需求： 在11.0的产品开发中，对于定制功能的需求很多，有些机型要求可以修改系统属性值，对于系统本身在10.0以后为了系统安全性，不允许修改ro开头的SystemProperties的值，所以如果要求修改ro的相关系统属性，就得看在设置SystemProperties的相关值的要求，修改这部分要求就可以了
动态修改SystemProperties中ro开头系统属性的值的核心代码
frameworks/base/core/java/android/os/SystemProperties.java
/system/core/init/property_service.cpp2.动态修改SystemProperties中ro开头系统属性的值的功能分析和实现功能
2.1 关于系统属性SystemProperty分析
系统属性，肯定对整个系统全局共享。通常程序的执行以进程为单位各自相互独立，如何实现全局共享呢？属性系统是android的一个重要特性。它作为一个服务运行，管理系统配置和状态。所有这些配置和状态都是属性。SystemProperties.java每个属性是一个键值对（key/value pair），其类型都是字符串
接下来看下SystemProperties.java相关方法
private static native String native_get(String key);
private static native String native_get(String key, String def);
private static native int native_get_int(String key, int def);
@UnsupportedAppUsage
private static native long native_get_long(String key, long def);
private static native boolean native_get_boolean(String key, boolean def);
private static native void native_set(String key, String def);
/**
* Get the String value for the given {@code key}.
*
* @param key the key to lookup
* @param def the default value in case the property is not set or empty
* @return if the {@code key} isn't found, return {@code def} if it isn't null, or an empty
* string otherwise
* @hide
*/
@NonNull
@SystemApi
@TestApi
public static String get(@NonNull String key, @Nullable String def) {
if (TRACK_KEY_ACCESS) onKeyAccess(key);
return native_get(key, def);
}
/**
* Get the value for the given {@code key}, and return as an integer.
*
* @param key the key to lookup
* @param def a default value to return
* @return the key parsed as an integer, or def if the key isn't found or
* cannot be parsed
* @hide
*/
@SystemApi
public static int getInt(@NonNull String key, int def) {
if (TRACK_KEY_ACCESS) onKeyAccess(key);
return native_get_int(key, def);
}
/**
* Get the value for the given {@code key}, and return as a long.
*
* @param key the key to lookup
* @param def a default value to return
* @return the key parsed as a long, or def if the key isn't found or
* cannot be parsed
* @hide
*/
@SystemApi
public static long getLong(@NonNull String key, long def) {
if (TRACK_KEY_ACCESS) onKeyAccess(key);
return native_get_long(key, def);
}
@SystemApi
@TestApi
public static boolean getBoolean(@NonNull String key, boolean def) {
if (TRACK_KEY_ACCESS) onKeyAccess(key);
return native_get_boolean(key, def);
}
/**
* Set the value for the given {@code key} to {@code val}.
*
* @throws IllegalArgumentException if the {@code val} exceeds 91 characters
* @hide
*/
@UnsupportedAppUsage
public static void set(@NonNull String key, @Nullable String val) {
if (val != null && !val.startsWith("ro.") && val.length() > PROP_VALUE_MAX) {
throw new IllegalArgumentException("value of system property '" + key
+ "' is longer than " + PROP_VALUE_MAX + " characters: " + val);
}
if (TRACK_KEY_ACCESS) onKeyAccess(key);
native_set(key, val);
}通过上述get()和set()发现 最终是通过jni的方法设置相关的值
最终通过查阅资料发现是在property_service.cpp中来设置系统相关属性的 接下来看下property_service.cpp
设置属性的相关代码
static uint32_t PropertySet(const std::string& name, const std::string& value, std::string* error) {
size_t valuelen = value.size();
if (!IsLegalPropertyName(name)) {
*error = "Illegal property name";
return PROP_ERROR_INVALID_NAME;
}
if (auto result = IsLegalPropertyValue(name, value); !result.ok()) {
*error = result.error().message();
return PROP_ERROR_INVALID_VALUE;
}
prop_info* pi = (prop_info*) __system_property_find(name.c_str());
if (pi != nullptr) {
// ro.* properties are actually "write-once".
// 判断是否ro开头的属性 这只为读的属性 不能修改值
if (StartsWith(name, "ro.")) {
*error = "Read-only property was already set";
return PROP_ERROR_READ_ONLY_PROPERTY;
}
__system_property_update(pi, value.c_str(), valuelen);
} else {
int rc = __system_property_add(name.c_str(), name.size(), value.c_str(), valuelen);
if (rc < 0) {
*error = "__system_property_add failed";
return PROP_ERROR_SET_FAILED;
}
}
// Don't write properties to disk until after we have read all default
// properties to prevent them from being overwritten by default values.
if (persistent_properties_loaded && StartsWith(name, "persist.")) {
WritePersistentProperty(name, value);
}
// If init hasn't started its main loop, then it won't be handling property changed messages
// anyway, so there's no need to try to send them.
