linux-kernel - Re: [PATCH v2] lib/kstrtox.c: Add "false"/"true" support to kstrtobool

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Date:   Tue, 26 Apr 2022 15:33:52 +0530
From:   Jagdish Gediya <jvgediya@...ux.ibm.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        ying.huang@...el.com, dave.hansen@...el.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: Re: [PATCH v2] lib/kstrtox.c: Add "false"/"true" support to
 kstrtobool

On Tue, Apr 26, 2022 at 11:39:57AM +0200, Petr Mladek wrote:
> On Tue 2022-04-26 12:10:01, Jagdish Gediya 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, kstrtobool can be utilized at such places but
> > currently kstrtobool doesn't have support to "false"/"true".
> >
> > Add "false"/"true" support to kstrtobool while string conversion
> > to bool. Modify existing manual sysfs conversions to use kstrtobool().
> 
> It looks reasonable. I would just do it slightly other way, see
> below.
> 
> > This patch doesn't have any functionality change.
> 
> This is not true. All kstrtobool() callers will react differently
> on the "true"/"false" input.

how? Is it related to performance as more characters are compared?
otherwise semantic wise they will get the expected response, correct?

> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > Cc: Richard Fitzgerald <rf@...nsource.cirrus.com>
> > Cc: Petr Mladek <pmladek@...e.com>
> > Signed-off-by: Jagdish Gediya <jvgediya@...ux.ibm.com>
> > ---
> > change in v2:
> > Modified kstrtobool to handle "false"/"true". Removed
> > new function sysfs_strbool introduced in v1.
> > 
> >  lib/kstrtox.c   | 7 +++++++
> >  mm/migrate.c    | 6 +-----
> >  mm/swap_state.c | 6 +-----
> >  3 files changed, 9 insertions(+), 10 deletions(-)
> > 
> > diff --git a/lib/kstrtox.c b/lib/kstrtox.c
> > index 886510d248e5..3a5e29557838 100644
> > --- a/lib/kstrtox.c
> > +++ b/lib/kstrtox.c
> > @@ -377,6 +377,13 @@ int kstrtobool(const char *s, bool *res)
> >  		}
> >  		break;
> >  	default:
> > +		if (!strncmp(s, "true", 4)) {
> > +			*res = true;
> > +			return 0;
> > +		} else if (!strncmp(s, "false", 5)) {
> > +			*res = false;
> > +			return 0;
> 
> It should be enough to check the first letter like we do in
> the other cases. I mean to set true when s[0] is 'T' or 't'
> and false when s[0] is 'F' or 'f'.

For "on" and "off", 2 characters are matched, so is it good enough
to compare only single character for strings "true" and "false"?

> Also please update comment above the function definition.
> 
> 
> > +		}
> >  		break;
> >  	}
> >  
> 
> Best Regards,
> Petr
>