(dump_file0): The conditional at line

(dump_file0): The conditional at line
1296 prevented incremental backups on individual files
from working, as reported by Andreas Schuldei
<andreas@schuldei.org>.

This is due to the condition

  (0 < top_level || !incremental_option)

Removing it makes incremental backups work for individual
files as well as for directories. On the other hand, it does
not affect other functionality, as shown by the reasoning below:

To begin with, the two parts of this condition are mutually
superfluous, because

  1) when top_level < 0, incremental_option == 1
  so the condition yields false
  2) when top_level >= 0, incremental_option == 0
  so the condition yields true.

In other words, it is completely equivalent to

      (!incremental_option)

Now, let's consider the effect of its removal. There are two cases:

1) when incremental_option==1
This means incremental backup in progress. In this case dump_file
is invoked only for directories or for files marked with 'Y' by
get_directory_contents. The latter are those that did not meet the
condition in incremen.c:242, which is exactly the same condition
as this at create.c:1296. So, for these files the check
(!incremental_option) is useless, since the rest of the
conditional will yield false anyway. On the other hand, if
dump_file is invoked on a directory, the conditional will yield
false due to !S_ISDIR assertion, so these will be processed as usual.

Thus, for this case the extra condition (!incremental_option) is
irrelevant, and its removal won't alter the behavior of tar,
*except* that it will enable incremental backups on individual
files, which is the wanted effect.

2) when incremental_option==0
In this case the condition yields true and its removal does not
affect the functionality.