linux-kernel - Re: [PATCH v2 2/2] mm: Covert sysfs input to bool using kstrtobool()

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Date:   Thu, 12 May 2022 18:05:37 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jagdish Gediya <jvgediya@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Jonathan.Cameron@...wei.com, adobriyan@...il.com,
        rf@...nsource.cirrus.com, pmladek@...e.com, ying.huang@...el.com,
        dave.hansen@...el.com
Subject: Re: [PATCH v2 2/2] mm: Covert sysfs input to bool using
 kstrtobool()

On Wed, 27 Apr 2022 18:17:29 +0300 Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> On Tue, Apr 26, 2022 at 10:30:40PM +0530, Jagdish Gediya wrote:
> > Sysfs input conversion to corrosponding bool value e.g. "false" or "0"
> > to false, "true" or "1" to true are currently handled through strncmp
> > at multiple places. Use kstrtobool() to convert sysfs input to bool
> > value.
> 
> ...
> 
> > +	if (kstrtobool(buf, &numa_demotion_enabled))
> >  		return -EINVAL;
> 
> Hmm... The commit message doesn't explain what's wrong with the error codes
> returned by kstrtobool(). Can't it be
> 
> 	ret = kstrtobool();
> 	if (ret)
> 		return ret;
> 
> ?

Jagdish fell asleep.

Yes, I agree.  It has no practical difference at present because
kstrtobool() can only return 0 or -EINVAL.  I did this:

--- a/mm/migrate.c~mm-convert-sysfs-input-to-bool-using-kstrtobool-fix
+++ a/mm/migrate.c
@@ -2523,8 +2523,10 @@ static ssize_t numa_demotion_enabled_sto
 					   struct kobj_attribute *attr,
 					   const char *buf, size_t count)
 {
-	if (kstrtobool(buf, &numa_demotion_enabled))
-		return -EINVAL;
+	ssize_t ret;
+
+	ret = kstrtobool(buf, &numa_demotion_enabled);
+		return ret;
 
 	return count;
 }
--- a/mm/swap_state.c~mm-convert-sysfs-input-to-bool-using-kstrtobool-fix
+++ a/mm/swap_state.c
@@ -874,8 +874,11 @@ static ssize_t vma_ra_enabled_store(stru
 				      struct kobj_attribute *attr,
 				      const char *buf, size_t count)
 {
-	if (kstrtobool(buf, &enable_vma_readahead))
-		return -EINVAL;
+	ssize_t ret;
+
+	ret = kstrtobool(buf, &enable_vma_readahead);
+	if (ret)
+		return ret;
 
 	return count;
 }
_