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From: J Wunsch <j@uriah.heep.sax.de>
Message-Id: <199508060621.IAA04695@uriah.heep.sax.de>
Subject: Re: Backup of 32bit dev entries
To: current@freebsd.org
Date: Sun, 6 Aug 1995 08:21:39 +0200 (MET DST)
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In-Reply-To: <199508050248.MAA30049@godzilla.zeta.org.au> from "Bruce Evans" at Aug 5, 95 12:48:45 pm
Reply-To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch)
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As Bruce Evans wrote:
> 
> 	pax -x sv4cpio -w -f /tmp/ttt *		# works
> 	pax -x sv4crc  -w -f /tmp/ttt *		# works

> 	find . | cpio -H newc -o > /tmp/ttt	# equiv to above pax command
> 	find . | cpio -H crc  -o > /tmp/ttt	# equiv to above pax command

> >Allowing 32 bits in before we could easily back them up seems strange,
> 
> 5 ways to back them up seems enough :-).

Why don't we change the defaults for cpio and pax?  For cpio, this is
no problem since it's not mentioned by Posix, and cpio's are supposed
to recognize all formats automatically.  (Of course, transfer to older
cpio's will be affected, but people exchanging data between different
architectures will always first have to check whether the intented
archive format will work.)  I'd suggest ``crc''.  Computing the CRC
doesn't cost too much time, and having a checksummed archive seems to
be a Good Thing(tm).


For pax, Posix.2 says the following:

 The supported archive formats shall be automatically detected on input.
 The default output archive format shall be implementation defined.
...

    -x format   Specify the output archive format.  The pax utility shall
                recognize the following formats:

                   cpio     The extended cpio interchange format specified
                            in POSIX.1 {8} 10.1.2.  The default blocksize   1
                            for this format for character special archive   1
                            files shall be 5120.  Implementations shall     1
...

Bruce, do you know which format the ``extended cpio interchange format
specified in POSIX.1 {8} 10.1.2'' does exactly refer to?  I believe
it's cpio's ``crc'' format, but i don't have a Posix.1 doc handy.

If this is true, we should make pax default to this cpio format,
otherwise we should probably pick ustar format (the second one
mentioned in Posix), since it can at least back up 21 bits of the
device number.  (While Posix doesn't forbid to make one of the
implementation-defined formats the standard, i think this is not a
good idea.)

-- 
cheers, J"org

joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/
Never trust an operating system you don't have sources for. ;-)