From 1a9dfe22ba21da12a2e069d1c085c5a4d6194060 Mon Sep 17 00:00:00 2001
From: colin <colin@uninsane.org>
Date: Mon, 1 Aug 2022 14:37:19 -0700
Subject: [PATCH] image builder: integrate impermanence so that we create such
 things as /var/log

untested
---
 modules/image.nix        | 20 +++++++++-----------
 modules/impermanence.nix |  1 +
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/modules/image.nix b/modules/image.nix
index 1125ee59..64190b97 100644
--- a/modules/image.nix
+++ b/modules/image.nix
@@ -12,6 +12,12 @@ in
       default = [];
       type = types.listOf types.package;
     };
+    # extra (empty) directories to create in the rootfs.
+    # for example, /var/log might be required by the boot process, so ensure it exists.
+    sane.image.extraDirectories = mkOption {
+      default = [];
+      type = types.listOf types.str;
+    };
 
     # the GPT header is fixed to Logical Block Address 1,
     # but we can actually put the partition entries anywhere.
@@ -46,6 +52,7 @@ in
       (builtins.substring 0 (builtins.stringLength sub) super) == sub
     );
     # return the (string) path to get from `stem` to `path`
+    # XXX: not sure how this behaves if the path doesn't contain the stem.
     relPath = stem: path: (
       builtins.head (builtins.match "^${stem}(.+)" path)
     );
@@ -56,14 +63,6 @@ in
     # resolves to e.g. "nix/store", "/store" or ""
     storeRelPath = relPath nixFs.mountPoint "/nix/store";
 
-    # return a list of all the `device` values -- one for each fileSystems."$x"
-    devices = builtins.attrValues (builtins.mapAttrs (mount: entry: entry.device) fileSystems);
-    # filter the devices to just those which sit under nixFs
-    subNixMounts = builtins.filter (a: startsWith (builtins.toString a) nixFs.mountPoint) devices;
-    # e.g. ["/nix/persist/var"] -> ["/persist/var"] if nixFs sits at /nix
-    subNixRelMounts = builtins.map (m: relPath nixFs.mountPoint m) subNixMounts;
-    makeSubNixMounts = builtins.toString (builtins.map (m: "mkdir -p ./${m};") subNixRelMounts);
-
     uuidFromFs = fs: builtins.head (builtins.match "/dev/disk/by-uuid/(.+)" fs.device);
     vfatUuidFromFs = fs: builtins.replaceStrings ["-"] [""] (uuidFromFs fs);
 
@@ -113,11 +112,10 @@ in
           populateCommands =
           let
             closureInfo = buildPackages.closureInfo { rootPaths = config.system.build.toplevel; };
+            extraRelPaths = builtins.map (p: relPath nixFs.mountPoint m) cfg.extraDirectories;
           in
           ''
-            mkdir -p ./${storeRelPath}
-            # TODO: we should create the dirs required for boot (/var/log?). the rest are populated automatically.
-            # $(makeSubNixMounts)
+            mkdir -p ./${storeRelPath} ${extraRelPaths}
             echo "Copying system closure..."
             while IFS= read -r path; do
               echo "  Copying $path"
diff --git a/modules/impermanence.nix b/modules/impermanence.nix
index 6836b981..95967569 100644
--- a/modules/impermanence.nix
+++ b/modules/impermanence.nix
@@ -36,6 +36,7 @@ in
     map-sys-dirs = map-dirs { user = "root"; group = "root"; mode = "0755"; directory = ""; };
     map-service-dirs = map-dirs { user = "root"; group = "root"; mode = "0755"; directory = ""; };
   in mkIf cfg.enable {
+    sane.image.extraDirectories = [ "/nix/persist/var/log" ];
     environment.persistence."/nix/persist" = {
       directories = (map-home-dirs ([
         # cache is probably too big to fit on the tmpfs