[PATCH-e2fsprogs] filefrag: fix fm_start in filefrag_fiemap loop

[PATCH-e2fsprogs] filefrag: fix fm_start in filefrag_fiemap loop

[Peng Tao]

Signed-off-by: Peng Tao <bergwolf@gmail.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

Re: [PATCH-e2fsprogs] filefrag: fix fm_start in filefrag_fiemap loop

[Andreas Dilger]

Can you please provide some more details of the problem this solves.

On Jun 03, 2009  02:03 +0800, Peng Tao wrote:
> Signed-off-by: Peng Tao <bergwolf@gmail.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.

Re: [PATCH-e2fsprogs] filefrag: fix fm_start in filefrag_fiemap loop

[Peng Tao]

On Wed, Jun 3, 2009 at 2:35 AM, Andreas Dilger <adilger@sun.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@gmail.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
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.
>
>



-- 
Cheers,
Bergwolf
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Re: [PATCH-e2fsprogs] filefrag: fix fm_start in filefrag_fiemap loop

[Andreas Dilger]

On Jun 03, 2009  09:21 +0800, Peng Tao wrote:
> 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?

Yes, please do.  I verified that the code as modified (just '=') is also
present in the Lustre fiemap patch, so I'm not sure how it got += there.
Possibly from an older version of the patch.

> > On Jun 03, 2009  02:03 +0800, Peng Tao wrote:
> >> Signed-off-by: Peng Tao <bergwolf@gmail.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

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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