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Date: Tue, 17 Mar 2020 13:16:03 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Setting termios VMIN > 0 and VTIME > 0 on non blocking file
Message-ID: <20200317121603.GI512788@calimero.vinschen.de>
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Hi =C3=85ke,

On Mar 16 10:35, Corinna Vinschen wrote:
> On Mar 14 11:36, =C3=85ke Rehnman via Cygwin wrote:
> > On 2020-03-14 11:23, =C3=85ke Rehnman wrote:
> > > > > BTW there is a gremlin in the "else if (ev)" line....
> > > > A gremlin?=C2=A0 Would you mind to explain?=C2=A0 Btw., if you find=
 a bug
> > > > in the code, we do take patches :) https://cygwin.com/contrib.html
> > > If we have an error event in ev it will make a blocking read even if
> > > VTIME=3D=3D0.
>=20
> Ah, yeah, I was aware of that, I just ignored it for now since I'm not
> sure what the best way to handle that is.
>=20
> Two options come to mind, either ignoring these errors entirely, or
> returning -1 with errno set to EIO, along the lines of the Linux test
> for tty_io_error() at the start of tty_read.
>=20
> However, I have a sinking feeling that the function needs a rewrite
> anyway.
>=20
> For instance, consider reading in blocking mode, which may result in
> running the for loop more than once.  If the first loop successfully
> read 4 bytes, and the second loop runs into an error from
> ClearCommError, the function will return -1 with errno set, completely
> ignoring the fact that 4 bytes have been read already.
>=20
> It should return 4 in this case, and only the next run of
> fhandler_serial::raw_read *might* return -1.
>=20
> This code really shows its age...

I have revamped the fhandler_serial::raw_read function, but I need
somebody for testing.  Any chance you volunteer for that job?
We may need a couple of days to iron out all problems, but I think
the code is more sound now than the original function.  I even
added a couple of comments to the code (*gasp*) so there's stuff
to discuss and to see why I did it that way.

For a quicker turn around we can also use Freenode IRC, see
https://cygwin.com/irc.html

Interested?


Thanks,
Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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