linux-ext4 - Re: [PATCH-e2fsprogs] filefrag: fix fm_start in filefrag

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Date:	Wed, 3 Jun 2009 09:21:40 +0800
From:	Peng Tao <bergwolf@...il.com>
To:	Andreas Dilger <adilger@....com>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH-e2fsprogs] filefrag: fix fm_start in filefrag_fiemap loop

On Wed, Jun 3, 2009 at 2:35 AM, Andreas Dilger <adilger@....com> wrote:
> Can you please provide some more details of the problem this solves.
Sorry for the late reply.

When used with -v and the targeted file has more than 144
extents(double of the length of fm_extents array provided by buf),
filefrag_fiemap loops and calls fiemap ioctl() multiple times to
calculate the actual number of extents in a file. Each call to fiemap
ioctl() uses  fm_start as the starting logical offset. The patch fixes
fm_start in each loop( except for the first one) and makes the extent
calculation correct for files with more that 144 extents.

To produce the problem, first run filefrag -v on a highly fragmented
file. Then change the buf size in filefrag_fiemap to make it large
enough to have all the extent mapped in a single loop and run filefrag
-v after recompiling. The former will produce a much smaller extent
count because of the false fm_start used in the loop. And the two will
produce different extent output since the 145th extent.

BTW, should I resend the patch to include the above explanation?
>
> On Jun 03, 2009  02:03 +0800, Peng Tao wrote:
>> Signed-off-by: Peng Tao <bergwolf@...il.com>
>> ---
>>  misc/filefrag.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/misc/filefrag.c b/misc/filefrag.c
>> index 6bea2cd..7786646 100644
>> --- a/misc/filefrag.c
>> +++ b/misc/filefrag.c
>> @@ -239,7 +239,7 @@ int filefrag_fiemap(int fd, int blk_shift, int *num_extents)
>>                       n++;
>>               }
>>
>> -             fiemap->fm_start += fm_ext[i-1].fe_logical +
>> +             fiemap->fm_start = fm_ext[i-1].fe_logical +
>>                                                       fm_ext[i-1].fe_length;
>>       } while (last == 0);
>>
>> --
>> 1.6.2.GIT
>>
>> --
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>
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.
>
>



-- 
Cheers,
Bergwolf
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