modules: add disko partition module for common partition patterns

modules/nixos/disk-partitions/btrfs.nix

@@ -0,0 +1,46 @@
+{
+  size = "100%";
+  content = {
+    type = "btrfs";
+    extraArgs = [ "-f" ]; # Override existing partition
+    # Subvolumes must set a mountpoint in order to be mounted,
+    # unless their parent is mounted
+    subvolumes = {
+      # Subvolume name is different from mountpoint
+      "/rootfs" = {
+        mountpoint = "/";
+      };
+      # Subvolume name is the same as the mountpoint
+      "/home" = {
+        mountOptions = [ "compress=zstd" ];
+        mountpoint = "/home";
+      };
+      # Parent is not mounted so the mountpoint must be set
+      "/nix" = {
+        mountOptions = [
+          "compress=zstd"
+          "noatime"
+        ];
+        mountpoint = "/nix";
+      };
+      "/persistent" = {
+        mountOptions = [
+          "compress=zstd"
+          "noatime"
+          # Lots of dbs in /var/lib, let's disable cow
+          "nodatacow"
+        ];
+        mountpoint = "/var/lib";
+      };
+      # Subvolume for the swapfile
+      "/swap" = {
+        mountpoint = "/.swapvol";
+        swap = {
+          swapfile.size = "2G";
+        };
+      };
+    };
+
+    mountpoint = "/partition-root";
+  };
+}

modules/nixos/disk-partitions/default.nix

@@ -0,0 +1,15 @@
+{ lib, ... }:
+{
+  options = {
+    diskPartitions = lib.mkOption {
+      type = lib.types.attrs;
+      default = { };
+    };
+  };
+  config = {
+    diskPartitions = {
+      btrfs = import ./btrfs.nix;
+      grubMbr = import ./grub-mbr.nix;
+    };
+  };
+}

modules/nixos/disk-partitions/grub-mbr.nix

@@ -0,0 +1,4 @@
+{
+  size = "1M";
+  type = "EF02"; # for grub MBR
+}