轉自：https://blog.csdn.net/u010961173/article/details/96422441
1 概述
（1）mailbox是一種框架，通過消息隊列和中斷驅動信號處理多處理器間的通訊；
（2）mailbox的實現分為contoller和client。簡單的說就是client 可以通過controller提供的channel發送信息給controller；
（3）在drivers/mailbox下實現的都是controller的源碼；
具體到某個廠商的硬件，則描述如下：
Kconfig文件：內核開關，用於配置mbox模塊是否編譯到內核；
config ARM_MHU
tristate "ARM MHU Mailbox"
depends on ARM_AMBA help
Say Y here if you want to build the ARM MHU controller driver. The controller has 3 mailbox channels, the last of which can be used in Secure mode only.
Makefile文件：根據Kconfig編譯相應的模塊；
我們知道要實現mailbox的源文件其實只有兩個
obj-$(CONFIG_MAILBOX) += mailbox.o
obj-$(CONFIG_ARM_MHU) += arm_mhu.o
其中，mailbox.c 是kernel提供的framework，arm_mhu.c 則是具體廠商的實現
（4）client 通過mbox_send_message給controller發送數據的時候必須指定channel；
int mbox_send_message(struct mbox_chan *chan, void *mssg)
（5）client 在通過mbox_send_message給controller發送數據的時候必須指定channel,channel可以通過以下方式獲得。
目前kernel提供了兩種方法得到mailbox的channel
struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,const char *name);
struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
使用完成后調用mbox_free_channel 釋放channel，這樣別人就可以繼續使用這個channel；
void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
其中，mbox_request_channel_byname是mbox_request_channel的一個封裝。
2 基本框架
目錄：
drivers/mailbox
mailbox.c/mailbox.h/mailbox-test.c/<vendor>-mailbox.c
3 關鍵數據結構
struct mbox_controller {
struct device *dev; // 特定mailbox驅動probe時賦值 dev = &pdev->dev
const struct mbox_chan_ops *ops; // mailbox channel需要實現的功能函數
struct mbox_chan *chans; // mailbox channel指針數組
int num_chans; // mailbox channel個數
bool txdone_irq; // 通過中斷來判斷上次傳輸是否完成
bool txdone_poll; // 通過poll機制來判斷上次傳輸是否完成
unsigned txpoll_period; // POLL 周期, 以ms計
struct mbox_chan *(*of_xlate)(struct mbox_controller *mbox,
const struct of_phandle_args *sp); // 獲取特定channel的回調函數
/* Internal to API */
struct hrtimer poll_hrt;
struct list_head node;
};
struct mbox_chan {
struct mbox_controller *mbox; // contronller指針
unsigned txdone_method;
struct mbox_client *cl; // client指針
struct completion tx_complete; //
void *active_req;
unsigned msg_count, msg_free;
void *msg_data[MBOX_TX_QUEUE_LEN];
spinlock_t lock; /* Serialise access to the channel */
void *con_priv;
};
struct mbox_chan_ops {
int (*send_data)(struct mbox_chan *chan, void *data); // 發送數據（需要last data sent）
int (*startup)(struct mbox_chan *chan); // 特定mailbox 啟動
void (*shutdown)(struct mbox_chan *chan); // 特定mailbox 關閉
bool (*last_tx_done)(struct mbox_chan *chan); // 如果TXDONE_BY_POLL 該回調會被使用
bool (*peek_data)(struct mbox_chan *chan); // 檢測是否有數據
};
struct mbox_client {
struct device *dev; // client 設備
bool tx_block; // block until last data is all transmitted
unsigned long tx_tout; // max block period for timeout
bool knows_txdone; // txdone 回調，如果controller已經有txdone，則該配置無效
void (*rx_callback)(struct mbox_client *cl, void *mssg); // 收到數據
void (*tx_prepare)(struct mbox_client *cl, void *mssg); // 准備數據
void (*tx_done)(struct mbox_client *cl, void *mssg, int r); // 檢測txdone
};
4 函數接口
4.1 mailbox controller api
文件：kernel/include/linux/mailbox_controller.h
（1）注冊、注銷控制器
