From 985547acc664a8c802688ebd1724f6f9f7811a73 Mon Sep 17 00:00:00 2001
From: lassulus <lassulus@lassul.us>
Date: Thu, 24 Nov 2022 17:30:37 +0000
Subject: [PATCH] kexec: restore static ips after kexec

---
 nix/kexec-installer.nix | 20 ++++++++++
 nix/restore_routes.py   | 83 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 nix/restore_routes.py

diff --git a/nix/kexec-installer.nix b/nix/kexec-installer.nix
index 698f850..2518bae 100644
--- a/nix/kexec-installer.nix
+++ b/nix/kexec-installer.nix
@@ -29,6 +29,11 @@
     for p in /etc/ssh/ssh_host_*; do
       cp -a "$p" ssh
     done
+
+    # save the networking config for later use
+    ip --json addr > addrs.json
+    ip --json route > routes.json
+
     find | cpio -o -H newc | gzip -9 > ../extra.gz
     popd
     cat "''${SCRIPT_DIR}/initrd" extra.gz > final-initrd
@@ -76,14 +81,29 @@
   # for detection if we are on kexec
   environment.etc.is_kexec.text = "true";
 
+  systemd.services.restoreNetwork = {
+    path = [
+      pkgs.iproute2
+    ];
+    wantedBy = [ "multi-user.target" ];
+    after = [ "network.target" ];
+    serviceConfig.ExecStart = "/run/current-system/sw/bin/restore_network /root/network/addrs.json /root/network/routes.json";
+  };
+
+  environment.systemPackages = [
+    (pkgs.writers.writePython3Bin "restore_network" { flakeIgnore = ["E501"]; } ./restore_routes.py)
+  ];
+
   # Restore ssh host and user keys if they are available.
   # This avoids warnings of unknown ssh keys.
   boot.initrd.postMountCommands = ''
     mkdir -m 700 -p /mnt-root/root/.ssh
     mkdir -m 755 -p /mnt-root/etc/ssh
+    mkdir -m 755 -p /mnt-root/root/network
     if [[ -f ssh/authorized_keys ]]; then
       install -m 400 ssh/authorized_keys /mnt-root/root/.ssh
     fi
     install -m 400 ssh/ssh_host_* /mnt-root/etc/ssh
+    cp *.json /mnt-root/root/network/
   '';
 }
diff --git a/nix/restore_routes.py b/nix/restore_routes.py
new file mode 100644
index 0000000..7ca4969
--- /dev/null
+++ b/nix/restore_routes.py
@@ -0,0 +1,83 @@
+import json
+import sys
+import subprocess
+
+
+def filter_interfaces(network):
+    output = []
+    for net in network:
+        if net["ifname"] == "lo":
+            continue
+        addr_info = []
+        for addr in net["addr_info"]:
+            if addr.get("dynamic", False):
+                pass
+            elif addr["local"].startswith("fe80"):
+                pass
+            else:
+                addr_info.append(addr)
+        if addr_info != []:
+            net["addr_info"] = addr_info
+            output.append(net)
+
+    return output
+
+
+def main():
+    with open(sys.argv[1]) as f:
+        addresses = json.load(f)
+    with open(sys.argv[2]) as f:
+        routes = json.load(f)
+    relevant_interfaces = filter_interfaces(addresses)
+    current_interfaces = json.loads(
+        subprocess.run(
+            ["ip", "--json", "addr"],
+            capture_output=True,
+        ).stdout
+    )
+
+    for interface in relevant_interfaces:
+        for current_interface in current_interfaces:
+            if "address" in interface and "address" in current_interface:
+                if interface["address"] == current_interface["address"]:
+                    for addr in interface["addr_info"]:
+                        subprocess.run(
+                            [
+                                "ip",
+                                "addr",
+                                "add",
+                                "dev",
+                                current_interface["ifname"],
+                                f'{addr["local"]}/{addr["prefixlen"]}',
+                            ]
+                        )
+                    for route in routes:
+                        if route["dev"] == interface["ifname"]:
+                            if route.get("gateway", False):
+                                subprocess.run(
+                                    [
+                                        "ip",
+                                        "route",
+                                        "add",
+                                        route["dst"],
+                                        "via",
+                                        route["gateway"],
+                                        "dev",
+                                        current_interface["ifname"],
+                                    ]
+                                )
+                            else:
+                                subprocess.run(
+                                    [
+                                        "ip",
+                                        "route",
+                                        "add",
+                                        route["dst"],
+                                        "dev",
+                                        current_interface["ifname"],
+                                    ]
+                                )
+
+
+if __name__ == "__main__":
+    main()