linux-kernel - Re: [RESEND PATCH] string_helpers: sysfs: Add helper to get bool from string

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Message-ID: <YmeUKg9s5AZUKXj8@li-6e1fa1cc-351b-11b2-a85c-b897023bb5f3.ibm.com>
Date:   Tue, 26 Apr 2022 12:11:46 +0530
From:   Jagdish Gediya <jvgediya@...ux.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     andy@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        minchan@...nel.org, ying.huang@...el.com, dave.hansen@...el.com
Subject: Re: [RESEND PATCH] string_helpers: sysfs: Add helper to get bool
 from string

On Mon, Apr 25, 2022 at 03:00:46PM -0700, Andrew Morton wrote:
> On Mon, 25 Apr 2022 14:22:33 +0530 Jagdish Gediya <jvgediya@...ux.ibm.com> wrote:
> 
> > At many places in kernel, It is necessary to convert sysfs input
> > to corrosponding bool value e.g. "false" or "0" need to be converted
> > to bool false, "true" or "1" need to be converted to bool true,
> > places where such conversion is needed currently check the input
> > string manually. Also, such conversions compare sysfs input using
> > strncmp functions so even if certain number of character match in the
> > beginning, they assume the string as valid bool, which is not the
> > right semantic e.g. false is bool but falseX is not.
> > 
> > Introduce new string helper function to convert sysfs input to
> > corrosponding bool value. Modify existing such conversions to use
> > this new function.
> > 
> > logs,
> > $ cat /sys/kernel/mm/numa/demotion_enabled
> > false
> > $ echo true > /sys/kernel/mm/numa/demotion_enabled
> > $ cat demotion_enabled
> > true
> > $ echo truex > /sys/kernel/mm/numa/demotion_enabled
> > -bash: echo: write error: Invalid argument
> > $ echo 10 > /sys/kernel/mm/numa/demotion_enabled
> > -bash: echo: write error: Invalid argument
> > $ echo false > /sys/kernel/mm/numa/demotion_enabled
> > $ cat demotion_enabled
> > false
> > $ echo falseabc > /sys/kernel/mm/numa/demotion_enabled
> > -bash: echo: write error: Invalid argument
> > $ echo 1 > /sys/kernel/mm/numa/demotion_enabled
> > $ cat demotion_enabled
> > true
> > $ echo 0 > /sys/kernel/mm/numa/demotion_enabled
> > $ cat demotion_enabled
> > false
> > 
> > This patch doesn't have any functionality change.
> > 
> > ...
> >
> > --- a/lib/string_helpers.c
> > +++ b/lib/string_helpers.c
> > @@ -967,6 +967,26 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
> >  }
> >  EXPORT_SYMBOL(memcpy_and_pad);
> >  
> > +/**
> > + * sysfs_strbool - Get bool value corrosponding to string
> > + * @s: The string to operate on.
> > + * @output: Pointer to fill resulting bool value
> > + *
> > + * Returns 1 if string represents bool value, 0 otherwise
> > + */
> > +int sysfs_strbool(const char *s, bool *output)
> > +{
> > +	if (sysfs_streq(s, "1") || sysfs_streq(s, "true"))
> > +		*output = true;
> > +	else if (sysfs_streq(s, "0") || sysfs_streq(s, "false"))
> > +		*output = false;
> > +	else
> > +		return 0;
> > +
> > +	return 1;
> > +}
> > +EXPORT_SYMBOL(sysfs_strbool);
> > +
> 
> Can we teach kstrtobool() about "true" and "false" then use that?

I think we can do that, I have sent v2. Thanks