int mbox_controller_register(struct mbox_controller *mbox); /* can sleep */--------probe中調用
void mbox_controller_unregister(struct mbox_controller *mbox); /* can sleep */-------probe中調用
（2）（對外接口）將底層收到的數據回調給上層應用
void mbox_chan_received_data(struct mbox_chan *chan, void *data); /* atomic */
（3）通知上層當前數據已經發送完成
void mbox_chan_txdone(struct mbox_chan *chan, int r); /* atomic */
4.2 mailbox client api
文件：kernel/include/linux/mailbox_client.h
（1）發送數據前，申請通道
struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
const char *name);
struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
（2）數據發送
int mbox_send_message(struct mbox_chan *chan, void *mssg);
void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */
（3）數據記錄
bool mbox_client_peek_data(struct mbox_chan *chan); /* atomic */
（4）釋放通道
void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
5 Device Tree中的寫法
kernel4.14/Documentation/devicetree/bindings/mailbox/hisilicon,hi6220-mailbox.txt
Hisilicon Hi6220 Mailbox Driver
===============================
Hisilicon Hi6220 mailbox supports up to 32 channels. Each channel
is unidirectional with a maximum message size of 8 words. I/O is
performed using register access (there is no DMA) and the cell
raises an interrupt when messages are received.
Mailbox Device Node（Controller）:（設備節點相關的設備樹）
====================
Required properties:
--------------------
- compatible: Shall be "hisilicon,hi6220-mbox"
- reg: Contains the mailbox register address range (base
address and length); the first item is for IPC
registers, the second item is shared buffer for
slots.
- #mbox-cells: Common mailbox binding property to identify the number
of cells required for the mailbox specifier. Must be 3.
<&phandle slot_id dst_irq ack_irq>
phandle: Label name of mailbox controller
slot_id: Slot id used either for TX or RX
dst_irq: IRQ identifier index number which used by MCU
ack_irq: IRQ identifier index number with generating a
TX/RX interrupt to application processor,
mailbox driver uses it to acknowledge interrupt
- interrupts: Contains the interrupt information for the mailbox
device. The format is dependent on which interrupt
controller the SoCs use.
Optional Properties:
--------------------
- hi6220,mbox-tx-noirq: Property of MCU firmware's feature, so mailbox driver
use this flag to ask MCU to enable "automatic idle
flag" mode or IRQ generated mode to acknowledge a TX
completion.
Example:
--------
mailbox: mailbox@f7510000 {
compatible = "hisilicon,hi6220-mbox";
reg = <0x0 0xf7510000 0x0 0x1000>, /* IPC_S */
<0x0 0x06dff800 0x0 0x0800>; /* Mailbox */
interrupt-parent = <&gic>;
interrupts = <GIC_SPI 94 IRQ_TYPE_LEVEL_HIGH>;
#mbox-cells = <3>;
};
Mailbox client（client相關的設備樹）
===============
Required properties:
--------------------
- compatible: Many (See the client docs).
- mboxes: Standard property to specify a Mailbox (See ./mailbox.txt)
Cells must match 'mbox-cells' (See Mailbox Device Node above).
Optional Properties:
--------------------
- mbox-names: Name given to channels seen in the 'mboxes' property.
