Android编译基本流程
（1）source build/envsetup.sh
（2）lunch xxx // lunch 之后 选择xxx index
（3）make -j16
envsetup.sh 主要是设置编译时的一些系统环境变量，加载 vendor，device 目录(及子目录)下所有vendorsetup.sh ，接着lunch来选择设备类型，编译类型，
并且运行完脚本之后会增加了一些命令mmm,mm,croot ....
Android 生成的目标文件
编译完整个android系统源码之后会生成一些文件也即是目标文件system.img，recovery.img, boot.img, userdata.img,cache.img ...,这些镜像文件就是直接烧写到
android各个对应的分区里面，有的平台是将所有的需要的镜像文件打包成USB bin文件进行增量升级，下面以system.img为例进行分析。
目标文件生成的基本流程
设置完环境变量之后， make systemimage
首先我们可以查看主目录的Makefile
### DO NOT EDIT THIS FILE ###
include build/core/main.mk
### DO NOT EDIT THIS FILE ###
此处主要就是导入了build/core/main.mk,我们看到一下目标
# Build files and then package it into the rom formats
.PHONY: droidcore
droidcore: files \
systemimage \
$(INSTALLED_BOOTIMAGE_TARGET) \
$(INSTALLED_RECOVERYIMAGE_TARGET) \
$(INSTALLED_USERDATAIMAGE_TARGET) \
$(INSTALLED_CACHEIMAGE_TARGET) \
$(INSTALLED_VENDORIMAGE_TARGET) \
$(INSTALLED_FILES_FILE)
这里面systemimage就是生成system.img 文件的为目标，接着我们可以发现build/core/Makefile中有它的依赖关系
systemimage: $(INSTALLED_SYSTEMIMAGE)
INSTALLED_SYSTEMIMAGE名称定义
INSTALLED_SYSTEMIMAGE := $(PRODUCT_OUT)/system.img
INSTALLED_SYSTEMIMAGE依赖关系
$(INSTALLED_SYSTEMIMAGE): $(BUILT_SYSTEMIMAGE) $(RECOVERY_FROM_BOOT_PATCH) | $(ACP)
@echo "Install system fs image: $@"
$(copy-file-to-target)
$(hide) $(call assert-max-image-size,$@ $(RECOVERY_FROM_BOOT_PATCH),$(BOARD_SYSTEMIMAGE_PARTITION_SIZE))
我们进一步看其子目标BUILT_SYSTEMIMAGE，名称定义以及依赖关系
BUILT_SYSTEMIMAGE := $(systemimage_intermediates)/system.img
BUILT_SYSTEMIMAGE依赖关系
$(BUILT_SYSTEMIMAGE): $(FULL_SYSTEMIMAGE_DEPS) $(INSTALLED_FILES_FILE)
$(call build-systemimage-target,$@)
其中INSTALLED_FILES_FILE是system.img生成时需要所有安装文件，查看installed-files.txt即可知道system.img 打包了哪些文件，
FULL_SYSTEMIMAGE_DEPS
也是其依赖文件
INSTALLED_FILES_FILE := $(PRODUCT_OUT)/installed-files.txt
$(INSTALLED_FILES_FILE): $(FULL_SYSTEMIMAGE_DEPS)
@echo Installed file list: $@
@mkdir -p $(dir $@)
@rm -f $@
$(hide) build/tools/fileslist.py $(TARGET_OUT) > $@
接着就会调用build-systemimage-target 来完成system.img 的打包流程
define build-systemimage-target
@echo "Target system fs image: $(1)"
$(call create-system-vendor-symlink)
@mkdir -p $(dir $(1)) $(systemimage_intermediates) && rm -rf $(systemimage_intermediates)/system_image_info.txt
$(call generate-userimage-prop-dictionary, $(systemimage_intermediates)/system_image_info.txt, \
skip_fsck=true)
$(hide) PATH=$(foreach p,$(INTERNAL_USERIMAGES_BINARY_PATHS),$(p):)$$PATH \
./build/tools/releasetools/build_image.py \
$(TARGET_OUT) $(systemimage_intermediates)/system_image_info.txt $(1) \
|| ( echo "Out of space? the tree size of $(TARGET_OUT) is (MB): " 1>&2 ;\
du -sm $(TARGET_OUT) 1>&2;\
echo "The max is $$(( $(BOARD_SYSTEMIMAGE_PARTITION_SIZE) / 1048576 )) MB." 1>&2 ;\
mkdir -p $(DIST_DIR); cp $(INSTALLED_FILES_FILE) $(DIST_DIR)/installed-files-rescued.txt; \
exit 1 )
从上面定义的编译命令包来看，主要干活的脚本是build/tools/releasetools/build_image.py,调用该脚本时，传入了三个参数：
（1）打包的system.img需要的文件目录； // 通常为 ${ANDROID_PRODUCT_OUT}/system
（2）生成system.img 时，需要的配置信息文件； // ${ANDROID_PRODUCT_OUT}/obj/PACKAGING/systemimage_intermediates/system_image_info.txt
（3）输出的目标文件 ； // 也即生成的system.img 的完整输出路径和文件名，${ANDROID_PRODUCT_OUT}/obj/PACKAGING/systemimage_intermediates/system.img
接着我们分析一下build_image.py脚本和配置文件system_image_info.txt
System_image_info.txt 分析
fs_type=ext4
