cloud-hypervisor-gpu: make it easier to ignore patches from other ovrlays

pkgs/cloud-hypervisor-gpu.nix

@@ -7,6 +7,7 @@
 }:
 
 let
+  inherit (lib) optionals optionalString;
   spectrum = builtins.fetchTree {
     url = "https://spectrum-os.org/git/spectrum";
     type = "git";
@@ -15,37 +16,60 @@ let
 in
 cloud-hypervisor.overrideAttrs (
   finalAttrs: oldAttrs:
-  {
-    # Verbatim from spectrum
-    postUnpack = oldAttrs.postUnpack or "" + ''
-      unpackFile $vhost
-      chmod -R +w vhost
-    '';
-    vhost = fetchFromGitHub {
-      name = "vhost";
-      owner = "rust-vmm";
-      repo = "vhost";
-      rev = "vhost-user-backend-v0.20.0";
-      hash = "sha256-KK1+mwYQr7YkyGT9+51v7TJael9D0lle2JXfRoTqYq8=";
+  let
+    patchesFromDir =
+      root:
+      builtins.concatMap (name: lib.optionals (lib.hasSuffix ".patch" name) [ (root + "/${name}") ]) (
+        builtins.attrNames (builtins.readDir root)
+      );
+    spectrumPatches = {
+      version = "2025-12-20";
+      vhost = fetchFromGitHub {
+        name = "vhost";
+        owner = "rust-vmm";
+        repo = "vhost";
+        rev = "vhost-user-backend-v0.20.0";
+        hash = "sha256-KK1+mwYQr7YkyGT9+51v7TJael9D0lle2JXfRoTqYq8=";
+      };
+      patches = patchesFromDir (spectrum + "/pkgs/cloud-hypervisor");
+      vhostPatches = patchesFromDir (spectrum + "/pkgs/cloud-hypervisor/vhost");
     };
+    previouslyPatched = oldAttrs ? spectrumPatches;
+    patchPhases = !previouslyPatched;
+    overridePatches =
+      lib.versionOlder oldAttrs.spectrumPatches.version or "2000-00-00"
+        spectrumPatches.version;
+    oldPatches = oldAttrs.spectrumPatches.patches or [ ];
+    removeAll = removeElts: lst: builtins.filter (x: !(builtins.elem x removeElts)) lst;
+  in
+  {
+    passthru =
+      oldAttrs.passthru or { }
+      // lib.optionalAttrs overridePatches {
+        inherit spectrumPatches;
+      };
+    # Verbatim from spectrum
+    postUnpack =
+      oldAttrs.postUnpack or ""
+      + optionalString patchPhases ''
+        unpackFile $vhost
+        chmod -R +w vhost
+      '';
+    vhost = if overridePatches then spectrumPatches.vhost else oldAttrs.vhost or null;
 
-    patches = oldAttrs.patches or [ ] ++ [
-      "${spectrum}/pkgs/cloud-hypervisor/0001-build-use-local-vhost.patch"
-      "${spectrum}/pkgs/cloud-hypervisor/0002-virtio-devices-add-a-GPU-device.patch"
-    ];
-    vhostPatches = builtins.concatMap (
-      name:
-      lib.optionals (lib.hasSuffix ".patch" name) [ "${spectrum}/pkgs/cloud-hypervisor/vhost/${name}" ]
-    ) (builtins.attrNames (builtins.readDir "${spectrum}/pkgs/cloud-hypervisor/vhost"));
+    patches =
+      removeAll oldPatches (oldAttrs.patches or [ ]) ++ optionals overridePatches spectrumPatches.patches;
     # Verbatim copy from spectrum
-    postPatch = oldAttrs.postPatch or "" + ''
-      pushd ../vhost
-      for patch in $vhostPatches; do
-          echo applying patch $patch
-          patch -p1 < $patch
-      done
-      popd
-    '';
+    postPatch =
+      oldAttrs.postPatch or ""
+      + optionalString (!previouslyPatched) ''
+        pushd ../vhost
+        for patch in $vhostPatches; do
+            echo applying patch $patch
+            patch -p1 < $patch
+        done
+        popd
+      '';
     cargoDeps = rustPlatform.fetchCargoVendor {
       inherit (finalAttrs) patches;
       inherit (oldAttrs) src;