grub_install.sh: Compress modules with xz instead of gzip to save space

Giving the --best or -9 option results in a heavier decompression cost
with no gain on such small files.

Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>

build_library/grub_install.sh

@@ -41,7 +41,7 @@ switch_to_strict_mode
 GRUB_DIR="flatcar/grub/${FLAGS_target}"
 
 # Modules required to boot a standard CoreOS configuration
-CORE_MODULES=( normal search test fat part_gpt search_fs_uuid gzio search_part_label terminal gptprio configfile memdisk tar echo read btrfs )
+CORE_MODULES=( normal search test fat part_gpt search_fs_uuid xzio search_part_label terminal gptprio configfile memdisk tar echo read btrfs )
 
 SBAT_ARG=()
 
@@ -137,7 +137,7 @@ case "${FLAGS_target}" in
                 [[ ${file} == ${GRUB_SRC}/${core_mod}.mod ]] && continue 2
             done
             out="${ESP_DIR}/${GRUB_DIR}/${file##*/}"
-            gzip --best --stdout "${file}" | sudo_clobber "${out}"
+            xz --stdout "${file}" | sudo_clobber "${out}"
         done
         ;;
 esac
@@ -178,7 +178,7 @@ fi
 
 info "Generating ${GRUB_IMAGE}"
 sudo grub-mkimage \
-    --compression=auto \
+    --compression=xz \
     --format "${FLAGS_target}" \
     --directory "${GRUB_SRC}" \
     --config "${ESP_DIR}/${GRUB_DIR}/load.cfg" \

changelog/changes/2024-11-18-grub-modules.md

@@ -1 +1,2 @@
 - Additional GRUB modules are no longer installed for UEFI platforms to save space and also because they cannot be loaded with Secure Boot enabled. This does not affect existing installations.
+- The GRUB modules on non-UEFI platforms are now compressed with xz rather than gzip to save even more space. This does not affect existing installations.