android build system中product的继承(inherit-product)，加载(import-products)和选择(lunch)
一、前言
android源码中有很多product，进行配置时，会将源码中所有product的信息都读进来(不用的product的信息也会被读进来)，其中每个product，可以包含如下信息
#
# Functions for including product makefiles
#
_product_var_list := \
PRODUCT_NAME \
PRODUCT_MODEL \
PRODUCT_LOCALES \
PRODUCT_AAPT_CONFIG \
PRODUCT_AAPT_PREF_CONFIG \
PRODUCT_AAPT_PREBUILT_DPI \
PRODUCT_PACKAGES \
PRODUCT_PACKAGES_DEBUG \
PRODUCT_PACKAGES_ENG \
PRODUCT_PACKAGES_TESTS \
PRODUCT_DEVICE \
PRODUCT_MANUFACTURER \
PRODUCT_BRAND \
PRODUCT_PROPERTY_OVERRIDES \
PRODUCT_DEFAULT_PROPERTY_OVERRIDES \
PRODUCT_CHARACTERISTICS \
PRODUCT_COPY_FILES \
PRODUCT_OTA_PUBLIC_KEYS \
PRODUCT_EXTRA_RECOVERY_KEYS \
PRODUCT_PACKAGE_OVERLAYS \
DEVICE_PACKAGE_OVERLAYS \
PRODUCT_SDK_ATREE_FILES \
PRODUCT_SDK_ADDON_NAME \
PRODUCT_SDK_ADDON_COPY_FILES \
PRODUCT_SDK_ADDON_COPY_MODULES \
PRODUCT_SDK_ADDON_DOC_MODULES \
PRODUCT_SDK_ADDON_SYS_IMG_SOURCE_PROP \
PRODUCT_DEFAULT_WIFI_CHANNELS \
PRODUCT_DEFAULT_DEV_CERTIFICATE \
PRODUCT_RESTRICT_VENDOR_FILES \
PRODUCT_VENDOR_KERNEL_HEADERS \
PRODUCT_BOOT_JARS \
PRODUCT_SUPPORTS_BOOT_SIGNER \
PRODUCT_SUPPORTS_VBOOT \
PRODUCT_SUPPORTS_VERITY \
PRODUCT_SUPPORTS_VERITY_FEC \
PRODUCT_OEM_PROPERTIES \
PRODUCT_SYSTEM_PROPERTY_BLACKLIST \
PRODUCT_SYSTEM_SERVER_JARS \
PRODUCT_VBOOT_SIGNING_KEY \
PRODUCT_VBOOT_SIGNING_SUBKEY \
PRODUCT_VERITY_SIGNING_KEY \
PRODUCT_SYSTEM_VERITY_PARTITION \
PRODUCT_VENDOR_VERITY_PARTITION \
PRODUCT_DEX_PREOPT_MODULE_CONFIGS \
PRODUCT_DEX_PREOPT_DEFAULT_FLAGS \
PRODUCT_DEX_PREOPT_BOOT_FLAGS \
PRODUCT_SANITIZER_MODULE_CONFIGS \
PRODUCT_SYSTEM_BASE_FS_PATH \
PRODUCT_VENDOR_BASE_FS_PATH \
PRODUCT_SHIPPING_API_LEVEL \lunch时，比如选择了aosp_arm-eng这个product，那么build system能找到对应的Makefile为build/target/product/aosp_arm.mkaosp_arm.mk(后面将介绍如何找)，从而可以获得aosp_arm-eng产品对应的PRODUCT_PACKAGES、PRODUCT_PROPERTY_OVERRIDES等信息，从而可以进行编译
不同的product，有一些公用的信息，如何复用这些公用的信息，是一个问题
比较直观的做法是使用include，但是会带来一些问题：
1、假如A.mk中定义PRODUCT_PACKAGES := liba.so；B.mk中定义PRODUCT_PACKAGES := libb.so。C.mk想同时编译A.mk和B.mk中指定的模块，在C.mk中先include A，再include B，得到的是PRODUCT_PACKAGES := libb.so，但是我们想要的是PRODUCT_PACKAGES := liba.so libb.so
2、重复include同一个文件的问题
所以android使用了inherit-product的方式，去处理这个问题
二、inherit-product
打开build/target/product/aosp_arm.mk可以看到：
