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Re: xfsprogs: Fix for xfstest 252 hang on ext4

To: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
Subject: Re: xfsprogs: Fix for xfstest 252 hang on ext4
From: Allison Henderson <achender@xxxxxxxxxxxxxxxxxx>
Date: Mon, 23 May 2011 19:38:04 -0700
Cc: xfs-oss <xfs@xxxxxxxxxxx>, Ext4 Developers List <linux-ext4@xxxxxxxxxxxxxxx>
In-reply-to: <BANLkTiks0NSDTSPN8n446JHWhKtM61_=Mw@xxxxxxxxxxxxxx>
References: <4DDAC4EF.1050702@xxxxxxxxxxxxxxxxxx> <BANLkTiks0NSDTSPN8n446JHWhKtM61_=Mw@xxxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20110414 Thunderbird/3.1.10
On 5/23/2011 6:16 PM, Yongqiang Yang wrote:
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!


Hi there,

The block size I've been using is 4096. As long as that behavior is expected, I think the test will be ok with just the xfsprogs fix, though. Thx!

Allison Henderson

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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