Example:
--------
stub_clock: stub_clock {
compatible = "hisilicon,hi6220-stub-clk";
hisilicon,hi6220-clk-sram = <&sram>;
#clock-cells = <1>;
mbox-names = "mbox-tx", "mbox-rx";
mboxes = <&mailbox 1 0 11>, <&mailbox 0 1 10>;
};
Example：
kernel4.14/arch/arm64/boot/dts/hisilicon/hi6220.dtsi
mailbox: mailbox@f7510000 {
compatible = "hisilicon,hi6220-mbox";
reg = <0x0 0xf7510000 0x0 0x1000>, /* IPC_S */
<0x0 0x06dff800 0x0 0x0800>; /* Mailbox */
interrupt-parent = <&gic>;
interrupts = <GIC_SPI 94 IRQ_TYPE_LEVEL_HIGH>;
#mbox-cells = <3>;
};
Example:
--------
stub_clock: stub_clock {
compatible = "hisilicon,hi6220-stub-clk";
hisilicon,hi6220-clk-sram = <&sram>;
#clock-cells = <1>;
mbox-names = "mbox-tx", "mbox-rx";
mboxes = <&mailbox 1 0 11>, <&mailbox 0 1 10>; <phandle channel_index dst_irq ack_irq>
};
6 原理詳解
6.1 原理概述
（1）driver 通過mbox_controller_register 注冊controller；
（2）client 通過mbox_request_channel調用driver->startup；
（3）client 通過mbox_send_message調用driver->send_data，並等待txdone；
（4）driver 收到remote的中斷讀取數據調用mbox_chan_received_data將數據放到 client->rx_buffer中；
6.1.1 mailbox driver流程
（1）配置controller屬性:
（2）申請chan，配置chan個數
（3）配置of_xlate回調，獲取chan
（4）配置chan_ops
（5）配置txdone判斷方式
（6）通過mailbox_controller_register 注冊controller；
6.1.2 mailbox client 流程
（1）通過mbox_request_channel_byname 根據"mbox-names"申請channel；
（2）創建mbox設備；
（3）通過mbox設備的write/read 函數訪問controller；
其中，
write 通過調用mbox_send_message，add_to_rbuf拷貝msg到chan->msg_data[MAX = 20]，msg_submit讀取msg_data[idx]，放到tx_prepare中，調用具體驅動的send message寫寄存器；
read 通過irq驅動，irq讀取寄存器得到消息，調用mailbox.c中的mbox_chan_received_data，再調用client的rx_callback將得到的數據放到client->rx_buffer中；
6.2 Mailbox Controller驅動
6.2.1 Mailbox Controller驅動初始化
6.2.1.1 mbox controller初始化函數
core_initcall(hi6220_mbox_init)
>>>platform_driver_register(&hi6220_mbox_driver);
module_exit(hi6220_mbox_exit);
>>>platform_driver_unregister(&hi6220_mbox_driver);
static struct platform_driver hi6220_mbox_driver = {
.driver = {
.name = "hi6220-mbox",
.owner = THIS_MODULE,
.of_match_table = hi6220_mbox_of_match,
},
.probe = hi6220_mbox_probe,//mbox controller drivers 初始化函數
.remove = hi6220_mbox_remove, //mbox controller drivers 逆初始化函數
};
static const struct of_device_id hi6220_mbox_of_match[] = {
{ .compatible = "hisilicon,hi6220-mbox", },
{},
};
6.2.1.2 調用probe/remove 函數
probe()函數主要用於初始化mbox controller.
hi6220_mbox_probe(struct platform_device *pdev)
>>>mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);//分配vendor設備結構體struct hi6220_mbox *mbox
>>>初始化struct hi6220_mbox *mbox中的相關成員變量
>>>mbox->mchan = devm_kzalloc(dev,mbox->chan_num * sizeof(*mbox->mchan), GFP_KERNEL);//為chan_num個struct hi6220_mbox_chan申請內存
>>>mbox->chan = devm_kzalloc(dev,mbox->chan_num * sizeof(*mbox->chan), GFP_KERNEL);//為chan_num個struct mbox_chan申請內存
>>>mbox->irq = platform_get_irq(pdev, 0);
>>>res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
mbox->ipc = devm_ioremap_resource(dev, res);
>>> res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
mbox->base = devm_ioremap_resource(dev, res);
>>>申請中斷
err = devm_request_irq(dev, mbox->irq, hi6220_mbox_interrupt, 0, dev_name(dev), mbox);//其中，hi6220_mbox_interrupt為中斷mbox->irq對應的服務函數
