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

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Date:   Wed, 14 Sep 2022 07:26:36 +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 9/13/2022 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?

--
Thanks, Eliav