Mount unionfs-fuse filesystems using the normal fileSystems option

nixos/modules/installer/cd-dvd/iso-image.nix

@@ -191,6 +191,8 @@ in
         noCheck = true;
       };
 
+    # In stage 1, mount a tmpfs on top of /nix/store (the squashfs
+    # image) to make this a live CD.
     fileSystems."/nix/.ro-store" =
       { fsType = "squashfs";
         device = "/iso/nix-store.squashfs";
@@ -204,18 +206,16 @@ in
         neededForBoot = true;
       };
 
+    fileSystems."/nix/store" =
+      { fsType = "unionfs-fuse";
+        device = "unionfs";
+        options = "allow_other,cow,nonempty,chroot=/mnt-root,max_files=32768,hide_meta_files,dirs=/nix/.rw-store=rw:/nix/.ro-store=ro";
+      };
+
     boot.initrd.availableKernelModules = [ "squashfs" "iso9660" ];
 
     boot.initrd.kernelModules = [ "loop" ];
 
-    # In stage 1, mount a tmpfs on top of /nix/store (the squashfs
-    # image) to make this a live CD.
-    boot.initrd.postMountCommands =
-      ''
-        mkdir -p $targetRoot/nix/store
-        unionfs -o allow_other,cow,nonempty,chroot=$targetRoot,max_files=32768 /nix/.rw-store=RW:/nix/.ro-store=RO $targetRoot/nix/store
-      '';
-
     # Closures to be copied to the Nix store on the CD, namely the init
     # script and the top-level system configuration directory.
     isoImage.storeContents =
@@ -311,8 +311,8 @@ in
       '';
 
     # Add vfat support to the initrd to enable people to copy the
-    # contents of the CD to a bootable USB stick. Need unionfs-fuse for union mounts
+    # contents of the CD to a bootable USB stick.
-    boot.initrd.supportedFilesystems = [ "vfat" "unionfs-fuse" ];
+    boot.initrd.supportedFilesystems = [ "vfat" ];
 
   };
 

nixos/modules/system/boot/stage-1-init.sh

@@ -4,7 +4,8 @@ targetRoot=/mnt-root
 console=tty1
 
 export LD_LIBRARY_PATH=@extraUtils@/lib
-export PATH=@extraUtils@/bin:@extraUtils@/sbin
+export PATH=@extraUtils@/bin
+ln -s @extraUtils@/bin /bin
 
 
 fail() {
@@ -262,6 +263,13 @@ mountFS() {
 
     checkFS "$device" "$fsType"
 
+    # Create backing directories for unionfs-fuse.
+    if [ "$fsType" = unionfs-fuse ]; then
+        for i in $(IFS=:; echo ${options##*,dirs=}); do
+            mkdir -m 0700 -p /mnt-root"${i%=*}"
+        done
+    fi
+
     echo "mounting $device on $mountPoint..."
 
     mkdir -p "/mnt-root$mountPoint" || true

nixos/modules/system/boot/stage-1.nix

@@ -35,6 +35,7 @@ let
     }
     ''
       mkdir -p $out/bin $out/lib
+      ln -s $out/bin $out/sbin
 
       # Copy what we need from Glibc.
       cp -pv ${pkgs.glibc}/lib/ld*.so.? $out/lib
@@ -46,11 +47,10 @@ let
       cp -pv ${pkgs.gcc.gcc}/lib*/libgcc_s.so.* $out/lib
 
       # Copy BusyBox.
-      cp -rvd ${pkgs.busybox}/{bin,sbin} $out/
+      cp -pvd ${pkgs.busybox}/bin/* ${pkgs.busybox}/sbin/* $out/bin/
-      chmod -R u+w $out
 
       # Copy some utillinux stuff.
-      cp -v ${pkgs.utillinux}/sbin/blkid $out/bin
+      cp -vf ${pkgs.utillinux}/sbin/blkid $out/bin
       cp -pdv ${pkgs.utillinux}/lib/libblkid*.so.* $out/lib
       cp -pdv ${pkgs.utillinux}/lib/libuuid*.so.* $out/lib
 
@@ -73,7 +73,7 @@ let
 
       # Copy modprobe.
       cp -v ${pkgs.kmod}/bin/kmod $out/bin/
-      ln -s kmod $out/bin/modprobe
+      ln -sf kmod $out/bin/modprobe
 
       ${config.boot.initrd.extraUtilsCommands}
 

nixos/modules/tasks/filesystems.nix

@@ -68,7 +68,7 @@ let
 
     config = {
       mountPoint = mkDefault name;
-      device = mkIf (config.fsType == "tmpfs") config.fsType;
+      device = mkIf (config.fsType == "tmpfs") (mkDefault config.fsType);
     };
 
