linux-kernel - Re: [PATCH 0/2] usb: serial: handle -ENODEV and -EPROTO quietly

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Date:	Mon, 15 Dec 2014 23:10:37 -0800
From:	Jeremiah Mahler <jmmahler@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Johan Hovold <johan@...nel.org>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] usb: serial: handle -ENODEV and -EPROTO quietly

Greg,

On Mon, Dec 15, 2014 at 08:38:01AM -0800, Greg Kroah-Hartman wrote:
> On Mon, Dec 15, 2014 at 04:53:05AM -0800, Jeremiah Mahler wrote:
> > Johan,
> > 
> > On Mon, Dec 15, 2014 at 11:23:21AM +0100, Johan Hovold wrote:
> > > On Thu, Dec 11, 2014 at 03:29:52PM -0800, Jeremiah Mahler wrote:
> > > > If a USB serial device (e.g. /dev/ttyUSB0) with an active program is
> > > > unplugged, a bunch of -ENODEV and -EPROTO errors will be produced in the
> > > > logs.  This patch set quiets these messages without changing the
> > > > original behavior.
> > > 
> > > Don't unplug devices that are in use then. ;)
> > > 
> > I knew someone was going to say that :-)
> > 
> > > > This change is beneficial when using daemons such as slcand, which is
> > > > similar to pppd or slip, that cannot determine whether they should exit
> > > > until after the USB serial device is unplugged.  Producing these error
> > > > messages for a normal use case is not helpful.
> > > 
> > > Your patches would hide these errors when they occur during normal use
> > > (e.g. EPROTO).
> > > 
> > > Receiving an error message when unplugging an active device should not
> > > surprise anyone. And at least you know where it came from (and it's
> > > right there in the logs as well).
> > > 
> > > Johan
> > 
> > Hmm.  Yes, I can see why quieting -EPROTO would be bad because it would
> > hide protocol errors which we want to know about.
> 
> Do you really want to "know about" them?  What can a user do with them?
> Nothing, so just resubmit and you should be fine.
> 
> > I need to re-think this patch.
> > Nack.
> 
> I like this patch, putting crud in the kernel log that no one can do
> anything with for a "normal" operation like yanking a USB device out
> while it is open should not happen.
> 
> thanks,
> 
> greg k-h

Perhaps something at a lower level could return a more apt error number
such as -ENODEV.  Then there would be no conflict with -EPROTO.

I will look in to it again and re-submit the patches.

-- 
- Jeremiah Mahler
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