* Use unionfs to provide a real Live CD, i.e., the files on the CD

appear writable (though all writes go to a tmpfs).  This allows you
  to run Nix operations on the Live CD.  However, we're not quite
  there yet since the CD doesn't have a valid Nix database.  So for
  instance a garbage collect will cause everything to be deleted,
  hanging the system.

svn path=/nixos/trunk/; revision=10276

boot/boot-stage-1-init.sh

@@ -211,6 +211,19 @@ else
     
 fi
 
+
+# If this is a live-CD/DVD, then union-mount a tmpfs on top of the
+# original root.
+targetRoot=/mnt/root
+if test -n "@isLiveCD@"; then
+    mkdir /mnt/tmpfs
+    mount -n -t tmpfs -o "mode=755" none /mnt/tmpfs
+    mkdir /mnt/union
+    mount -t unionfs -o dirs=/mnt/tmpfs=rw:$targetRoot=ro none /mnt/union
+    targetRoot=/mnt/union
+fi
+
+
 if test -n "$debug1mounts"; then fail; fi
 
 
@@ -218,7 +231,7 @@ if test -n "$debug1mounts"; then fail; fi
 # !!! Note: we can't use pivot_root here (the kernel gods have
 # decreed), but we could use run-init from klibc, which deletes all
 # files in the initramfs, remounts the target root on /, and chroots.
-cd /mnt/root
+cd "$targetRoot"
 mount --move . /
 umount /proc # cleanup
 umount /sys

boot/boot-stage-1.nix

@@ -20,8 +20,12 @@
   # must at least be a file system for the / mount point in this list.
   fileSystems ? []
 
-  # If scanning, we need a disk label.
-, rootLabel
+, # If scanning, we need a disk label.
+  rootLabel
+
+, # Whether the root device is read-only and should be made writable
+  # through a unionfs.
+  isLiveCD
 
 , # The path of the stage 2 init to call once we've mounted the root
   # device.
@@ -44,7 +48,7 @@ substituteAll {
   src = ./boot-stage-1-init.sh;
   isExecutable = true;
   inherit staticShell modules modulesDir;
-  inherit autoDetectRootDevice mountPoints devices fsTypes optionss;
+  inherit autoDetectRootDevice isLiveCD mountPoints devices fsTypes optionss;
   rootLabel = if autoDetectRootDevice then rootLabel else "";
   path = [
     staticTools

boot/boot-stage-2-init.sh

@@ -25,19 +25,9 @@ setPath "@path@"
 
 
 # Mount special file systems.
-
-needWritableDir() {
-    if test -n "@readOnlyRoot@"; then
-        mount -t tmpfs -o "mode=$2" none $1 $3
-    else
-        mkdir -m $2 -p $1
-    fi
-}
-
-needWritableDir /etc 0755 -n # to shut up mount
-
-test -e /etc/fstab || touch /etc/fstab # idem
-
+mkdir -m 0755 -p /etc
+test -e /etc/fstab || touch /etc/fstab # to shut up mount
+mkdir -m 0755 -p /proc
 mount -n -t proc none /proc
 cat /proc/mounts > /etc/mtab
 
@@ -71,19 +61,20 @@ done
 
 
 # More special file systems, initialise required directories.
+mkdir -m 0755 -p /sys 
 mount -t sysfs none /sys
+mkdir -m 0755 -p /dev
 mount -t tmpfs -o "mode=0755" none /dev
 mkdir -m 0755 -p /dev/pts
 mount -t devpts none /dev/pts
 mount -t usbfs none /proc/bus/usb
-needWritableDir /tmp 01777
-needWritableDir /var 0755
-needWritableDir /nix/var 0755
-needWritableDir /root 0700
-needWritableDir /bin 0755 # for the /bin/sh symlink
-if test -d /home ; then
-	needWritableDir /home 0777
-fi
+mkdir -m 01777 /tmp 
+mkdir -m 0755 /var
+mkdir -m 0755 /nix/var
+mkdir -m 0700 /root
+mkdir -m 0755 /bin # for the /bin/sh symlink
+mkdir -m 0755 /home
+
 
