linux-kernel - Re: [PATCH v2] Btrfs: use do_div to avoid compile errors on 32bit box

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Date:	Sat, 20 Aug 2011 08:21:44 -0400
From:	Josef Bacik <josef@...hat.com>
To:	Liu Bo <liubo2009@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	mingo@...nel.org, jwboyer@...il.com, linux-btrfs@...r.kernel.org,
	chris.mason@...cle.com, dave@...os.cz
Subject: Re: [PATCH v2] Btrfs: use do_div to avoid compile errors on 32bit
 box

On 08/19/2011 10:17 PM, Liu Bo wrote:
> When doing div operation of u64 type, we need to be careful and use do_div
> to avoid compile ERROR on 32bit box:
> 
> "ERROR: "__udivdi3" [fs/btrfs/btrfs.ko] undefined!
> make[1]: *** [__modpost] Error 1
> 
> v1->v2:
> - fix stupid do_div() with type "signed integer".
> 
> Signed-off-by: Liu Bo <liubo2009@...fujitsu.com>
> ---
>  fs/btrfs/extent-tree.c |   11 ++++++-----
>  1 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 80d6148..e43e4f1 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -6735,9 +6735,10 @@ int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr)
>  	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
>  	struct btrfs_device *device;
>  	u64 min_free;
> +	u32 dev_min = 1;
> +	u32 dev_nr = 0;
> +	u32 dup = 2;
>  	int index;
> -	int dev_nr = 0;
> -	int dev_min = 1;
>  	int full = 0;
>  	int ret = 0;
>  
> @@ -6796,14 +6797,14 @@ int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr)
>  	index = get_block_group_index(block_group);
>  	if (index == 0) {
>  		dev_min = 4;
> -		min_free /= 2;
> +		do_div(min_free, dup);

I think Linus was less complaining about how you're dividing here and
more about the fact that you are.  A divide by 2 is the same as a >> 1.
 I'll send a patch to fix this.  Thanks,

Josef
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