Bug#268631: force preference of IPv4 over IPv6
> The basic idea is that we want to make sure that either there's no
> IPv6 at all, or IPv6 works fine.
where by "fine" you actually mean something much stronger:
> IPv6 at least as good as IPv4
Okay, let's consider people who want IPv6 but (for whatever reason)
cannot ensure that their IPv6 is better than their IPv4. Wouldn't it
be a good idea to make their lives a little easier? Eg, /etc/gai.conf
could have an accompanying /etc/gai.conf.d/ directory, in the Debian
tradition, that would have the files it contains implicitly scanned.
This would make it easier to "prefer IPv4" in a way that won't require
manual intervention on every upgrade. E.g., by including a file
containing one line.
It would also make it easier for slow-IPv6-provision gizmos, like
miredo or aiccu, to indicate that IPv4 is preferred in a way that is
easy to automatically turn back off when said systems are disabled.
These systems could put a symlink, e.g.,
/etc/gai.conf.d/aiccu -> /var/run/whatever
and create/delete the /var/run/whatever file when their slow IPv6 link
goes up and down.