linux-kernel - Re: fiemap is broken for sparse file in ext4?

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Message-ID: <4C12CAD7.3030008@oracle.com>
Date:	Sat, 12 Jun 2010 07:46:31 +0800
From:	Tao Ma <tao.ma@...cle.com>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	Greg Freemyer <greg.freemyer@...il.com>,
	linux-ext4@...r.kernel.org, Theodore Tso <tytso@....edu>,
	linux-kernel@...r.kernel.org
Subject: Re: fiemap is broken for sparse file in ext4?

Hi Eric,
Eric Sandeen wrote:
> Greg Freemyer wrote:
>   
>> On Fri, Jun 11, 2010 at 11:46 AM, Eric Sandeen <sandeen@...hat.com> wrote:
>>     
>>> Tao Ma wrote:
>>>
>>>       
>>>>> What are you using to call fiemap?  Here it seems to be working:
>>>>>           
>>>> I just wrote a simple test program by calling ioctl. It is attached.
>>>> btw, you need to call it immediately after dd so that we have a chance
>>>> that ext4 don't have time to allocate extents. ;)
>>>>         
>>> OK I take it back, I do see it.  *cough* too many different filesystems
>>> on this box ... ;)
>>>
>>> Yes, it does look like a bug.
>>>
>>> -Eric
>>>       
>> I'm not clear how this is supposed to work.
>>
>> Is this just a userspace bug in that FIEMAP_FLAG_SYNC is needed in the
>> fiemap call, or is there a kernel bug as well?
>>     
>
> The flag is optional, though maybe filefrag should use it.
>
> Without it, we should get the proper logical offset and a delalloc-flagged
> extent returned
>
>   
>> If fiemap is called with the FIEMAP_FLAG_SYNC flag is there currently a problem?
>>     
>
> yep, we should get one delalloc extent in the results and we don't.
>   
With FIEMAP_FLAG_SYNC set, my test shows that we get one extent without 
dealloc flags. So no problem with it.
We have another different test result? ;)

Regards,
Tao

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