From 54a1ab3529c9294d12e1a3f4e0a7c5c8897afd0d Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Tue, 4 Apr 2023 23:35:49 +0100
Subject: [PATCH] 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
---
 modules/initramfs.nix         | 79 +++++++++++++++++++++++++++++++++++
 modules/jffs2.nix             | 49 ++++++++++++++++++++++
 pkgs/default.nix              |  1 +
 pkgs/mips-vm/mips-vm.sh       | 20 +++++++--
 pkgs/systemconfig/default.nix | 60 ++++++++++++++++++++++++++
 5 files changed, 206 insertions(+), 3 deletions(-)
 create mode 100644 modules/initramfs.nix
 create mode 100644 modules/jffs2.nix
 create mode 100644 pkgs/systemconfig/default.nix

diff --git a/modules/initramfs.nix b/modules/initramfs.nix
new file mode 100644
index 0000000..c963bcf
--- /dev/null
+++ b/modules/initramfs.nix
@@ -0,0 +1,79 @@
+{
+  config
+, pkgs
+, lib
+, ...
+}:
+let
+#  inherit (lib) mkOption types concatStringsSep;
+  inherit (pkgs) runCommand callPackage writeText;
+in
+{
+  config = {
+    kernel.config.BLK_DEV_INITRD = "y";
+
+    outputs = {
+      initramfs =
+        let
+          bb = pkgs.busybox.override {
+            enableStatic = true;
+            enableMinimal = true;
+            enableAppletSymlinks  = false;
+            extraConfig  = ''
+              CONFIG_ASH y
+              CONFIG_LS y
+              CONFIG_LN y
+              CONFIG_CAT y
+              CONFIG_MOUNT y
+              CONFIG_PRINTF y
+              CONFIG_FEATURE_MOUNT_FLAGS y
+              CONFIG_FEATURE_MOUNT_VERBOSE y
+              CONFIG_ECHO y
+              CONFIG_CHROOT y
+              CONFIG_CHMOD y
+              CONFIG_MKDIR y
+              CONFIG_MKNOD y
+              CONFIG_SH_IS_ASH y
+              CONFIG_BASH_IS_NONE y
+            '';
+          };
+          slashinit = pkgs.writeScript "init" ''
+            #!/bin/sh
+            exec >/dev/console
+            echo IT MOVES
+            mount -t proc none /proc
+            mount -t jffs2 mtd0 /target/persist
+            mount -o bind /target/persist/nix /target/nix
+            sh /target/persist/activate /target
+            cd /target
+            mount -o bind /target /
+            exec chroot . /bin/init "$@"
+          '';
+          refs = pkgs.writeReferencesToFile bb;
+          gen_init_cpio = pkgs.pkgsBuildBuild.gen_init_cpio;
+        in runCommand "initramfs" {} ''
+          cat << SPECIALS | ${gen_init_cpio}/bin/gen_init_cpio /dev/stdin > $out
+          dir /proc 0755 0 0
+          dir /dev 0755 0 0
+          nod /dev/mtdblock0 0600 0 0 b 31 0
+          dir /target 0755 0 0
+          dir /target/persist 0755 0 0
+          dir /target/nix 0755 0 0
+          nod /dev/console 0600 0 0 c 5 1
+          dir /bin 0755 0 0
+          file /bin/busybox ${bb}/bin/busybox 0755 0 0
+          slink /bin/sh /bin/busybox 0755 0 0
+          slink /bin/echo /bin/busybox 0755 0 0
+          slink /bin/mount /bin/busybox 0755 0 0
+          slink /bin/chroot /bin/busybox 0755 0 0
+          slink /bin/chmod /bin/busybox 0755 0 0
+          slink /bin/ln /bin/busybox 0755 0 0
+          slink /bin/mkdir /bin/busybox 0755 0 0
+          slink /bin/mknod /bin/busybox 0755 0 0
+          slink /bin/printf /bin/busybox 0755 0 0
+          file /init ${slashinit} 0755 0 0
+          SPECIALS
+        '';
+    };
+  };
+}
diff --git a/modules/jffs2.nix b/modules/jffs2.nix
new file mode 100644
index 0000000..2479803
--- /dev/null
+++ b/modules/jffs2.nix
@@ -0,0 +1,49 @@
+{
+  config
+, pkgs
+, lib
+, ...
+}:
+let
+  inherit (lib) mkOption types concatStringsSep;
+  inherit (pkgs) liminix callPackage writeText closureInfo;
+in
+{
+  imports = [
+    ./initramfs.nix
+  ];
+  config = {
+    kernel.config.JFFS2_FS = "y";
+    outputs = rec {
+      systemConfiguration =
+        let inherit (pkgs.pkgsBuildBuild) systemconfig;
+        in systemconfig config.filesystem.contents;
+      jffs2fs =
+        let
+          inherit (pkgs.pkgsBuildBuild) runCommand systemconfig mtdutils;
+          sysconf = systemConfiguration;
+        in runCommand "make-jffs2" {
+          depsBuildBuild = [ mtdutils ];
+        } ''
+          mkdir -p $TMPDIR/empty/nix/store/
+          cp ${sysconf}/activate  $TMPDIR/empty/activate
+          pkgClosure=${closureInfo { rootPaths = [ sysconf ]; }}
+          cp $pkgClosure/registration nix-path-registration
+          grafts=$(sed < $pkgClosure/store-paths 's/^\(.*\)$/--graft \1:\1/g')
+          mkfs.jffs2 --pad  --big-endian --root $TMPDIR/empty --output $out  $grafts  --verbose
+        '';
+      jffs2boot =
+        let o = config.outputs; in
+        pkgs.runCommand "jffs2boot" {} ''
+          mkdir $out
+          cd $out
+          ln -s ${o.jffs2fs} rootfs
+          ln -s ${o.kernel} vmlinux
+          ln -s ${o.manifest} manifest
+          ln -s ${o.initramfs} initramfs
+       '';
+
+
+    };
+  };
+}
diff --git a/pkgs/default.nix b/pkgs/default.nix
index 2e62701..a284f53 100644
--- a/pkgs/default.nix
+++ b/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 {};
diff --git a/pkgs/mips-vm/mips-vm.sh b/pkgs/mips-vm/mips-vm.sh
index 2de14fa..fa090fa 100755
--- a/pkgs/mips-vm/mips-vm.sh
+++ b/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 \
+    ${initramfs} \
     -netdev socket,id=access,mcast=230.0.0.1:1234,localaddr=127.0.0.1 \
     -device virtio-net-pci,disable-legacy=on,disable-modern=off,netdev=access,mac=ba:ad:1d:ea:21:02 \
     -netdev socket,id=lan,mcast=230.0.0.1:1235,localaddr=127.0.0.1 \
diff --git a/pkgs/systemconfig/default.nix b/pkgs/systemconfig/default.nix
new file mode 100644
index 0000000..9ab33e7
--- /dev/null
+++ b/pkgs/systemconfig/default.nix
@@ -0,0 +1,60 @@
+# The ideal is that a Liminix system can boot with only the files in
+# /nix/store.  This package generates a script that is run at early
+# boot (from the initramfs) to populate directories such as /etc,
+# /bin, /home according to whatever the configuration says
+# they should contain
+
+{
+  writeText
+, runCommand
+, lib
+}:
+let
+  inherit (lib.attrsets) mapAttrsToList;
+  escaped = msg : builtins.replaceStrings
+    ["\n"  "="   "\""  "$"  ]
+    ["\\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
+  ''