>>>初始化controller
mbox->controller.dev = dev;
mbox->controller.chans = &mbox->chan[0];
mbox->controller.num_chans = mbox->chan_num;
mbox->controller.ops = &hi6220_mbox_ops;
mbox->controller.of_xlate = hi6220_mbox_xlate;
for (i = 0; i < mbox->chan_num; i++) {
mbox->chan[i].con_priv = &mbox->mchan[i];
mbox->irq_map_chan[i] = NULL;
mbox->mchan[i].parent = mbox;
mbox->mchan[i].slot = i;
}
>>>mask and clear all interrupt vectors
writel(0x0, ACK_INT_MSK_REG(mbox->ipc));
writel(~0x0, ACK_INT_CLR_REG(mbox->ipc));
>>>判斷中斷使用poll方式還是中斷方式
/* use interrupt for tx's ack */
if (of_find_property(node, "hi6220,mbox-tx-noirq", NULL))
mbox->tx_irq_mode = false;
else
mbox->tx_irq_mode = true;
if (mbox->tx_irq_mode)
mbox->controller.txdone_irq = true;
else {
mbox->controller.txdone_poll = true;
mbox->controller.txpoll_period = 5;
}
>>>注冊控制器
err = mbox_controller_register(&mbox->controller);
>>>保存mbox設備數據到pdev->dev->driver_data
platform_set_drvdata(pdev, mbox);
hi6220_mbox_remove(struct platform_device *pdev)
>>>struct hi6220_mbox *mbox = platform_get_drvdata(pdev);
>>>mbox_controller_unregister(&mbox->controller);
6.2.1.3 中斷處理流程
probe函數中注冊中斷，driver 收到remote的中斷，讀取數據調用mbox_chan_received_data將數據放到 client->rx_buffer中
static irqreturn_t hi6220_mbox_interrupt(int irq, void *p)
>>>讀取中斷狀態(哪個子中斷置位？？？)
state = readl(ACK_INT_STAT_REG(mbox->ipc));
>>> 查詢每個子中斷的狀態並進行響應
while (state) {
>>>查詢中斷狀態中的最高置1的位
intr_bit = __ffs(state);//
state &= (state - 1);
chan = mbox->irq_map_chan[intr_bit];//每個中斷位對應一個中斷通道
if (!chan) {
dev_warn(mbox->dev, "%s: unexpected irq vector %d\n",
__func__, intr_bit);
continue;
}
mchan = chan->con_priv; //通道私有數據
if (mchan->dir == MBOX_TX) //若該通道（中斷）為發送方向
mbox_chan_txdone(chan, 0);
else { //若該通道（中斷）為接受方向
for (i = 0; i < MBOX_MSG_LEN; i++)
msg[i] = readl(mbox->base +MBOX_DATA_REG(mchan->slot) + i * 4);//讀取數據
mbox_chan_received_data(chan, (void *)msg); //將數據交給數據接受函數進行處理
}
/* clear IRQ source */清中斷
writel(BIT(mchan->ack_irq), ACK_INT_CLR_REG(mbox->ipc));
mbox_set_state(mbox, mchan->slot, MBOX_STATE_IDLE);
}
6.2.2 數據接收流程
數據接收是以中斷的方式進行的。
hi6220_mbox_interrupt()
>>>for (i = 0; i < MBOX_MSG_LEN; i++)
msg[i] = readl(mbox->base +MBOX_DATA_REG(mchan->slot) + i * 4);//讀取數據
>>>mbox_chan_received_data(chan, (void *)msg); //講數據交給數據接受函數進行處理
>>>chan->cl->rx_callback(chan->cl, mssg); //上層client回調
6.2.3 數據發送流程
6.2.3.1 數據發送分為三種方式
中斷方式，polling方式，ACK方式
#define TXDONE_BY_IRQ BIT(0) /* controller has remote RTR irq */
#define TXDONE_BY_POLL BIT(1) /* controller can read status of last TX */
#define TXDONE_BY_ACK BIT(2) /* S/W ACK recevied by Client ticks the TX */
6.2.3.2 數據發送的基本流程
1 獲取mailbox的channel
1）申請通道時，client對象指定了自己的需求和能力；
2）在原子上下文中不能調用；
3）通道在一個client占用之后，沒有釋放之前，不能被其它client使用；
4）分配完成之后，任何此通道上接受的數據包將通過rx_callback傳遞到客戶端
5）使用完成后調用mbox_free_channel 釋放channel，這樣別人就可以繼續使用這個channel
void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,const char *name);
struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
函數功能：通過dts中配置的channel index申請通道
>>>of_parse_phandle_with_args(dev->of_node, "mboxes", "#mbox-cells", index, &spec)
>>>根據dts中配置的channel index獲得mbox_chan
list_for_each_entry(mbox, &mbox_cons, node)
