Restore squashfs support with a dubious kludge

[nixos-qemu-vm-isolation] / modules / qemu-vm-isolation.nix

diff --git a/modules/qemu-vm-isolation.nix b/modules/qemu-vm-isolation.nix
index a9bf0dfc8177d28376c004c3aafd964ec5e19de6..a7189e56a02ce64b89e96e2fa80ef4d93a72e821 100644 (file)
--- a/modules/qemu-vm-isolation.nix
+++ b/modules/qemu-vm-isolation.nix
@@ -1,52 +1,121 @@
 { config, lib, modulesPath, pkgs, ... }:
 let
-  inherit (lib) findSingle mkForce mkVMOverride;
+  inherit (lib)
+    escapeShellArg mkForce mkIf mkMerge mkOption mkVMOverride optional;
 
-  lookupDriveDeviceName = driveName: driveList:
-    (findSingle (drive: drive.name == driveName)
-      (throw "Drive ${driveName} not found")
-      (throw "Multiple drives named ${driveName}") driveList).device;
+  cfg = config.virtualisation.qemu.isolation;
 
   storeMountPath = if config.virtualisation.writableStore then
     "/nix/.ro-store"
   else
     "/nix/store";
 
+  hostPkgs = config.virtualisation.host.pkgs;
+
+  storeContents =
+    hostPkgs.closureInfo { rootPaths = config.virtualisation.additionalPaths; };
+
+  nixStoreImages = {
+    ext4 = "${
+        import (modulesPath + "/../lib/make-disk-image.nix") {
+          inherit pkgs config lib;
+          additionalPaths = [ storeContents ];
+          onlyNixStore = true;
+          label = "nix-store";
+          partitionTableType = "none";
+          installBootLoader = false;
+          diskSize = "auto";
+          additionalSpace = "0M";
+          copyChannel = false;
+        }
+      }/nixos.img";
+    erofs = "${
+        hostPkgs.runCommand "nix-store-image" { } ''
+          mkdir $out
+          cd ${builtins.storeDir}
+          ${hostPkgs.erofs-utils}/bin/mkfs.erofs \
+            --force-uid=0 \
+            --force-gid=0 \
+            -L nix-store \
+            -U eb176051-bd15-49b7-9e6b-462e0b467019 \
+            -T 0 \
+            --exclude-regex="$(
+              <${storeContents}/store-paths \
+                sed -e 's^.*/^^g' \
+              | cut -c -10 \
+              | ${hostPkgs.python3}/bin/python -c ${
+                escapeShellArg (builtins.readFile
+                  (modulesPath + "/virtualisation/includes-to-excludes.py"))
+              } )" \
+            $out/nix-store.img \
+            .
+        ''
+      }/nix-store.img";
+    squashfs =
+      "${hostPkgs.callPackage (modulesPath + "/../lib/make-squashfs.nix") {
+        storeContents = config.virtualisation.additionalPaths;
+      }}";
+  };
+
 in {
+  options = {
+    virtualisation.qemu.isolation.nixStoreFilesystemType = mkOption {
+      description = ''
+        What filesystem to use for the guest's Nix store.
 
-  boot.initrd.availableKernelModules = [ "squashfs" ];
+        erofs is more compact than ext4, but less mature.
 
-  fileSystems = mkVMOverride {
-    "${storeMountPath}" = {
-      device =
-        lookupDriveDeviceName "nixstore" config.virtualisation.qemu.drives;
-      fsType = "squashfs";
-      options = [ "ro" ];
-      neededForBoot = true;
+        squashfs support currently requires a dubious kludge that results in these
+        VMs not being able to mount any other squashfs volumes besides the nix store.
+      '';
+      type = lib.types.enum [ "ext4" "erofs" "squashfs" ];
+      default = "ext4";
     };
   };
+  config = mkMerge [
+    {
+      boot.initrd.kernelModules =
+        optional (cfg.nixStoreFilesystemType == "erofs") "erofs";
 
-  system.build.squashfsStore =
-    pkgs.callPackage (modulesPath + "/../lib/make-squashfs.nix") {
-      storeContents = config.virtualisation.additionalPaths;
-    };
+      nixpkgs.overlays = optional (cfg.nixStoreFilesystemType == "squashfs")
+        (final: prev: {
+          util-linux = prev.util-linux.overrideAttrs (old: {
+            patches = (old.patches or [ ])
+              ++ [ ./libblkid-squashfs-nix-store-kludge.patch ];
+          });
+        });
 
-  virtualisation = {
+      fileSystems = mkVMOverride {
+        "${storeMountPath}" = {
+          fsType = cfg.nixStoreFilesystemType;
+          options = [ "ro" ];
+          neededForBoot = true;
+          label = "nix-store";
+        };
+      };
 
-    # This should be the default.
-    bootDevice = lookupDriveDeviceName "root" config.virtualisation.qemu.drives;
+      system.build.nixStoreImage =
+        nixStoreImages."${cfg.nixStoreFilesystemType}";
 
-    sharedDirectories = mkForce { };
+      virtualisation = {
 
-    qemu.drives = [{
-      name = "nixstore";
-      file = "${config.system.build.squashfsStore}";
-      driveExtraOpts = {
-        format = "raw";
-        read-only = "on";
-        werror = "report";
-      };
-    }];
+        sharedDirectories = mkForce { };
 
-  };
+        qemu.drives = [{
+          file = config.system.build.nixStoreImage;
+          driveExtraOpts = {
+            format = "raw";
+            read-only = "on";
+            werror = "report";
+          };
+        }];
+
+      };
+    }
+    (mkIf (cfg.nixStoreFilesystemType == "ext4") {
+      # We use this to disable fsck runs on the ext4 nix store image because stage-1
+      # fsck crashes (maybe because the device is read-only?), halting boot.
+      boot.initrd.checkJournalingFS = false;
+    })
+  ];
 }