请教一个 XML 序列化问题

我要生成如下 xml 文件

<?xml version="1.0" encoding="UTF-8"?>
<svc_init ver="2.0.0">
	<sms ver="2.0.0">
		<client>
			<id>id</id>
			<pwd>pwd</pwd>
			<serviceid>serviceid</serviceid>
		</client>
		<sms_info>
			<phone>13013001300</phone>
			<content>测试</content>
		</sms_info>
	</sms>
</svc_init>

代码为

package main

import (
	"encoding/xml"
	"fmt"
	"os"
)

type Client struct {
	Id        string `xml:"client>id"`
	Pwd       string `xml:"client>pwd"`
	Serviceid string `xml:"client>serviceid"`
}

type Sms_info struct {
	Phone   string `xml:"sms_info>phone"`
	Content string `xml:"sms_info>content"`
}

type Sms struct {
	XMLName xml.Name `xml:"sms"`
	Ver     string   `xml:"ver,attr"`
	Client
	Sms_info
}

type Svc_init struct {
	XMLName xml.Name `xml:"svc_init"`
	Ver     string   `xml:"ver,attr"`
	Sms
}

func main() {
	id := "id"
	pwd := "pwd"
	serviceid := "serviceid"

	client := Client{Id: id, Pwd: pwd, Serviceid: serviceid}
	sms_info := Sms_info{Phone: "13013001300", Content: "测试"}

	sms := Sms{Ver: "2.0.0", Client: client, Sms_info: sms_info}

	v := Svc_init{Ver: "2.0.0", Sms: sms}

	fmt.Println(v)
	output, _ := xml.MarshalIndent(v, "  ", "    ")

	os.Stdout.Write(output)
}

运行后生成

<svc_init ver="2.0.0">
	<client>
		<id>id</id>
		<pwd>pwd</pwd>
		<serviceid>serviceid</serviceid>
	</client>
	<sms_info>
		<phone>13013001300</phone>
		<content>测试</content>
	</sms_info>
</svc_init>

可以看到结果的 sms 结构丢失了 但是我直接打印 v 值

{{ } 2.0.0 {{ } 2.0.0 {id pwd serviceid} {13013001300 测试}}}

可以看到 sms 结构还在 请问为什么会这样，然后如何修复呢，感谢。