nix-required-mounts: guest and host paths may differ

nixos/modules/programs/nix-required-mounts.nix

@@ -5,16 +5,23 @@ let
   package = pkgs.nix-required-mounts;
   overridenPackage = package.override { inherit (cfg) allowedPatterns; };
 
+  Mount = with lib; types.submodule {
+    options.host = mkOption { type = types.str; description = "Host path to mount"; };
+    options.guest = mkOption {
+      type = types.str;
+      description = "Location in the sandbox to mount the host path at";
+    };
+  };
   Pattern = with lib.types;
-    submodule ({ config, name, ... }: {
+    types.submodule ({ config, name, ... }: {
       options.onFeatures = lib.mkOption {
-        type = listOf str;
+        type = listOf types.str;
         description =
           "Which requiredSystemFeatures should trigger relaxation of the sandbox";
         default = [ name ];
       };
       options.paths = lib.mkOption {
-        type = listOf path;
+        type = listOf (oneOf [ path Mount ]);
         description =
           "A list of glob patterns, indicating which paths to expose to the sandbox";
       };

nixos/tests/nix-required-mounts/default.nix

@@ -19,10 +19,19 @@ in
     programs.nix-required-mounts.enable = true;
     programs.nix-required-mounts.allowedPatterns.supported-feature = {
       onFeatures = [ "supported-feature" ];
-      paths = [ "/supported-feature-files" ];
+      paths = [
+        "/supported-feature-files"
+        {
+          host = "/usr/lib/imaginary-fhs-drivers";
+          guest = "/run/opengl-driver/lib";
+        }
+      ];
     };
     users.users.person.isNormalUser = true;
-    virtualisation.fileSystems."/supported-feature-files".fsType = "tmpfs";
+    systemd.tmpfiles.rules = [
+      "d /supported-feature-files 0755 person users -"
+      "f /usr/lib/imaginary-fhs-drivers/libcuda.so 0444 root root -"
+    ];
   };
   testScript = ''
     import shlex

nixos/tests/nix-required-mounts/test-require-feature.nix

@@ -4,9 +4,13 @@ pkgs.runCommandNoCC "${feature}-present"
 {
   requiredSystemFeatures = [ feature ];
 } ''
-  if [[ -e /${feature}-files ]]; then
+  if [[ ! -e /${feature}-files ]]; then
-    touch $out
-  else
     echo "The host declares ${feature} support, but doesn't expose /${feature}-files" >&2
+    exit 1
   fi
+  if [[ ! -f /run/opengl-driver/lib/libcuda.so ]] ; then
+    echo "The host declares ${feature} support, but it the hook fails to handle the hostPath != guestPath cases" >&2
+    exit 1
+  fi
+  touch $out
 ''

pkgs/by-name/ni/nix-required-mounts/nix_required_mounts.py

@@ -8,12 +8,20 @@ from argparse import ArgumentParser
 from itertools import chain
 from pathlib import Path
 from sys import stderr
-from typing import Dict, List, TypedDict
+from typing import Dict, List, Tuple, TypeAlias, TypedDict
+
+Glob: TypeAlias = str
+PathString: TypeAlias = str
+
+
+class Mount(TypedDict):
+    host: PathString
+    guest: PathString
 
 
 class Pattern(TypedDict):
     onFeatures: List[str]
-    paths: List[str]  # List of glob patterns
+    paths: List[Glob | Mount]
 
 
 class HookConfig(TypedDict):
@@ -106,12 +114,21 @@ def entrypoint():
     features = get_strings(drv_env, "requiredSystemFeatures")
     features = list(filter(known_features.__contains__, features))
 
-    patterns = list(
+    patterns: List[PathString | Mount] = list(
         chain.from_iterable(allowed_patterns[f]["paths"] for f in features)
     )  # noqa: E501
 
-    roots = sorted(
+    # TODO: Would it make sense to preserve the original order instead?
-        set(Path(path) for pattern in patterns for path in glob.glob(pattern))
+    roots: List[Tuple[PathString, PathString]] = sorted(
+        set(
+            mnt
+            for pattern in patterns
+            for mnt in (
+                ((path, path) for path in glob.glob(pattern))
+                if isinstance(pattern, PathString)
+                else [(pattern["guest"], pattern["host"])]
+            )
+        )
     )
 
     # the pre-build-hook command
@@ -121,8 +138,7 @@ def entrypoint():
         print("extra-sandbox-paths")
 
     # arguments, one per line
-    for p in roots:
+    for guest_path, host_path in roots:
-        guest_path, host_path = p, p
         print(f"{guest_path}={host_path}")
 
     # terminated by an empty line

pkgs/by-name/ni/nix-required-mounts/package.nix

@@ -3,7 +3,7 @@
 , allowedPatterns ? rec {
     # This config is just an example.
     # When the hook observes either of the following requiredSystemFeatures:
-    nvidia-gpu.onFeatures = [ "gpu" "opengl" "vulkan" "cuda" ];
+    nvidia-gpu.onFeatures = [ "gpu" "nvidia-gpu" "opengl" "cuda" ];
     # It exposes these paths in the sandbox:
     nvidia-gpu.paths = [
       # Note that mounting /run/opengl-driver/lib actually isn't sufficient,