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Re: xfsprogs: Fix for xfstest 252 hang on ext4

To: xfs-oss <xfs@xxxxxxxxxxx>, Ext4 Developers List <linux-ext4@xxxxxxxxxxxxxxx>
Subject: Re: xfsprogs: Fix for xfstest 252 hang on ext4
From: Allison Henderson <achender@xxxxxxxxxxxxxxxxxx>
Date: Thu, 26 May 2011 11:32:57 -0700
In-reply-to: <4DDAC4EF.1050702@xxxxxxxxxxxxxxxxxx>
References: <4DDAC4EF.1050702@xxxxxxxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.17) Gecko/20110414 Thunderbird/3.1.10
On 5/23/2011 1:34 PM, Allison Henderson 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:

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

Hi all,

I haven't heard much back on this patch, so Im just poking this thread to make sure it doesn't get forgotten. I have some patches out there for punch hole, and I'm currently looking at fixing up some older punch hole tests in the dmapi code, but they wont do much good for ext4 with out this fix. If I could get a quick peek from some one on the xfs list for this patch, that would be much appreciated. Thx all!

Allison Henderson
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