system_size=0x28A00000
userdata_size=0x40000000
cache_fs_type=ext4
cache_size=0x40000000
selinux_fc=out/target/product/cibn/root/file_contexts
skip_fsck=true
文件中之处了system.img 时，文件系统的类型ext4, system.img的大小，已经依赖的文件file_contexts文件路径
build_image.py脚本
下面先看一下主函数main
def main(argv):
if len(argv) != 3:
print __doc__
sys.exit(1)
in_dir = argv[0]
glob_dict_file = argv[1]
out_file = argv[2]
glob_dict = LoadGlobalDict(glob_dict_file)
image_filename = os.path.basename(out_file)
mount_point = ""
if image_filename == "system.img":
mount_point = "system"
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"
else:
print >> sys.stderr, "error: unknown image file name ", image_filename
exit(1)
image_properties = ImagePropFromGlobalDict(glob_dict, mount_point)
if not BuildImage(in_dir, image_properties, out_file):
print >> sys.stderr, "error: failed to build %s from %s" % (out_file, in_dir)
exit(1)
LoadGlobalDict, ImagePropFromGlobalDict 主要解析BuildImage需要的参数
def LoadGlobalDict(filename):
"""Load "name=value" pairs from filename"""
d = {}
f = open(filename)
for line in f:
line = line.strip()
if not line or line.startswith("#"):
continue
k, v = line.split("=", 1)
d[k] = v
f.close()
return d
LoadGlobalDict
def ImagePropFromGlobalDict(glob_dict, mount_point):
"""Build an image property dictionary from the global dictionary.
Args:
glob_dict: the global dictionary from the build system.
mount_point: such as "system", "data" etc.
"""
d = {}
if "build.prop" in glob_dict:
bp = glob_dict["build.prop"]
if "ro.build.date.utc" in bp:
d["timestamp"] = bp["ro.build.date.utc"]
def copy_prop(src_p, dest_p):
if src_p in glob_dict:
d[dest_p] = str(glob_dict[src_p])
common_props = (
"extfs_sparse_flag",
"mkyaffs2_extra_flags",
"selinux_fc",
"skip_fsck",
"verity",
"verity_key",
"verity_signer_cmd"
)
for p in common_props:
copy_prop(p, p)
d["mount_point"] = mount_point
if mount_point == "system":
copy_prop("fs_type", "fs_type")
copy_prop("system_size", "partition_size")
copy_prop("system_verity_block_device", "verity_block_device")
elif mount_point == "data":
# Copy the generic fs type first, override with specific one if available.
copy_prop("fs_type", "fs_type")
copy_prop("userdata_fs_type", "fs_type")
copy_prop("userdata_size", "partition_size")
elif mount_point == "cache":
copy_prop("cache_fs_type", "fs_type")
copy_prop("cache_size", "partition_size")
elif mount_point == "vendor":
copy_prop("vendor_fs_type", "fs_type")
copy_prop("vendor_size", "partition_size")
copy_prop("vendor_verity_block_device", "verity_block_device")
elif mount_point == "oem":
copy_prop("fs_type", "fs_type")
copy_prop("oem_size", "partition_size")
return d
接着看最主要的动作BuildImage，打包system.img
def BuildImage(in_dir, prop_dict, out_file,
fs_config=None,
fc_config=None,
block_list=None):
"""Build an image to out_file from in_dir with property prop_dict.
Args:
in_dir: path of input directory.
prop_dict: property dictionary.
out_file: path of the output image file.
fs_config: path to the fs_config file (typically
META/filesystem_config.txt). If None then the configuration in
the local client will be used.
fc_config: path to the SELinux file_contexts file. If None then
the value from prop_dict['selinux_fc'] will be used.
Returns:
True iff the image is built successfully.
