1 Android netd DNS
libcore/ojluni/src/main/java/java/net/InetAddress.java
netd中dns server设置文件：ResolverController.cpp
netd中域名解析文件：DnsProxyListener.cpp
Figure 1-1 Android netd DNS
2 libc DNS解析函数
bionic/libc/dns/net/getaddrinfo.c
getaddrinfo()
bionic/libc/dns/net/getnameinfo.c
getnameinfo()
bionic/libc/dns/net/gethnamaddr.c
gethostbyname()
通过netd获取DNS服务器的IP地址（Ubuntu通过进程dnsmasq和配置文件/etc/resolv.conf），然后构建DNS请求包，查询域名对应的IP地址，并且按照netid的分类缓存到netd中：
bionic/libc/dns/net/gethnamaddr.c
gethostbyname_internal_real()
3 ndc
3.1 查询可用命令表
ndc interface list
3.2 清除netd DNS缓存
ndc resolver flushif eth0
ndc resolver flushdefaultif -- flush default DNS resolver
Android 8.0没有导出刷新DNS缓存的接口，可以调用如下API添加。
bionic/libc/dns/resolv/res_cache.c
_resolv_flush_cache_for_net(netId)
3.3 设置netd DNS
ndc resolver setnetdns <netid> <domain> <dns1> <dns2> ...
ndc resolver setnetdns eth0 "" 8.8.8.8 192.168.1.1
ndc resolver setnetdns eth0 localdomain 8.8.8.8 192.168.1.1
4 URLs
Android DNS解析
https://blog.csdn.net/fcability/article/details/44676929
cernekee/dnsproxy2
https://github.com/cernekee/dnsproxy2
5 Abbreviations
mdnsd: multicast DNS，组播DNS
ndc：Native Daemon Connector
ojluni：Android libcore中的模块，包含OpenJDK、Language、Util、Net、IO
