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

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Message-ID: <CAHp75Vct+J7=BaUdzBktQvKvThCuC-HmyRP2s4LRJvgsE2A2UA@mail.gmail.com>
Date:   Tue, 1 Dec 2020 15:49:19 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     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 1, 2020 at 3:21 PM Johan Hovold <johan@...nel.org> wrote:
> On Tue, Dec 01, 2020 at 01:19:30PM +0200, Andy Shevchenko wrote:
> > On Tue, Dec 1, 2020 at 1:04 PM Johan Hovold <johan@...nel.org> wrote:

...

> > > 0x01 is 1 and is generally treated as boolean true as you know.
> >
> > Depends how you interpret this. kstrtobool() uses one character (and
> > in some cases two) of the input. Everything else is garbage.
> > Should we interpret garbage?
>
> No, ideally we should reject the input.

We can do it by the way in kstrtobool() and see if anybody complains
(I believe the world is saner than relying on 0x01 for false and 123
for true.

...

> > > So why should a sysfs-interface accept it as valid input and treat it as
> > > false? That's just bad design.
> >
> > I can agree with this.
>
> Looks like part of the problem are commits like 4cc7ecb7f2a6 ("param:
> convert some "on"/"off" users to strtobool") which destroyed perfectly
> well-defined interfaces.

Oh, but the strtobool() in ABI was before that, for instance
 % git grep -n -p -w strtobool v3.14
shows a few dozens of users and some of them looks like ABI.

...

> > Somehow cifs uses kstrtobool() in conjunction with the wider ranges. Nobody
> > complained so far. But maybe they had it from day 1.
>
> Wow, that's pretty nasty.

I have checked, the wider range fits one character. So, basically they
had this kind of interface from day 1.

...

> > So, we have two issues here: kstrtobool() doesn't report an error of
> > input when it has garbage, the user may rely on garbage to be
> > discarded.
>
> Right, parsing is too allowing and there are too many ways to say
> true/false.
>
> The power-management attributes use 0 and 1 for boolean like I do here,
> and I'd prefer to stick to that until we have deprecated the current
> kstrtobool.

Okay!


-- 
With Best Regards,
Andy Shevchenko