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最近在调android ethernet功能，android本身不带 ethernet 功能，需要打patch。这个patch可以在setting里出来 ethernet configuration 选项。即添加了用户配置IP的功能。

我打上patch之后，点击选上DHCP功能，结果路由器一直不能自动分配IP。

经检测，命令行里运行 netcfg eth0 up dhcp 时，ethernet能被正常启动，DHCP能分配到IP。

但是Setting里选上时，dhcp却不能正常分配IP。 这很费解，我先后查看了，

/system/core/libnetutils/*

/externel/dhcpcd/* 

发现都没什么问题。

在Setting中点击turn on ethernet选项时，从log看到能调到

E/EthernetStateTracker( 185): DhcpHandler: DHCP request failed: Timed out waiting for dhcpcd to start
D/EthernetStateTracker( 185): DhcpHandler: DHCP request started

说明patch是好的能正常工作，能正常掉用dhcp，只是DHCP运行不成功。

然后我查了 getprop: 显示 init.svc.dhcpcd_eth0 = stop

正常应该是running的，这样DHCP 才能运行成功。

最后调试了两天，才搞明白，原来是 init.rc 中 dhcpcd_eth0 守护进程的问题：

改成：

on property:init.svc.dhcpcd_eth0=stopped
    start dhcpcd_eth0

service dhcpcd_eth0 /system/bin/dhcpcd -ABKL -f /system/etc/dhcpcd/dhcpcd.conf -d eth0
    class main
    disabled
    oneshot

这样就可以了。

这时init.svc.dhcpcd_eth0 就会是 running 了。这时再点击Setting -> ethernet configuration, DHCP就能正常分配IP了。

libnetutils 和dhcpcd 调用过程如下：

1. libnetutils 调用过程：

jni
=>runDhcp
=>android_net_utils_runDhcp
libs/netutils/dhcp_utils.c
=>dhcp_do_request
=>
static const char DAEMON_NAME[] = "dhcpcd";
static const char DAEMON_PROP_NAME[] = "init.svc.dhcpcd";
static const char DHCP_PROP_NAME_PREFIX[] = "dhcp";
const char *ctrl_prop = "ctl.start";
const char *desired_status = "running";
snprintf(result_prop_name, sizeof(result_prop_name), "%s.%s.result",
DHCP_PROP_NAME_PREFIX,
interface);
property_set(result_prop_name, "");//设置dhcp.eth0.result="";等到成功完成dhcp之后,
property_set(ctrl_prop, DAEMON_NAME);//向名字为dhcpcd的service,发送"ctrl.start"启动命令字,该service在init.rc中
//init.rc中dhcpcd服务进程命令字
//service dhcpcd /system/bin/dhcpcd eth0
// disabled
// oneshot
wait_for_property(DAEMON_PROP_NAME, desired_status, 10);
//init.c=>init进程
//=>handle_property_set_fd因为是"ctrl.start"命令字,所以调用handle_control_message处理控制信息
//=>handle_control_message
//=>msg_start
//=>
// struct service *svc = service_find_by_name(name);
// service_start(svc);//启动svc,即执行：/system/bin/dhcpcd eth0
//=>service_start
//=>pid = fork();
// if(pid == 0)execve(svc->args[0], (char**) svc->args, (char**) ENV);子进程执行execve运行/system/bin/dhcpcd,参数为eth0
//=>否则父进程,即init进程将
//=>notify_service_state(svc->name, "running");设置该svc的状态prop
// snprintf(pname, sizeof(pname), "init.svc.%s", name);
// property_set(pname, state);//所以这样上面wait_for_property(DAEMON_PROP_NAME, desired_status, 10);也才能够正常pass[luther.gliethttp].
wait_for_property(result_prop_name, NULL, 15);//等待dhcp.eth0.result=非空

2. dhcpcd 调用过程：

       system/extra/dhcpcd-4.0.0-beta9/dhcpcd.c
dhcpcd
=>main
# define SYSCONFDIR "/system/etc/dhcpcd"
#define PACKAGE "dhcpcd"
# define CONFIG SYSCONFDIR "/" PACKAGE ".conf"
# define LIBEXECDIR "/system/etc/dhcpcd"
# define SCRIPT LIBEXECDIR "/" PACKAGE "-run-hooks"
=>strlcpy(options->script, SCRIPT, sizeof(options->script));//默认的options->script="/system/etc/dhcpcd /dhcpcd-run-hooks"
=>f = fopen(cf ? cf : CONFIG, "r");//如果没有指定.conf文件,那么使用默认.conf文件
=>parse_config_line//解析"/system/etc/dhcpcd/dhcpcd.conf"默认配置文件
=>parse_option
=>如果在"/system/etc/dhcpcd/dhcpcd.conf"有"script"这个节
=>那么执行strlcpy(options->script, oarg, sizeof(options->script));直接拷贝
/*
{"script", required_argument, NULL, 'c'},
{"option", required_argument, NULL, 'o'},
"/system/etc/dhcpcd/dhcpcd.conf"中的部分内容如下：
...
option domain_name_servers, domain_name, domain_search, host_name
...
*/
=>dhcp_run
=>handle_dhcp_packet
=>handle_dhcp
=>bind_dhcp
  reason = "TIMEOUT";reason = "BOUND";reason = "REBIND";reason = "RENEW";
system/extra/dhcpcd-4.0.0-beta9/configure.c
=> configure(iface, reason, state->new, state->old, &state->lease, options, 1);
//如果dhcp超时或者dhcp成功,都会调用exec_script来执行脚本,
//执行setprop dhcp.${interface}.result "failed"或者
//执行setprop dhcp.${interface}.result "ok"
=>exec_script(options, iface->name, reason, NULL, old);
=>然后configure_env通过环境变量将reason传递到脚本中
int exec_script(const struct options *options, const char *iface, const char *reason,
     const struct dhcp_message *dhcpn, const struct dhcp_message *dhcpo)
=>pid = fork();
=>if(pid == 0)execve(options->script, argv, env);//子进程执行脚本,默认"/system/etc/dhcpcd/dhcpcd-run-hooks"
//dhcpcd-run-hooks脚本会根据level值,决定是否执行system/etc/dhcpcd/dhcpcd-hook/*目录下的相应文件
//我们的系统在该system/etc/dhcpcd/dhcpcd-hook/*目录下有如下3个文件
//95-configured
//20-dns.conf
//01-test
=>父进程返回while (waitpid(pid, &status, 0) == -1)等待子进程脚本执行完成

system/extra/dhcpcd-4.0.0-beta9/dhcpcd-hooks/20-dns.conf
system/extra/dhcpcd-4.0.0-beta9/dhcpcd-hooks/95-configured
    ...
    setprop dhcp.${interface}.ipaddress "${new_ip_address}"
    setprop dhcp.${interface}.result "ok"//设置属性为ok
    setprop dhcp.${interface}.result "failed"
    ...