chan = mbox->of_xlate(mbox, &spec);
>>>初始化mbox
chan->msg_free = 0;
chan->msg_count = 0;
chan->active_req = NULL;
chan->cl = cl;
init_completion(&chan->tx_complete);
>>>啟動通道
ret = chan->mbox->ops->startup(chan);
struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,const char *name);
函數功能：通過channel name 申請通道，調用mbox_request_channel()函數來實現
2 使用mbox_send_message給controller發送數據
函數功能：在client提交數據到controller進而發送到目標處理器的過程中。
若client設置為tx_block，此函數調用只有在遠程已經完成數據接受或tx_out（超時）才能返回；
若client設置為非block模式下，client的每個請求將被此API進行緩存，並返回一個非負數；
若client請求沒有進入queue,將返回一個負數。
無論失敗，還是成功，API將調用tx_done；
int mbox_send_message(struct mbox_chan *chan, void *mssg)
>>> t = add_to_rbuf(chan, mssg); //將要發送的msg發暫存到對應通道的rbuf中
>>>msg_submit(chan);
>>>data = chan->msg_data[idx];
>>>chan->cl->tx_prepare(chan->cl, data); //發到緩存
>>>err = chan->mbox->ops->send_data(chan, data); //發送數據 hi6220_mbox_send_data,
>>>mbox_set_state(mbox, slot, MBOX_STATE_TX);
>>>if (mbox->tx_irq_mode)
mbox_set_mode(mbox, slot, MBOX_ACK_IRQ);
>>>發送數據
for (i = 0; i < MBOX_MSG_LEN; i++)
writel(buf[i], mbox->base + MBOX_DATA_REG(slot) + i * 4);
>>>/* trigger remote request */
writel(BIT(mchan->dst_irq), DST_INT_RAW_REG(mbox->ipc));
等待中斷。。。。。。。。。。
------------------------------------------------------
在中斷服務函數中
發送完成中斷到來----------->
>>>hi6220_mbox_interrupt
>>>mbox_chan_txdone(chan, 0);
>>>tx_tick(chan, r);
>>>msg_submit(chan);
>>>chan->cl->tx_done(chan->cl, mssg, r);
------------------------------------------------------
>>>若為polling方式下，啟定時器
hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL);
>>>若為block形式的發送
>>>設置超時時間
wait = msecs_to_jiffies(3600000);//永不超時
wait = msecs_to_jiffies(chan->cl->tx_tout);
>>>阻塞等待超時或完成
ret = wait_for_completion_timeout(&chan->tx_complete, wait);
>>>若超時時間到
tx_tick(chan, t);
>>>chan->cl->tx_done(chan->cl, mssg, r);
>>>complete(&chan->tx_complete);
6.3 Mailbox Client驅動
以mailbox-test為例說明。
struct mbox_test_device {
struct device *dev;
void __iomem *tx_mmio;
void __iomem *rx_mmio;
struct mbox_chan *tx_channel;
struct mbox_chan *rx_channel;
char *rx_buffer;
char *signal;
char *message;
spinlock_t lock;
wait_queue_head_t waitq;
struct fasync_struct *async_queue;
};
6.3.1 Client 設備樹相關的配置
Controller
----------
Required properties:
- compatible : Should be "st,stih407-mailbox"
- reg : Offset and length of the device's register set
- mbox-name : Name of the mailbox
- #mbox-cells: : Must be 2
<&phandle instance channel direction>
phandle : Label name of controller
instance : Instance number
channel : Channel number
Optional properties
- interrupts : Contains the IRQ line for a Rx mailbox
Example:
mailbox0: mailbox@0 {
compatible = "st,stih407-mailbox";
reg = <0x08f00000 0x1000>;
interrupts = <GIC_SPI 1 IRQ_TYPE_NONE>;
#mbox-cells = <2>;
mbox-name = "a9";
};
Client
------
Required properties:
- compatible : Many (See the client docs)
- reg : Shared (between Application and Remote) memory address
- mboxes : Standard property to specify a Mailbox (See ./mailbox.txt)
Cells must match 'mbox-cells' (See Controller docs above)
Optional properties
- mbox-names : Name given to channels seen in the 'mboxes' property.
