[rdiff-backup-users] Updated temp file does not match source -- Strange cause

[Robert Nichols]

"UpdateError {pathname} Updated mirror temp file {pathname} does not
match source"

No, the file is not changing. No, nothing is running out of space.  I
see this happening consistently for files with more than one hard link,
and only under very specific conditions:

1. The archive's file system must be ext4.
2. The file system must be mounted with an SELinux context override.
3. The file needs to have more than 1 hard link. (The first link
   gets processed correctly.)

The problem does not occur with ext3. I started seeing it when I
formatted a new backup disk with ext4. (Naturally, there were a lot of
other changes at the time, including the librsync update.  It took me a
long time to discover this "least likely" cause.)

Is there anyone with enough familiarity with the rdiff-backup source to
guide me to a likely spot to start looking? The sensitivity to file
system type makes it look like a kernel bug, but there is no point in
reporting it if I can't pin it down to a particular operation.

Note: The SELinux context override is because this is an external disk
      that is shared among systems, some without SELinux or with a
      different SELinux policy. Bad things happen if one system tries
      to believe what some other system has recorded there or finds
      that some files have no SELinux context.
      (mount -o context=system_u:object_r:default_t:s0,...)

--
Bob Nichols     "NOSPAM" is really part of my email address.
                Do NOT delete it.