linux-kernel - Re: [PATCH v2 1/2] USB: serial: ark3116: Remove unused TIOCSSERIAL ioctl case.

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Date:   Tue, 9 Jan 2018 00:45:30 +0300
From:   Mikhail Zaytsev <flashed@...l.ru>
To:     Johan Hovold <johan@...nel.org>
Cc:     Oliver Neukum <oneukum@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 1/2] USB: serial: ark3116: Remove unused TIOCSSERIAL
 ioctl case.

On Mon, 8 Jan 2018 16:28:58 +0100 Johan Hovold <johan@...nel.org> wrote:

> On Mon, Jan 08, 2018 at 11:33:32AM +0100, Oliver Neukum wrote:
> > Am Samstag, den 06.01.2018, 20:14 +0300 schrieb Mikhail Zaytsev:  
> > > The patch removes unused TIOCSSERIAL ioctl case and adds the default block
> > > to the switch. This will make the ioctl return -ENOTTY to user space (e.g.
> > > setserial), because TIOCSSERIAL really isn't supported for these devices
> > > currently.  
> > 
> > Hi,
> > 
> > this will break software that is now running on these devices,
> > won't it? Do you know why those devices basically ignore the
> > ioctl?  
> 
> Yeah, that was my initial reactions as well, but then again, any sane
> user space cannot rely on these ioctl being implemented for all tty
> devices.
> 
> I did some digging now and these (dummy) ioctl implementations where
> added by commit 2f430b4bbae7 ("USB: ark3116: Add TIOCGSERIAL and
> TIOCSSERIAL ioctl calls.") back in 2006.  This in turn appears to have
> been triggered by a change in a user space tool, wvdial, which started
> erroring out if either was missing.
> 
> I found a couple of bug reports about that through google, and looking
> at the wvstreams (library) code now, it looks like the issue has indeed
> been resolved by handling errors more gracefully (e.g. just logging
> them).
> 
> So I'm willing to give this a try, and if anyone complains later we add
> back (or implement) TIOCSSERIAL.
> 

Thanks Johan. I looked the commit 2f430b4bbae7. Author just did a cut'n'paste
 from other USB serial drivers. I think that it would be better remove
the TIOCGSERIAL implementation too.

Mikhail