include $(SRC_TARGET_DIR)/product/full.mk
PRODUCT_NAME := aosp_arm$(call inherit-product, $(SRC_TARGET_DIR)/product/aosp_base_telephony.mk)
$(call inherit-product, $(SRC_TARGET_DIR)/board/generic/device.mk)
include $(SRC_TARGET_DIR)/product/emulator.mk
# Overrides
PRODUCT_NAME := full
PRODUCT_DEVICE := generic
PRODUCT_BRAND := Android
PRODUCT_MODEL := AOSP on ARM Emulatoraosp_base_telephony.mk和device.mk包含了一些比较通用的信息
inherit-product的定义为：
#
# $(1): product to inherit
#
# Does three things:
# 1. Inherits all of the variables from $1.
# 2. Records the inheritance in the .INHERITS_FROM variable
# 3. Records that we've visited this node, in ALL_PRODUCTS
#
define inherit-product
$(if $(findstring ../,$(1)),\
$(eval np := $(call normalize-paths,$(1))),\
$(eval np := $(strip $(1))))\
$(foreach v,$(_product_var_list), \
$(eval $(v) := $($(v)) $(INHERIT_TAG)$(np))) \
$(eval inherit_var := \
PRODUCTS.$(strip $(word 1,$(_include_stack))).INHERITS_FROM) \
$(eval $(inherit_var) := $(sort $($(inherit_var)) $(np))) \
$(eval inherit_var:=) \
$(eval ALL_PRODUCTS := $(sort $(ALL_PRODUCTS) $(word 1,$(_include_stack))))
endef $(if $(findstring ../,$(1)),\
$(eval np := $(call normalize-paths,$(1))),\
$(eval np := $(strip $(1))))\对于product的每一个信息，记录下信息需要从哪些文件继承
$(foreach v,$(_product_var_list), \
$(eval $(v) := $($(v)) $(INHERIT_TAG)$(np))) \经过上述for循环的处理后，Makefile中包含了这样的代码
PRODUCT_PACKAGES := @inherit:
PRODUCT_PROPERTY_OVERRIDES := @inherit:
......
这里的@inherit只是一个标记，目前还没有起到什么作用。所以inherit-product命令是用来打一些标记，记录继承关系的，在这里并不会执行被继承的.mk文件
这些@inherit的标记是在import-products中进行处理的
后面的几行是定义了一些变量，用于记录一些信息，可以在调试函数中打印出来
三、import-products
我们需要找到android源码中所有product所对应的Makefile，而product对应的Makefile是记录在AndroidProducts.mk文件中的，比如build/target/product/AndroidProducts.mk：
PRODUCT_MAKEFILES := \
$(LOCAL_DIR)/aosp_arm.mk \
$(LOCAL_DIR)/full.mk \
$(LOCAL_DIR)/generic_armv5.mk \
$(LOCAL_DIR)/emulator_phone.mk \
$(LOCAL_DIR)/full_x86.mk \
$(LOCAL_DIR)/aosp_mips.mk \
$(LOCAL_DIR)/full_mips.mk \
$(LOCAL_DIR)/aosp_arm64.mk \
$(LOCAL_DIR)/aosp_mips64.mk \
$(LOCAL_DIR)/aosp_x86_64.mk所以，我们需要先找到android源码中所有的AndroidProducts.mk，调用_find-android-products-files函数，即可在device(推荐位置)，vendor(旧的位置)，product(旧的位置)目录下搜索AndroidProducts.mk，再加上一个默认的$(SRC_TARGET_DIR)/product/AndroidProducts.mk
