[dm-devel] [PATCH] dm-raid: fix bug when round up region_size

[NeilBrown]

On Tue, 30 Sep 2014 13:00:36 +0200 heinzm at redhat.com wrote:

> From: Heinz Mauelshagen <heinzm at redhat.com>
> 
> Liong,
> thanks for the catch.
> Introduced minor modification utilizing the is_power_of_2() inline.
> 
> ---
> 
> If region_size is not supplied by userspace and the device is very
> large, there is a bug in current code preventing region_size from being
> correctly set.
> 
> 
> Signed-off-by: Lidong Zhong <lzhong at suse.com>
> Acked-by:      Heinz Mauelshagen <heinzm at redhat.com>
> Tested-by:     Heinz Mauelshagen <heinzm at redhat.com>
> 
> ---
>  drivers/md/dm-raid.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
> index 4880b69..264aef4 100644
> --- a/drivers/md/dm-raid.c
> +++ b/drivers/md/dm-raid.c
> @@ -325,8 +325,10 @@ static int validate_region_size(struct raid_set *rs, unsigned long region_size)
>  		 */
>  		if (min_region_size > (1 << 13)) {
>  			/* If not a power of 2, make it the next power of 2 */
> -			if (min_region_size & (min_region_size - 1))
> -				region_size = 1 << fls(region_size);
> +			if (is_power_of_2(min_region_size))
> +				region_size = min_region_size;
> +			else
> +				region_size = 1 << fls(min_region_size);
>  			DMINFO("Choosing default region size of %lu sectors",
>  			       region_size);
>  		} else {

If you really wanted to optimize, you could just do
   region_size = roundup_pow_of_two(min_region_size);

there is all sorts of cool stuff in log2.h !!

NeilBrown
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