add outputs.manifest for diagnosing image size problems

we use a custom installPhase so we don't drag in a bunch of
scripts that we don't need and don't work

README.md

@@ -114,6 +114,16 @@ Assuming you have nixpkgs checked out in a peer directory of this one,
 
     NIX_PATH=nixpkgs=../nixpkgs:$NIX_PATH ./run-tests.sh
 
+## Diagnosing unexpectedly large images
+
+Sometimes you can add a package and it causes the image size to balloon
+because it has dependencies on other things you didn't know about. Build the
+`outputs.manifest` attribute, which is a json representation of the
+filesystem, and you can run `nix-store --query` on it:
+
+    NIX_PATH=nixpkgs=../nixpkgs:$NIX_PATH NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1 nix-build -I liminix-config=path/to/your/configuration.nix --arg device "import ./devices/qemu.nix" -A outputs.manifest -o manifest
+    nix-store -q --tree manifest
+
 
 ## Articles of interest
 

THOUGHTS.txt

@@ -186,7 +186,7 @@ creates the interface instead of using an existing unconfigured one
 
 5) write a test for udhcp
 
-6) squashfs size is ~ 14MB for a configuration with not much in it,
+DONE 6) squashfs size is ~ 14MB for a configuration with not much in it,
 look for obvious wastes of space
 
 7) some of the pppoe config should be moved into a ppp service
@@ -207,7 +207,13 @@ is that specified or fluke?
 
 19) syslogd - use busybox or s6?
 
-20) The option currently called defaultPackages needs a better name as
+DONE 20) The option currently called defaultPackages needs a better name as
 it doesn't have the same semantics as nixos
 environment.defaultPackages.  maybe call it packagesInProfile or
 packagesOnPath. or defaultProfile.packages
+
+
+Tue Sep 27 22:00:36 BST 2022
+
+Found the cause of huge image size: rp-pppoe ships with scripts that
+reference build-time packages, so we have x86-64 glibc in there

default.nix

@@ -4,14 +4,14 @@
 let
   overlay = import ./overlay.nix;
   nixpkgs = import <nixpkgs> ( device.system // {overlays = [overlay]; });
-  inherit (nixpkgs.pkgs) callPackage liminix;
+  inherit (nixpkgs.pkgs) callPackage writeText liminix;
   config = (import ./merge-modules.nix) [
     ./modules/base.nix
     ({ lib, ... } : { config = { inherit (device) kernel; }; })
     <liminix-config>
     ./modules/s6
   ] nixpkgs.pkgs;
-  squashfs = liminix.builders.squashfs config;
+  squashfs = liminix.builders.squashfs config.filesystem.contents;
   kernel = callPackage ./kernel {
     inherit (config.kernel) config;
   };
@@ -24,6 +24,9 @@ in {
       ln -s ${squashfs} squashfs
       ln -s ${kernel.vmlinux} vmlinux
    '';
+    # this exists so that you can run "nix-store -q --tree" on it and find
+    # out what's in the image, which is nice if it's unexpectedly huge
+    manifest = writeText "manifest.json" (builtins.toJSON config.filesystem.contents);
   };
   # this is just here as a convenience, so that we can get a
   # cross-compiling nix-shell for any package we're customizing

overlay.nix

@@ -12,15 +12,7 @@ final: prev: {
   s6-init-bin =  final.callPackage ./pkgs/s6-init-bin {};
   s6-rc-database = final.callPackage ./pkgs/s6-rc-database {};
 
-  pppoe = prev.rpPPPoE.overrideAttrs (o: {
-    # use newer rp-pppoe, it builds cleanly
-    src = final.fetchFromGitHub {
-      owner = "dfskoll";
-      repo = "rp-pppoe";
-      rev = "7cfd8c0405d14cf1c8d799d41d8207fd707979c1";
-      hash = "sha256-MFdCwNj8c52blxEuXH5ltT2yYDmKMH5MLUgtddZV25E=";
-    };
-  });
+  pppoe = final.callPackage ./pkgs/pppoe {};
   ppp =
     (prev.ppp.override {
       libpcap = null;

pkgs/liminix-tools/builders/squashfs.nix

@@ -6,10 +6,9 @@
 , pseudofile
 , runCommand
 , writeText
-} : config :
+} : filesystem :
 let
-  pseudofiles =
-    pseudofile.write "files.pf" (config.filesystem.contents);
+  pseudofiles = pseudofile.write "files.pf" filesystem;
 
   storefs = callPackage <nixpkgs/nixos/lib/make-squashfs.nix> {
     # 1) Every required package is referenced from somewhere

pkgs/pppoe/default.nix

@@ -0,0 +1,46 @@
+{ lib
+, stdenv
+, fetchFromGitHub
+, ppp } :
+let
+in
+stdenv.mkDerivation rec {
+  pname = "rp-pppoe";
+  version = "3.15";
+
+  src = fetchFromGitHub {
+    owner = "dfskoll";
+    repo = "rp-pppoe";
+    rev = "7cfd8c0405d14cf1c8d799d41d8207fd707979c1";
+    hash = "sha256-MFdCwNj8c52blxEuXH5ltT2yYDmKMH5MLUgtddZV25E=";
+  };
+
+  buildInputs = [ ppp ];
+
+  preConfigure = ''
+    cd src
+    export PPPD=${ppp}/sbin/pppd
+  '';
+
+  configureFlags = lib.optionals (stdenv.buildPlatform != stdenv.hostPlatform) [ "rpppoe_cv_pack_bitfields=rev" ];
+
+  postConfigure = ''
+    sed -i Makefile -e 's@DESTDIR)/etc/ppp@out)/etc/ppp@'
+    sed -i Makefile -e 's@PPPOESERVER_PPPD_OPTIONS=@&$(out)@'
+  '';
+
+  installPhase = ''
+    mkdir -p $out/bin $out/lib
+    cp pppoe pppoe-server $out/bin # ppoe-relay pppoe-sniff?
+    test -e rp-pppoe.so && cp rp-pppoe.so $out/lib
+    true
+  '';
+  makeFlags = [ "AR:=$(AR)" ];
+
+  meta = with lib; {
+    description = "Roaring Penguin Point-to-Point over Ethernet tool";
+    platforms = platforms.linux;
+    homepage = "https://www.roaringpenguin.com/products/pppoe";
+    license = licenses.gpl2Plus;
+  };
+}