Re: [PATCH] Btrfs: fix compile warning from __btrfs_map_block

[liubo <liubo2009@cn.fujitsu.com>]

On 03/31/2011 08:10 PM, Chris Mason wrote:
> Excerpts from liubo's message of 2011-03-31 05:45:20 -0400:
>> While compile btrfs modules on 32bit box, I encounter the following:
>>
>> WARNING: "__umoddi3" [fs/btrfs/btrfs.ko] undefined!
>>
>> The WARNING comes from that __btrfs_map_block does not use do_div() for
>> relative operations, this will cause problems on 32bit box, for values
>> with "u64" type should use do_div() instead of a direct "%".
> 
> Which kernel tree was this against?  I had rebased the for-linus and
> for-linus-unmerged branch to get rid of it.
> 
> Sorry for the confusion.

Ah, it is my fault to neglect the version, I found this warning while compiling
the latest for-linus tree (top commit: c1e1f82c56af1a286fd747e809c94628c2ca15fb).

thanks,
liubo

> 
> -chris
> 
>> Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
>> ---
>>  fs/btrfs/volumes.c |   23 +++++++++++++++--------
>>  1 files changed, 15 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 41afd50..7b23d0f 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -3076,16 +3076,19 @@ again:
>>              multi->stripes[i].dev = map->stripes[stripe_index].dev;
>>  
>>              if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
>> -                u64 stripes;
>> -                int last_stripe = (stripe_nr_end - 1) %
>> -                    map->num_stripes;
>> +                u64 stripes = stripe_nr_end - 1;
>> +                int last_stripe = do_div(stripes,
>> +                    map->num_stripes);
>>                  int j;
>>  
>>                  for (j = 0; j < map->num_stripes; j++) {
>> -                    if ((stripe_nr_end - 1 - j) %
>> -                          map->num_stripes == stripe_index)
>> +                    stripes = stripe_nr_end - 1 - j;
>> +
>> +                    if (do_div(stripes, map->num_stripes) ==
>> +                        stripe_index)
>>                          break;
>>                  }
>> +
>>                  stripes = stripe_nr_end - 1 - j;
>>                  do_div(stripes, map->num_stripes);
>>                  multi->stripes[i].length = map->stripe_len *
>> @@ -3100,18 +3103,22 @@ again:
>>                      multi->stripes[i].length -=
>>                          stripe_end_offset;
>>              } else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
>> -                u64 stripes;
>> +                u64 stripes = stripe_nr_end - 1;
>>                  int j;
>>                  int factor = map->num_stripes /
>>                           map->sub_stripes;
>> -                int last_stripe = (stripe_nr_end - 1) % factor;
>> +                int last_stripe = do_div(stripes, factor);
>> +
>>                  last_stripe *= map->sub_stripes;
>>  
>>                  for (j = 0; j < factor; j++) {
>> -                    if ((stripe_nr_end - 1 - j) % factor ==
>> +                    stripes = stripe_nr_end - 1 - j;
>> +
>> +                    if (do_div(stripes, factor) ==
>>                          stripe_index / map->sub_stripes)
>>                          break;
>>                  }
>> +
>>                  stripes = stripe_nr_end - 1 - j;
>>                  do_div(stripes, factor);
>>                  multi->stripes[i].length = map->stripe_len *
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