Subject: bug#6131: [PATCH]: fiemap support for efficient sparse file copy

From: "jeff.liu" <[email-masked]>
Date: Wed, 16 Jun 2010 15:22:08 +0800

Tao Ma wrote:
> Hi Paul,
> 
> On 06/16/2010 05:11 AM, Paul Eggert wrote:
>> On 06/10/2010 05:35 PM, Tao Ma wrote:
>>
>>> there is a flag FIEMAP_EXTENT_DELALLOC in fiemap ...
>>> with dd if=/dev/zero of=/mnt/ext4/a bs=1M count=1 seek=1
>>> the ext4 can't return a valid fiemap extent.
>>
>> Hmm, this sounds like a fairly serious bug, in that it would prevent this
>> part of cp from working.  What does the fiemap ioctl return in this
>> buggy case?
In this case, fiemap ioctl returns successfully, but 'fm_mapped_extents' will set to ZERO to
indicate there is no extents allocated for the file.
>> Is there some way that cp can detect the bug, and report it to the user,
>> or work around it?
work around is add FIEMAP_FLAG_SYNC to fiemap ioctl at the moment.

Thanks,
-Jeff
Or should we just assume that the bug will get fixed
>> and that cp shouldn't worry about it?
> I have prompted this to the linux ext4
> community(http://lkml.org/lkml/2010/6/10/412), they are working on it
> now I guess.
> 
> Regards,
> Tao

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