setup erofs for tiny rootfs! (#68)

Author: adeebshihadeh

kernel/configs/vamos.config

@@ -89,5 +89,10 @@ CONFIG_TOUCHSCREEN_S6SY761=y
 CONFIG_EXPERT=y
 CONFIG_GPIO_SYSFS=y
 
+# EROFS
+CONFIG_EROFS_FS=y
+CONFIG_EROFS_FS_ZIP=y
+CONFIG_EROFS_FS_ZIP_LZ4=y
+
 # Misc
 CONFIG_LOCALVERSION_AUTO=n

tools/build/Dockerfile.builder

@@ -19,10 +19,24 @@ RUN apk add --no-cache \
     git \
     libcap \
     linux-headers \
+    lz4-dev \
     openssl \
     openssl-dev \
     perl \
-    python3
+    python3 \
+    util-linux-dev \
+    xz-dev
+
+# Build erofs-utils from source (not packaged in Alpine)
+RUN git clone https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git /tmp/erofs-utils \
+    && cd /tmp/erofs-utils \
+    && git checkout v1.8.5 \
+    && apk add --no-cache autoconf automake libtool \
+    && autoreconf -fi \
+    && ./configure --enable-lz4 --enable-lzma --disable-fuse \
+    && make -j$(nproc) \
+    && make install \
+    && rm -rf /tmp/erofs-utils
 
 # Cross-compiler for x86_64 hosts building aarch64 kernel
 # gcc-aarch64-none-elf is bare-metal but works for kernel (freestanding code)

tools/build/build_system.sh

@@ -129,6 +129,17 @@ MOUNT_CONTAINER_ID="$MOUNT_CONTAINER_ID" ROOTFS_DIR="$ROOTFS_DIR" \
   ROOTFS_IMAGE="$ROOTFS_IMAGE" OUTPUT_DIR="$OUTPUT_DIR" \
   "$DIR/vamos" profile
 
+# Build EROFS image (before unmount, while rootfs is still mounted)
+EROFS_IMAGE="$BUILD_DIR/system.erofs.img"
+OUT_EROFS_IMAGE="$OUTPUT_DIR/system.erofs.img"
+echo "Building EROFS image (LZ4HC, 64K clusters)"
+exec_as_root mkfs.erofs \
+  -zlz4hc,12 \
+  -C65536 \
+  -T0 \
+  --all-root \
+  "$EROFS_IMAGE" "$ROOTFS_DIR"
+
 # Unmount image
 echo "Unmount filesystem"
 exec_as_root umount -l "$ROOTFS_DIR"
@@ -137,6 +148,9 @@ exec_as_root umount -l "$ROOTFS_DIR"
 echo "Sparsifying system image"
 exec_as_user img2simg "$ROOTFS_IMAGE" "$OUT_IMAGE"
 
+# Copy EROFS image to output
+cp "$EROFS_IMAGE" "$OUT_EROFS_IMAGE"
+
 # Patch sparse image size into profile JSON
 SPARSE_SIZE=$(stat -c%s "$OUT_IMAGE" 2>/dev/null || stat -f%z "$OUT_IMAGE")
 if command -v jq &>/dev/null; then
@@ -145,4 +159,13 @@ if command -v jq &>/dev/null; then
     mv "$OUTPUT_DIR/rootfs-profile.json.tmp" "$OUTPUT_DIR/rootfs-profile.json"
 fi
 
+# Size comparison
+EXT4_SPARSE_SIZE=$(stat -c%s "$OUT_IMAGE" 2>/dev/null || stat -f%z "$OUT_IMAGE")
+EROFS_SIZE=$(stat -c%s "$OUT_EROFS_IMAGE" 2>/dev/null || stat -f%z "$OUT_EROFS_IMAGE")
+echo ""
+echo "=== Image size comparison ==="
+echo "ext4 (sparse): $(numfmt --to=iec-i --suffix=B "$EXT4_SPARSE_SIZE") ($EXT4_SPARSE_SIZE bytes)"
+echo "EROFS (LZ4HC): $(numfmt --to=iec-i --suffix=B "$EROFS_SIZE") ($EROFS_SIZE bytes)"
+echo ""
+
 echo "Done!"