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Date:   Mon, 25 Jul 2022 16:21:11 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Jagdish Gediya <jvgediya@linux.ibm.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        ying.huang@intel.com, dave.hansen@intel.com,
        Jonathan.Cameron@huawei.com, adobriyan@gmail.com,
        akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
        rf@opensource.cirrus.com, pmladek@suse.com, will@kernel.org
Subject: Re: [PATCH v3 1/2] lib/kstrtox.c: Add "false"/"true" support to
 kstrtobool()
Message-ID: <Yt605xj898VSAsA3@casper.infradead.org>
References: <20220426180203.70782-1-jvgediya@linux.ibm.com>
 <Yt6u34sigPEkeZ0Y@FVFF77S0Q05N.cambridge.arm.com>
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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@linux.ibm.com>
> > Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.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"?