linux kernel poll & 等待队列

1.等待队列

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

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);

（2）定义并且初始化等待队列

static DECLARE_WAIT_QUEUE_HEAD(button_waitq);

1.3让等待队列中的进程休眠/唤醒 函数

（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

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

wake_up(button_waitq)

2.poll

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

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;
}

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");