On Fri, Aug 15, 2008 at 01:59:41PM -0700, Tim Kientzle wrote: > 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.
OK, this is good to know. I'm not saying one or the other program is wrong, but having a piece of documentation describing an implementation is of course not the same as a standard. > > I'm a little unclear what pax implementation you're > discussing. Based on the description below, I would The discusison started with the OpenBSD pax implementation, which also does cpio. OpenBSD pax has the same roots as the FreeBSD one, so I suspect some of the problems are shared. > 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. OpenBSD pax does store multiple copies of hard linked files (at least when using the sv4cpio (SVR4 hex cpio) format, as you may have notited, the divergence between gnu cpcio and bsd cpio already starts with the names of the formats :-( > > 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. yep, thanks ;-) > > 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. I am not sure if libarchive and pax on FreeBSD share this. Which implementation of cpio is used on FreeBSD by default? >> >> 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 I think it would be good to compare to OpenSolaris cpio, being a third independent implementation of cpio. At the moment I do not have access to one, but I'll try to setup something today. -Otto -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
