From 1cc0b13b57511b4d094c9dd59070c78b01331385 Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Sat, 15 Apr 2023 17:15:44 +0100
Subject: [PATCH] rewrite systemconfig in C and link statically

systemconfig (a.k.a "activate") is run from the initramfs. Converting
it from a shell script to an executable means it doesn't depend on
there being a shell in the initramfs
---
 modules/jffs2.nix             |  5 +--
 pkgs/systemconfig/default.nix | 61 +++++++++++++++++++++--------------
 pkgs/systemconfig/defs.h      | 37 +++++++++++++++++++++
 3 files changed, 77 insertions(+), 26 deletions(-)
 create mode 100644 pkgs/systemconfig/defs.h

diff --git a/modules/jffs2.nix b/modules/jffs2.nix
index 7ceaff68..088489cd 100644
--- a/modules/jffs2.nix
+++ b/modules/jffs2.nix
@@ -17,7 +17,7 @@ in
     boot.initramfs.enable = true;
     outputs = rec {
       systemConfiguration =
-        pkgs.pkgsBuildBuild.systemconfig config.filesystem.contents;
+        pkgs.systemconfig config.filesystem.contents;
       rootfs =
         let
           inherit (pkgs.pkgsBuildBuild) runCommand mtdutils;
@@ -27,7 +27,8 @@ in
           depsBuildBuild = [ mtdutils ];
         } ''
           mkdir -p $TMPDIR/empty/nix/store/
-          cp ${systemConfiguration}/activate  $TMPDIR/empty/activate
+          cp ${systemConfiguration}/bin/activate $TMPDIR/empty/activate
+          ln -s ${pkgs.s6-init-bin}/bin/init $TMPDIR/empty/init
           pkgClosure=${closureInfo {
              rootPaths = [ systemConfiguration ];
            }}
diff --git a/pkgs/systemconfig/default.nix b/pkgs/systemconfig/default.nix
index fff53e34..3f675fa3 100644
--- a/pkgs/systemconfig/default.nix
+++ b/pkgs/systemconfig/default.nix
@@ -1,13 +1,13 @@
 # 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
+# /nix/store.  This package generates a small program 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
+, stdenv
 }:
 let
   inherit (lib.attrsets) mapAttrsToList;
@@ -32,33 +32,46 @@ let
           assert gid == 0;
           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} ${pathname}");
+            qpathname = builtins.toJSON pathname;
+            mode' = if mode != null
+                    then mode
+                    else
+                      (if type == "d" then "0755" else "0644");
             cmds = {
-              "f" = "printf \"${escaped file}\" > ${pathname}";
-              "d" = "mkdir ${pathname}\n"  +
+              "f" = "PRINTFILE(${qpathname}, ${mode'}, ${builtins.toJSON (escaped file)});";
+              "d" = "MKDIR(${qpathname}, ${mode'});\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 ${pathname} p";
+              "c" = "MKNOD_C(${qpathname}, ${mode'}, ${major}, ${minor});";
+              "b" = "MKNOD_B(${qpathname}, ${mode'}, ${major}, ${minor});";
+              "s" = "LN_S(${builtins.toJSON target}, ${qpathname});";
+              "l" = "LN(${builtins.toJSON target}, ${qpathname})";
+              "i" = "MKNOD_P(${qpathname}, ${mode'});";
             };
             cmd = cmds.${type};
-          in "${cmd}${chmod}";
+          in "${cmd}";
     in mapAttrsToList (makeFile prefix) attrset;
-  activateScript = attrset: writeText "systemConfig" ''
-    #!/bin/sh
-    t=$1
-    ${(builtins.concatStringsSep "\n" (visit "$t" attrset))}
+  activateScript = attrset: writeText "makedevs.c" ''
+    #include "defs.h"
+    int main(int argc, char* argv[]) {
+      chdir(argv[1]);
+      ${(builtins.concatStringsSep "\n" (visit "." attrset))}
+    }
   '';
 in attrset:
-  runCommand "make-stuff" {} ''
-    mkdir -p $out
-    ln -s ${activateScript attrset} $out/activate
-  ''
+  stdenv.mkDerivation {
+    name="make-stuff";
+    src = ./.;
+
+    CFLAGS = "-Os";
+    LDFLAGS  = "-static";
+
+    postConfigure = ''
+      cp ${activateScript attrset} makedevs.c
+    '';
+    makeFlags = ["makedevs"];
+    installPhase = ''
+      mkdir -p $out/bin
+      $STRIP --remove-section=.note --remove-section=.comment --strip-all makedevs -o $out/bin/activate
+    '';
+  }
diff --git a/pkgs/systemconfig/defs.h b/pkgs/systemconfig/defs.h
new file mode 100644
index 00000000..5b7094fc
--- /dev/null
+++ b/pkgs/systemconfig/defs.h
@@ -0,0 +1,37 @@
+#include <sys/stat.h>
+#include <unistd.h>
+#include <sys/sysmacros.h>
+#include <fcntl.h>
+#include <string.h>
+#include <stdlib.h>
+
+void print_file(char * path, mode_t mode, char * text) {
+  int fd = open(path, O_CREAT | O_WRONLY, mode);
+  char *p, *nxt;
+  char b[1];
+  if(fd >=0) {
+    p = text;
+    while(nxt = strchr(p, '\\')) {
+      char upper = nxt[2];
+      char lower = nxt[3];
+      upper = (upper>'9') ? ((upper | 32) - 'a' + 10) : (upper - '0');
+      lower = (lower>'9') ? ((lower | 32) - 'a' + 10) : (lower - '0');
+      b[0] = (upper << 4) + lower;
+      write(fd, p, nxt-p);
+      write(fd, b, 1);
+      p=nxt+4;
+    }
+    write(fd, p, strlen(p));
+    close(fd);
+  }
+}
+
+
+
+#define PRINTFILE(path, mode, text) print_file(path, (mode_t) mode, text)
+#define MKDIR(path, mode) mkdir(path, mode)
+#define MKNOD_C(path, mode, major,minor) mknod(path, mode | S_IFCHR, makedev(major, minor))
+#define MKNOD_B(path, mode, major,minor) mknod(path, mode | S_IFBLK, makedev(major, minor))
+#define LN_S(target, path) (void)symlink(target, path)
+#define LN(target, path) link(target, path)
+#define MKNOD_P(path, mode) mkfifo(path, mode)