   };

nixos/modules/tasks/filesystems/unionfs-fuse.nix

@@ -2,14 +2,21 @@
 
 {
   config = lib.mkMerge [
+
     (lib.mkIf (lib.any (fs: fs == "unionfs-fuse") config.boot.initrd.supportedFilesystems) {
       boot.initrd.kernelModules = [ "fuse" ];
-  
+
       boot.initrd.extraUtilsCommands = ''
         cp -v ${pkgs.fuse}/lib/libfuse* $out/lib
+        cp -v ${pkgs.fuse}/sbin/mount.fuse $out/bin
         cp -v ${pkgs.unionfs-fuse}/bin/unionfs $out/bin
+        substitute ${pkgs.unionfs-fuse}/sbin/mount.unionfs-fuse $out/bin/mount.unionfs-fuse \
+          --replace '${pkgs.bash}/bin/bash' /bin/sh \
+          --replace '${pkgs.fuse}/sbin' /bin \
+          --replace '${pkgs.unionfs-fuse}/bin' /bin
+        chmod +x $out/bin/mount.unionfs-fuse
       '';
-  
+
       boot.initrd.postDeviceCommands = ''
           # Hacky!!! fuse hard-codes the path to mount
           mkdir -p /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-${pkgs.utillinux.name}/bin
@@ -17,8 +24,10 @@
           ln -s $(which umount) /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-${pkgs.utillinux.name}/bin
         '';
     })
+
     (lib.mkIf (lib.any (fs: fs == "unionfs-fuse") config.boot.supportedFilesystems) {
       system.fsPackages = [ pkgs.unionfs-fuse ];
     })
+
   ];
 }

nixos/modules/virtualisation/qemu-vm.nix

@@ -275,12 +275,10 @@ in
 
     boot.loader.grub.device = mkVMOverride "/dev/vda";
 
-    boot.initrd.supportedFilesystems = optional cfg.writableStore "unionfs-fuse";
-
     boot.initrd.extraUtilsCommands =
       ''
         # We need mke2fs in the initrd.
-        cp ${pkgs.e2fsprogs}/sbin/mke2fs $out/bin
+        cp -f ${pkgs.e2fsprogs}/sbin/mke2fs $out/bin
       '';
 
     boot.initrd.postDeviceCommands =
@@ -303,20 +301,6 @@ in
         chmod 1777 $targetRoot/tmp
 
         mkdir -p $targetRoot/boot
-        ${optionalString cfg.writableStore ''
-          mkdir -p /unionfs-chroot/ro-store
-          mount --rbind $targetRoot/nix/store /unionfs-chroot/ro-store
-
-          mkdir /unionfs-chroot/rw-store
-          ${if cfg.writableStoreUseTmpfs then ''
-          mount -t tmpfs -o "mode=755" none /unionfs-chroot/rw-store
-          '' else ''
-          mkdir $targetRoot/.nix-rw-store
-          mount --bind $targetRoot/.nix-rw-store /unionfs-chroot/rw-store
-          ''}
-
-          unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768,hide_meta_files /rw-store=RW:/ro-store=RO $targetRoot/nix/store
-        ''}
       '';
 
     # After booting, register the closure of the paths in
@@ -343,12 +327,13 @@ in
     # configuration, where the regular value for the `fileSystems'
     # attribute should be disregarded for the purpose of building a VM
     # test image (since those filesystems don't exist in the VM).
-    fileSystems = mkVMOverride
+    fileSystems = mkVMOverride (
       { "/".device = "/dev/vda";
-        "/nix/store" =
+        ${if cfg.writableStore then "/nix/.ro-store" else "/nix/store"} =
           { device = "store";
             fsType = "9p";
             options = "trans=virtio,version=9p2000.L,msize=1048576,cache=loose";
+            neededForBoot = true;
           };
         "/tmp/xchg" =
           { device = "xchg";
@@ -362,6 +347,18 @@ in
             options = "trans=virtio,version=9p2000.L,msize=1048576";
             neededForBoot = true;
           };
+      } // optionalAttrs cfg.writableStore
+      { "/nix/store" =
+          { fsType = "unionfs-fuse";
+            device = "unionfs";
+            options = "allow_other,cow,nonempty,chroot=/mnt-root,max_files=32768,hide_meta_files,dirs=/nix/.rw-store=rw:/nix/.ro-store=ro";
+          };
+      } // optionalAttrs (cfg.writableStore && cfg.writableStoreUseTmpfs)
+      { "/nix/.rw-store" =
+          { fsType = "tmpfs";
+            options = "mode=0755";
+            neededForBoot = true;
+          };
       } // optionalAttrs cfg.useBootLoader
       { "/boot" =
           { device = "/dev/disk/by-label/boot";
@@ -369,7 +366,7 @@ in
             options = "ro";
             noCheck = true; # fsck fails on a r/o filesystem
           };
-      };
+      });
 
     swapDevices = mkVMOverride [ ];
     boot.initrd.luks.devices = mkVMOverride [];