My documentation for "newc" is based primarily on studying the implementation of GNU cpio. I've not found any good references for the history of this format.
I'm a little unclear what pax implementation you're discussing. Based on the description below, I would suggest you test whether this program duplicates bodies for each hardlink it stores. This is easy to test: Make two hardlinks to the same large file, archive them and see if the resulting archive is twice as big as the file. The "odc" (POSIX-1988) format should duplicate bodies for hardlinks. GNU cpio's implementation of "newc" format does not. Tar formats (including the POSIX-2001 pax extended format) do not as a rule, though the pax extended format does permit it as an option. My sympathies for the maintainers of the pax you're discussing; it is surprisingly difficult to correctly handle all three common approaches for hardlink management within a single program. Tim Kientzle Daniel Kahn Gillmor wrote:
Tim Kientzle of FreeBSD (author of libarchive, attempting to CC here) describes the cpio format here: http://people.freebsd.org/~kientzle/libarchive/man/cpio.5.txt This document states about the SRV4 (newc) format (magic 070701, which is what we're dealing with): In this format, hardlinked files are handled by setting the filesize to zero for each entry except the last one that appears in the archive. So this is interpretation is shared by at least GNU and FreeBSD, afaict. pax appears to be in disagreement with these systems as far as its creation of SRV4/newc archives goes, since it stores a non-zero filesize for each entry of a hardlinked file. It's in dangerous disagreement with GNU and FreeBSD during the unpacking stage, because it re-creates hardlinked files as 0 bytes in length if it encounters archives created by the other utilities. Hope this is a useful reference, --dkg For Tim's reference: we're discussing pax here: http://bugs.debian.org/42158
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