Re: silent random symbolic link corruption

[David Arendt <admin-/LHdS3kC8BfYtjvyW6yDsg@public.gmane.org>]

Hi,

I am still inverstigating here, I created tar files with 100000 symbolic
links, and they extracted without any problem. Only a tar of my whole
nfsroot directory fails to extract properly to nilfs2, but does
correctly to ext4.I wouldn't mind giving you that files, but it are
3.3gbytes. What is also curious is that the stat calls in tar seem to
return the right inode number, but at the check, it is 0. I am currently
adding debugging printfs to tar in hope to catch the problem this way.

Bye,
David Arendt

Ryusuke Konishi wrote:
> Hi David,
> On Sun, 01 Feb 2009 00:21:23 +0100, David Arendt wrote:
>   
>> Hi,
>>
>> I narrowed the problem down. I'm not sure if it's a problem of tar or of
>> nifls2.
>>
>> Tar handles symbolic links this way:
>>
>> during extraction: if symbolic link and absolute path create a 0 byte
>> file and record link and stat information
>>
>> after extraction: for every symbolic link verify that actual
>> st_dev,st_ino and st_mtime are the same as on creation of the 0 byte
>> file, and only then create the link
>>
>> for some 0 byte files st_ino is different between the first and the
>> second stat of the 0 byte file. As I don't know the nilfs2 internal
>> behavior, so could  you please tell me if this is the normal behavior of
>> nilfs2 or if there is something strange with this ? If it's the normal
>> behavior, maybe I should file a bug for tar ?
>>     
>
> This behavior seems unusual.
> Could you send me a small tar file which can reproduce the problem ?
>  
>   
>> This patch for tar 1.21 solves the symlink problem but I don't know if
>> the problem is to be solved on the tar end or on the nilfs2 end.
>>
>>
>> diff -Naur tar-1.21/src/extract.c tar-1.21.new/src/extract.c
>> --- tar-1.21/src/extract.c	2008-10-30 15:10:28.000000000 +0100
>> +++ tar-1.21.new/src/extract.c	2009-01-31 23:32:03.000000000 +0100
>> @@ -1267,7 +1267,6 @@
>>  	     removed by a later extraction.  */
>>  	  if (lstat (source, &st) == 0
>>  	      && st.st_dev == ds->dev
>> -	      && st.st_ino == ds->ino
>>  	      && timespec_cmp (get_stat_mtime (&st), ds->mtime) == 0)
>>  	    {
>>  	      /* Unlink the placeholder, then create a hard link if possible,
>>
>>
>> What do you think ?
>>     
>
> I think this comparision is appropriate to confirm identity of the
> placeholder file.
>
> I have no idea why inode number had changed as you reported.
> Symbolic links of nilfs2 are simply implemented.
>
> If it's unique to nilfs2, you may hit some sort of timing issue.
> I think a sample tar file would be helpful to figure out what's
> happening.
>
> Regards,
> Ryusuke Konishi
>
>   
>> David Arendt wrote:
>>     
>>> Hi,
>>>
>>> After using nilfs2 for half a year now on data partitions without any
>>> problems, I wanted to try it for the root partition. This way I
>>> discovered a silent random symbolic link corruption problem.
>>>
>>> Versions:
>>>
>>> latest nilfs2 git module
>>> kernel 2.6.28.2
>>> tar 1.20
>>>
>>> Step to reproduce it:
>>>
>>> tar -xpf zz1.tar (where zz1.tar is a tar file containing many symbolic
>>> links (in my case a directory containing 2 root filesystems for remote
>>> booting)
>>>
>>> On  untar some symbolic links are missing and 0 byte files are existing
>>> instead.
>>>
>>> I repeated the test 3 times on a freshly formated nilfs2 partition and
>>> always had other links missing.
>>>
>>> I am currently trying to bzip2 the big tar file and untar this one in
>>> order to verify if there are no timing issues and will report back when
>>> this test is finished.
>>>
>>> Could you please look into this ?
>>>
>>> Thanks in advance
>>> Bye,
>>> David Arendt
>>>
>>> _______________________________________________
>>> users mailing list
>>> users-JrjvKiOkagjYtjvyW6yDsg@public.gmane.org
>>> https://www.nilfs.org/mailman/listinfo/users
>>>   
>>>       
>> _______________________________________________
>> users mailing list
>> users-JrjvKiOkagjYtjvyW6yDsg@public.gmane.org
>> https://www.nilfs.org/mailman/listinfo/users
>>     
> _______________________________________________
> users mailing list
> users-JrjvKiOkagjYtjvyW6yDsg@public.gmane.org
> https://www.nilfs.org/mailman/listinfo/users
>