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

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Message-ID: <4C126AAB.4040802@redhat.com>
Date:	Fri, 11 Jun 2010 11:56:11 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Greg Freemyer <greg.freemyer@...il.com>
CC:	Tao Ma <tao.ma@...cle.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?

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.

-Eric

> Thanks
> Greg

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