linux-kernel - Re: [PATCH V4 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

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Date:   Mon, 18 May 2020 09:23:08 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     tglx@...utronix.de, fenghua.yu@...el.com, bp@...en8.de,
        tony.luck@...el.com, kuo-lang.tseng@...el.com,
        ravi.v.shankar@...el.com, mingo@...hat.com, babu.moger@....com,
        hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 4/4] x86/resctrl: Use appropriate API for strings
 terminated by newline

Hi Andy,

On 5/18/2020 9:06 AM, Reinette Chatre wrote:
> On 5/18/2020 4:50 AM, Andy Shevchenko wrote:
>> On Sat, May 16, 2020 at 11:28:41AM -0700, Reinette Chatre wrote:
>>> The user input to files in the resctrl filesystem are expected to be
>>> terminated with a newline. Testing the user input includes a test for
>>> the presence of a newline and then replacing the newline with NUL
>>> byte followed by comparison using strcmp().
>>>
>>> sysfs_streq() exists to test if strings are equal, treating both NUL and
>>> newline-then-NUL as equivalent string terminations. Even more,
>>> sysfs_match_string() exists to match a given string in an array using
>>> sysfs_streq().
>>>
>>> Replace existing strcmp() comparisons of strings that are terminated
>>> with a newline with more appropriate sysfs_streq() via the
>>> sysfs_match_string() API that can perform the match across the different
>>> mode strings that are already maintained in an array.
>>
>> Sorry for late comment, but just have noticed...
> 
> No problem. I do appreciate your feedback because it helps me to improve
> the code.
> 
>>
>>>  	if (mode == RDT_MODE_PSEUDO_LOCKED) {
>>> @@ -1445,14 +1450,14 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
>>>  		goto out;
>>>  	}
>>>  
>>> -	if (!strcmp(buf, "shareable")) {
>>> +	if (user_m == RDT_MODE_SHAREABLE) {
>>>  		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
>>>  			ret = rdtgroup_locksetup_exit(rdtgrp);
>>>  			if (ret)
>>>  				goto out;
>>>  		}
>>
>>>  		rdtgrp->mode = RDT_MODE_SHAREABLE;
>>
>> ...can we simple move this and similar (in other branches) to...
>>
>>
>>> -	} else {
>>> -		rdt_last_cmd_puts("Unknown or unsupported mode\n");
>>> -		ret = -EINVAL;
>>>  	}
>>
>> ...here as
>>
>> 		rdtgrp->mode = user_m;
> 
> Will do.

Actually ... now that I take a closer look, this would let an invalid
mode change (RDT_MODE_PSEUDO_LOCKED) slip through so I plan to keep this
code as is.

> It also looks like the only reason for the "mode" local variable was to
> make those earlier "strcmp" lines shorter. With those long lines removed
> in this patch this local variable is no longer needed and I will remove
> it also.

I will still do this.

Reinette