nixos/udev: compress firmware with zstd if possible

Closes #267442

    $ nix path-info -Sh /nix/store/qj1dm7wfw5m3mxf1gn3fdm0az9y1h5ny-linux-firmware-20240312-xz
    /nix/store/qj1dm7wfw5m3mxf1gn3fdm0az9y1h5ny-linux-firmware-20240312-xz	440.3M
    $ nix path-info -Sh /nix/store/c3szcjxb3g990dbiz7llwmkaf0bi98j2-linux-firmware-20240312-zstd
    /nix/store/c3szcjxb3g990dbiz7llwmkaf0bi98j2-linux-firmware-20240312-zstd	460.6M

This is an increase of 4.4%, but OTOH zstd has a significantly higher
decompression speed[1].

[1] https://gregoryszorc.com/blog/2017/03/07/better-compression-with-zstandard/

2 files changed, 43 insertions, 29 deletions

diff --git a/pkgs/build-support/kernel/compress-firmware-xz.nix b/pkgs/build-support/kernel/compress-firmware-xz.nix
deleted file mode 100644
index cb9ce7a713389..0000000000000
--- a/pkgs/build-support/kernel/compress-firmware-xz.nix
+++ /dev/null
@@ -1,29 +0,0 @@
-{ runCommand, lib }:
-
-firmware:
-
-let
-  args = {
-    allowedRequisites = [];
-  } // lib.optionalAttrs (firmware ? meta) { inherit (firmware) meta; };
-in
-
-runCommand "${firmware.name}-xz" args ''
-  mkdir -p $out/lib
-  (cd ${firmware} && find lib/firmware -type d -print0) |
-      (cd $out && xargs -0 mkdir -v --)
-  (cd ${firmware} && find lib/firmware -type f -print0) |
-      (cd $out && xargs -0rtP "$NIX_BUILD_CORES" -n1 \
-          sh -c 'xz -9c -T1 -C crc32 --lzma2=dict=2MiB "${firmware}/$1" > "$1.xz"' --)
-  (cd ${firmware} && find lib/firmware -type l) | while read link; do
-      target="$(readlink "${firmware}/$link")"
-      if [ -f "${firmware}/$link" ]; then
-        ln -vs -- "''${target/^${firmware}/$out}.xz" "$out/$link.xz"
-      else
-        ln -vs -- "''${target/^${firmware}/$out}" "$out/$link"
-      fi
-  done
-
-  echo "Checking for broken symlinks:"
-  find -L $out -type l -print -execdir false -- '{}' '+'
-''
diff --git a/pkgs/build-support/kernel/compress-firmware.nix b/pkgs/build-support/kernel/compress-firmware.nix
new file mode 100644
index 0000000000000..0949036d5127f
--- /dev/null
+++ b/pkgs/build-support/kernel/compress-firmware.nix
@@ -0,0 +1,43 @@
+{ runCommand, lib, type ? "zstd", zstd }:
+
+firmware:
+
+let
+  compressor = {
+    xz = {
+      ext = "xz";
+      nativeBuildInputs = [ ];
+      cmd = file: target: ''xz -9c -T1 -C crc32 --lzma2=dict=2MiB "${file}" > "${target}"'';
+    };
+    zstd = {
+      ext = "zst";
+      nativeBuildInputs = [ zstd ];
+      cmd = file: target: ''zstd -T1 -19 --long --check -f "${file}" -o "${target}"'';
+    };
+  }.${type} or (throw "Unsupported compressor type for firmware.");
+
+  args = {
+    allowedRequisites = [];
+    inherit (compressor) nativeBuildInputs;
+  } // lib.optionalAttrs (firmware ? meta) { inherit (firmware) meta; };
+in
+
+runCommand "${firmware.name}-${type}" args ''
+  mkdir -p $out/lib
+  (cd ${firmware} && find lib/firmware -type d -print0) |
+      (cd $out && xargs -0 mkdir -v --)
+  (cd ${firmware} && find lib/firmware -type f -print0) |
+      (cd $out && xargs -0rtP "$NIX_BUILD_CORES" -n1 \
+          sh -c '${compressor.cmd "${firmware}/$1" "$1.${compressor.ext}"}' --)
+  (cd ${firmware} && find lib/firmware -type l) | while read link; do
+      target="$(readlink "${firmware}/$link")"
+      if [ -f "${firmware}/$link" ]; then
+        ln -vs -- "''${target/^${firmware}/$out}.${compressor.ext}" "$out/$link.${compressor.ext}"
+      else
+        ln -vs -- "''${target/^${firmware}/$out}" "$out/$link"
+      fi
+  done
+
+  echo "Checking for broken symlinks:"
+  find -L $out -type l -print -execdir false -- '{}' '+'
+''