linux-kernel - Re: [PATCH V3 5/9] tracing/trace: Add a generic function to read/write u64 values from tracefs

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Date:   Fri, 4 Jun 2021 18:34:02 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Kate Carcia <kcarcia@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Clark Willaims <williams@...hat.com>,
        John Kacur <jkacur@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH V3 5/9] tracing/trace: Add a generic function to
 read/write u64 values from tracefs

On 6/4/21 6:18 PM, Steven Rostedt wrote:
> On Fri, 4 Jun 2021 18:05:06 +0200
> Daniel Bristot de Oliveira <bristot@...hat.com> wrote:
> 
>>
>> The reason for this patch is that hwlat, osnoise, and timerlat have "u64 config"
>> options that are read/write via tracefs "files." In the previous version, I had
>> multiple functions doing basically the same thing:
>>
>> A write function that:
>> 	read a u64 from user-space
>> 	get a lock,
>> 	check for min/max acceptable values
>> 		save the value
>> 	release the lock.
>>
>> and a read function that:
>> 	write the config value to the "read" buffer.
>>
>> And so, I tried to come up with a way to avoid code duplication.
>>
>> question: are only the names that are bad? (I agree that they are bad) or do you
>> think that the overall idea is bad? :-)
>>
>> Suggestions?
> 
> I don't think the overall idea is bad, if it is what I think you are
> doing. I just don't believe you articulated what you are doing.

I see!

> It has nothing to do with 64 bit reads and writes, but instead has to
> do with reading and writing values that depend on each other for what
> is acceptable.

yeah, that is a better (starting point for an) explanation.

> Perhaps have it called trace_min_max_write() and trace_min_max_read(),
> and document what it is used for.

I will do that!

-- Daniel

> -- Steve
>