[Rdiff-backup-bugs] [bug #26848] Restoring hardlinked files: "Hash for foo missing, cannot check"

[Joe Steele]

URL:
  <http://savannah.nongnu.org/bugs/?26848>

                 Summary: Restoring hardlinked files: "Hash for foo missing,
cannot check"
                 Project: rdiff-backup
            Submitted by: j_steele
            Submitted on: Fri 19 Jun 2009 09:30:56 PM GMT
                Category: None
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

The following series of commands will result in a "Hash for f3 missing,
cannot check" error during the last restore command (using rdiff-backup
1.2.8):

#!/bin/bash
# Create a directory with 2 hardlinked files and back it up:
mkdir d1
touch d1/f1
link d1/f1 d1/f3
rdiff-backup d1 d2
# Now add a 3rd hardlinked file (but don't name it 
# to be the first of the 3) and back up again:
link d1/f1 d1/f2
sleep 1
rdiff-backup d1 d2
# The following restore generates an error:
rdiff-backup -r now d2 d3


Furthermore, the metadata file for the second backup looks like this (note
the discrepancy for 'NumHardLinks'):

File .
  Type dir
  ModTime 1245442871
  Uid 0
  Uname root
  Gid 0
  Gname root
  Permissions 493
File f1
  Type reg
  Size 0
  NumHardLinks 2
  Inode 79457
  DeviceLoc 64775
  SHA1Digest da39a3ee5e6b4b0d3255bfef95601890afd80709
  ModTime 1245442871
  Uid 0
  Uname root
  Gid 0
  Gname root
  Permissions 420
File f2
  Type reg
  Size 0
  NumHardLinks 3
  Inode 79457
  DeviceLoc 64775
  ModTime 1245442871
  Uid 0
  Uname root
  Gid 0
  Gname root
  Permissions 420
File f3
  Type reg
  Size 0
  NumHardLinks 2
  Inode 79457
  DeviceLoc 64775
  ModTime 1245442871
  Uid 0
  Uname root
  Gid 0
  Gname root
  Permissions 420

Furthermore, the restored files are linked differently from the original
files:

# ls -li d[13]/
d1:
total 12
79457 -rw-r--r--  3 root root 0 Jun 19 16:21 f1
79457 -rw-r--r--  3 root root 0 Jun 19 16:21 f2
79457 -rw-r--r--  3 root root 0 Jun 19 16:21 f3

d3:
total 12
79492 -rw-r--r--  2 root root 0 Jun 19 16:21 f1
79492 -rw-r--r--  2 root root 0 Jun 19 16:21 f2
79493 -rw-r--r--  1 root root 0 Jun 19 16:21 f3
#


I've attached a file to this bug report which contains a possible patch for
Hardlink.py that seems to fix this bug for me.

A real life example (on a CentOS-4 system) of this bug occurs if you have a
few kernel-devel RPMs installed (for different kernels) and you back up the
system, then you install another kernel-devel RPM for a newer kernel and you
back up the system again, then you try to restore the most recent backup.  The
restore will generate numerous (4,495 in my case) "Hash for foo missing,
cannot check" errors.  The reason is because the kernel-devel RPM has a
post-install script like this:

cd /usr/src/kernels/2.6.9-78.0.22.EL-i686
find . -type f | while read f; do hardlink -c /usr/src/kernels/*/$f $f ;
done

As noted in the man page for hardlink:

"hardlink  traverses  one  or more directories searching for duplicate files.
 When it finds duplicate files, it uses one of them as the master.  It then
removes all other duplicates and places a hardlink for each one pointing to
the master file.  This allows for conservation of disk space where multiple
directories on a  single  filesystem contain many duplicate files."

So the hardlink command is adding new hardlinks to files that were already
hardlinked, which triggers the bug in rdiff-backup.






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File Attachments:


-------------------------------------------------------
Date: Fri 19 Jun 2009 09:30:56 PM GMT  Name: Hardlink.py.patch.txt  Size:
473B   By: j_steele

<http://savannah.nongnu.org/bugs/download.php?file_id=18294>

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