#
# Functions for including AndroidProducts.mk files
# PRODUCT_MAKEFILES is set up in AndroidProducts.mks.
# Format of PRODUCT_MAKEFILES:
# :
# If the is the same as the base file name (without dir
# and the .mk suffix) of the product makefile, ":" can be
# omitted.
# Search for AndroidProducts.mks in the given dir.
# $(1): the path to the dir
define _search-android-products-files-in-dir
$(sort $(shell test -d $(1) && find -L $(1) \
-maxdepth 6 \
-name .git -prune \
-o -name AndroidProducts.mk -print))
endef
#
# Returns the list of all AndroidProducts.mk files.
# $(call ) isn't necessary.
#
define _find-android-products-files
$(foreach d, device vendor product,$(call _search-android-products-files-in-dir,$(d))) \
$(SRC_TARGET_DIR)/product/AndroidProducts.mk
endef 找到所有的AndroidProducts.mk之后，调用get-all-product-makefiles函数，可以得到所有的AndroidProducts.mk中定义的PRODUCT_MAKEFILES，也就可以得到所有product的Makefile
#
# Returns the sorted concatenation of PRODUCT_MAKEFILES
# variables set in the given AndroidProducts.mk files.
# $(1): the list of AndroidProducts.mk files.
#
define get-product-makefiles
$(sort \
$(foreach f,$(1), \
$(eval PRODUCT_MAKEFILES :=) \
$(eval LOCAL_DIR := $(patsubst %/,%,$(dir $(f)))) \
$(eval include $(f)) \
$(PRODUCT_MAKEFILES) \
) \
$(eval PRODUCT_MAKEFILES :=) \
$(eval LOCAL_DIR :=) \
)
endef
#
# Returns the sorted concatenation of all PRODUCT_MAKEFILES
# variables set in all AndroidProducts.mk files.
# $(call ) isn't necessary.
#
define get-all-product-makefiles
$(call get-product-makefiles,$(_find-android-products-files))
endef然后调用import-products，导入所有产品的信息
#
# $(1): product makefile list
#
#TODO: check to make sure that products have all the necessary vars defined
define import-products
$(call import-nodes,PRODUCTS,$(1),$(_product_var_list))
endefimport-nodes函数的第一个参数是一个前缀，第二个参数是所有prodcut的Makefile，第三个参数是_product_var_list
#
# $(1): output list variable name, like "PRODUCTS" or "DEVICES"
# $(2): list of makefiles representing nodes to import
# $(3): list of node variable names
#
define import-nodes
$(if \
$(foreach _in,$(2), \
$(eval _node_import_context := _nic.$(1).[[$(_in)]]) \
$(if $(_include_stack),$(eval $(error ASSERTION FAILED: _include_stack \
should be empty here: $(_include_stack))),) \
$(eval _include_stack := ) \
$(call _import-nodes-inner,$(_node_import_context),$(_in),$(3)) \
$(call move-var-list,$(_node_import_context).$(_in),$(1).$(_in),$(3)) \
$(eval _node_import_context :=) \
$(eval $(1) := $($(1)) $(_in)) \
$(if $(_include_stack),$(eval $(error ASSERTION FAILED: _include_stack \
should be empty here: $(_include_stack))),) \
) \
,)
endefif是检查，可以先不看
_node_import_context有点像结构体，和一个product对应。
_node_import_context.
$(_node_import_context).
$(_node_import_context).
在_import-node函数中，会真正得去include某个.mk，得到该.mk中PRODUCT_PACKAGES这样的变量的值，并通过copy-var-list，保存为$(_node_import_context).
然后在$(_node_import_context).