Example:
mailbox_test {
compatible = "mailbox-test";
reg = <0x[shared_memory_address], [shared_memory_size]>;
mboxes = <&mailbox2 0 1>, <&mailbox0 2 1>;
mbox-names = "tx", "rx";
};
6.3.2 Client初始化
static struct platform_driver mbox_test_driver = {
.driver = {
.name = "mailbox_test",
.of_match_table = mbox_test_match,
},
.probe = mbox_test_probe,
.remove = mbox_test_remove,
};
module_platform_driver(mbox_test_driver);
static int mbox_test_probe(struct platform_device *pdev)
>>>tdev = devm_kzalloc(&pdev->dev, sizeof(*tdev), GFP_KERNEL);
>>>res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>>size = resource_size(res);
>>>tdev->tx_mmio = devm_ioremap_resource(&pdev->dev, res);
>>>申請通道
tdev->tx_channel = mbox_test_request_channel(pdev, "tx");
tdev->rx_channel = mbox_test_request_channel(pdev, "rx");
>>> client = devm_kzalloc(&pdev->dev, sizeof(*client), GFP_KERNEL);
>>> client->dev = &pdev->dev;
>>> client->rx_callback = mbox_test_receive_message;
>>> client->tx_prepare = mbox_test_prepare_message;
>>> client->tx_done = mbox_test_message_sent;
>>> client->tx_block = true;
>>> client->knows_txdone = false;
>>> client->tx_tout = 500;
>>> channel = mbox_request_channel_byname(client, name); //調用API申請通道
>>>platform_set_drvdata(pdev, tdev);
>>>spin_lock_init(&tdev->lock);
>>>tdev->rx_buffer = devm_kzalloc(&pdev->dev,
MBOX_MAX_MSG_LEN, GFP_KERNEL);
>>>ret = mbox_test_add_debugfs(pdev, tdev);
>>>init_waitqueue_head(&tdev->waitq);
static int mbox_test_remove(struct platform_device *pdev)
>>> debugfs_remove_recursive(root_debugfs_dir);
>>> mbox_free_channel(tdev->tx_channel);
>>> mbox_free_channel(tdev->rx_channel);
6.3.3 Client數據收發
數據接收（回調函數）
static void mbox_test_receive_message(struct mbox_client *client, void *message)
spin_lock_irqsave(&tdev->lock, flags);
if (tdev->rx_mmio) {
memcpy_fromio(tdev->rx_buffer, tdev->rx_mmio, MBOX_MAX_MSG_LEN);
} else if (message) {
memcpy(tdev->rx_buffer, message, MBOX_MAX_MSG_LEN);
}
mbox_data_ready = true;
spin_unlock_irqrestore(&tdev->lock, flags);
wake_up_interruptible(&tdev->waitq);
kill_fasync(&tdev->async_queue, SIGIO, POLL_IN);
數據發送
static void mbox_test_prepare_message(struct mbox_client *client, void *message)
{
struct mbox_test_device *tdev = dev_get_drvdata(client->dev);
if (tdev->tx_mmio) {
if (tdev->signal)
memcpy_toio(tdev->tx_mmio, tdev->message, MBOX_MAX_MSG_LEN);
else
memcpy_toio(tdev->tx_mmio, message, MBOX_MAX_MSG_LEN);
}
}
static void mbox_test_message_sent(struct mbox_client *client,
void *message, int r)
{
if (r)
dev_warn(client->dev,
"Client: Message could not be sent: %d\n", r);
else
dev_info(client->dev,
"Client: Message sent\n");
}
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版權聲明：本文為CSDN博主「huofengfeihu」的原創文章，遵循CC 4.0 BY-SA版權協議，轉載請附上原文出處鏈接及本聲明。
原文鏈接：https://blog.csdn.net/u010961173/article/details/96422441