Android P环境，mkfs.erofs is required firstly. Let's build vendor.img with erofs format.

build process for vendor with ext4

看下vendor image with ext4过程：

core/main.mk:1111:vendorimage: $(INSTALLED_VENDORIMAGE_TARGET)
# We just build this directly to the install location.
INSTALLED_VENDORIMAGE_TARGET := $(BUILT_VENDORIMAGE_TARGET)
$(INSTALLED_VENDORIMAGE_TARGET): $(INTERNAL_USERIMAGES_DEPS) $(INTERNAL_VENDORIMAGE_FILES) $(INSTALLED_FILES_FILE_VENDOR) $(BUILD_IMAGE_SRCS) $(DEPMOD) $(BOARD_VENDOR_KERNEL_MODULES)
        $(build-vendorimage-target)
BUILT_VENDORIMAGE_TARGET := $(PRODUCT_OUT)/vendor.img
define build-vendorimage-target
  $(call pretty,"Target vendor fs image: $(INSTALLED_VENDORIMAGE_TARGET)")
  @mkdir -p $(TARGET_OUT_VENDOR)
  @mkdir -p $(vendorimage_intermediates) && rm -rf $(vendorimage_intermediates)/vendor_image_info.txt
  $(call generate-userimage-prop-dictionary, $(vendorimage_intermediates)/vendor_image_info.txt, skip_fsck=true)
  $(if $(BOARD_VENDOR_KERNEL_MODULES), \
    $(call build-image-kernel-modules,$(BOARD_VENDOR_KERNEL_MODULES),$(TARGET_OUT_VENDOR),vendor/,$(call intermediates-dir-for,PACKAGING,depmod_vendor)))
  $(hide) PATH=$(foreach p,$(INTERNAL_USERIMAGES_BINARY_PATHS),$(p):)$$PATH \
      build/make/tools/releasetools/build_image.py \
      $(TARGET_OUT_VENDOR) $(vendorimage_intermediates)/vendor_image_info.txt $(INSTALLED_VENDORIMAGE_TARGET) $(TARGET_OUT)
  $(hide) $(call assert-max-image-size,$(INSTALLED_VENDORIMAGE_TARGET),$(BOARD_VENDORIMAGE_PARTITION_SIZE))
endef

制作img的工具：

ifeq ($(INTERNAL_USERIMAGES_USE_EXT),true)
INTERNAL_USERIMAGES_DEPS := $(SIMG2IMG)
INTERNAL_USERIMAGES_DEPS += $(MKEXTUSERIMG) $(MAKE_EXT4FS) $(E2FSCK)
ifeq ($(TARGET_USERIMAGES_USE_F2FS),true)
INTERNAL_USERIMAGES_DEPS += $(MKF2FSUSERIMG) $(MAKE_F2FS)
endif
endif

工具定义：

./core/config.mk:668:MKEXTUSERIMG := $(HOST_OUT_EXECUTABLES)/mkuserimg_mke2fs.sh

用build/make/tools/releasetools/build_image.py去生成:

def BuildImage(in_dir, prop_dict, out_file, target_out=None):
  """Build an image to out_file from in_dir with property prop_dict.
    if image_filename == "system.img":
      mount_point = "system"
    elif image_filename == "system_other.img":
      mount_point = "system_other"
    elif image_filename == "userdata.img":
      mount_point = "data"
    elif image_filename == "cache.img":
      mount_point = "cache"
    elif image_filename == "vendor.img":
      mount_point = "vendor"
    elif image_filename == "oem.img":
      mount_point = "oem"
    elif image_filename == "product.img":
      mount_point = "product"
    else:
      print("error: unknown image file name ", image_filename, file=sys.stderr)
      sys.exit(1)

    image_properties = ImagePropFromGlobalDict(glob_dict, mount_point)

  if not BuildImage(in_dir, image_properties, out_file, target_out):

ok，下来就可以添加了。

add support for erofs image

@@ -1095,6 +1095,11 @@ ifneq ($(filter $(BOARD_PRODUCTIMAGE_FILE_SYSTEM_TYPE) $(BOARD_VENDORIMAGE_FILE_
 INTERNAL_USERIMAGES_DEPS += $(MAKE_SQUASHFS) $(MKSQUASHFSUSERIMG) $(IMG2SIMG)
 endif

