support jffs2, with initramfs

the jffs2 filesystem contains only /nix/store and a script which is
run in early init (initramfs) and is responsible for recreating
"traditional" directories (/bin /etc/**/* /var &c) based on the
configuration.

this is tested only in qemu so far and could use some cleanup

pkgs/default.nix

@@ -12,6 +12,7 @@
     };
   };
   writeAshScript = callPackage ./write-ash-script {};
+  systemconfig = callPackage ./systemconfig {};
   s6-init-bin =  callPackage ./s6-init-bin {};
   s6-rc-database = callPackage ./s6-rc-database {};
   mips-vm = callPackage ./mips-vm {};

pkgs/mips-vm/mips-vm.sh

@@ -1,7 +1,13 @@
 #!/usr/bin/env bash
 
+cleanup(){
+    test -n "$rootfs" && test -f $rootfs && rm $rootfs
+}
+trap 'exit 1' INT HUP QUIT TERM ALRM USR1
+trap 'cleanup' EXIT
+
 usage(){
-    echo "usage: $(basename $0) [--background /path/to/state_directory] kernel rootimg"
+    echo "usage: $(basename $0) [--background /path/to/state_directory] kernel rootimg [initramfs]"
     echo -e "\nWithout --background, use C-p c (not C-a c) to switch to the monitor"
     exit 1
 }
@@ -23,14 +29,22 @@ fi
 
 test -n "$2" || usage
 
+rootfs=$(mktemp mips-vm-fs-XXXXXX)
+dd if=$2 of=$rootfs bs=65536 conv=sync
+
+if test -n "$3"; then
+    initramfs="-initrd $3"
+fi
+
 
 INIT=${INIT-/bin/init}
 echo $QEMU_OPTIONS
 qemu-system-mips \
     -M malta -m 256 \
     -echr 16 \
-    -append "liminix default console=ttyS0,38400n8 panic=10 oops=panic init=$INIT loglevel=8 root=/dev/mtdblock0 block2mtd.block2mtd=/dev/vda,4096" \
-    -drive file=$2,format=raw,readonly=on,if=virtio \
+    -append "liminix default console=ttyS0,38400n8 panic=10 oops=panic init=$INIT loglevel=8 root=/dev/mtdblock0 block2mtd.block2mtd=/dev/vda,65536" \
+    -drive file=$rootfs,format=raw,readonly=on,if=virtio \
+    ${initramfs} \
     -netdev socket,id=access,mcast=230.0.0.1:1234,localaddr=127.0.0.1 \
     -device virtio-net-pci,disable-legacy=on,disable-modern=off,netdev=access,mac=ba:ad:1d:ea:21:02 \
     -netdev socket,id=lan,mcast=230.0.0.1:1235,localaddr=127.0.0.1 \

pkgs/systemconfig/default.nix

@@ -0,0 +1,60 @@
+# The ideal is that a Liminix system can boot with only the files in
+# /nix/store.  This package generates a script that is run at early
+# boot (from the initramfs) to populate directories such as /etc,
+# /bin, /home according to whatever the configuration says
+# they should contain
+
+{
+  writeText
+, runCommand
+, lib
+}:
+let
+  inherit (lib.attrsets) mapAttrsToList;
+  escaped = msg : builtins.replaceStrings
+    ["\n"  "="   "\""  "$"  ]
+    ["\\x0a" "\\x3d" "\\x22" "\\x24"]
+    msg;
+
+  visit = prefix: attrset:
+    let makeFile = prefix : filename: {
+          type ? "f"
+          , mode ? null
+          , target ? null
+          , contents ? null
+          , file ? null
+          , major ? null
+          , minor ? null
+        }:
+          let
+            pathname = "${prefix}/${filename}";
+            chmod =
+              let m = if mode != null then mode else
+                    (if type == "d" then "0755" else "0644");
+              in (if type == "s"
+                  then ""
+                  else "\nchmod ${m} ${pathname}");
+            cmds = {
+              "f" = "printf \"${escaped file}\" > ${pathname}";
+              "d" = "mkdir ${pathname}\n"  +
+                    (builtins.concatStringsSep "\n"
+                      (visit pathname contents));
+              "c" = "mknod ${pathname} c ${major} ${minor}";
+              "b" = "mknod ${pathname} b ${major} ${minor}";
+              "s" = "ln -s ${target} ${pathname}";
+              "l" = "ln ${target} ${pathname}";
+              "i" = "mknod ${pathname} p";
+            };
+            cmd = cmds.${type};
+          in "${cmd}${chmod}";
+    in mapAttrsToList (makeFile prefix) attrset;
+  activateScript = attrset: writeText "systemConfig" ''
+    #!/bin/sh
+    t=$1
+    ${(builtins.concatStringsSep "\n" (visit "$t" attrset))}
+  '';
+in attrset:
+  runCommand "make-stuff" {} ''
+    mkdir -p $out
+    ln -s ${activateScript attrset} $out/activate
+  ''