一、DHCP client 和 dhcpcd server直接的信息交互：

Client 和server 通过property_get/set 共享内存来共享信息。

property_get/set(key,value)，保存在共享内存中，系统中的各个进程可以通过property_service访问。

二、DHCP 客户端：

启动dhcp 请求：

源码：Gingerbread/System/core/libnetutils/dhcp_utils.c

int dhcp_do_request(const char *interface, in_addr_t *ipaddr, in_addr_t *gateway, in_addr_t *mask, in_addr_t *dns1, in_addr_t *dns2, in_addr_t *server, uint32_t  *lease)

{

property_set(“dhcp_eth0.result”, "");

property_set("ctl.start", "dhcpcd_eth0");

wait_for_property(“init.svc.dhcpcd_eth0”,” running”, 10);

wait_for_property(“dhcp_eth0.result”, NULL, 30);

property_get(“dhcp_eth0.result”, prop_value, NULL));

if (strcmp(prop_value, "ok") == 0) {

fill_ip_info(interface, ipaddr, gateway, mask, dns1, dns2, server, lease);

return 0;

} else {

snprintf(errmsg, sizeof(errmsg), "DHCP result was %s", prop_value);

return -1;

}

}

static void fill_ip_info(const char *interface, in_addr_t *ipaddr, in_addr_t *gateway, in_addr_t *mask, in_addr_t *dns1, in_addr_t *dns2, in_addr_t *server, uint32_t  *lease)

{

property_get(“dhcp.eth0. ipaddress”, prop_value,NULL);

property_get(“dhcp.eth0. gateway”, prop_value,NULL);

property_get(“dhcp.eth0. mask”, prop_value,NULL);

property_get(“dhcp.eth0. dns1”, prop_value,NULL);

property_get(“dhcp.eth0. dns2”, prop_value,NULL);

property_get(“dhcp.eth0. server”, prop_value,NULL);

property_get(“dhcp.eth0. leasetime”, prop_value,NULL);

}

三、Dchpcd 服务端进程：

源码：Gingerbread/external/dhcpcd/dhcpcd.c

Main()

{

dhcp_run(options, &pid_fd);

}

dhcp_run()

{

client_setup(state, options);

for (;;) {

if (r == 0)

r = handle_timeout(state, options); /client状态机处理，发送dhcp 请求/

else if (r > 0) {

handle_dhcp_packet(state, options);

}

handle_timeout(struct if_state *state, const struct options *options)

{

switch(state->state) {

case STATE_RENEW_REQUESTED:

state->state = STATE_REBINDING;

case STATE_INIT:

state->state = STATE_REQUESTING;

}

switch (state->state) {

case STATE_DISCOVERING:

send_message(state, DHCP_DISCOVER, options);

break;

case STATE_REQUESTING:

if (state->options & DHCPCD_INFORM) {

send_message(state, DHCP_INFORM, options);

break;

}

case STATE_RENEWING:

case STATE_REBINDING:

if (iface->raw_fd == -1)

do_socket(state, SOCKET_OPEN);

send_message(state, DHCP_REQUEST, options);

break;

}}

handle_dhcp_packet()àhandle_dhcp()àbind_dhcp()àconfigure()àrun_script()

执行脚本文件/system/etc/dhcpcd/dhcpcd-run-hooks,脚本文件调用setprop命令设置dhcp相关参数，并设置dhcp result.

case "${reason}" in

BOUND|INFORM|REBIND|REBOOT|RENEW|TIMEOUT)

setprop dhcp.${interface}.ipaddress "${new_ip_address}"

setprop dhcp.${interface}.gateway   "${new_routers%% *}"

setprop dhcp.${interface}.mask      "${new_subnet_mask}"

setprop dhcp.${interface}.leasetime "${new_dhcp_lease_time}"

setprop dhcp.${interface}.server    "${new_dhcp_server_identifier}"

setprop dhcp.${interface}.result "ok"

;;

EXPIRE|FAIL|IPV4LL|STOP)

setprop dhcp.${interface}.result "failed"

;;

RELEASE)

setprop dhcp.${interface}.result "released"

;;