+INTERNAL_USERIMAGES_SPARSE_EROFS_FLAG := -s
+ifneq ($(filter $(BOARD_PRODUCTIMAGE_FILE_SYSTEM_TYPE) $(BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE) $(BOARD_SYSTEMIMAGE_FILE_SYSTEM_TYPE),erofs),)
+INTERNAL_USERIMAGES_DEPS += $(MAKE_EROFS) $(MKEROFSUSERIMG) $(IMG2SIMG)
+endif
+
 INTERNAL_USERIMAGES_BINARY_PATHS := $(sort $(dir $(INTERNAL_USERIMAGES_DEPS)))

 ifeq (true,$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VERITY))
@@ -1162,6 +1167,7 @@ $(if $(BOARD_OEMIMAGE_EXTFS_INODE_COUNT),$(hide) echo "oem_extfs_inode_count=$(B
 $(if $(BOARD_OEMIMAGE_EXTFS_RSV_PCT),$(hide) echo "oem_extfs_rsv_pct=$(BOARD_OEMIMAGE_EXTFS_RSV_PCT)" >> $(1))
 $(if $(INTERNAL_USERIMAGES_SPARSE_EXT_FLAG),$(hide) echo "extfs_sparse_flag=$(INTERNAL_USERIMAGES_SPARSE_EXT_FLAG)" >> $(1))
 $(if $(INTERNAL_USERIMAGES_SPARSE_SQUASHFS_FLAG),$(hide) echo "squashfs_sparse_flag=$(INTERNAL_USERIMAGES_SPARSE_SQUASHFS_FLAG)" >> $(1))
+$(if $(INTERNAL_USERIMAGES_SPARSE_EROFS_FLAG),$(hide) echo "erofs_sparse_flag=$(INTERNAL_USERIMAGES_SPARSE_EROFS_FLAG)" >> $(1))

build/make/core/config.mk:

 MKF2FSUSERIMG := $(HOST_OUT_EXECUTABLES)/mkf2fsuserimg.sh
+MAKE_EROFS := $(HOST_OUT_EXECUTABLES)/mkfs.erofs
+MKEROFSUSERIMG := $(HOST_OUT_EXECUTABLES)/mkerofsimage.sh
 SIMG2IMG := $(HOST_OUT_EXECUTABLES)/simg2img$(HOST_EXECUTABLE_SUFFIX)

build/make/tools/releasetools/build_image.py:

@@ -597,6 +597,20 @@ def BuildImage(in_dir, prop_dict, out_file, target_out=None):
     if "timestamp" in prop_dict:
       build_command.extend(["-T", str(prop_dict["timestamp"])])
     build_command.extend(["-L", prop_dict["mount_point"]])
+  elif fs_type.startswith("erofs"):
+    build_command = ["mkerofsimage.sh"]
+    build_command.extend([in_dir, out_file])
+    if "erofs_sparse_flag" in prop_dict:
+      build_command.extend([prop_dict["erofs_sparse_flag"]])
+    build_command.extend(["-m", prop_dict["mount_point"]])
+    if target_out:
+      build_command.extend(["-d", target_out])
+    if fs_config:
+      build_command.extend(["-C", fs_config])
+    if "selinux_fc" in prop_dict:
+      build_command.extend(["-c", prop_dict["selinux_fc"]])
+    if "erofs_compressor" in prop_dict:
+      build_command.extend(["-z", prop_dict["erofs_compressor"]])
   else:
     print("Error: unknown filesystem type '%s'" % (fs_type))
     return False
@@ -704,6 +718,7 @@ def ImagePropFromGlobalDict(glob_dict, mount_point):
   common_props = (
       "extfs_sparse_flag",
       "squashfs_sparse_flag",
+      "erofs_sparse_flag",
       "selinux_fc",

system/extras添加erofs_utils:

tj@ubuntu:~/work/code/system/extras/erofs_utils$ ls
Android.mk  mkerofsimage.sh  mkfs.erofs

mkerofsimage.sh主要参考ext4,squashfs:

MAKE_EROFS_CMD="mkfs.erofs $OUTPUT_FILE $SRC_DIR/"
echo $MAKE_EROFS_CMD
$MAKE_EROFS_CMD

