linux-kernel - Re: [PATCH v2 0/4] debugfs: Add simple min/max "files" to debugfs to fix sched debug code.

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Date:   Tue, 30 May 2023 17:41:29 -0400
From:   chris hyser <chris.hyser@...cle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v2 0/4] debugfs: Add simple min/max "files" to debugfs to
 fix sched debug code.

On 5/30/23 16:18, Greg KH wrote:
> On Tue, May 30, 2023 at 03:40:08PM -0400, chris hyser wrote:
>> v2:
>> Apologies. I sent this the first time without including lkml.
>>
>> v1:
>> This originally started as an attempt to solve a divide by zero issue in sched
>> debug code that was introduced when a sysctl value with non-zero checking was
>> moved to a simple u32 debugfs file. In looking at ways to solve this, it was
>> mentioned I should look at providing general debugfs files with min/max
>> checking.
>>
>> One problem was that a check for greater than zero for say a u8 succeeds for a
>> number like 256 (but stores a zero anyway) as the upper bits that don't fit into
>> storage are silently dropped. Therefore values greater than the storage capacity
>> must also fail. Getting an error when what the user wrote is not what was
>> actually stored, seems like a useful requirement for the other simple files and
>> so I moved the check into there.
>>
>> To enable easy testing, a test module and test script are provided which can
>> validate the new functions as well as check the new limits on the older
>> functions. This was stuck under selftests, but it is not currently tied into the
>> testing infrastructure.
> 
> This is a lot of new infrastructure for a single debugfs file that you
> could just check for in the file write callback instead.
> 
> I'm all for cool new features, but wow, this seems like major overkill.
> Are you _SURE_ you need it all?

The current use case obviously does not require all of this. The idea 
was instead of a one off fix, it might be useful to provide a generic 
solution to a common class of problems.

So sending this out hopefully would help determine the perceived usefulness.

-chrish