From: Yongqiang Yang <xiaoqiangnk@gmail.com>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
Date: Thu, 5 May 2011 19:47:29 +0800
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Cc: Eric Sandeen <sandeen@sandeen.net>, xfs-oss <xfs@oss.sgi.com>,
	linux-ext4@vger.kernel.org, coreutils@gnu.org,
	Markus Trippelsdorf <markus@trippelsdorf.de>
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2011/5/5 P=E1draig Brady <P@draigbrady.com>:
> On 14/04/11 17:10, Yongqiang Yang wrote:
>> Hi,
>>
>> I am off my working computer. =A0Maybe below fix could fix the probl=
em.
>>
>> fs/ext4/extent.c
>> static int ext4_ext_walk_space(struct inode *inode, ext4_lblk_t bloc=
k,
>> 1877 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 } else if (block >=3D le32_to_c=
pu(ex->ee_block)) {
>> 1878 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /*
>> 1879 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* some part =
of requested space is covered
>> 1880 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* by found e=
xtent
>> 1881 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0*/
>> 1882 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 start =3D block=
;
>> 1883 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 end =3D le32_to=
_cpu(ex->ee_block)
>> 1884 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 + ext4_ext_get_actual_len(ex);
>> 1885 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (block + num=
 < end)
>> 1886 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 end =3D block + num;
>> =A0 =A0 =A0 =A0+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (=
!ext4_ext_is_uninitialized(ex))
>> 1887 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 exists =3D 1;
>> 1888 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 } else {
>> 1889 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 BUG();
>> 1890 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
>
> Hi,
>
> To follow up on the above. =A0I'm under the impression
> that ext4 is expected to return extents for what
> is written, irrespective of whether it's reached the
> disk or not. I.E. the preallocation case where this fails
No.  It just returns extent info now - allocated extents and delayed
extents.  In the preallocation case, it returns unwritten extents.
And the code above does not work.

> was an oversite, for which the above might fix.
>
> So is the above summary correct, and has there
> been any more thoughts on a fix?
>
> cheers,
> P=E1draig.
>



--=20
Best Wishes
Yongqiang Yang
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