SPARSE_SUFFIX=".sparse"
if [ "$SPARSE" = true ]; then
    img2simg $OUTPUT_FILE $OUTPUT_FILE$SPARSE_SUFFIX
    if [ $? -ne 0 ]; then
        exit 4
    fi
    mv $OUTPUT_FILE$SPARSE_SUFFIX $OUTPUT_FILE
fi

项目启用BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE为erofs, build is ok:

[ 99% 7719/7720] Installed file list: out/.../installed-files-vendor.txt
[100% 7720/7720] Target vendor fs image: out/.../vendor.img
...
mkfs.erofs out/.../vendor.img out/.../vendor/
  c_version:           [0.1   Jul  9 2019 03:24:50]
  c_img_path:          [out/.../vendor.img]
  c_src_path:          [out/.../vendor]
  c_dbg_lvl:           [       0]
  c_dry_run:           [       0]
  c_alg_name:          [    none]
  c_compr_maxsz:       [  921600]
  c_compr_lvl:         [       0]
  c_compr_boundary:    [     128]
  c_compr_ratio_limit: [     100]

### build completed successfully (04:10 (mm:ss)) ####

QCOM P vendor mount移到了dts下，ext4改为erofs后可以mount ok。

[   11.566421] erofs: mounted on /dev/block/platform/soc/7824900.sdhci/by-name/vendor with ...
[   11.569767] init: [libfs_mgr]__mount(source=/dev/block/platform/soc/7824900.sdhci/by-name/vendor,target=/vendor,type=erofs)=0: Success

权限问题，待check。

ps: squashfs也是只读文件系统，提个patch给维护人Phillip，半天不回，算了，懒得看了。。。

mkerofsimage.sh参考实现：

#!/bin/bash
#
# To call this script, make sure mkfs.erofs is somewhere in PATH

function usage() {
cat<<EOT
Usage:
${0##*/} SRC_DIR OUTPUT_FILE [-s] [-m MOUNT_POINT] [-d PRODUCT_OUT] [-C FS_CONFIG ] [-c FILE_CONTEXTS] [-z COMPRESSOR]
EOT
}

echo "in mkerofsimage.sh PATH=$PATH"

if [ $# -lt 2 ]; then
    usage
    exit 1
fi

SRC_DIR=$1
if [ ! -d $SRC_DIR ]; then
  echo "Can not find directory $SRC_DIR!"
  exit 2
fi
OUTPUT_FILE=$2
shift; shift

SPARSE=false
if [[ "$1" == "-s" ]]; then
    SPARSE=true
    shift;
fi

MOUNT_POINT=
if [[ "$1" == "-m" ]]; then
    MOUNT_POINT=$2
    shift; shift
fi

PRODUCT_OUT=
if [[ "$1" == "-d" ]]; then
    PRODUCT_OUT=$2
    shift; shift
fi

FS_CONFIG=
if [[ "$1" == "-C" ]]; then
    FS_CONFIG=$2
    shift; shift
fi

FILE_CONTEXTS=
if [[ "$1" == "-c" ]]; then
    FILE_CONTEXTS=$2
    shift; shift
fi

COMPRESSOR="lz4"
COMPRESSOR_OPT="-Xhc"
if [[ "$1" == "-z" ]]; then
    COMPRESSOR=$2
    COMPRESSOR_OPT=
    shift; shift
fi

OPT=""
if [ -n "$MOUNT_POINT" ]; then
  OPT="$OPT -mount-point $MOUNT_POINT"
fi
if [ -n "$PRODUCT_OUT" ]; then
  OPT="$OPT -product-out $PRODUCT_OUT"
fi
if [ -n "$FS_CONFIG" ]; then
  OPT="$OPT -fs-config-file $FS_CONFIG"
fi
if [ -n "$FILE_CONTEXTS" ]; then
  OPT="$OPT -context-file $FILE_CONTEXTS"
fi

MAKE_EROFS_CMD="mkfs.erofs $OUTPUT_FILE $SRC_DIR/"
echo $MAKE_EROFS_CMD
$MAKE_EROFS_CMD

if [ $? -ne 0 ]; then
    exit 4
fi

SPARSE_SUFFIX=".sparse"
if [ "$SPARSE" = true ]; then
    img2simg $OUTPUT_FILE $OUTPUT_FILE$SPARSE_SUFFIX
    if [ $? -ne 0 ]; then
        exit 4
    fi
    mv $OUTPUT_FILE$SPARSE_SUFFIX $OUTPUT_FILE
fi