Currently both callers in podman and buildah join and inspect the netns
to get the local ip configured by pasta in order to add it to
/etc/hosts. So instead of doing this in two places let's just do it here
once and return the result to the caller.

In order to not cause vendoring issues I decided against breaking the
API and added a new Setup2 function instead. I will then update
podman and buildah to make use of it.

Also I plan on adding more fields in the result, i.e. dns address.

Because this now depends on linux only functionality make sure to only
build it on linux, pasta only works on linux anyway so this is not a
problem.

Signed-off-by: Paul Holzinger <[email protected]>

This reverts commit 92784a2.
I plan on using --dns-forward now so we do not want to disable dns by
default, see [1].

[1] containers/podman#19213

Signed-off-by: Paul Holzinger <[email protected]>

By default set 169.254.0.1 as nameserver in the container, right now we
do not do special dns handling which means if a user has only localhost
resolver or the same nameserver ip as the host ip used by pasta then dns
will most likely fail.

pasta allows us to remap one ipv4 for dns which will then automatically
get remapped to the host dns server from resolv.conf. For that we must
use --dns-forward, now the choice of which ip is arbitrary but using the
local link address 169.254.0.1 is unlikely to be used so it should avoid
conflicts.

Also return the ip in the result together with a ipv6 bool so that
podman can create a correct resolv.conf with that ip for the container.

Signed-off-by: Paul Holzinger <[email protected]>

This tells us if ipv6 is supported. And we should use the forward ips as
dns servers to make sure we can read localhost resolvers on the host.

Signed-off-by: Paul Holzinger <[email protected]>

For some cases it may be required to get a local ip while excluding a
certain ip. This will be used to set a better host.containers.internal
name for pasta networks as it is likely that host eth0 ip == container
ip so in this case we must use different host ip.

Signed-off-by: Paul Holzinger <[email protected]>

For callers like podman we might have to exclude certain ips for the use
of host.containers.internal as they might conflict with the inside
container ip otherwise.

Signed-off-by: Paul Holzinger <[email protected]>

My plan is to directly use the result in podman on the Container struct,
this is shared with freebsd even though slirp4netns will never be used
there. Thus we can simply move the type definition to the file that is
shared to not cause build problems.

Signed-off-by: Paul Holzinger <[email protected]>

[v0.58] Backport pasta fixes

Signed-off-by: Matt Heon <[email protected]>