客戶端程式

[email protected]:/proc/1679# ps -w | grep udh
 1679 root      1484 S    udhcpc -p /var/run/udhcpc-eth0.2.pid -s /lib/netifd/dhcp.script -f -t 0 -i eth0.2 -V 3830d84fd8bc77bf -C

其父程序為 netifd

[email protected]:/proc/1679# cat stat
1679 (udhcpc) S 1593 0 0 0 -1 4194560 167 1266 0 0 0 3 8 6 20 0 1 0 3924 1519616 110 2147483647 4194304 4613096 2146095136 2146093040 1997973920 0 0 4100 114688 2149225712 0 0 18 0 0 0 0 0 0 4678632 4679983 10878976 2146098997 2146099102 2146099102 2146099183 0

下面來看udhcpc這個程式是如何被執行的：

首先來看下面的dhcp.sh檔案

[email protected]:/lib/netifd/proto# ls
3g.sh    dhcp.sh  ppp.sh   qmi.sh

找到下面的程式碼

	proto_run_command "$config" udhcpc \
		-p /var/run/udhcpc-$iface.pid \
		-s /lib/netifd/dhcp.script \
		-f -t 0 -i "$iface" \
		${ipaddr:+-r $ipaddr} \
		${hostname:+-H $hostname} \
		${vendorid:+-V $vendorid} \
		$clientid $broadcast $dhcpopts
 

dhcp客戶端就是通過上面的指令碼呼叫執行的

proto_run_command函式在netifd-proto.sh中有定義
函式的最後一句是：

_proto_notify "$interface"

_proto_notify() {
	local interface="$1"
	local options="$2"
	json_add_string "interface" "$interface"
	ubus $options call network.interface notify_proto "$(json_dump)"
}

接下來進入netifd的原始碼裡，在ubus.c檔案中

static struct ubus_method iface_object_methods[] = {
	{ .name = "lds", .handler = netifd_handle_down },
	{ .name = "up", .handler = netifd_handle_up },
	{ .name = "down", .handler = netifd_handle_down },
	{ .name = "status", .handler = netifd_handle_status },
	{ .name = "prepare", .handler = netifd_handle_iface_prepare },
	{ .name = "dump", .handler = netifd_handle_dump },
	UBUS_METHOD("add_device", netifd_iface_handle_device, dev_link_policy ),
	UBUS_METHOD("remove_device", netifd_iface_handle_device, dev_link_policy ),
	{ .name = "notify_proto", .handler = netifd_iface_notify_proto },
	{ .name = "remove", .handler = netifd_iface_remove },
	{ .name = "set_data", .handler = netifd_handle_set_data },
};

proto_shell_notify函式->proto_shell_run_command->netifd_start_process->建立子程序並執行

還有個問題沒有解決是，最開始的dhcp.sh是如何被執行的？

該指令碼執行有兩個入口點，第一處在netifd初始化過程中

static void
netifd_parse_script_handler(const char *name, script_dump_cb cb)
{
	struct json_tokener *tok = NULL;
	json_object *obj;
	static char buf[512];
	char *start, *cmd;
	FILE *f;
	int len;

#define DUMP_SUFFIX	" '' dump"

	cmd = alloca(strlen(name) + 1 + sizeof(DUMP_SUFFIX));
	sprintf(cmd, "%s" DUMP_SUFFIX, name);

	f = popen(cmd, "r");
	if (!f)
		return;
...

第二處為proto_shell_handler->netifd_start_process->分配子程序執行

以上內容僅供參考