linux-kernel - Re: [PATCH v5 20/21] hwmon: (mr75203) add debugfs to read and write temperature coefficients

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Message-ID: <fa5e1e3b-b040-c7d7-a93f-700552c7b252@amazon.com>
Date:   Thu, 15 Sep 2022 12:17:28 +0300
From:   "Farber, Eliav" <farbere@...zon.com>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
CC:     <jdelvare@...e.com>, <linux@...ck-us.net>, <robh+dt@...nel.org>,
        <p.zabel@...gutronix.de>, <rtanwar@...linear.com>,
        <linux-hwmon@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <hhhawa@...zon.com>,
        <jonnyc@...zon.com>, "Farber, Eliav" <farbere@...zon.com>
Subject: Re: [PATCH v5 20/21] hwmon: (mr75203) add debugfs to read and write
 temperature coefficients

On 9/14/2022 5:08 PM, Andy Shevchenko wrote:
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> On Wed, Sep 14, 2022 at 05:03:09PM +0300, Andy Shevchenko wrote:
>> On Wed, Sep 14, 2022 at 12:32:47PM +0300, Andy Shevchenko wrote:
>> > On Wed, Sep 14, 2022 at 07:26:36AM +0300, Farber, Eliav wrote:
>> > > On 9/13/2022 8:01 PM, Andy Shevchenko wrote:
>> > > > On Tue, Sep 13, 2022 at 05:40:16PM +0300, Farber, Eliav wrote:
>> > > > > On 9/13/2022 4:06 PM, Farber, Eliav wrote:
>
> ...
>
>> > > > > It seems like debugfs_attr_write() calls simple_attr_write() 
>> and it uses
>> > > > > kstrtoull(), which is why it fails when setting a negative 
>> value.
>> > > > > This is the same also in v6.0-rc5.
>> > > > >
>> > > > > debugfs_attr_read() on the other hand does show the correct 
>> value also
>> > > > > when j is negative.
>> > > >
>> > > > Which puzzles me since there is a few drivers that use %lld.
>> > > > Yeah, changing it to
>> > > >
>> > > >        ret = sscanf(attr->set_buf, attr->fmt, &val);
>> > > >        if (ret != 1)
>> > > >                ret = -EINVAL;
>> > > >
>> > > > probably can fix that. Dunno if debugfs maintainer is okay with 
>> this.
>> > > >
>> > > > P.S. This needs revisiting all format strings to see if there 
>> are no
>> > > > additional
>> > > > characters, otherwise that needs to be addressed first, if 
>> feasible.
>> > >
>> > > I was thinking of making such a correction:
>> > >
>> > > -       ret = kstrtoull(attr->set_buf, 0, &val);
>> > > +       if (attr->set_buf[0] == '-')
>> > > +               ret = kstrtoll(attr->set_buf, 0, &val);
>> > > +       else
>> > > +               ret = kstrtoull(attr->set_buf, 0, &val);
>> > >
>> > > and when I tested the change it worked, but then I noticed this 
>> commit:
>> > >
>> > > 
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/fs/libfs.c?h=v6.0-rc5&id=488dac0c9237647e9b8f788b6a342595bfa40bda
>> > >
>> > > According to this, it previously used simple_strtoll() which 
>> supports
>> > > negative values, but was changed to use kstrtoull() to deliberately
>> > > return '-EINVAL' if it gets a negative value.
>> > >
>> > > So I’m not sure debugfs maintainers will be okay with a fix that
>> > > basically reverts the commit I mentioned.
>> > > Hence, what do you suggest to do with my commit?
>> > > Is it ok to leave it as it is today?
>> >
>> > Meanwhile asking is not a problem, at least we will know for sure.
>> > And yes, leave it as is, but point to the thread where you asking
>> > the clarification.
>>
>> For the record:
>>
>> $ git grep -n -A1 -w DEFINE_DEBUGFS_ATTRIBUTE | grep ');' | sed 
>> 's,.*\(".*%.*"\).*,\1,' | sort | uniq -c
>>   1 "%08llx\n"
>>   5 "0x%016llx\n"
>>   5 "0x%02llx\n"
>>   5 "0x%04llx\n"
>>  13 "0x%08llx\n"
>>   1 "0x%4.4llx\n"
>>   3 "0x%.4llx\n"
>>   4 "0x%llx\n"
>>   1 "%1lld\n"
>>  40 "%lld\n"
>>   2 "%lli\n"
>> 129 "%llu\n"
>>   1 "%#llx\n"
>>   2 "%llx\n"
>>
>> means that sscanf() should work and fix the issue. You may even 
>> propose a patch
>> as a starter for a discussion.


I proposed a patch with the fix you suggested.

--
Thanks, Eliav