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

[Peter Koch]

Dear Joerg:

Thank's for the quick response. In the meantime I have tried
star which I had not used before. Wonderful programm but its
decision on which files will be included into an incremental
backup seems to be based on the same algorithm that gtar is
using - i.e. mtime-/ctime > date of last backup.

> My guess is that tar does a stat()-call on x/f2 and notices
> that the st_nlink-value has increased.

This guess was wrong. Neither gtar nor star care about the
st_nlink count. No wonder I could not find the
string "st_nlink" in their sources.

So my next guess is: Creating a hardlink will not only change
the st_nlink value but the ctime-value as well. And this makes
gtar and star believe that the file or its metadata has been
changed. If ctime has changed there's no way to find out wether
this was caused by a real change of the files metadata (like
changing the ownership or permissions or acls or whatever) or
wether just the st_nlink-value was changed.

What if I change the kernel and prevent ctime-changes if only
st_nlink was changed?

Would that have any unexpected side-effects?

Kind regards

Peter Koch