modules/nixos/common/update: switch to apply script, refactor

modules/nixos/common/update.bash

@@ -6,25 +6,36 @@ if [[ "$(readlink /run/current-system)" == "$p" ]]; then
   exit 0
 fi
 
-nix-store --option narinfo-cache-negative-ttl 0 --realise "$p"
-nix-env --profile /nix/var/nix/profiles/system --set "$p"
+nix-store \
+  --option narinfo-cache-negative-ttl 0 \
+  --add-root /run/inbound-system \
+  --realise "$p"
 
-booted="$(readlink /run/booted-system/{initrd,kernel,kernel-modules} && cat /run/booted-system/kernel-params)"
-built="$(readlink "$p"/{initrd,kernel,kernel-modules} && cat "$p"/kernel-params)"
-if [[ $booted != "$built" ]]; then
-  if [[ -e /run/current-system ]]; then
-    echo "--- diff to current-system"
-    nvd diff /run/current-system "$p"
-    echo "---"
-  fi
-  /nix/var/nix/profiles/system/bin/switch-to-configuration boot
+booted="$(
+  readlink /run/booted-system/{initrd,kernel,kernel-modules} &&
+    cat /run/booted-system/kernel-params
+)"
+
+inbound="$(
+  readlink /run/inbound-system/{initrd,kernel,kernel-modules} &&
+    cat /run/inbound-system/kernel-params
+)"
+
+if [[ $booted != "$inbound" ]]; then
+  echo "--- diff to current-system"
+  nvd diff /run/current-system /run/inbound-system
+  echo "---"
+  /run/inbound-system/bin/apply boot
   # don't use kexec if system is virtualized, reboots are fast enough
   if ! systemd-detect-virt -q; then
-    kexec --load "$p"/kernel --initrd="$p"/initrd --append="$(cat "$p"/kernel-params) init=$p/init"
+    kexec \
+      --load /run/inbound-system/kernel \
+      --initrd=/run/inbound-system/initrd \
+      --append="$(cat /run/inbound-system/kernel-params) init=/run/inbound-system/init"
   fi
   if [[ ! -e /run/systemd/shutdown/scheduled ]]; then
     shutdown -r "+$(shuf -i 5-60 -n 1)"
   fi
 else
-  /nix/var/nix/profiles/system/bin/switch-to-configuration switch
+  /run/inbound-system/bin/apply switch
 fi