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

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Message-ID: <Yt64gbsRWY3RIPOy@FVFF77S0Q05N.cambridge.arm.com>
Date:   Mon, 25 Jul 2022 16:36:33 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     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, andriy.shevchenko@...ux.intel.com,
        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 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,

> > 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.

Ah; I had mistakenly thought this was new in v5.19, and so a revert was fine. I
see that it made it in for v5.18.

> As a quick fix, how about only allowing either "f\0" or "fa"?

TBH I reckon it's best to go for reworking the "rodata=" parsing, and
backporting that to stable, since people could be relying on any "f*" string by
now...

I'll have a go at that rework...

Mark.