"""
build_command = []
fs_type = prop_dict.get("fs_type", "")
run_fsck = False
is_verity_partition = "verity_block_device" in prop_dict
verity_supported = prop_dict.get("verity") == "true"
# adjust the partition size to make room for the hashes if this is to be verified
if verity_supported and is_verity_partition:
partition_size = int(prop_dict.get("partition_size"))
adjusted_size = AdjustPartitionSizeForVerity(partition_size)
if not adjusted_size:
return False
prop_dict["partition_size"] = str(adjusted_size)
prop_dict["original_partition_size"] = str(partition_size)
if fs_type.startswith("ext"):
build_command = ["mkuserimg.sh"]
if "extfs_sparse_flag" in prop_dict:
build_command.append(prop_dict["extfs_sparse_flag"])
run_fsck = True
build_command.extend([in_dir, out_file, fs_type,
prop_dict["mount_point"]])
build_command.append(prop_dict["partition_size"])
if "timestamp" in prop_dict:
build_command.extend(["-T", str(prop_dict["timestamp"])])
if fs_config is not None:
build_command.extend(["-C", fs_config])
if block_list is not None:
build_command.extend(["-B", block_list])
if fc_config is not None:
build_command.append(fc_config)
elif "selinux_fc" in prop_dict:
build_command.append(prop_dict["selinux_fc"])
elif fs_type.startswith("f2fs"):
build_command = ["mkf2fsuserimg.sh"]
build_command.extend([out_file, prop_dict["partition_size"]])
else:
build_command = ["mkyaffs2image", "-f"]
if prop_dict.get("mkyaffs2_extra_flags", None):
build_command.extend(prop_dict["mkyaffs2_extra_flags"].split())
build_command.append(in_dir)
build_command.append(out_file)
if "selinux_fc" in prop_dict:
build_command.append(prop_dict["selinux_fc"])
build_command.append(prop_dict["mount_point"])
exit_code = RunCommand(build_command)
if exit_code != 0:
return False
# create the verified image if this is to be verified
if verity_supported and is_verity_partition:
if not MakeVerityEnabledImage(out_file, prop_dict):
return False
if run_fsck and prop_dict.get("skip_fsck") != "true":
success, unsparse_image = UnsparseImage(out_file, replace=False)
if not success:
return False
# Run e2fsck on the inflated image file
e2fsck_command = ["e2fsck", "-f", "-n", unsparse_image]
exit_code = RunCommand(e2fsck_command)
os.remove(unsparse_image)
return exit_code == 0
由于system.img 定义的文件系统类型的ext4,我们就从if fs_type.startswith("ext"): 处看起，一直在封装打包命令build_command，最后调用Rumcommand(cmd)运行
def RunCommand(cmd):
""" Echo and run the given command
Args:
cmd: the command represented as a list of strings.
Returns:
The exit code.
"""
print "Running: ", " ".join(cmd)
p = subprocess.Popen(cmd)
p.communicate()
return p.returncode
其实运行的命令如下：
mkuserimg.sh out/target/product/cibn/system out/target/product/cibn/obj/PACKAGING/systemimage_intermediates/system.img ext4 system 0x28A00000 out/target/product/cibn/root/file_contexts
而mkuserimg.sh是编译完系统之后生成，mkuserimg.sh在${ANDROID_PRODUCT_OUT}/out/host/linux-x86/bin/目录下
xxxxxx@yf153:~/Mstar_828$ ls /home/backup/xxxxxx/Mstar_828/out/host/linux-x86/bin/
aapt alignment.exe bcc_strip_attr clang-tblgen dex2oat dx imgdiff make_ext4fs mkuserimg.sh simg2img
acp apicheck bsdiff crc dexdeps e2fsck insertkeys.py minigzip oatdump SubSecureInfoGen.exe
adb aprotoc checkfc dalvikvm dexdump fastboot llvm-rs-cc mkbootfs patchoat validatekeymaps
aescrypt2.exe backtrace_test checkpolicy dalvikvm32 dexlist hierarchyviewer1 llvm-tblgen mkimage rmtypedefs zipalign
aidl bcc checkseapp dalvikvm64 dmtracedump hprof-conv lzop mksdcard rsa_sign
根据上面的分析，我们可以在编译完一次android系统之后，直接使用一下命令来生成system.img 文件
xxxxxx@yf153:~/project_name$ croot
xxxxxx@yf153:~/project_name$ mkuserimg.sh out/target/product/cibn/system out/target/product/cibn/obj/PACKAGING/systemimage_intermediates/system.img ext4 system 0x28A00000 out/target/product/cibn/root/file_contexts
