2=A0=C2=A0 =C2=A0{
> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0 set_errno (EINVAL);=C2=A0=C2=A0=C2=A0 /* =
FIXME: Use correct errno */
> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0 res =3D -1;
> =C2=A0=C2=A0=C2=A0 =C2=A0}
> =C2=A0=C2=A0=C2=A0=C2=A0 else
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 ipbuf =3D st.cbInQue;
> =C2=A0=C2=A0=C2=A0=C2=A0 break;

I'm not familiar with serial I/O and the code is pretty stable(*).

- 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...?

- 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


Corinna

(*) euphemistically for "nobody looked into the code for a long time"


--=20
Corinna Vinschen
Cygwin Maintainer

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