Re: [PATCH] change default --format from gnu to posix

[Antonio Diaz Diaz]

Paul Eggert wrote:
> This discussion suggests the need for a new, easy-to use format option,
> which is like '-Hpax' except that it omits atime and ctime, and omits
> the subseconds part of mtime. Using this format would mean that pax
> extensions won't be used unless they're needed (a file with a long name,
> a timestamp past the year 2246, etc.) and so the tarball would be more
> portable to platforms with older or buggy tarball extractors.
>
> Maybe we could call this the 'art' format, for "archive reproducible
> tarball", so that people could use 'tar -Hart' for it. Like 'ustar',
> 'art' format would be a strict subset of 'pax' format so it would be
> POSIX-conforming.
>
> We could introduce the new option in the next release of GNU tar, and
> think about changing the default format to it in a later release.
>
> What do you think?

I like the idea. In fact is what I do in tarlz. I would only suggest to make 
'tar -Hart' protect the extended records with a CRC as tarlz does. See

http://www.nongnu.org/lzip/manual/tarlz_manual.html#Amendments-to-pax-format

and

http://www.nongnu.org/lzip/manual/tarlz_manual.html#key_005fcrc32
GNU.crc32
    CRC32-C (Castagnoli) of the extended header data excluding the 8 bytes 
representing the CRC <value> itself. The <value> is represented as 8 
hexadecimal digits in big endian order, '22 GNU.crc32=00000000\n'. The 
keyword of the CRC record is protected by the CRC to guarante that 
corruption is always detected (except in case of CRC collision). A CRC was 
chosen because a checksum is too weak for a potentially large list of 
variable sized records. A checksum can't detect simple errors like the 
swapping of two bytes.

Antonio.