auto lock = std::lock_guard{accept_messages_lock};
if (accept_messages) {
PropertyChanged(name, value);
}
return PROP_SUCCESS;
}
// This returns one of the enum of PROP_SUCCESS or PROP_ERROR*.
uint32_t HandlePropertySet(const std::string& name, const std::string& value,
const std::string& source_context, const ucred& cr,
SocketConnection* socket, std::string* error) {
if (auto ret = CheckPermissions(name, value, source_context, cr, error); ret != PROP_SUCCESS) {
return ret;
}
if (StartsWith(name, "ctl.")) {
return SendControlMessage(name.c_str() + 4, value, cr.pid, socket, error);
}
// sys.powerctl is a special property that is used to make the device reboot. We want to log
// any process that sets this property to be able to accurately blame the cause of a shutdown.
if (name == "sys.powerctl") {
std::string cmdline_path = StringPrintf("proc/%d/cmdline", cr.pid);
std::string process_cmdline;
std::string process_log_string;
if (ReadFileToString(cmdline_path, &process_cmdline)) {
// Since cmdline is null deliminated, .c_str() conveniently gives us just the process
// path.
process_log_string = StringPrintf(" (%s)", process_cmdline.c_str());
}
LOG(INFO) << "Received sys.powerctl='" << value << "' from pid: " << cr.pid
<< process_log_string;
if (value == "reboot,userspace" && !is_userspace_reboot_supported().value_or(false)) {
*error = "Userspace reboot is not supported by this device";
return PROP_ERROR_INVALID_VALUE;
}
}
// If a process other than init is writing a non-empty value, it means that process is
// requesting that init performs a restorecon operation on the path specified by 'value'.
// We use a thread to do this restorecon operation to prevent holding up init, as it may take
// a long time to complete.
if (name == kRestoreconProperty && cr.pid != 1 && !value.empty()) {
static AsyncRestorecon async_restorecon;
async_restorecon.TriggerRestorecon(value);
return PROP_SUCCESS;
}
return PropertySet(name, value, error);
}
uint32_t InitPropertySet(const std::string& name, const std::string& value) {
uint32_t result = 0;
ucred cr = {.pid = 1, .uid = 0, .gid = 0};//获取cr参数
std::string error;
result = HandlePropertySet(name, value, kInitContext, cr, nullptr, &error);
if (result != PROP_SUCCESS) {
LOG(ERROR) << "Init cannot set '" << name << "' to '" << value << "': " << error;
}
return result;
}在进入property_service修改系统属性时，先调用InitPropertySet(const std::string& name, const std::string& value)
在通过HandlePropertySet(name, value, kInitContext, cr, nullptr, &error) 来获取返回值
在HandlePropertySet(）中根据参数name的值分别调用相关的方法来设置值ro 开头的值 最终是由
PropertySet(name, value, error);来设置值时会判断ro开头的值 只读不让修改 所以要修改就去了这个限制文章来源：https://www.toymoban.com/news/detail-447188.html
具体修改为:文章来源地址https://www.toymoban.com/news/detail-447188.html
static uint32_t PropertySet(const std::string& name, const std::string& value, std::string* error) {
size_t valuelen = value.size();
if (!IsLegalPropertyName(name)) {
*error = "Illegal property name";
return PROP_ERROR_INVALID_NAME;
}
if (auto result = IsLegalPropertyValue(name, value); !result.ok()) {
*error = result.error().message();
return PROP_ERROR_INVALID_VALUE;
}
prop_info* pi = (prop_info*) __system_property_find(name.c_str());
if (pi != nullptr) {
// ro.* properties are actually "write-once".
// 判断是否ro开头的属性 这只为读的属性 不能修改值
// 修改开始 注释掉这部分代码
/* if (StartsWith(name, "ro.")) {
*error = "Read-only property was already set";
return PROP_ERROR_READ_ONLY_PROPERTY;
}*/
// 修改完毕
__system_property_update(pi, value.c_str(), valuelen);
} else {
int rc = __system_property_add(name.c_str(), name.size(), value.c_str(), valuelen);
if (rc < 0) {
*error = "__system_property_add failed";
return PROP_ERROR_SET_FAILED;
}
}
// Don't write properties to disk until after we have read all default
// properties to prevent them from being overwritten by default values.
if (persistent_properties_loaded && StartsWith(name, "persist.")) {
WritePersistentProperty(name, value);
}
// If init hasn't started its main loop, then it won't be handling property changed messages
// anyway, so there's no need to try to send them.
auto lock = std::lock_guard{accept_messages_lock};
if (accept_messages) {
PropertyChanged(name, value);
}
return PROP_SUCCESS;
}到了这里，关于Android 11.0 动态修改SystemProperties中ro开头系统属性的值的文章就介绍完了。如果您还想了解更多内容，请在右上角搜索TOY模板网以前的文章或继续浏览下面的相关文章，希望大家以后多多支持TOY模板网！
