From 55dd84d67da8fb6e70aed7b921d05b66748546e1 Mon Sep 17 00:00:00 2001
From: Kleidi Bujari <mail@4kb.net>
Date: Sun, 30 Aug 2026 13:57:27 -0700
Subject: [nixos/disk] experiment with autosizing zfs partitions in initrd

---
 modules/disk.nix | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

(limited to 'modules')

diff --git a/modules/disk.nix b/modules/disk.nix
index 071c9ea..757d436 100644
--- a/modules/disk.nix
+++ b/modules/disk.nix
@@ -61,6 +61,7 @@ in
       kernelParams = [
         "nohibernate"
         "elevator=none"
+        "rd.systemd.unit=rescue.target"
       ];
       supportedFilesystems = [
         "vfat"
@@ -115,6 +116,44 @@ in
       };
     };
 
+    boot.initrd.systemd.services."growroot" = {
+      description = "Grow main partition into any unused disk space.";
+      serviceConfig.Type = "oneshot";
+
+      # If dry-run fails, there is nothing to grow
+      serviceConfig.ExecCondition = "${pkgs.cloud-utils}/bin/growpart /dev/vda 2 --dry-run";
+
+      wantedBy = [ "zfs.target" ];
+      before = [ "zfs-import-zroot.service" ];
+
+      script = "growpart /dev/vda 2 --verbose";
+    };
+
+    boot.initrd.systemd.services."expand-zroot" = {
+      description = "Expand zroot to take up entire partition.";
+      serviceConfig.Type = "oneshot";
+
+      wantedBy = ["zfs.target"];
+      after = ["zfs-import-zroot.service"];
+
+      script = ''
+        # pull partuuid from zpool
+        GUID=$(zpool list -v --json | jq --raw-output '.pools.zroot.vdevs.[].name')
+
+        # re-mark pool as online with '-e' to expand
+        zpool online -e zroot $GUID
+      '';
+    };
+
+    boot.initrd.systemd.emergencyAccess = true;
+    boot.initrd.systemd.initrdBin = [
+      pkgs.cloud-utils
+      pkgs.util-linux
+      pkgs.busybox
+      pkgs.jq
+      pkgs.zfs
+    ];
+
     image.modules.depot =
       { config, modulesPath, ... }:
       {
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