Re: [PATCH] imsm: fix: does not allow to use invalid chunk size

[NeilBrown <neilb@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 1410 bytes --]

On Fri, 25 Nov 2011 13:12:04 +0100 Przemyslaw Czarnowski
<przemyslaw.hawrylewicz.czarnowski@intel.com> wrote:

> Only least significant bit of chunk size provided by user has been used
> in test with OROM capabilities. This way user could pass value which is
> not a power of 2.
> 
> Signed-off-by: Przemyslaw Czarnowski <przemyslaw.hawrylewicz.czarnowski@intel.com>
> ---
>  platform-intel.h |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/platform-intel.h b/platform-intel.h
> index 6c094d7..99450ba 100644
> --- a/platform-intel.h
> +++ b/platform-intel.h
> @@ -124,11 +124,13 @@ static inline int imsm_orom_has_raid5(const struct imsm_orom *orom)
>  static inline int imsm_orom_has_chunk(const struct imsm_orom *orom, int chunk)
>  {
>  	int fs = ffs(chunk);
> +	int orom_chunk_bit;
>  
>  	if (!fs)
>  		return 0;
>  	fs--; /* bit num to bit index */
> -	return !!(orom->sss & (1 << (fs - 1)));
> +	orom_chunk_bit = (orom->sss & (1 << (fs - 1)));
> +	return orom_chunk_bit && 1 << orom_chunk_bit == chunk;
>  }
>  
>  

applied, thanks.

However it feels a bit clumsy, though maybe that is just me.
I would use a separate explicit test for "is a power of 2".
ie.

  if (chunk & (chunk-1))
        return 0; /* not a power of 2 */
  fs = ffs(chunk);
  return !!(orom->sss & (1 << (fs-2)));

or something like that.

NeilBrown

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 828 bytes --]