make_ext4fs -T -1 -S out/target/product/cibn/root/file_contexts -l 0x28A00000 -a system out/target/product/cibn/obj/PACKAGING/systemimage_intermediates/system.img out/target/product/cibn/system
Creating filesystem with parameters:
Size: 681574400
Block size: 4096
Blocks per group: 32768
Inodes per group: 6944
Inode size: 256
Journal blocks: 2600
Label:
Flexbg size: 8
Flexbg groups: 1
Blocks: 166400
Block groups: 6
Reserved block group size: 47
Created filesystem with 1762/41664 inodes and 130806/166400 blocks
可以看到直接输入一下参数：
out/target/product/cibn/system， // 输入打包目录
out/target/product/cibn/obj/PACKAGING/systemimage_intermediates/system.img， // 生成的输出文件
ext4， // 文件系统类型
system， // system.img 文件在系统的挂载点
0x28A00000，// system.img 文件的大小
out/target/product/cibn/root/file_contexts， // selinux_fc 系统安装策略配置文件
接下来我们看一下文件mkuserimg.sh。
mkuserimg.sh
android5.1 下的路径是 external/qemu/distrib/ext4_utils/src/mkuserimg.sh ，详细内容如下：
#!/bin/bash -x
#
# To call this script, make sure make_ext4fs is somewhere in PATH
function usage() {
cat<<EOT
Usage:
mkuserimg.sh [-s] SRC_DIR OUTPUT_FILE EXT_VARIANT MOUNT_POINT SIZE [FILE_CONTEXTS]
EOT
}
echo "in mkuserimg.sh PATH=$PATH"
ENABLE_SPARSE_IMAGE=
if [ "$1" = "-s" ]; then
ENABLE_SPARSE_IMAGE="-s"
shift
fi
if [ $# -ne 5 -a $# -ne 6 ]; 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
EXT_VARIANT=$3
MOUNT_POINT=$4
SIZE=$5
FC=$6
case $EXT_VARIANT in
ext4) ;;
*) echo "Only ext4 is supported!"; exit 3 ;;
esac
if [ -z $MOUNT_POINT ]; then
echo "Mount point is required"
exit 2
fi
if [ -z $SIZE ]; then
echo "Need size of filesystem"
exit 2
fi
if [ -n "$FC" ]; then
FCOPT="-S $FC"
fi
MAKE_EXT4FS_CMD="make_ext4fs $ENABLE_SPARSE_IMAGE $FCOPT -l $SIZE -a $MOUNT_POINT $OUTPUT_FILE $SRC_DIR"
echo $MAKE_EXT4FS_CMD
$MAKE_EXT4FS_CMD
if [ $? -ne 0 ]; then
exit 4
fi
mkuserimg.sh调用make_ext4fs ，而工具make_ext4fs又是在哪里，我们可以找一下
kehuanyu@yf153:~/Mstar_828$ find . -name "*.mk" |xargs -i grep -rwnH "make_ext4fs" {}
./external/qemu/distrib/ext4_utils/sources.mk:12: src/make_ext4fs.c \
./external/qemu/distrib/ext4_utils/src/Android.mk:6: make_ext4fs.c \
./external/qemu/distrib/ext4_utils/src/Android.mk:37:LOCAL_MODULE := make_ext4fs
./external/qemu/distrib/ext4_utils/src/Android.mk:78:LOCAL_MODULE := make_ext4fs
在/external/qemu/distrib/ext4_utils/src/下，由make_ext4fs.c , make_ext4fs_main.c 文件编译生成，后面mkuserimg.sh转调make_ext4fs的命令是：
make_ext4fs -T -1 -S out/target/product/cibn/root/file_contexts -l 0x28A00000 -a system out/target/product/cibn/obj/PACKAGING/systemimage_intermediates/system.img out/target/product/cibn/system
mkuserimg.sh, make_ext4fs 的参数基本类似，有了这个命令，我们可以最大限度的去定制android所需要的镜像文件(*.img)
镜像文件的切分
有一些镜像文件比较大，而tftp烧录文件时，内存大小只有大约200M，所以必要时要进行拆分，压缩，使用的命令split , lzop
xxxxxx@yf153:~/projectName/out/target/product/cibn/temp$ ls
system.img
xxxxxx@yf153:~/projectName/out/target/product/cibn/temp$ split -b 150m system.img system.img
xxxxxx@yf153:~/projectName/out/target/product/cibn/temp$ ls
system.img system.imgaa system.imgab system.imgac system.imgad system.imgae
xxxxxx@yf153:~/projectName/out/target/product/cibn/temp$ lzop -f -o system.imga
system.imgaa system.imgab system.imgac system.imgad system.imgae
xxxxxx@yf153:~/projectName/out/target/product/cibn/temp$ lzop -f -o system.imgaa.lzo system.imgaa
xxxxxx@yf153:~/projectName/out/target/product/cibn/temp$ ls system.imgaa*
system.imgaa system.imgaa.lzo
xxxxxx@yf153:~/projectName/out/target/product/cibn/temp$ ls system.imgaa* -al
-rw-rw-r-- 1 xxxxxx xxxxxx 157286400 7月 28 20:08 system.imgaa
-rw-rw-r-- 1 xxxxxx xxxxxx 95970609 7月 28 20:08 system.imgaa.lzo
可以看到命令：
split -b 150m system.img system.img // 按照150M进行拆分，生成文件system.img**
lzop -f -o system.imgaa.lzo system.imgaa本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
