Re: [Bug-tar] Different behavior between versions with option --listed-incremental

[Nathan Stratton Treadway]

On Tue, Mar 26, 2013 at 14:19:22 -0400, Nathan Stratton Treadway wrote:
> I get the same behavior as you report (also using Ubuntu's GNU tar 1.26).
> 
> However, the "aaa" file is deleted correctly if I don't use the -C
> option:
> 
>   $ mkdir ext
>   $ cd ext
>   $ tar -G -vxf ../test.0.tar
>   aaa/
>   aaa/aaa
>   aaa/bbb
>   $ tar -G -vxf ../test.1.tar
>   aaa/
>   aaa/ccc
>   $ tar -G -vxf ../test.2.tar
>   aaa/
>   tar: Deleting `aaa/aaa'
>  
> 
> Interestingly, even using -C, "ccc" is deleted if I then extract
> test.0.tar a second time:
> 
>   $ cd ..
>   $ tar -G -vxf test.0.tar -C ext/
>   aaa/
>   tar: Deleting `aaa/ccc'
>   aaa/aaa
>   aaa/bbb
> 
> But I'm not sure off hand what that tells us...

Well, this turned out to be a hint that the _check_ for files which need
to be deleted ignores the -C option (though the actual deletion process
does not); in this case, the "ccc" file gets deleted because it still
exists in the original "aaa" directory, while in the earlier test.2.tar
case "aaa/aaa" did not exist.

In other words, with the "-C ext" option, tar 1.26 will delete the file
"aaa" only if it exists in both the "aaa/" and "ext/aaa/" directories:

  $ ls aaa/aaa ext/aaa/aaa
  ls: cannot access aaa/aaa: No such file or directory
  ext/aaa/aaa
  $ tar -G -vxf test.2.tar -C ext/
  aaa/
  $ touch aaa/aaa
  $ ls aaa/aaa ext/aaa/aaa
  aaa/aaa  ext/aaa/aaa
  $ tar -G -vxf test.2.tar -C ext/
  aaa/
  tar: Deleting `aaa/aaa'
  $ ls aaa/aaa ext/aaa/aaa
  ls: cannot access ext/aaa/aaa: No such file or directory
  aaa/aaa


After some debugging, I tracked the problem down to the
  current_dir = savedir (directory_name);
line near the top of incremen.c:try_purge_directory(), since savedir()
processes the passed directory by name ("aaa" in this case) without any
reference to chdir_fd anywhere.


Looking back over the changes committed since GNU tar 1.23, it seems
pretty likely that this problem originated with commit 4bde4f39d08f000
"tar: prefer openat-style functions"; if that's true, then the problem
is present in versions 1.24 and later.


In any case, I see in that commit the following change was made to
update.c:update_archive()

-                       dirp = savedir (name->name);
-                       if (!dirp)
+                       DIR *stream;
+                       int fd = openat (chdir_fd, name->name,
+                                        open_read_flags | O_DIRECTORY);
+                       if (fd < 0)
+                         open_error (name->name);
+                       else if (! ((stream = fdopendir (fd))
+                                   && (dirp = streamsavedir (stream))))

Perhaps a similar change would work in try_purge_directory() ?

                                                                Nathan



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