linux-kernel - Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

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Date:   Tue, 19 May 2020 10:54:52 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>, kuo-lang.tseng@...el.com,
        ravi.v.shankar@...el.com, Ingo Molnar <mingo@...hat.com>,
        Babu Moger <babu.moger@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings
 terminated by newline

Hi Andy,

On 5/19/2020 9:07 AM, Andy Shevchenko wrote:
> On Tue, May 19, 2020 at 08:50:22AM -0700, Reinette Chatre wrote:
>> On 5/19/2020 1:28 AM, Andy Shevchenko wrote:
>>> On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
>>> <reinette.chatre@...el.com> wrote:
> 
> ...
> 
>>>> +       ret = sysfs_match_string(rdt_mode_str, buf);
>>>> +       if (ret < 0) {
>>>> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
>>>> +               ret = -EINVAL;
>>>> +               goto out;
>>>> +       }
>>
>> From your previous email ...
>>
>>>> +       ret = sysfs_match_string(rdt_mode_str, buf);
>>>> +       if (ret < 0) {
>>>> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
>>>
>>>> +               ret = -EINVAL;
>>>
>>> This is redundant.
>>
>> I understand that shadowing an error code is generally of concern. In
>> this case the error code is set to -EINVAL to ensure that it is the same
>> error code that was returned to user space originally and will continue
>> to be so no matter what changes may come to sysfs_match_string().
> 
> It returns -EINVAL and if that will be ever changed this driver would be one of
> hundreds who suffers.

Not if we keep this change ... but that is no longer of concern with the
removal of the check as you propose later.

> 
> ...
> 
>>> Can't we unify latter with a former like ...
> 
>> This would have been ideal if done from the start but currently "0" is
>> returned if the current mode is pseudo-locked and user attempts to
>> change the mode to pseudo-locked. Thus, to maintain the current user
>> interface the check if user wants to set pseudo-locked mode is moved
>> after the check if new mode is same as existing mode and thus not
>> unified because that will result in an error returned always when user
>> requests pseudo-locked mode.
> 
> Ah, I see now.
> 
> But we can then drop the check from sysfs_match_string() returned value, like
> 
> 	user_m = sysfs_match_string();
> 	if (...) {
> 		...
> 	} else { // w/o even checking for the PSEUDO_LOCKED
> 		...
> 		goto out;
> 	}
> 
> Can we?
> 

Yes, we can. Will do.

Reinette