Re: [Bug-tar] Re: [PATCH] Extended attribute support for tar

[Joerg Schilling]

James Antill <address@hidden> wrote:

> > It should be limited to POSIX.1-2001 format only (POSIX_FORMAT). 

This format is called "pax"

>  This would mean the default would have to change when you enable that
> option[1], is there a reason to not allow it with the gnu format? Also

The "GNU tar" archive format is neither POSIX (not even POSIX.1-1988)
nor really compatible to historical tar formats.

The "pax" format is a compliant extension to the POSIX.1-1988 tar format.
The "exustar" format is compliant extension to the POSIX.1-2001 "pax"
format.

You cannot add POSIX features to a non-POSIX format.

If you did, you will break the format detection of various programs
like e.g. "star" and David Korn's / Glenn Fowler's "pax".


> to be compatible[2] with star we need to at least extract from ustar
> typed archives (star's exustar is treated by GNUtar as ustar ... AIUI).

This needs to be called a bug in GNU tar.

>  What are the downsides to changing the default to be posix -- which is
> basically what would be happening as xattr usage is leaking into more
> and more applications. The documentation says that this is planned when
> full support for posix archives is done, is this close to happening?
>
>
> [1] Or have the horribly ugly UI that star has where you need to specify
> --xattrs and --format=posix or it'd fail, which seems to be much worse
> for no real gain.

I belioeve that that it's rather the GNU tar UI that is horribly ugly.
In contrary to GNU tar's UI, star's UI is SUSv2 compliant and well defined:

-       Star is a multi format archiver that also supports various CPIO
        archive formats. "allowable" features thus needs to be derived
        from the the selected archive format - not the other way round.

-       Star has well planned options that try to implement as much 
        features as possible with a small number of options.
        This may e.g. be verified by the fact that star allows to use
        "libfind" and thus alows you to use find(1) expressions in 
        creat and extract/list mode rather than implementing less 
        powerful options that need to be learned separately.

-       Star implements roughly 2x as much features as GNU tar does.
        This obviously makes the man page more complex.

-       If you take one day to learn the philosophy behind star, you 
        will never like to miss star ;-)


Jörg

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