From 6ba47ed9892fb8c985a6dc490765661cb55e17f6 Mon Sep 17 00:00:00 2001
From: liberodark <liberodark@gmail.com>
Date: Wed, 20 Nov 2024 11:00:42 +0100
Subject: [PATCH] nixos/hot-resize: init

---
 nixos/modules/services/system/hot-resize.nix | 149 +++++++++++++++++++
 1 file changed, 149 insertions(+)
 create mode 100644 nixos/modules/services/system/hot-resize.nix

diff --git a/nixos/modules/services/system/hot-resize.nix b/nixos/modules/services/system/hot-resize.nix
new file mode 100644
index 00000000000000..e22fedbd35e595
--- /dev/null
+++ b/nixos/modules/services/system/hot-resize.nix
@@ -0,0 +1,149 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.services.hotResize;
+
+  resize-script = pkgs.writeShellApplication {
+    name = "hot-resize";
+    runtimeInputs = with pkgs; [
+      cloud-utils
+      e2fsprogs
+      parted
+      util-linux
+      btrfs-progs
+      xfsprogs
+      coreutils
+    ];
+
+    text = ''
+      process_device() {
+        local device="$1"
+        local fstype="$2"
+        local mountpoint="$3"
+
+        echo "Processing $device ($fstype) mounted at $mountpoint..."
+
+        REAL_DEVICE=$(readlink -f "$device")
+        DISK=$(lsblk -Pno pkname "$REAL_DEVICE" | sed 's/PKNAME="\(.*\)"/\1/')
+        PART_NUM=$(echo "$device" | grep -o '[0-9]*$')
+
+        if [ -z "$DISK" ] || [ -z "$PART_NUM" ]; then
+          echo "Failed to determine disk and partition number for $device"
+          return 1
+        fi
+
+        echo "Growing partition /dev/$DISK partition $PART_NUM..."
+        GROWPART_OUTPUT=$(growpart "/dev/$DISK" "$PART_NUM" 2>&1) || {
+        EXIT_CODE=$?
+        if [ $EXIT_CODE -eq 2 ] || ([ $EXIT_CODE -eq 1 ] && echo "$GROWPART_OUTPUT" | grep -q "NOCHANGE"); then
+           echo "Partition is already at maximum size, continuing with filesystem resize..."
+        else
+           echo "Failed to grow partition: $GROWPART_OUTPUT"
+          return $EXIT_CODE
+        fi
+        }
+
+        echo "Resizing filesystem..."
+        case "$fstype" in
+          ext4)
+            resize2fs "$device"
+            ;;
+          xfs)
+            xfs_growfs "$mountpoint"
+            ;;
+          btrfs)
+            btrfs filesystem resize max "$mountpoint"
+            ;;
+          *)
+            echo "Unsupported filesystem type: $fstype"
+            return 1
+            ;;
+        esac
+
+        echo "Current size:"
+        df -h "$mountpoint"
+        echo "---"
+      }
+
+      process_device "$@"
+    '';
+  };
+
+in
+{
+  options.services.hotResize = {
+    enable = lib.mkEnableOption "the hot resize service for filesystems";
+
+    devices = lib.mkOption {
+      type = lib.types.listOf (
+        lib.types.submodule {
+          options = {
+            device = lib.mkOption {
+              type = lib.types.str;
+              example = "/dev/sda1";
+              description = "Block device path to resize";
+            };
+
+            fsType = lib.mkOption {
+              type = lib.types.enum [
+                "ext4"
+                "xfs"
+                "btrfs"
+              ];
+              default = "ext4";
+              description = "Filesystem type (supported: ext4, xfs, btrfs)";
+            };
+
+            mountPoint = lib.mkOption {
+              type = lib.types.str;
+              example = "/";
+              description = "Mount point of the filesystem to resize";
+            };
+          };
+        }
+      );
+      default = [ ];
+      example = lib.literalExpression ''
+        [
+          {
+            device = "/dev/sda1";
+            fsType = "ext4";
+            mountPoint = "/";
+          }
+          {
+            device = "/dev/sdb1";
+            fsType = "xfs";
+            mountPoint = "/data";
+          }
+        ]
+      '';
+      description = "List of devices to monitor for resizing";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.services.hotResize = {
+      description = "Hot resize service for filesystems";
+      wantedBy = [ "multi-user.target" ];
+      requires = [ "local-fs-pre.target" ];
+      after = [ "local-fs-pre.target" ];
+
+      serviceConfig = {
+        Type = "oneshot";
+        RemainAfterExit = false;
+        ExecStart =
+          let
+            deviceArgs = lib.concatMapStrings (
+              dev: ''"${dev.device}" "${dev.fsType}" "${dev.mountPoint}" ''
+            ) cfg.devices;
+          in
+          "${lib.getExe resize-script} ${deviceArgs}";
+      };
+    };
+  };
+}