[PATCH installer v2 9/9] unconfigured: try to retrieve IPv6 SLAAC addresses on startup

[Christoph Heiss <c.heiss@proxmox.com>]

Uses `rdisc6` to send IPv6 router solicitations, in order to get
potential router advertisements. The kernel then auto-configures any
retrieved IPv6 address on the corresponding interface.

`rdnssd` is used to to retrieve IPv6 (recursive) DNS servers from these
router advertisements.

Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
---
Changes v1 -> v2:
  * give routers a 2sec window to respond to router solicitations

 debian/control  |  2 ++
 unconfigured.sh | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/debian/control b/debian/control
index 8049dd6..3c9de71 100644
--- a/debian/control
+++ b/debian/control
@@ -50,7 +50,9 @@ Depends: chrony,
          libgtk3-perl,
          libgtk3-webkit2-perl,
          libjson-perl,
+         ndisc6,
          proxmox-kernel-helper,
+         rdnssd,
          squashfs-tools,
          util-linux-extra,
          ${misc:Depends},
diff --git a/unconfigured.sh b/unconfigured.sh
index 7445ac4..8b1ee51 100755
--- a/unconfigured.sh
+++ b/unconfigured.sh
@@ -218,6 +218,16 @@ handle_wireless() {
     fi
 }
 
+# Iterates over all UP interfaces and sends a router solicitation on each.
+ipv6_send_router_solicitation() {
+    local devs
+    devs="$(ip -6 addr show scope link up | grep -oP '^\d+: \K\S+(?=:)')"
+
+    for dev in $devs; do
+        rdisc6 -1 --retry 1 "$dev" || true
+    done
+}
+
 PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin
 
 echo "Starting Proxmox installation"
@@ -311,6 +321,23 @@ echo -n "Attempting to get DHCP leases... "
 dhclient -v
 echo "done"
 
+# start rdnssd in the background first
+# the default merge hook just appends it to /etc/resolv.conf, which is what we want
+# also need to create the run-directory for rdnssd, otherwise it will silently
+# fail to write out new entries
+echo "Starting rdnssd for retrieving IPv6 nameservers..."
+mkdir -p /run/rdnssd
+rdnssd --merge-hook /etc/rdnssd/merge-hook --user root || echo "starting rdnssd failed ($?)"
+
+# check for IPv6 SLAAC by sending a router solicitation
+# rdnssd will pick up any nameservers, and the kernel interface addresses
+echo "Sending IPv6 router solicitations..."
+ipv6_send_router_solicitation
+# give routers a reasonable window to respond, so that
+# `proxmox-low-level-installer dump-env` can pick them up
+sleep 2
+echo "Done sending IPv6 router solicitations."
+
 echo "Starting chrony for opportunistic time-sync... "
 chronyd || echo "starting chrony failed ($?)"
 
-- 
2.53.0