linux-kernel - Re: [PATCH 2/2] x86/resctrl: Use appropriate API for strings terminated by newline

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Date:   Thu, 2 Apr 2020 14:19:07 -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, mingo@...hat.com,
        babu.moger@....com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/resctrl: Use appropriate API for strings
 terminated by newline

Hi Andy,

(Your two responses have been merged)

On 4/2/2020 6:06 AM, Andy Shevchenko wrote:
> On Wed, Apr 01, 2020 at 11:30:48AM -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.
>>
>> Suggested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
>> ---
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 25 +++++++++++++------------
>>  1 file changed, 13 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index fbee891a7d6e..623e33c0a290 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -1412,11 +1412,11 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
>>  	struct rdtgroup *rdtgrp;
>>  	enum rdtgrp_mode mode;
>>  	int ret = 0;
>> +	int user_m;
>>  

>
> ...and forgot to mention this...
>
> 	int user_m;
> 	int ret;
>

> 
>>  	/* Valid input requires a trailing newline */
>>  	if (nbytes == 0 || buf[nbytes - 1] != '\n')
>>  		return -EINVAL;
>> -	buf[nbytes - 1] = '\0';
> 
> The above test is not needed and comment now is misleading.
> WRT nbytes I believe that kernel fs code checks for that.

If nbytes is 0 it is still passed to this function. You are correct that
those tests are not needed though (if nbytes is 0 then
sysfs_match_string() will not find a match and return EINVAL via that path).

Thank you for catching this. I'll remove those unnecessary checks.

> 
>>  	rdtgrp = rdtgroup_kn_lock_live(of->kn);
>>  	if (!rdtgrp) {
>> @@ -1428,11 +1428,15 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
>>  
>>  	mode = rdtgrp->mode;
>>  
>> -	if ((!strcmp(buf, "shareable") && mode == RDT_MODE_SHAREABLE) ||
>> -	    (!strcmp(buf, "exclusive") && mode == RDT_MODE_EXCLUSIVE) ||
>> -	    (!strcmp(buf, "pseudo-locksetup") &&
>> -	     mode == RDT_MODE_PSEUDO_LOCKSETUP) ||
>> -	    (!strcmp(buf, "pseudo-locked") && mode == RDT_MODE_PSEUDO_LOCKED))
>> +	user_m = sysfs_match_string(rdt_mode_str, buf);
>> +	if (user_m < 0) {
>> +		rdt_last_cmd_puts("Unknown or unsupported mode\n");
>> +		ret = user_m;
>> +		goto out;
>> +	}
> 
> You can do it the way
> 
> 	ret = sysfs_match_string(...);
> 	if (ret < 0) {
> 		...
> 	}
> 	user_m = ret;
>
> ...and this changes
>
> 	ret = 0;
>
> 

ok, I'll do it this way in the next version.

Thank you

Reinette