linux kernel poll & 等待队列

1.等待队列

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1.1概念

保存进程的容器
- 阻塞时，将进程放入等待队列
- 唤醒进程时，从等待队列中取出进程

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1.2 等待队列的初始化

等待队列的定义和初始化–可以分部完成也可以一步完成

（1）定义等待队列、初始化

wait_queue_head_t wait;             init_waitqueue_head(&wait);

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（2）定义并且初始化等待队列

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

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1.3让等待队列中的进程休眠/唤醒 函数

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（1）休眠/唤醒

/* 一般用于read函数中，去读取按键中断是否发生,如果发生了就不休眠，如果没有按键事件发生休眠 */wait_event_interruptible(button_waitq, ev_press);  //  p2为假时立刻休眠，为真时不休眠----------/* 用户中断处理函数中，前面read会使进程休眠，这里发生了中断唤醒前面执行read的进程 */wake_up_interruptible(&button_waitq);                   // 唤醒休眠的进程 

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（2）唤醒 TAST_UNINTERRUPTIBLE、TAST_INTERRUPTIBLE、TASK_KILLABLE 所有状态的进程

wake_up(button_waitq)

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2.poll

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2.1原理

poll实现中通过返回不同mask决定等待队列休眠或者不休眠

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2.2 内核实现

内核中poll实现非常固定，就以下两个步骤

static unsigned forth_drv_poll(struct file *file, poll_table *wait){    unsigned int mask = 0;// 1. 将button_waitq添加到等待队列        poll_wait(file, &button_waitq, wait); // 不会立即休眠    if (ev_press) // 如果有按键按下了，返回的掩码表示不休眠        mask |= POLLIN | POLLRDNORM;// 2. 返回掩码    return mask;}

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3.demo

等待队列、中断、阻塞读、poll

#include <linux/module.h>#include <linux/kernel.h>#include <linux/fs.h>#include <linux/init.h>#include <linux/delay.h>#include <linux/irq.h>#include <asm/uaccess.h>#include <asm/irq.h>#include <asm/io.h>#include <asm/arch/regs-gpio.h>#include <asm/hardware.h>#include <linux/poll.h>static struct class *forthdrv_class;static struct class_device  *forthdrv_class_dev;volatile unsigned long *gpfcon;volatile unsigned long *gpfdat;volatile unsigned long *gpgcon;volatile unsigned long *gpgdat;// 定义初始化一个等待队列static DECLARE_WAIT_QUEUE_HEAD(button_waitq);/* 中断事件标志, 中断服务程序将它置1，forth_drv_read将它清0 */static volatile int ev_press = 0;struct pin_desc{    unsigned int pin;    unsigned int key_val;};/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 *//* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */static unsigned char key_val;struct pin_desc pins_desc[4] = {    {S3C2410_GPF0, 0x01},    {S3C2410_GPF2, 0x02},    {S3C2410_GPG3, 0x03},    {S3C2410_GPG11, 0x04},};/*  * 确定按键值  */static irqreturn_t buttons_irq(int irq, void *dev_id){    struct pin_desc * pindesc = (struct pin_desc *)dev_id;    unsigned int pinval;    pinval = s3c2410_gpio_getpin(pindesc->pin);    if (pinval)    {        /* 松开 */        key_val = 0x80 | pindesc->key_val;    }    else    {        /* 按下 */        key_val = pindesc->key_val;    }    ev_press = 1;                  /* 表示中断发生了 */    wake_up_interruptible(&button_waitq);   /* 唤醒休眠的进程 */    return IRQ_RETVAL(IRQ_HANDLED);}static int forth_drv_open(struct inode *inode, struct file *file){    /* 配置GPF0,2为输入引脚 */    /* 配置GPG3,11为输入引脚 */    request_irq(IRQ_EINT0,  buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);    request_irq(IRQ_EINT2,  buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);    request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);    request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]);       return 0;}ssize_t forth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos){    if (size != 1)        return -EINVAL;    /* 如果没有按键动作, 休眠 */    /*    有条件的休眠 按键已经按下时立即返回    */    wait_event_interruptible(button_waitq, ev_press);  //  //p2为假时立刻休眠，为真时不休眠    /* 如果有按键动作, 返回键值 */    copy_to_user(buf, &key_val, 1);    ev_press = 0;    return 1;}int forth_drv_close(struct inode *inode, struct file *file){    free_irq(IRQ_EINT0, &pins_desc[0]);    free_irq(IRQ_EINT2, &pins_desc[1]);    free_irq(IRQ_EINT11, &pins_desc[2]);    free_irq(IRQ_EINT19, &pins_desc[3]);    return 0;}/* 固定模式 */static unsigned forth_drv_poll(struct file *file, poll_table *wait){    unsigned int mask = 0;// 1. 将button_waitq添加到等待队列        poll_wait(file, &button_waitq, wait); // 不会立即休眠    if (ev_press) // 如果有按键按下了，返回的掩码表示不休眠        mask |= POLLIN | POLLRDNORM;// 2. 返回掩码    return mask;}static struct file_operations sencod_drv_fops = {    .owner   =  THIS_MODULE,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */    .open    =  forth_drv_open,         .read    =  forth_drv_read,        .release =  forth_drv_close,    .poll    =  forth_drv_poll,};int major;static int forth_drv_init(void){    major = register_chrdev(0, "forth_drv", &sencod_drv_fops);    forthdrv_class = class_create(THIS_MODULE, "forth_drv");    forthdrv_class_dev = class_device_create(forthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */    gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);    gpfdat = gpfcon + 1;    gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);    gpgdat = gpgcon + 1;    return 0;}static void forth_drv_exit(void){    unregister_chrdev(major, "forth_drv");    class_device_unregister(forthdrv_class_dev);    class_destroy(forthdrv_class);    iounmap(gpfcon);    iounmap(gpgcon);    return 0;}module_init(forth_drv_init);module_exit(forth_drv_exit);MODULE_LICENSE("GPL");