[Bug-tar] unmodified files included in incremental tar if link count was changed

[Peter Koch]

Dear tar-experts:

I have learned that changing the kernel to not modify ctime
when just the nlink-value has changed in an inode was a nice
idea but has some unwanted side-effects.

Also it's too hard for me to implement. Whenever a changed
inode is written to disk, its ctime value will be set to
current time. At that point the kernel does not know what
part of the inode has changed. There's no easy way to
distinguish "real" changes (i.e. permission, mtime, acl)
from "technical" changes (st_nlink-changes only).

So I have to change our backup-strategy which now does
a lot of hard-linking, due to
  resync -aHAx --link-dest=lastbackup src/ newbackup
This saves a lot of space since unmodified files in
lastbackup will be hardlinked into newbackup but it
will change the ctime value of all unmodified files
in both lastbackup and newbackup.

So my final conclusion is: rsync aint no backup tool!

Thank you all for your helpfull comments.

Peter