驱动程序函数中的静态全局变量和静态局部变量

发布于 2024-11-06 20:18:55 字数 842 浏览 0 评论 0原文

在我的一个示例 Linux 内核模块中，我有一个在所有函数外部声明为静态的变量 Device_Open 和在函数 device_open 内部声明的静态变量 counter 。在 device_open 内部，我增加了 Device_Open 和 counter。该模块插入内核时没有任何错误，并且我为模块 /dev/chardev 创建了一个设备文件。

我执行cat /dev/chardev。我可以看到的是，每次调用 cat /dev/chardev 时，counter 都会增加，但 Device_Open 始终保持为 0。原因是什么与增加变量值相关的行为差异？

下面是代码片段，方便理解

static int Device_Open = 0;

static int device_open(struct inode *inode, struct file *file)
{
    static int counter = 0;

    printk(KERN_INFO "Device_Open = %d", Device_Open);
    printk(KERN_INFO "counter = %d", counter);

    if (Device_Open)
        return -EBUSY;

    Device_Open++;
        counter++;

    try_module_get(THIS_MODULE);

    return SUCCESS;
}

原文

In one of my sample Linux kernel module, I have a variable Device_Open declared static outside all functions and a static variable counter declared inside a function device_open. Inside device_open, i increment both Device_Open and counter. The module is inserted without any errors into the kernel and i created a device file for my module /dev/chardev.

I do cat /dev/chardev. What i can see is that counter gets incremented for each invocation of cat /dev/chardev, but Device_Open always remains 0. What is the reason for the difference in behavior related to incrementing the value of the variables ?

Below is the code snippet for understanding

static int Device_Open = 0;

static int device_open(struct inode *inode, struct file *file)
{
    static int counter = 0;

    printk(KERN_INFO "Device_Open = %d", Device_Open);
    printk(KERN_INFO "counter = %d", counter);

    if (Device_Open)
        return -EBUSY;

    Device_Open++;
        counter++;

    try_module_get(THIS_MODULE);

    return SUCCESS;
}

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千柳 2024-11-13 20:18:55

我搜索“Device_open”，找到了其对应的设备版本。你确定没有这个功能吗？我在 TLDP 找到了它。

static int device_release(struct inode *inode, struct file *file)
{
#ifdef DEBUG
    printk(KERN_INFO "device_release(%p,%p)\n", inode, file);
#endif

    /* 
     * We're now ready for our next caller 
     */
    Device_Open--;

    module_put(THIS_MODULE);
    return SUCCESS;
}

I searched for "Device_open" and I found its corresponding device release. Are you sure you don't have this function ? I found it at TLDP.

static int device_release(struct inode *inode, struct file *file)
{
#ifdef DEBUG
    printk(KERN_INFO "device_release(%p,%p)\n", inode, file);
#endif

    /* 
     * We're now ready for our next caller 
     */
    Device_Open--;

    module_put(THIS_MODULE);
    return SUCCESS;
}

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