Re: [PATCH] mm/thp: Use conventional format for boolean attributes

[David Rientjes <rientjes@google.com>]

On Tue, 22 Mar 2011, Ben Hutchings wrote:

> The conventional format for boolean attributes in sysfs is numeric
> ("0" or "1" followed by new-line).  Any boolean attribute can then be
> read and written using a generic function.  Using the strings
> "yes [no]", "[yes] no" (read), "yes" and "no" (write) will frustrate
> this.
> 
> Cc'd to stable in order to change this before many scripts depend on
> the current strings.
> 

I agree with this in general, it's certainly the standard way of altering 
a boolean tunable throughout the kernel so it would be nice to use the 
same userspace libraries with THP.

Let's cc Andrew on this since it will go through the -mm tree if it's 
merged.

> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> Cc: stable@kernel.org [2.6.38]
> ---
>  mm/huge_memory.c |   21 +++++++++++----------
>  1 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 113e35c..dc0b3f0 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -244,24 +244,25 @@ static ssize_t single_flag_show(struct kobject *kobj,
>  				struct kobj_attribute *attr, char *buf,
>  				enum transparent_hugepage_flag flag)
>  {
> -	if (test_bit(flag, &transparent_hugepage_flags))
> -		return sprintf(buf, "[yes] no\n");
> -	else
> -		return sprintf(buf, "yes [no]\n");
> +	return sprintf(buf, "%d\n",
> +		       test_bit(flag, &transparent_hugepage_flags));
>  }
>  static ssize_t single_flag_store(struct kobject *kobj,
>  				 struct kobj_attribute *attr,
>  				 const char *buf, size_t count,
>  				 enum transparent_hugepage_flag flag)
>  {
> -	if (!memcmp("yes", buf,
> -		    min(sizeof("yes")-1, count))) {
> +	unsigned long value;
> +	char *endp;
> +
> +	value = simple_strtoul(buf, &endp, 0);
> +	if (endp == buf || value > 1)
> +		return -EINVAL;
> +
> +	if (value)
>  		set_bit(flag, &transparent_hugepage_flags);
> -	} else if (!memcmp("no", buf,
> -			   min(sizeof("no")-1, count))) {
> +	else
>  		clear_bit(flag, &transparent_hugepage_flags);
> -	} else
> -		return -EINVAL;
>  
>  	return count;
>  }

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