 # Miscellaneous boot time cleanup.
 rm -rf /var/run

boot/boot-stage-2.nix

@@ -2,9 +2,9 @@
 , utillinux, kernel, udev, upstart
 , activateConfiguration
 
-, # Whether the root device is root only.  If so, we'll mount a
-  # ramdisk on /etc, /var and so on.
-  readOnlyRoot
+, # Whether the root device is read-only and should be made writable
+  # through a unionfs.
+  isLiveCD
 
 , # Path for Upstart jobs.  Should be quite minimal.
   upstartPath
@@ -16,7 +16,7 @@
 substituteAll {
   src = ./boot-stage-2-init.sh;
   isExecutable = true;
-  inherit kernel upstart readOnlyRoot activateConfiguration upstartPath;
+  inherit kernel upstart isLiveCD activateConfiguration upstartPath;
   path = [
     coreutils
     utillinux

configuration/rescue-cd.nix

@@ -11,10 +11,15 @@ rec {
   
     boot = {
       autoDetectRootDevice = true;
-      readOnlyRoot = true;
+      isLiveCD = true;
       # The label used to identify the installation CD.
       rootLabel = "NIXOS";
       extraTTYs = [7 8]; # manual, rogue
+      initrd = {
+        extraKernelModules = [
+          "unionfs" # needed for live-CD operation
+        ];
+      };
     };
     
     services = {
@@ -48,6 +53,7 @@ rec {
         # Show the NixOS manual on tty7.
         { name = "manual";
           job = "
+            env HOME=/root
             start on udev
             stop on shutdown
             respawn ${pkgs.w3m}/bin/w3m ${manual} < /dev/tty7 > /dev/tty7 2>&1
@@ -58,6 +64,7 @@ rec {
         # for the installation to finish.
         { name = "rogue";
           job = "
+            env HOME=/root
             start on udev
             stop on shutdown
             respawn ${pkgs.rogue}/bin/rogue < /dev/tty8 > /dev/tty8 2>&1
@@ -112,6 +119,7 @@ rec {
         pkgs.vim
         pkgs.subversion # for nixos-checkout
         pkgs.w3m # needed for the manual anyway
+        pkgs.gdb # for debugging Nix
       ];
     };
    
@@ -135,15 +143,6 @@ rec {
     else pkgs.writeText "dummy-manual" "Manual not included in this build!";
 
 
-  # Since the CD is read-only, the mount points must be on disk.
-  cdMountPoints = pkgs.runCommand "mount-points" {} "
-    ensureDir $out
-    cd $out
-    mkdir proc sys tmp etc dev var mnt nix nix/var root bin
-    touch $out/${configuration.boot.rootLabel}
-  ";
-
-
   # We need a copy of the Nix expressions for Nixpkgs and NixOS on the
   # CD.  We put them in a tarball because accessing that many small
   # files from a slow device like a CD-ROM takes too long.
@@ -213,15 +212,15 @@ rec {
       { source = system.config.boot.grubSplashImage;
         target = "boot/background.xpm.gz";
       }
-      { source = cdMountPoints;
-        target = "/";
-      }
       { source = nixosTarball + "/" + nixosTarball.tarName;
         target = "/" + nixosTarball.tarName;
       }
       { source = nixpkgsTarball;
         target = "/nixpkgs.tar.bz2";
       }
+      { source = pkgs.writeText "label" "";
+        target = "/${configuration.boot.rootLabel}";
+      }
     ];
 
