linux-kernel - [PATCH V2 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

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Message-Id: <d1e508e76d09e6de90a961aeefbc04021ab0f0ea.1586801373.git.reinette.chatre@intel.com>
Date:   Mon, 13 Apr 2020 13:58:03 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
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, 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 V2 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>
---
Changes since V1:
- Remove unnecessary checks on user input (Andy Shevchenko)
- Change code style surrounding usage of sysfs_match_string() (Andy Shevchenko)

 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 d4e9b8a204d6..a8cbec226633 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;
 
-	/* 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