Re: git-archive's wrong documentation: really write pax rather than tar

["René Scharfe" <rene.scharfe@lsrfire.ath.cx>]

Am 04.08.2011 04:29, schrieb Jeff King:
> On Wed, Aug 03, 2011 at 07:25:32PM -0700, Junio C Hamano wrote:
> 
>>> Actually, it is relevant for zip, too. The option should really be
>>> called "--no-commit-id" or something similar. I don't think it's as big
>>> a deal with zip (because there is no compatibility issue), but you may
>>> want to omit the header for other reasons (e.g., because you know it
>>> doesn't point to a commit that is public).
>>
>> Hmm, perhaps. It indeed is an implementation detail of the tar backend
>> that the commit object name is stored in pax header, so --no-commit-id
>> might make sense from "git" point of view, but from the point of view of
>> OP that started this thread, he wouldn't care what that extra information
>> is --- it can be a commit object name or it can be phase of the moon when
>> the archive was made --- he just wants the extra header dropped.
>>
>> So I dunno.
> 
> If the intent of the option is "write plain-vanilla ustar" (I really
> hope it doesn't need to be "plain-vanilla 4.3BSD tar"), then I think we
> would do better to have a new --format type. Because from the OP's
> perspective, it's not "drop this header that I don't like" but "make
> something compatible with older versions of tar".

Yes, the commit ID header is just one part of this.  Extended pax
headers are also used to store file names or symlink targets that are
too long.  If none of this applies, the output should be pure ustar, though.

POSIX says that programs should treat unknown entry types just like
plain files and print an error message.  You'd get an extra file named
pax_global_header, containing only the commit ID, and for long file
names extra files that contain them (and your original files would get
short names based on their object ID).

Looking at the web page linked to in the original post, the problem
seems to be that R (probably http://www.r-project.org/) uses "tar" as a
package format, seems to accept the ustar format but refuses pax
extended headers and thus is incompatible with "POSIX tar" and also
doesn't follow the suggestion to treat unknown entries as plain files.

We could add a "ustar" format that doesn't write commit ID comments and
errors out on file names that are too long.

René