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

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Message-ID: <Yme97bRH3hLcqGfC@alley>
Date:   Tue, 26 Apr 2022 11:39:57 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Jagdish Gediya <jvgediya@...ux.ibm.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 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.

> 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'.

Also please update comment above the function definition.


> +		}
>  		break;
>  	}
>  

Best Regards,
Petr