linux-kernel - RE: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

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Message-ID: <9c7a011c-2946-102c-5cdd-9dc5155533ec@amd.com>
Date:   Thu, 14 May 2020 14:05:17 -0500
From:   Babu Moger <babu.moger@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>
Cc:     "kuo-lang.tseng@...el.com" <kuo-lang.tseng@...el.com>,
        "ravi.v.shankar@...el.com" <ravi.v.shankar@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: RE: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings
 terminated by newline



> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@...el.com>
> Sent: Wednesday, May 6, 2020 6:50 PM
> To: tglx@...utronix.de; fenghua.yu@...el.com; bp@...en8.de;
> tony.luck@...el.com
> Cc: kuo-lang.tseng@...el.com; ravi.v.shankar@...el.com; mingo@...hat.com;
> Moger, Babu <Babu.Moger@....com>; hpa@...or.com; x86@...nel.org;
> linux-kernel@...r.kernel.org; Reinette Chatre <reinette.chatre@...el.com>;
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Subject: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings terminated
> by newline
> 
> 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 | 32 ++++++++++++++------------
>  1 file changed, 17 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index c60a3b307f7d..e70694892c02 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1408,12 +1408,11 @@ static ssize_t rdtgroup_mode_write(struct
> kernfs_open_file *of,
>  {
>  	struct rdtgroup *rdtgrp;
>  	enum rdtgrp_mode mode;
> -	int ret = 0;
> +	int user_m;
> +	int ret;

This is bit confusing here. Mode and user_m should have been of same type.
You can define user_m to user_mode to be very clear.

You can completely remove "mode" and directly use rdtgrp->mode instead. It
is left to you.

> > -	/* Valid input requires a trailing newline */
> -	if (nbytes == 0 || buf[nbytes - 1] != '\n')
> +	if (nbytes == 0)
>  		return -EINVAL;
> -	buf[nbytes - 1] = '\0';
> 
>  	rdtgrp = rdtgroup_kn_lock_live(of->kn);
>  	if (!rdtgrp) {
> @@ -1425,11 +1424,17 @@ 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))
> +	ret = sysfs_match_string(rdt_mode_str, buf);
> +	if (ret < 0) {
> +		rdt_last_cmd_puts("Unknown or unsupported mode\n");
> +		goto out;
> +	}
> +
> +	user_m = ret;
> +	ret = 0;
> +
> +	/* Do nothing and return success if user asks for current mode */
> +	if (user_m == mode)
>  		goto out;
> 
>  	if (mode == RDT_MODE_PSEUDO_LOCKED) {
> @@ -1438,14 +1443,14 @@ 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;
> @@ -1456,14 +1461,11 @@ 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