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

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Message-ID: <X8ZDfvuRbxqsKZMh@localhost>
Date:   Tue, 1 Dec 2020 14:22:06 +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 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.

> > 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.

> > 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").
> 
> 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.

> 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.

Johan