lib: add fetchb4

README.md

@@ -182,6 +182,25 @@ pkgs.fetchFromSteam {
 }
 ```
 
+### [`fetchb4`](./lib/fetchb4)
+
+A fetcher that uses `b4` to download patchsets from <https://lore.kernel.org> so that they can be applied in `boot.kernelPatches`
+
+Usage:
+
+```nix
+pkgs.fetchb4 {
+  msgid = "2024042069.1337-example@example";
+  hash = pkgs.lib.fakeHash;
+
+  # optional args
+  version = "3"; # default: latest
+  single_message = true; # default: false
+}
+```
+
+note that not specifying a version may make cause future invocations to return different output if a newer version is sent to the thread
+
 ### [`mkNginxServer`](./lib/dev-nginx)
 
 creates a shell script that launches nginx in the foreground as the current user. the nginx is

default.nix

@@ -8,6 +8,7 @@
   nixpkgs.overlays = [
     (final: prev: {
       fetchFromSteam = prev.callPackage ./lib/fetchsteam {};
+      fetchb4 = prev.callPackage ./lib/fetchb4 {};
 
       gitSource = prev.callPackage ./lib/git-source {};
 

lib/fetchb4/builder.sh

@@ -0,0 +1,6 @@
+if [ -e "$NIX_ATTRS_SH_FILE" ]; then . "$NIX_ATTRS_SH_FILE"; elif [ -f .attrs.sh ]; then . .attrs.sh; fi
+source $stdenv/setup
+
+echo "Downloading kernel patch $msgid into $out"
+export HOME="/tmp"
+PYTHONHASHSEED=0 b4 am -C -T $b4_flags -o- "$msgid" > "$out"

lib/fetchb4/default.nix

@@ -0,0 +1,23 @@
+{ lib, stdenvNoCC, b4, git, cacert }:
+
+{
+  msgid,
+  hash,
+  single_message ? false,
+  version ? null
+}: stdenvNoCC.mkDerivation {
+  name = "patch-${msgid}";
+  builder = ./builder.sh;
+
+  inherit msgid;
+  b4_flags = with lib.strings; concatStringsSep " " [
+    (optionalString single_message "--single-message")
+    (optionalString (version != null) "--use-version ${version}")
+  ];
+
+  nativeBuildInputs = [ b4 git cacert ];
+  SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
+
+  outputHash = hash;
+  preferLocalBuild = true;
+}