Re: [Bug-tar] Errors in "posix" format.

[Sergey Poznyakoff]

Tim Kientzle <address@hidden> wrote:

> I've been doing some interoperability testing between bsdtar
> and gtar's newly-implemented "posix" format and I have a few quibbles:

Great. Thanks for noticing the problems.

>  * No user/group stored with 'x' entry.

This is reasonable.

>  * Poor naming of 'x' entry.   Long filenames get
>    truncated at 100 characters.  Following the logic
>    above, this could result in readers overwriting
>    other files with the contents of 'x' entries.

According to PAX specs:

    If no -o exthdr.name= string is specified, pax shall use
    the following default value:

           %d/PaxHeaders.%p/%f

which is exactly what GNU tar does. However, the problem with truncating
long ids does exist. It will be solved in the next version. In the
meanwhile you may always work around it using --pax-option to change
the naming scheme. E.g.:

       --pax-option exthdr.name=././@PaxHeader

to imitate star naming of 'x' entries.
       
>    It is quite appropriate to use numeric extensions
>    (e.g., base-256) here.  Compliant readers should
>    ignore the value (in favor of the value stored in the
>    extended attribute entry), so it does not compromise
>    standards compliance, but does help ensure that
>    the widest possible array of readers can extract
>    the file (such as GNU tar 1.13 ;-).

Well, it sounds reasonable. At least for GNU tar. Although, if
one is worrying about compatibility with older applications,
one should not use pax format.

> Finally, I find the name "posix" for this format to
> be quite misleading;

Agreed.

> some people will think you're referring
> to "ustar" which is also a POSIX format.

GNU tar docs say:

   posix
        Archive format defined by POSIX.1-2001 specification. 

> The official
> name of this format in the Single Unix Standard is "pax extended."
> For reference, you might take a close look at two other open-source
> archivers that implement this format:  star refers to this format
> as "xustar" (extended ustar) and bsdtar refers to this as "pax".

The CVS version understads --format=pax as a synonim for --format=posix

Regards,
Sergey