Android的属性系统

网上有一篇文章介绍了Android的属性系统（http://blog.youkuaiyun.com/tekkamanitachi/archive/2009/06/18/4280982.aspx），我现在对其进行补充：

1. android现在好像只有/ default.prop，/system/build.prop两个文件，别的两个文件找不到

2. /data/property下有4个prop文件：persist.sys.timezone,persist.sys.language,persist.sys.country,persist.sys.localevar，里面保存着属性名称以“persist.”开头的属性值。

3. libcutils的源码位于system/core/libcutils/下面，获取和设置属性的代码在properties.c里面，读取属性通过读共享内存得到，设置属性通过发送请求到property_service进行设置。

4. 相关的函数有property_set，property_get，property_list。

5. 属性系统的初始化通过__system_properties_init函数完成，__system_properties_init函数代码如下：

int __system_properties_init(void) { prop_area *pa; int s, fd; unsigned sz; char *env; if(__system_property_area__ != ((void*) &dummy_props)) { return 0; } env = getenv("ANDROID_PROPERTY_WORKSPACE"); if (!env) { return -1; } fd = atoi(env); env = strchr(env, ','); if (!env) { return -1; } sz = atoi(env + 1); pa = mmap(0, sz, PROT_READ, MAP_SHARED, fd, 0); if(pa == MAP_FAILED) { return -1; } if((pa->magic != PROP_AREA_MAGIC) || (pa->version != PROP_AREA_VERSION)) { munmap(pa, sz); return -1; } __system_property_area__ = pa; return 0; } 

可以看到首先从环境变量里面获取ANDROID_PROPERTY_WORKSPACE，ANDROID_PROPERTY_WORKSPACE的值为如下形式：ANDROID_PROPERTY_WORKSPACE=9,32768。然后获取共享内存的文件句柄和长度，最后对共享内存进行检查并设置全局变量__system_property_area__的值，property_get就是从__system_property_area__里面读取的属性值。环境变量的初始化在init.c的service_start函数里面。

6. /init.rc里面有设置属性的代码，例如：

# Define the oom_adj values for the classes of processes that can be

# killed by the kernel. These are used in ActivityManagerService.

setprop ro.FOREGROUND_APP_ADJ 0

setprop ro.VISIBLE_APP_ADJ 1

setprop ro.SECONDARY_SERVER_ADJ 2

setprop ro.HOME_APP_ADJ 4

setprop ro.HIDDEN_APP_MIN_ADJ 7

setprop ro.CONTENT_PROVIDER_ADJ 14

setprop ro.EMPTY_APP_ADJ 15

7. 通过property_list可以枚举所有的属性，下面是一段打印所有属性的代码。

#include <cutils/properties.h> #include <stdio.h> void print_prop(const char* key,const char* value,void* cookie) { printf("key=%s,value=%s/n",key,value); } int main() { property_list(print_prop,NULL); } 

Android.mk文件：

LOCAL_PATH:= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_SRC_FILES:= /

list_property.cpp /

LOCAL_SHARED_LIBRARIES := /

libcutils /

libutils /

LOCAL_MODULE:= list_prop

include $(BUILD_EXECUTABLE)

include $(call all-makefiles-under,$(LOCAL_PATH))

