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From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Sascha Hauer <kernel@pengutronix.de>,
	"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jacek Anaszewski <jacek.anaszewski@gmail.com>,
	Pavel Machek <pavel@ucw.cz>, Jiri Slaby <jslaby@suse.com>,
	Linux LED Subsystem <linux-leds@vger.kernel.org>,
	Dan Murphy <dmurphy@ti.com>
Subject: Re: [PATCH v6 1/4] lib: new helper kstrtodev_t()
Date: Thu, 20 Feb 2020 11:57:18 +0100
Message-ID: <20200220105718.eoevd3kb63zzrotu@pengutronix.de> (raw)
In-Reply-To: <CAHp75VcxXWputX1y90t8f-c0a3dw2CHU6=ebQ+o6e8Z1GymiDw@mail.gmail.com>

Hello Andy,

On Thu, Feb 20, 2020 at 12:22:36PM +0200, Andy Shevchenko wrote:
> On Thu, Feb 20, 2020 at 9:49 AM Uwe Kleine-König
> <u.kleine-koenig@pengutronix.de> wrote:
> > On Wed, Feb 19, 2020 at 09:50:54PM +0200, Andy Shevchenko wrote:
> > > On Thu, Feb 13, 2020 at 11:27 AM Uwe Kleine-König <uwe@kleine-koenig.org> wrote:
> > > >
> > > > This function is in the same spirit as the other kstrto* functions and
> > > > uses the same calling convention. It expects the input string to be in
> > > > the format %u:%u and implements stricter parsing than sscanf as it
> > > > returns an error on trailing data (other than the usual \n).
> 
> ...
> 
> > > On top of that, why kstrtodev_t is so important? How many users are
> > > already in the kernel to get an advantage out of it?
> >
> > Does it need to be important? It matches the other kstrto* functions and
> > so it seemed more natural to me to put it near the other functions. I'm
> > not aware of other potential users and surprised you seem to suggest
> > this as a requirement.
> 
> Yes it does. The kstrtox() are quite generic, what you are proposing
> is rather one particular case with blurry understanding how many users
> will be out of it.

In my understanding one user is a hard requirement.

> If you had told "look, we have 1234 users which may benefit out of
> it", I would have given no comment against.

Sure, having >1000 potential users would be a good argument pro this
function. But having only one isn't a good contra IMHO.

> > > What to do with all other possible variants ("%d:%d", "%dx%d" and its
> > > %u variant, etc)?
> >
> > I don't see how %d:%d is relevant, major and minor cannot be negative
> > can they? I never saw 'x' as separator between major and minor. I
> > considered shortly parsing %u, but given that (I think) this is an
> > internal representation only I chose to not make it more visible than it
> > already is.
> 
> See above, if we are going to make it generic, perhaps better to cover
> more possible users, right?
> Otherwise your change provokes pile of (replaced)
> kstrto_resolution() /* %ux:%u */
> kstrto_range() /* %d:%d */
> kstrto_you_name_it()

Given there are respective types that this can be stored to, I don't
object more functions of this type and don't see a good reason to not
add such a function. And in my eyes I prefer to have such a function in
a visible place (i.e. where all the other kstrto* functions are) to
prevent code duplication.

Also I don't understand yet, what you want me to do. Assume I'd be
willing to use simple_strtoul, I'd still want to have a function that
gives me a dev_t from a given string. Should I put this directly in my
led-trigger driver?

> > > Why simple_strto*() can't be used?
> >
> > I didn't really consider it, but looking in more detail I don't like it
> > much. Without having tried it I think simple_strtoull accepts
> > "1000000000000000000000000000000000000000000" returning some arbitrary
> > value without an error indication.
> 
> So what? User has a lot of possibilities to shoot into the foot.
> Since you interpret this as device major:minor, not founding a device
> will be first level of error, next one when your code will try to do
> something out of it. It shouldn't be a problem of kstrtox generic
> helpers.

I fail to follow your argument here. In my eyes if the user writes a
valid major:minor it should work, and if they write an invalid one this
should result in an error and not a usage of a device that just happens
to have the major:minor that simple_strtoull happens to return for the
two components.

> > And given that I was asked for strict
> > parsing (i.e. not accepting 2:4:something) I'd say using simple_strto*
> > is a step backwards. Also simple_strtoul() has "This function is obsolete.
> > Please use kstrtoul instead." in its docstring which seems to apply to
> > the other simple_strto*() functions, too.
> 
> I specifically fixed a doc string to approve its use in the precisely
> cases you have here.

Can you please be a bit more constructive here and point to the change
you talk about? I didn't find a commit in next.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13  9:15 [PATCH v6 0/4] leds: trigger: implement a tty trigger Uwe Kleine-König
2020-02-13  9:15 ` [PATCH v6 1/4] lib: new helper kstrtodev_t() Uwe Kleine-König
2020-02-19 19:50   ` Andy Shevchenko
2020-02-20  7:49     ` Uwe Kleine-König
2020-02-20 10:22       ` Andy Shevchenko
2020-02-20 10:57         ` Uwe Kleine-König [this message]
2020-02-20 11:46           ` Andy Shevchenko
2020-02-20 11:57             ` Andy Shevchenko
2020-02-20 14:01             ` Uwe Kleine-König
2020-02-21  8:42               ` Andy Shevchenko
2020-02-21 10:53                 ` Uwe Kleine-König
2020-04-25  7:07           ` Pavel Machek
2020-02-13  9:15 ` [PATCH v6 2/4] tty: rename tty_kopen() and add new function tty_kopen_shared() Uwe Kleine-König
2020-02-19 13:21   ` Johan Hovold
2020-02-19 16:37     ` Uwe Kleine-König
2020-02-19 17:17       ` Johan Hovold
2020-02-20 11:04         ` Uwe Kleine-König
2020-02-25  8:55           ` Johan Hovold
2020-02-25  9:05             ` Uwe Kleine-König
2020-02-13  9:15 ` [PATCH v6 3/4] tty: new helper function tty_get_icount() Uwe Kleine-König
2020-02-13  9:16 ` [PATCH v6 4/4] leds: trigger: implement a tty trigger Uwe Kleine-König
2020-02-19 10:52   ` Johan Hovold
2020-02-19 11:03     ` Uwe Kleine-König
2020-02-19 11:19       ` Johan Hovold
2020-02-19 12:48         ` Johan Hovold
2020-02-19 10:40 ` [PATCH v6 0/4] " Greg Kroah-Hartman
2020-02-26 14:02   ` Pavel Machek

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