Re: silent random symbolic link corruption

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

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 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 ?


Thank in advance,
David Arendt

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
>
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