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

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Message-ID: <4C12CCD8.4070306@redhat.com>
Date:	Fri, 11 Jun 2010 18:55:04 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Tao Ma <tao.ma@...cle.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?

Tao Ma wrote:
> 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? ;)

No, I misread.  :(  Calling with FIEMAP_FLAG_SYNC works as expected.

-Eric

> Regards,
> Tao
> 

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