     # Closures to be copied to the Nix store on the CD.

helpers/make-iso9660-image.sh

@@ -20,7 +20,7 @@ if test -n "$bootable"; then
         fi
     done
 
-    bootFlags="-b $bootImage -c boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table"
+    bootFlags="-b $bootImage -c .boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table"
 fi
 
 touch pathlist
@@ -59,7 +59,7 @@ cat pathlist
 # !!! -f is a quick hack.
 ensureDir $out/iso
 genisoimage -r -J -o $out/iso/$isoName $bootFlags \
-    -graft-points -path-list pathlist
+    -hide-rr-moved -graft-points -path-list pathlist
 
 ensureDir $out/nix-support
 echo $system > $out/nix-support/system

system/activate-configuration.sh

@@ -104,22 +104,24 @@ fi
 
 
 # Set up Nix.
-if test -z "@readOnlyRoot@"; then
-    mkdir -p /nix/etc/nix
-    ln -sfn /etc/nix.conf /nix/etc/nix/nix.conf
-    chown root.nixbld /nix/store
-    chmod 1775 /nix/store
-fi
+mkdir -p /nix/etc/nix
+ln -sfn /etc/nix.conf /nix/etc/nix/nix.conf
+chown root.nixbld /nix/store
+chmod 1775 /nix/store
 
 
 # Nix initialisation.
-mkdir -m 0755 -p /nix/var/nix/db
-mkdir -m 0755 -p /nix/var/nix/gcroots
+mkdir -m 0755 -p \
+    /nix/var/nix/gcroots \
+    /nix/var/nix/temproots \
+    /nix/var/nix/manifests \
+    /nix/var/nix/userpool \
+    /nix/var/nix/profiles \
+    /nix/var/nix/db \
+    /nix/var/log/nix/drvs \
+    /nix/var/nix/channel-cache
 mkdir -m 1777 -p /nix/var/nix/gcroots/per-user
-mkdir -m 0755 -p /nix/var/nix/temproots
-mkdir -m 0755 -p /nix/var/nix/profiles
 mkdir -m 1777 -p /nix/var/nix/profiles/per-user
-mkdir -m 0755 -p /nix/var/nix/channel-cache
 
 ln -sf /nix/var/nix/profiles /nix/var/nix/gcroots/
 ln -sf /nix/var/nix/manifests /nix/var/nix/gcroots/

system/options.nix

@@ -25,11 +25,13 @@
       ";
     };
 
-    readOnlyRoot = mkOption {
+    isLiveCD = mkOption {
       default = false;
       description = "
-        Whether the root device is read-only.  This should be set when
-        booting from CD-ROM.
+        If set to true, the root device will be mounted read-only and
+        a ramdisk will be mounted on top of it using unionfs to
+        provide a writable root.  This is used for the NixOS
+        Live-CD/DVD.
       ";
     };
 

system/system.nix

@@ -78,7 +78,7 @@ rec {
     inherit (pkgs) substituteAll;
     inherit (pkgsDiet) module_init_tools;
     inherit extraUtils;
-    autoDetectRootDevice = config.boot.autoDetectRootDevice;
+    inherit (config.boot) autoDetectRootDevice isLiveCD;
     fileSystems =
       pkgs.lib.filter
         (fs: fs.mountPoint == "/" || (fs ? neededForBoot && fs.neededForBoot))
@@ -298,7 +298,6 @@ rec {
     isExecutable = true;
 
     inherit etc wrapperDir systemPath modprobe defaultShell kernel;
-    readOnlyRoot = config.boot.readOnlyRoot;
     hostName = config.networking.hostName;
     setuidPrograms =
       config.security.setuidPrograms ++
@@ -323,7 +322,7 @@ rec {
     inherit (pkgs) substituteAll writeText coreutils 
       utillinux udev upstart;
     inherit kernel activateConfiguration;
-    readOnlyRoot = config.boot.readOnlyRoot;
+    inherit (config.boot) isLiveCD;
     upstartPath = [
       pkgs.coreutils
       pkgs.findutils
@@ -359,8 +358,7 @@ rec {
     inherit (pkgs) grub coreutils gnused gnugrep diffutils findutils upstart;
     grubDevice = config.boot.grubDevice;
     kernelParams =
-      (config.boot.kernelParams) ++
-      (config.boot.extraKernelParams);
+      config.boot.kernelParams ++ config.boot.extraKernelParams;
     inherit bootStage2;
     inherit activateConfiguration;
     inherit grubMenuBuilder;