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

[Paul Eggert]

On 12/13/21 03:30, Sergey Poznyakoff wrote:
> Reproducible tarballs in PAX format are
> easily made with the following option:
>
>    --pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0,ctime:=0

I tried this, and unfortunately it introduced unnecessary extended pax 
records into the output. For example:

opts='--pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0,ctime:=0'
touch -d 2021-12-13T00:00:00Z foo
tar -cf t1 -H ustar foo
tar -cf t2 -H pax $opts foo

Although t1 and t2 should be identical, t2 contains an unnecessary pax 
extended header saying "ctime=0" and "atime=0".

I installed the attached patch to suggest --pax option 'delete=[ac]time' 
instead; this should work around the issue.

Perhaps 'tar' should be changed to not output unnecessary pax extended 
headers in cases like these; this would take some hacking, though, and 
I'm not sure it's worth it.

For tzdb I've suppressed mtime records in extended pax headers by 
touching all the files to integer-second-resolution timestamps as shown 
in the above example. I do this because I want the tarball timestamps to 
exactly match what's in Git.

Perhaps there should be a more convenient way for tar to generate 
pax-format tarballs without atime and ctime (and perhaps without 
extended mtime records too), as for software distro tarballs there's 
often little value and perhaps even some hassle with those 
subsecond-resolution timestamps.

Or simpler advice might be simply "use ustar format for software distros"...

0001-More-reproducible-tarball-doc.patch
Description: Text Data