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Re: xfsprogs: Fix for xfstest 252 hang on ext4

To: Allison Henderson <achender@xxxxxxxxxxxxxxxxxx>
Subject: Re: xfsprogs: Fix for xfstest 252 hang on ext4
From: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
Date: Tue, 24 May 2011 09:16:24 +0800
Cc: xfs-oss <xfs@xxxxxxxxxxx>, Ext4 Developers List <linux-ext4@xxxxxxxxxxxxxxx>
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On Tue, May 24, 2011 at 4:34 AM, Allison Henderson
<achender@xxxxxxxxxxxxxxxxxx> wrote:
> Hi all,
>
> While trying to add more punch hole tests to xfstest, I found that test 252 
> hangs on ext4 due to a loop in xfsprogs that does not exit.  XFS gets out of 
> this loop because there is logic in the loop that looks for the last extent 
> flag and breaks out.  But it looks like ext4 does not return a last extent 
> when the file has a hole at the end.  I am not sure if this is the correct 
> behavior or not, so I will copy the ext4 folks on this too.  Below is a copy 
> of the fix for xfsprogs:

Hi there,

What's blocksize of the tested ext4?    For now, ext4 returns
LAST_EXTENT if the logical offset covered by the extent is greater
than file size, so if there is a hole at the end, no last extent is
returned. Thx!

Yongqiang.

>
> diff --git a/io/fiemap.c b/io/fiemap.c
> index fa990cc..81fc92c 100644
> --- a/io/fiemap.c
> +++ b/io/fiemap.c
> @@ -246,7 +246,7 @@ fiemap_f(
>                       flg_w, _("FLAGS"));
>        }
>
> -       while (!last && ((cur_extent + 1) != max_extents)) {
> +       while (!last && (cur_extent <= max_extents)) {
>                if (max_extents)
>                        num_extents = min(num_extents,
>                                          max_extents - (cur_extent + 1));
>
>
> It looks like the loop enters with last=0, cur_extents=0, and max_extents = 
> 0, and on the first iteration cur_extents get set to 2, so we dont see 
> ((cur_extent + 1) == max_extents for a very long time.  I doubt the logic was 
> meant to work that way, so this patch should fix it, but I wanted to make 
> sure that the fiemap for ext4 is working as intended too.  Feed back 
> appreciated!  Thx all!
>
> Allison Henderson
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-- 
Best Wishes
Yongqiang Yang

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