fix: hdd storage - auto unlock after booted (#158)

hosts/idols-aquamarine/disko-fs.nix

@@ -1,8 +1,19 @@
 # auto disk partitioning:
 #   nix run github:nix-community/disko -- --mode disko ./disko-fs.nix
-{
+let
+  cryptKeyFile = "/etc/agenix/hdd-luks-crypt-key";
+  unlockDisk = "data-encrypted";
+in {
   fileSystems."/data/fileshare/public".depends = ["/data/fileshare"];
 
+  # By adding this crypttab entry, the disk will be unlocked by systemd-cryptsetup@xxx.service at boot time.
+  # This systemd service is running after agenix, so that the keyfile is already available.
+  environment.etc = {
+    "crypttab".text = ''
+      ${unlockDisk} /dev/disk/by-partlabel/disk-${unlockDisk}-luks ${cryptKeyFile} luks,discard,keyfile-size=32768,keyfile-offset=65536
+    '';
+  };
+
   disko.devices = {
     disk.data-encrypted = {
       type = "disk";
@@ -16,7 +27,7 @@
               type = "luks";
               name = "data-encrypted";
               settings = {
-                keyFile = "/etc/agenix/hdd-luks-crypt-key";
+                keyFile = cryptKeyFile;
                 # The maximum size of the keyfile is 8192 KiB
                 # type `cryptsetup --help` to see the compiled-in key and passphrase maximum sizes
                 # to generate a key file:
@@ -27,7 +38,8 @@
                 allowDiscards = true;
               };
               # Whether to add a boot.initrd.luks.devices entry for the specified disk.
-              # This data disk is not needed to boot the system, so we don't need to unlock it in the initrd.
+              # The keyfile do not exist before agenix decrypts its data, do we have to disable this option.
+              # Otherwise, the initrd will fail to unlock the disk, which causes the boot process to fail.
               initrdUnlock = false;
 
               # encrypt the root partition with luks2 and argon2id, will prompt for a passphrase, which will be used to unlock the partition.