由于继承可以有多层，所以会有递归调用_import-node和_import-nodes-inner。
通过_expand-inherited-values函数，使用真实值替换每一层的@inherit:标记。
最终将得到某个product完整的信息，记录在product的主Makefile对应的$(_node_import_context).
import-nodes函数最后，通过move-var-list函数，将记录在product的主Makefile对应的$(_node_import_context).
#
# $(1): context prefix
# $(2): makefile representing this node
# $(3): list of node variable names
#
# _include_stack contains the list of included files, with the most recent files first.
define _import-node
$(eval _include_stack := $(2) $$(_include_stack))
$(call clear-var-list, $(3))
$(eval LOCAL_PATH := $(patsubst %/,%,$(dir $(2))))
$(eval MAKEFILE_LIST :=)
$(eval include $(2))
$(eval _included := $(filter-out $(2),$(MAKEFILE_LIST)))
$(eval MAKEFILE_LIST :=)
$(eval LOCAL_PATH :=)
$(call copy-var-list, $(1).$(2), $(3))
$(call clear-var-list, $(3))
$(eval $(1).$(2).inherited := \
$(call get-inherited-nodes,$(1).$(2),$(3)))
$(call _import-nodes-inner,$(1),$($(1).$(2).inherited),$(3))
$(call _expand-inherited-values,$(1),$(2),$(3))
$(eval $(1).$(2).inherited :=)
$(eval _include_stack := $(wordlist 2,9999,$$(_include_stack)))
endef
#
# This will generate a warning for _included above
# $(if $(_included), \
# $(eval $(warning product spec file: $(2)))\
# $(foreach _inc,$(_included),$(eval $(warning $(space)$(space)$(space)includes: $(_inc)))),)
#
#
# $(1): context prefix
# $(2): list of makefiles representing nodes to import
# $(3): list of node variable names
#
#TODO: Make the "does not exist" message more helpful;
# should print out the name of the file trying to include it.
define _import-nodes-inner
$(foreach _in,$(2), \
$(if $(wildcard $(_in)), \
$(if $($(1).$(_in).seen), \
$(eval ### "skipping already-imported $(_in)") \
, \
$(eval $(1).$(_in).seen := true) \
$(call _import-node,$(1),$(strip $(_in)),$(3)) \
) \
, \
$(error $(1): "$(_in)" does not exist) \
) \
)
endef如何解析之前的PRODUCT_PACKAGES := @inherit:
INHERIT_TAG := @inherit:
#
# Walks through the list of variables, each qualified by the prefix,
# and finds instances of words beginning with INHERIT_TAG. Scrape
# off INHERIT_TAG from each matching word, and return the sorted,
# unique set of those words.
#
# E.g., given
# PREFIX.A := A $(INHERIT_TAG)aaa B C
# PREFIX.B := B $(INHERIT_TAG)aaa C $(INHERIT_TAG)bbb D E
# Then
# $(call get-inherited-nodes,PREFIX,A B)
# returns
# aaa bbb
#
# $(1): variable prefix
# $(2): list of variables to check
#
define get-inherited-nodes
$(sort \
$(subst $(INHERIT_TAG),, \
$(filter $(INHERIT_TAG)%, \
$(foreach v,$(2),$($(1).$(v))) \
)))
endef
基于$(_node_import_context).
PRODUCT_PACKAGES := @inherit:
递归的每一层处理一次，最终将替换所有的@inherit:标记，得到最终的值，记录在product的主Makefile对应的$(_node_import_context).
