linux-kernel - Re: [PATCH v3 1/2] lib/kstrtox.c: Add "false"/"true" support to kstrtobool()

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Message-ID: <YuPwgmHbcQYsA4Kp@smile.fi.intel.com>
Date:   Fri, 29 Jul 2022 17:36:50 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        ying.huang@...el.com, dave.hansen@...el.com,
        Jonathan.Cameron@...wei.com, adobriyan@...il.com,
        akpm@...ux-foundation.org, rf@...nsource.cirrus.com,
        pmladek@...e.com, will@...nel.org
Subject: Re: [PATCH v3 1/2] lib/kstrtox.c: Add "false"/"true" support to
 kstrtobool()

On Fri, Jul 29, 2022 at 05:35:26PM +0300, Andy Shevchenko wrote:
> On Mon, Jul 25, 2022 at 04:21:11PM +0100, Matthew Wilcox wrote:
> > On Mon, Jul 25, 2022 at 03:55:27PM +0100, Mark Rutland wrote:
> > > On Tue, Apr 26, 2022 at 11:32:02PM +0530, 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 it doesn't have support to accept "false"/"true".
> > > > 
> > > > Add support to accept "false"/"true" as valid string in kstrtobool().
> > > > 
> > > > Signed-off-by: Jagdish Gediya <jvgediya@...ux.ibm.com>
> > > > Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > > 
> > > I've just spotted that this broke arm64's "rodata=full" command line option,
> > 
> > That isn't a documented option.
> > 
> >         rodata=         [KNL]
> >                 on      Mark read-only kernel memory as read-only (default).
> >                 off     Leave read-only kernel memory writable for debugging.
> > 
> > Hopefully this is an object lesson in why you need to update the
> > documentation when you extend a feature.
> > 
> > > since "full" gets parsed as 'f' = FALSE, when previously that would have been
> > > rejected. So anyone passing "rodata=full" on the command line will have rodata
> > > disabled, which is not what they wanted.
> > > 
> > > The current state of things is a bit messy (we prase the option twice because
> > > arch code needs it early), and we can probably fix that with some refactoring,
> > > but I do wonder if we actually want to open up the sysfs parsing to accept
> > > anything *beginning* with [tTfF] rather than the full "true" and "false"
> > > strings as previously, or whether it's worth reverting this for now in case
> > > anything else is affected.
> > 
> > Well, that's going to break people who've started using the new option.
> > As a quick fix, how about only allowing either "f\0" or "fa"?
> 
> I think we need to be more strict in kstrtobool(), i.e. 'f\0' ('t\0') and 'fal'
> ('tru') perhaps?

Actually kstrtobool() has been designed as a generic parser that should have
lowest priority. It means that the code that uses it should take care of any
other custom cases _before_ calling for kstrtobool().

-- 
With Best Regards,
Andy Shevchenko