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 16:06:25 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Reinette Chatre <reinette.chatre@...el.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

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;
>  

>  	/* 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.

>  	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;

> +	/* Do nothing and return success if user asks for current mode */
> +	if (user_m == mode)
>  		goto out;
>  
>  	if (mode == RDT_MODE_PSEUDO_LOCKED) {
> @@ -1441,14 +1445,14 @@ 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;
> -	} else if (!strcmp(buf, "exclusive")) {
> +	} else if (user_m == RDT_MODE_EXCLUSIVE) {
>  		if (!rdtgroup_mode_test_exclusive(rdtgrp)) {
>  			ret = -EINVAL;
>  			goto out;
> @@ -1459,14 +1463,11 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
>  				goto out;
>  		}
>  		rdtgrp->mode = RDT_MODE_EXCLUSIVE;
> -	} else if (!strcmp(buf, "pseudo-locksetup")) {
> +	} else if (user_m == RDT_MODE_PSEUDO_LOCKSETUP) {
>  		ret = rdtgroup_locksetup_enter(rdtgrp);
>  		if (ret)
>  			goto out;
>  		rdtgrp->mode = RDT_MODE_PSEUDO_LOCKSETUP;
> -	} else {
> -		rdt_last_cmd_puts("Unknown or unsupported mode\n");
> -		ret = -EINVAL;
>  	}
>  
>  out:
> -- 
> 2.21.0
> 

-- 
With Best Regards,
Andy Shevchenko