different compression types for NetBSD-daily/netbsd-11/latest/ sets

[Steve Rikli <sr%genyosha.net@localhost>]

The recent thread about upgrading NetBSD 10.x reminded me of questions
I've had regarding the daily sets.

Today it looks like most binary sets files are .tgz, but not all.

For reference I'm looking here:

  https://nycdn.netbsd.org/pub/NetBSD-daily/netbsd-11/latest/

and spot-checking a few architectures' binary/sets/ directories, mostly
for systems I use today or in the past; I found:

  tgz : alpha i386 macppc sgimips sparc sparc64

  tar.xz : amd64 evbarm-aarch64

First question: is the difference intentional? E.g. is there some reason
tgz (tar.gz) is preferred over tar.xz for certain architectures?

Followup questions depend on the answer to the first. :-)  For most of
my systems I use sysupgrade for NetBSD upgrades, and I notice that
script has this code:

    if [ "$(uname -p)" = 'x86_64' ] || [ "$(uname -p)" = 'sparc64' ]; then
        shtk_config_set ARCHIVE_EXTENSION "tar.xz"
    else
        shtk_config_set ARCHIVE_EXTENSION "tgz"
    fi

to override the commented value in default /usr/pkg/etc/sysupgrade.conf :

  # Archive file extension of the sets. For now it can be either 'tgz' or
  # 'tar.xz'.
  #ARCHIVE_EXTENSION=tar.xz

Interestingly, it looks to me like the sparc64 code may be working at
cross purposes to the default config, whereas evbarm-aarch64 (et al?)
could make use of the override but isn't included.

I'd think having all system types use the same .tar.?? format might be
a good thing for consistency's sake, but I don't know the history here.

I keep notes to update sysupgrade.conf on my rpi4b during install; it's
not a huge issue since you already also need to modify RELEASEDIR for
evbarm-aarch64 ('uname -m' doesn't match the binary/sets/ directory
structure -- you need something like '$(uname -m)-$(uname -p)'.

Still, you do need to know/remember to do it. It feels like there may
be a PR in here somewhere, possibly on sysupgrade code and/or config
file, but I'd also like to understand why the different tar.* are used.

Cheers,
sr.