libstore/build: just copy the magic /etc files into the sandbox

Saves us a bunch of thinking about how to handle symlinks, and prevents
the DNS config from changing on the fly under the build, which may or may
not be a good thing?

Change-Id: I071e6ae7e220884690b788d94f480866f428db71

2 files changed, 30 insertions, 0 deletions

diff --git a/tests/nixos/default.nix b/tests/nixos/default.nix
index 547290188..14fc0da81 100644
--- a/tests/nixos/default.nix
+++ b/tests/nixos/default.nix
@@ -158,4 +158,6 @@ in
   ca-fd-leak = runNixOSTestFor "x86_64-linux" ./ca-fd-leak;
 
   fetch-git = runNixOSTestFor "x86_64-linux" ./fetch-git;
+
+  symlinkResolvconf = runNixOSTestFor "x86_64-linux" ./symlink-resolvconf.nix;
 }
diff --git a/tests/nixos/symlink-resolvconf.nix b/tests/nixos/symlink-resolvconf.nix
new file mode 100644
index 000000000..47df27524
--- /dev/null
+++ b/tests/nixos/symlink-resolvconf.nix
@@ -0,0 +1,28 @@
+{ pkgs, ... }:
+let
+  checkResolvconfInSandbox = pkgs.runCommand "resolvconf-works-in-sandbox" {
+    # must be an FOD to have a resolv.conf in the first place
+    outputHash = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=";
+    outputHashAlgo = "sha256";
+    outputHashType = "flat";
+  } ''
+    cat /etc/resolv.conf
+    touch $out
+  '';
+in {
+  name = "symlink-resolvconf";
+
+  nodes.machine = {
+    # Enabling resolved makes /etc/resolv.conf a symlink to /etc/static/resolv.conf, which is itself a symlink to /run.
+    # If this works, most other things probably will too.
+    services.resolved.enable = true;
+
+    virtualisation.additionalPaths = [checkResolvconfInSandbox.drvPath];
+  };
+
+  testScript = { nodes }: ''
+    start_all()
+
+    machine.succeed('nix-build --check ${checkResolvconfInSandbox.drvPath}')
+  '';
+}