linux-kernel - Re: [PATCH RFC] auxdisplay: charlcd: Fix and clean up handling of x/y commands

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Message-ID: <CAHp75VctsM0F4Ldf1zr4CJ2gF3ku3ejTHPYrUQKQ-rJVeX2Wog@mail.gmail.com>
Date:   Tue, 27 Feb 2018 22:52:24 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Willy Tarreau <w@....eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Robert Abel <rabel@...ertabel.eu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] auxdisplay: charlcd: Fix and clean up handling of x/y commands

On Tue, Feb 27, 2018 at 9:32 PM, Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
> The current version is not parsing multiple x/y commands as the code
> originally intended. On top of that, kstrtoul() expects
> NULL-terminated strings. Finally, the code had to do two passes over
> the string, while now only one is done.
>
> Some explanations about the supported syntax are added as well.

Something like this would work, but see my comments below.

> +/*
> + * Parses a base 10 number from a string, until a non-digit number is found or
> + * until PARSE_N_MAX_SIZE digits.
> + *
> + * See kstrtoul() for the meaning of the return value.
> + * It also returns the next character in the string, i.e. the first non-digit.
> + */
> +#define PARSE_N_MAX_SIZE (3)
> +static unsigned long parse_n(const char *s, unsigned long *res,
> +       const char **next_s)

static int parse_n(const char *s, unsigned long *res, const char **next_s)

> +{
> +       char tmp[PARSE_N_MAX_SIZE + 1];
> +       int i;
> +

First of all you need

unsigned int i = 0;

while (s[i] == '0')
 i++;

> +       for (i = 0; ; ++i) {
> +               if (!isdigit(s[i]))
> +                       break;
> +               if (i >= PARSE_N_MAX_SIZE)
> +                       return -EINVAL;
> +               tmp[i] = s[i];
> +       }

And here you partially open coded what simple_strto*() does.

> +
> +       tmp[i] = 0;
> +       *next_s = &s[i];
> +       return kstrtoul(tmp, 10, res);
> +}

It's over engineered. Just simple use simple_strto*() and that's all.
Do you really care about overflows? Is those numbers somehow critical?
What will go wrong?

-- 
With Best Regards,
Andy Shevchenko