* net/dns: export OSConfigurationReadWarnable
A natlab vmtest checks that a node is not reporting this warning. Exporting
the Warnable lets the test take the warning's text from it, instead of
keeping a copy of the wording that could stop matching without failing.
Updates #20825
Updates tailscale/corp#44793
Signed-off-by: Brendan Creane <bcreane@gmail.com>
* tstest/natlab/vmtest: add VM coverage for the openresolv DNS backend
dnsMode() picks one of five Linux DNS backends, and natlab could provision
only systemd-resolved and direct. Add a DNSOpenresolv mode and a VM test for
it, so the backend behind #20825 is covered.
No cloud image ships openresolv and a guest cannot download it, so its two
source files are vendored under testdata and installed with cloud-init's
write_files. openresolv's build is a set of sed substitutions with nothing to
compile, so resolvconf.go does the substitutions in process.
Updates #20825
Updates tailscale/corp#44793
Signed-off-by: Brendan Creane <bcreane@gmail.com>
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Signed-off-by: Brendan Creane <bcreane@gmail.com>
Brendan Creane
970cc199fe