rrayList<FeatureInfo> res = new ArrayList<>(mAvailableFeatures.values());
final FeatureInfo fi = new FeatureInfo();
fi.reqGlEsVersion = SystemProperties.getInt("ro.opengles.version",
FeatureInfo.GL_ES_VERSION_UNDEFINED);
res.add(fi);
return new ParceledListSlice<>(res);
}
}
@Override
public boolean hasSystemFeature(String name, int version) {
synchronized (mPackages) {
final FeatureInfo feat = mAvailableFeatures.get(name);
if (feat == null) {
return false;
} else {
return feat.version >= version;
}
}
}
这里的逻辑都是通过mAvailableFeatures得到所有的feature，查找该成员变量的相关代码
final ArrayMap<String, FeatureInfo> mAvailableFeatures;
SystemConfig systemConfig = SystemConfig.getInstance();
mGlobalGids = systemConfig.getGlobalGids();
mSystemPermissions = systemConfig.getSystemPermissions();
mAvailableFeatures = systemConfig.getAvailableFeatures();
了解到，首先获取一个SystemConfig的单例，然后通过getAvailableFeatures方法获取可用的feature。
SystemConfig.java
// These are the features this devices supports that were read from the
// system configuration files.
final ArrayMap<String, FeatureInfo> mAvailableFeatures = new ArrayMap<>();
public ArrayMap<String, FeatureInfo> getAvailableFeatures() {
return mAvailableFeatures;
}
private void addFeature(String name, int version) {
FeatureInfo fi = mAvailableFeatures.get(name);
if (fi == null) {
fi = new FeatureInfo();
fi.name = name;
fi.version = version;
mAvailableFeatures.put(name, fi);
} else {
fi.version = Math.max(fi.version, version);
}
}
private void removeFeature(String name) {
if (mAvailableFeatures.remove(name) != null) {
Slog.d(TAG, "Removed unavailable feature " + name);
}
}
根据mAvailableFeatures的注释，设备支持的feature是从配置文件里读取出来的。调用读取配置文件的地方是：
SystemConfig() {
// Read configuration from system
readPermissions(Environment.buildPath(
Environment.getRootDirectory(), "etc", "sysconfig"), ALLOW_ALL);
// Read configuration from the old permissions dir
readPermissions(Environment.buildPath(
Environment.getRootDirectory(), "etc", "permissions"), ALLOW_ALL);
// Allow ODM to customize system configs around libs, features and apps
int odmPermissionFlag = ALLOW_LIBS | ALLOW_FEATURES | ALLOW_APP_CONFIGS;
readPermissions(Environment.buildPath(
Environment.getOdmDirectory(), "etc", "sysconfig"), odmPermissionFlag);
readPermissions(Environment.buildPath(
Environment.getOdmDirectory(), "etc", "permissions"), odmPermissionFlag);
// Only allow OEM to customize features
readPermissions(Environment.buildPath(
Environment.getOemDirectory(), "etc", "sysconfig"), ALLOW_FEATURES);
readPermissions(Environment.buildPath(
Environment.getOemDirectory(), "etc", "permissions"), ALLOW_FEATURES);
}
到此就很明白了，它是读取了几个目录：
- /system/etc/permission
- /system/etc/sysconfig
- /oem/etc/permission
- /oem/etc/sysconfig
- /odm/etc/permission
- /odm/etc/sysconfig
然后遍历xml文件，进行解析处理。SystemFeature就是解析的Feature标签。
最后再总结一下加载流程：
屏蔽SystemFeature
知道原理就好做了，在系统扫描的几个目录中使用grep命令查找控制打印机的字串，找到:
/system/etc/permission/handheld_core_hardware.xml
<!-- basic system services -->
<feature name="an