#
# for each variable ( (prefix + name) * vars ):
# get list of inherited words; if not empty:
# for each inherit:
# replace the first occurrence with (prefix + inherited + var)
# clear the source var so we can't inherit the value twice
#
# $(1): context prefix
# $(2): name of this node
# $(3): list of variable names
#
define _expand-inherited-values
$(foreach v,$(3), \
$(eval ### "Shorthand for the name of the target variable") \
$(eval _eiv_tv := $(1).$(2).$(v)) \
$(eval ### "Get the list of nodes that this variable inherits") \
$(eval _eiv_i := \
$(sort \
$(patsubst $(INHERIT_TAG)%,%, \
$(filter $(INHERIT_TAG)%, $($(_eiv_tv)) \
)))) \
$(foreach i,$(_eiv_i), \
$(eval ### "Make sure that this inherit appears only once") \
$(eval $(_eiv_tv) := \
$(call uniq-word,$($(_eiv_tv)),$(INHERIT_TAG)$(i))) \
$(eval ### "Expand the inherit tag") \
$(eval $(_eiv_tv) := \
$(strip \
$(patsubst $(INHERIT_TAG)$(i),$($(1).$(i).$(v)), \
$($(_eiv_tv))))) \
$(eval ### "Clear the child so DAGs don't create duplicate entries" ) \
$(eval $(1).$(i).$(v) :=) \
$(eval ### "If we just inherited ourselves, it's a cycle.") \
$(if $(filter $(INHERIT_TAG)$(2),$($(_eiv_tv))), \
$(warning Cycle detected between "$(2)" and "$(i)" for context "$(1)") \
$(error import of "$(2)" failed) \
) \
) \
) \
$(eval _eiv_tv :=) \
$(eval _eiv_i :=)
endef四、lunch
执行source build/envsetup.sh时，会定义lunch函数和add_lunch_combo函数。执行lunch时，可以列出所有的产品，可以进行选择。add_lunch_combo是用来添加新的产品的，否则是无法在lunch时看到的。
在build/envsetup.sh的最后，有如下代码，搜索每一款产品所对应的vendorsetup.sh并执行，vendorsetup.sh中就包含了add_lunch_combo的调用，将本产品添加到lunch菜单中
# Execute the contents of any vendorsetup.sh files we can find.
for f in `test -d device && find -L device -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort` \
`test -d vendor && find -L vendor -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort` \
`test -d product && find -L product -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort`
do
echo "including $f"
. $f
done当我们lunch aosp_arm-eng时，lunch函数中会分隔得到TARGET_PRODUCT=aosp_arm，TARGET_BUILD_VARIANT=eng
五、使用product特定的信息
以PRODUCT_PACKAGES为例，如何得知aosp_arm-eng这个产品，需要编译哪些模块呢？
build/core/main.mk文件中的product_MODULES是需要编译的所有的模块，通过如下代码赋值
product_MODULES := $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES)INTERNAL_PRODUCT应当是build/target/product/aosp_arm.mk，从而我们可以使用之前得到的PRODUCTS.build/target/product/aosp_arm.mk.PRODUCT_PACKAGES变量
但是如何得知INTERNAL_PRODUCT是build/target/product/aosp_arm.mk呢，通过遍历所以产品的Makefile，找到PRODUCT_NAME和TARGET_PRODUCT相等的那个产品的Makefile即可
INTERNAL_PRODUCT := $(call resolve-short-product-name, $(TARGET_PRODUCT))
#
# Returns the product makefile path for the product with the provided name
#
# $(1): short product name like "generic"
#
define _resolve-short-product-name
$(eval pn := $(strip $(1)))
$(eval p := \
$(foreach p,$(PRODUCTS), \
$(if $(filter $(pn),$(PRODUCTS.$(p).PRODUCT_NAME)), \
$(p) \
)) \
)
$(eval p := $(sort $(p)))
$(if $(filter 1,$(words $(p))), \
$(p), \
$(if $(filter 0,$(words $(p))), \
$(error No matches for product "$(pn)"), \
$(error Product "$(pn)" ambiguous: matches $(p)) \
) \
)
endef
define resolve-short-product-name
$(strip $(call _resolve-short-product-name,$(1)))
endef这样，android build system就完成了product的继承，所有product的载入，以及根据lunch的product，找到需要编译的product的信息
参考：
http://baohaojun.github.io/blog/2012/09/17/Android-Product-Makefiles.html