linux-kernel - Re: [PATCH 2/5] serial: core: add sysfs attribute to suppress ready signalling on open

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Message-ID: <X8Yjc0+Q7fM0nZP+@localhost>
Date:   Tue, 1 Dec 2020 12:05:23 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "Mychaela N . Falconia" <falcon@...ecalypso.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] serial: core: add sysfs attribute to suppress ready
 signalling on open

On Tue, Dec 01, 2020 at 12:55:54PM +0200, Andy Shevchenko wrote:
> On Tue, Dec 1, 2020 at 10:20 AM Johan Hovold <johan@...nel.org> wrote:
> > On Mon, Nov 30, 2020 at 08:27:54PM +0200, Andy Shevchenko wrote:
> > > On Mon, Nov 30, 2020 at 5:42 PM Johan Hovold <johan@...nel.org> wrote:
> 
> > > > +       ret = kstrtouint(buf, 0, &val);
> > > > +       if (ret)
> > > > +               return ret;
> > >
> > > > +       if (val > 1)
> > > > +               return -EINVAL;
> > >
> > > Can't we utilise kstrtobool() instead?
> >
> > I chose not to as kstrtobool() results in a horrid interface. To many
> > options to do the same thing and you end up with confusing things like
> > "0x01" being accepted but treated as false (as only the first character
> > is considered).
> 
> And this is perfectly fine. 0x01 is not boolean.

0x01 is 1 and is generally treated as boolean true as you know.

So why should a sysfs-interface accept it as valid input and treat it as
false? That's just bad design.

> > Not sure how that ever made it into sysfs code...
> >
> > The attribute is read back as "0" or "1" and those are precisely the
> > values that can be written back (well, modulo radix).
> 
> So, how does it affect the kstrtobool() interface?
> You read back 0 and 1 and they are pretty much accepted by it.
> 
> > It's not relevant in this case, but tight control over the inputs also
> > allows for extending the range later.
> 
> And kstrtobool() does it. So I don't see any difference except a few
> less lines of code and actually *stricter* rules than kstrtouint()
> has.

You miss the point; kstrobool accepts "12" today and treats it as true.
You cannot extend such an interface to later accept a larger range than
0 and 1 as you didn't return an error for "12" from the start (as someone
might now rely on "12" being treated as "1").

Johan