所有的属性如下：

key=ro.secure,value=0

key=ro.allow.mock.location,value=1

key=ro.debuggable,value=1

key=persist.service.adb.enable,value=1

key=ro.kernel.qemu,value=1

key=ro.kernel.console,value=ttyS0

key=ro.kernel.android.checkjni,value=1

key=ro.kernel.android.qemud,value=ttyS1

key=ro.factorytest,value=0

key=ro.serialno,value=

key=ro.bootmode,value=unknown

key=ro.baseband,value=unknown

key=ro.carrier,value=unknown

key=ro.bootloader,value=unknown

key=ro.hardware,value=goldfish

key=ro.revision,value=0

key=ro.build.id,value=CUPCAKE

key=ro.build.display.id,value=sdk-eng 1.5 CUPCAKE 148875 test-keys

key=ro.build.version.incremental,value=148875

key=ro.build.version.sdk,value=3

key=ro.build.version.release,value=1.5

key=ro.build.date,value=Thu May 14 17:29:49 PDT 2009

key=ro.build.date.utc,value=1242347389

key=ro.build.type,value=eng

key=ro.build.user,value=android-build

key=ro.build.host,value=e-honda.mtv.corp.google.com

key=ro.build.tags,value=test-keys

key=ro.product.model,value=sdk

key=ro.product.brand,value=generic

key=ro.product.name,value=sdk

key=ro.product.device,value=generic

key=ro.product.board,value=

key=ro.product.manufacturer,value=unknown

key=ro.product.locale.language,value=en

key=ro.product.locale.region,value=US

key=ro.board.platform,value=

key=ro.build.product,value=generic

key=ro.build.description,value=sdk-eng 1.5 CUPCAKE 148875 test-keys

key=ro.build.fingerprint,value=generic/sdk/generic/:1.5/CUPCAKE/148875:eng/test-keys

key=rild.libpath,value=/system/lib/libreference-ril.so

key=rild.libargs,value=-d /dev/ttyS0

key=ro.config.notification_sound,value=F1_New_SMS.ogg

key=xmpp.auto-presence,value=true

key=ro.config.nocheckin,value=yes

key=net.bt.name,value=Android

key=net.change,value=net.gprs.local-ip

key=dalvik.vm.stack-trace-file,value=/data/anr/traces.txt

key=persist.sys.timezone,value=GMT

key=persist.sys.language,value=en

key=persist.sys.country,value=US

key=persist.sys.localevar,value=

key=ro.FOREGROUND_APP_ADJ,value=0

key=ro.VISIBLE_APP_ADJ,value=1

key=ro.SECONDARY_SERVER_ADJ,value=2

key=ro.HOME_APP_ADJ,value=4

key=ro.HIDDEN_APP_MIN_ADJ,value=7

key=ro.CONTENT_PROVIDER_ADJ,value=14

key=ro.EMPTY_APP_ADJ,value=15

key=ro.FOREGROUND_APP_MEM,value=1536

key=ro.VISIBLE_APP_MEM,value=2048

key=ro.SECONDARY_SERVER_MEM,value=4096

key=ro.HOME_APP_MEM,value=4096

key=ro.HIDDEN_APP_MEM,value=5120

key=ro.CONTENT_PROVIDER_MEM,value=5632

key=ro.EMPTY_APP_MEM,value=6144

key=net.tcp.buffersize.default,value=4096,87380,110208,4096,16384,110208

key=net.tcp.buffersize.wifi,value=4095,87380,110208,4096,16384,110208

key=net.tcp.buffersize.umts,value=4094,87380,110208,4096,16384,110208

key=net.tcp.buffersize.edge,value=4093,26280,35040,4096,16384,35040

key=net.tcp.buffersize.gprs,value=4092,8760,11680,4096,8760,11680

key=init.svc.console,value=running

key=init.svc.servicemanager,value=running

key=init.svc.vold,value=running

key=init.svc.debuggerd,value=running

key=init.svc.ril-daemon,value=running

key=init.svc.zygote,value=running

key=init.svc.media,value=running

key=init.svc.installd,value=running

key=init.svc.flash_recovery,value=stopped

key=init.svc.goldfish-setup,value=stopped

key=init.svc.qemud,value=stopped

key=init.svc.goldfish-logcat,value=stopped

key=ARGH,value=ARGH

key=net.eth0.dns1,value=10.0.2.3

key=net.gprs.local-ip,value=10.0.2.15

key=ro.radio.use-ppp,value=no

key=status.battery.state,value=Slow

key=status.battery.level,value=5

key=status.battery.level_raw,value=50

key=status.battery.level_scale,value=9

key=ro.setupwizard.mode,value=EMULATOR

key=ro.com.google.locationfeatures,value=1

key=init.svc.adbd,value=running

key=ro.qemu.init.completed,value=1

key=hw.keyboards.65536.devname,value=qwerty2

key=sys.settings_secure_version,value=2

key=dev.bootcomplete,value=1

key=sys.settings_system_version,value=6

key=gsm.sim.operator.numeric,value=

key=gsm.sim.operator.alpha,value=

key=gsm.sim.operator.iso-country,value=

key=gsm.sim.state,value=UNKNOWN

key=adb.connected,value=1