Add INITRAMFS_SKIP_GZIP option to make initramfs encoding/decoding faster

Makefile

@@ -112,6 +112,12 @@ ifeq ($(ENABLE_KVM), 1)
 CARGO_OSDK_ARGS += --qemu-args="-accel kvm"
 endif
 
+# Skip GZIP to make encoding and decoding of initramfs faster
+ifeq ($(INITRAMFS_SKIP_GZIP),1)
+CARGO_OSDK_INITRAMFS_OPTION := --initramfs=$(realpath test/build/initramfs.cpio)
+CARGO_OSDK_ARGS += $(CARGO_OSDK_INITRAMFS_OPTION)
+endif
+
 # Pass make variables to all subdirectory makes
 export
 
@@ -243,7 +249,7 @@ ktest: initramfs $(CARGO_OSDK)
 	@# Exclude linux-bzimage-setup from ktest since it's hard to be unit tested
 	@for dir in $(OSDK_CRATES); do \
 		[ $$dir = "ostd/libs/linux-bzimage/setup" ] && continue; \
-		(cd $$dir && OVMF=off cargo osdk test) || exit 1; \
+		(cd $$dir && OVMF=off cargo osdk test $(CARGO_OSDK_INITRAMFS_OPTION)) || exit 1; \
 		tail --lines 10 qemu.log | grep -q "^\\[ktest runner\\] All crates tested." \
 			|| (echo "Test failed" && exit 1); \
 	done

kernel/src/fs/rootfs.rs

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: MPL-2.0
 
+use core2::io::{Cursor, Read};
 use cpio_decoder::{CpioDecoder, FileType};
 use lending_iterator::LendingIterator;
 use libflate::gzip::Decoder as GZipDecoder;
@@ -14,17 +15,47 @@ use super::{
 };
 use crate::{fs::path::is_dot, prelude::*};
 
+struct BoxedReader<'a>(Box<dyn Read + 'a>);
+
+impl<'a> BoxedReader<'a> {
+    pub fn new(reader: Box<dyn Read + 'a>) -> Self {
+        BoxedReader(reader)
+    }
+}
+
+impl Read for BoxedReader<'_> {
+    fn read(&mut self, buf: &mut [u8]) -> core2::io::Result<usize> {
+        self.0.read(buf)
+    }
+}
+
 /// Unpack and prepare the rootfs from the initramfs CPIO buffer.
 pub fn init(initramfs_buf: &[u8]) -> Result<()> {
     init_root_mount();
     procfs::init();
 
-    println!("[kernel] unpacking the initramfs.cpio.gz to rootfs ...");
+    let reader = {
+        let mut initramfs_suffix = "";
+        let reader = match &initramfs_buf[..4] {
+            // Gzip magic number: 0x1F 0x8B
+            &[0x1F, 0x8B, _, _] => {
+                initramfs_suffix = ".gz";
+                let gzip_decoder = GZipDecoder::new(initramfs_buf)
+                    .map_err(|_| Error::with_message(Errno::EINVAL, "invalid gzip buffer"))?;
+                BoxedReader::new(Box::new(gzip_decoder))
+            }
+            _ => BoxedReader::new(Box::new(Cursor::new(initramfs_buf))),
+        };
+
+        println!(
+            "[kernel] unpacking the initramfs.cpio{} to rootfs ...",
+            initramfs_suffix
+        );
+
+        reader
+    };
+    let mut decoder = CpioDecoder::new(reader);
     let fs = FsResolver::new();
-    let mut decoder = CpioDecoder::new(
-        GZipDecoder::new(initramfs_buf)
-            .map_err(|_| Error::with_message(Errno::EINVAL, "invalid gzip buffer"))?,
-    );
 
     loop {
         let Some(entry_result) = decoder.next() else {

test/Makefile

@@ -9,7 +9,12 @@ ATOMIC_WGET := $(CUR_DIR)/../tools/atomic_wget.sh
 BUILD_DIR := $(CUR_DIR)/build
 INITRAMFS := $(BUILD_DIR)/initramfs
 INITRAMFS_FILELIST := $(BUILD_DIR)/initramfs.filelist
+INITRAMFS_SKIP_GZIP ?= 0
+ifeq ($(INITRAMFS_SKIP_GZIP),1)
+INITRAMFS_IMAGE := $(BUILD_DIR)/initramfs.cpio
+else
 INITRAMFS_IMAGE := $(BUILD_DIR)/initramfs.cpio.gz
+endif
 EXT2_IMAGE := $(BUILD_DIR)/ext2.img
 EXFAT_IMAGE := $(BUILD_DIR)/exfat.img
 INITRAMFS_EMPTY_DIRS := \
@@ -107,7 +112,7 @@ $(INITRAMFS)/usr/local:
 
 .PHONY: $(INITRAMFS)/test
 $(INITRAMFS)/test:
-	@make --no-print-directory -C apps
+	@$(MAKE) --no-print-directory -C apps
 
 $(INITRAMFS)/benchmark: | $(INITRAMFS)/benchmark/bin
 	@cp -rf $(CUR_DIR)/benchmark/* $@
@@ -134,11 +139,11 @@ $(INITRAMFS_EMPTY_DIRS):
 
 .PHONY: $(SYSCALL_TEST_DIR)
 $(SYSCALL_TEST_DIR):
-	@make --no-print-directory -C syscall_test
+	@$(MAKE) --no-print-directory -C syscall_test
 
 .PHONY: $(INITRAMFS_IMAGE)
 $(INITRAMFS_IMAGE): $(INITRAMFS_FILELIST)
-	@if ! cmp -s $(INITRAMFS_FILELIST) $(INITRAMFS_FILELIST).previous ; then \
+	@if ! cmp -s $(INITRAMFS_FILELIST) $(INITRAMFS_FILELIST).previous || ! test -f $@; then \
 		echo "Generating the initramfs image..."; \
 		cp -f $(INITRAMFS_FILELIST) $(INITRAMFS_FILELIST).previous; \
 		( \
@@ -148,7 +153,12 @@ $(INITRAMFS_IMAGE): $(INITRAMFS_FILELIST)
 			# `$(INITRAMFS)` in the second column. This prunes the first \
 			# column and passes the second column to `cpio`. \
 			cut -d " " -f 2- $(INITRAMFS_FILELIST) | \
-				cpio -o -H newc | gzip \
+				cpio -o -H newc | \
+					if [ "$(INITRAMFS_SKIP_GZIP)" != 1 ]; then \
+						gzip; \
+					else \
+						cat; \
+					fi \
 		) > $@; \
 	fi
 
@@ -175,11 +185,11 @@ build: $(INITRAMFS_IMAGE) $(EXT2_IMAGE) $(EXFAT_IMAGE)
 
 .PHONY: format
 format:
-	@make --no-print-directory -C apps format
+	@$(MAKE) --no-print-directory -C apps format
 
 .PHONY: check
 check:
-	@make --no-print-directory -C apps check
+	@$(MAKE) --no-print-directory -C apps check
 
 .PHONY: clean
 clean: