Add disk-size argument

Many formats generate an image only large enough for the generated NixOS
config. This quickly runs out of space for NixOS servers that are updated
over time rather than being redeployed with fresh images.

Signed-off-by: James Alseth <james@jalseth.me>

README.md

@@ -97,6 +97,27 @@ image was recently merged in nixpkgs):
 NIX_PATH=nixpkgs=../nixpkgs nixos-generate -f do
 ```
 
+## Setting the disk image size
+
+To specify the size of the generated disk image, use the `--disk-size` argument,
+specifying the size in megabytes. This is currently supported by the following
+formats. If this argument is unspecified it defaults to automatic sizing based
+on the generated NixOS build.
+
+- hyperv
+- proxmox
+- qcow
+- raw-efi
+- raw
+- vm
+- vm-nogui
+- vmware
+
+Example (20GB disk):
+```
+nixos-generate -c <your_config.nix> -f <format> --disk-size 20480
+```
+
 ## Cross Compiling
 
 To cross compile nixos images for other architectures you have to configure

formats/hyperv.nix

@@ -1,8 +1,18 @@
-{modulesPath, ...}: {
+{
+  modulesPath,
+  specialArgs,
+  lib,
+  ...
+}: {
   imports = [
     "${toString modulesPath}/virtualisation/hyperv-image.nix"
   ];
 
+  hyperv.baseImageSize =
+    if builtins.hasAttr "diskSize" specialArgs == false then "auto"
+    else if specialArgs.diskSize == "auto" then "auto"
+    else lib.strings.toIntBase10 specialArgs.diskSize;
+
   formatAttr = "hypervImage";
   fileExtension = ".vhdx";
 }

formats/proxmox.nix

@@ -1,7 +1,14 @@
-{modulesPath, ...}: {
+{
+  modulesPath,
+  specialArgs,
+  ...
+}: {
   imports = [
     "${toString modulesPath}/virtualisation/proxmox-image.nix"
   ];
+
+  proxmox.qemuConf.diskSize = specialArgs.diskSize or "auto";
+
   formatAttr = "VMA";
   fileExtension = ".vma.zst";
 }

formats/qcow.nix

@@ -3,6 +3,7 @@
   lib,
   pkgs,
   modulesPath,
+  specialArgs,
   ...
 }: {
   # for virtio kernel drivers
@@ -29,7 +30,7 @@
 
   system.build.qcow = import "${toString modulesPath}/../lib/make-disk-image.nix" {
     inherit lib config pkgs;
-    diskSize = 8192;
+    diskSize = specialArgs.diskSize or "auto";
     format = "qcow2";
     partitionTableType = "hybrid";
   };

formats/raw-efi.nix

@@ -4,6 +4,7 @@
   options,
   pkgs,
   modulesPath,
+  specialArgs,
   ...
 }: let
   inherit (import ../lib.nix {inherit lib options;}) maybe;
@@ -24,7 +25,7 @@ in {
   system.build.raw = maybe.mkOverride 99 (import "${toString modulesPath}/../lib/make-disk-image.nix" {
     inherit lib config pkgs;
     partitionTableType = "efi";
-    diskSize = "auto";
+    diskSize = specialArgs.diskSize or "auto";
     format = "raw";
   });
 }

formats/raw.nix

@@ -3,6 +3,7 @@
   lib,
   pkgs,
   modulesPath,
+  specialArgs,
   ...
 }: {
   fileSystems."/" = {
@@ -21,7 +22,7 @@
 
   system.build.raw = import "${toString modulesPath}/../lib/make-disk-image.nix" {
     inherit lib config pkgs;
-    diskSize = "auto";
+    diskSize = specialArgs.diskSize or "auto";
     format = "raw";
   };
 

formats/vm.nix

@@ -1,7 +1,16 @@
-{modulesPath, ...}: {
+{
+  modulesPath,
+  specialArgs,
+  lib,
+  ...
+}: {
   imports = [
     "${toString modulesPath}/virtualisation/qemu-vm.nix"
   ];
+  virtualisation.diskSize =
+    if builtins.hasAttr "diskSize" specialArgs == false then null
+    else if specialArgs.diskSize == "auto" then null
+    else lib.strings.toIntBase10 specialArgs.diskSize;
 
   formatAttr = "vm";
 }

formats/vmware.nix

@@ -1,8 +1,18 @@
-{modulesPath, ...}: {
+{
+  modulesPath,
+  specialArgs,
+  lib,
+  ...
+}: {
   imports = [
     "${toString modulesPath}/virtualisation/vmware-image.nix"
   ];
 
+  vmware.baseImageSize =
+    if builtins.hasAttr "diskSize" specialArgs == false then "auto"
+    else if specialArgs.diskSize == "auto" then "auto"
+    else lib.strings.toIntBase10 specialArgs.diskSize;
+
   formatAttr = "vmwareImage";
   fileExtension = ".vmdk";
 }

nixos-generate

@@ -79,6 +79,10 @@ while [[ $# -gt 0 ]]; do
       cores=$2
       shift
       ;;
+    --disk-size)
+      nix_build_args+=("--argstr" "diskSize" "$2")
+      shift
+      ;;
     --option)
       nix_build_args+=("$1" "$2" "$3")
       shift 2

nixos-generate.nix

@@ -2,6 +2,7 @@
   nixpkgs ? <nixpkgs>,
   configuration ? <nixos-config>,
   system ? builtins.currentSystem,
+  diskSize ? "auto",
   formatConfig,
   flakeUri ? null,
   flakeAttr ? null,
@@ -20,6 +21,9 @@ in
   else
     import "${toString nixpkgs}/nixos/lib/eval-config.nix" {
       inherit system;
+      specialArgs = {
+        diskSize = diskSize;
+      };
       modules = [
         module
         formatConfig