字符设备驱动第八课------读写锁

概述

忙等锁，临界区尽量不休眠。

函数接口

1.初始化：

<included/linux/rwloak.h> rwlock_init(lock)

2. 上写锁：

write_lock(lock)

3.解写锁：

write_unlock(lock)

4.上读锁：

read_lock(lock)

5.解读锁：

read_unlock(lock)

6.尝试上读锁

抢得到就抢。抢不到锁也返回往下走，一般下面会对其返回值做判断

/** 功能：尝试上读锁，不管抢到锁还是抢不到锁都返回* 返回值：抢到锁返回1，否则返回0*/read_trylock(lock)

7.尝试上写锁

/** 功能：尝试上写锁，不管抢到锁还是抢不到锁都返回* 返回值：抢到锁返回1，否则返回0*/write_trylock(lock)

工程实例

#include <linux/init.h>#include <linux/module.h>#include <linux/kernel.h>#include <linux/cdev.h>#include <linux/fs.h>#include <linux/errno.h>#include <asm/current.h>#include <linux/sched.h>#include <linux/uaccess.h>#include <asm/atomic.h>#include <linux/rwlock.h>#include <linux/delay.h>#include <linux/device.h>static struct class *cls = NULL;#include "mycmd.h"static int major = 0;static int minor = 0;const  int count = 6;#define DEVNAME "demo"static struct cdev *demop = NULL;#define KMAX 1024static int counter = 0;static char kbuf[KMAX];static atomic_t tv;static rwlock_t lock;//打开设备static int demo_open(struct inode *inode, struct file *filp){    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    //get major and minor from inode    printk(KERN_INFO "(major=%d, minor=%d), %s : %s : %d\n",        imajor(inode), iminor(inode), __FILE__, __func__, __LINE__);    if(!atomic_dec_and_test(&tv)){ //原子操作，自减且判断返回值是否为0        atomic_inc(&tv);//自加,以便其他地方检测，用于同步。可类比运用程序编程时的生产者消费者模型(sem_wait, sem_post信号灯)        return -EBUSY;    }    memset(kbuf, 0, KMAX);    counter = 0;    return 0;}//关闭设备static int demo_release(struct inode *inode, struct file *filp){    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    //get major and minor from inode    printk(KERN_INFO "(major=%d, minor=%d), %s : %s : %d\n",        imajor(inode), iminor(inode), __FILE__, __func__, __LINE__);    atomic_inc(&tv);    return 0;}//读设备//ssize_t read(int fd, void *buf, size_t count)static ssize_t demo_read(struct file *filp, char __user *buf, size_t size, loff_t *offset){    struct inode *inode = filp->f_path.dentry->d_inode;    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    //get major and minor from inode    printk(KERN_INFO "(major=%d, minor=%dspinlock_t), %s : %s : %d\n",        imajor(inode), iminor(inode), __FILE__, __func__, __LINE__);    read_lock(&lock);    //读之前上读锁    ssleep(30);    if(counter < size){        size = counter;    }    if(copy_to_user(buf, kbuf, size)){        read_unlock(&lock);        return -EAGAIN;    }    read_unlock(&lock);   //读完之后解锁    return size;}//写设备static ssize_t demo_write(struct file *filp, const char __user *buf, size_t size, loff_t *offset){    struct inode *inode = filp->f_path.dentry->d_inode;    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    //get major and minor from inode    printk(KERN_INFO "(major=%d, minor=%d), %s : %s : %d\n",        imajor(inode), iminor(inode), __FILE__, __func__, __LINE__);    if(size > KMAX){        return -ENOMEM;    }    write_lock(&lock); //写前上写锁    ssleep(30);    if(copy_from_user(kbuf, buf, size)){        write_unlock(&lock);        return -EAGAIN;    }    counter = size;    write_unlock(&lock);//写完解锁    return counter;}/* * read/write param * read status * contrl device */static long demo_ioctl(struct file *filp, unsigned int cmd, unsigned long arg){    static struct karg karg = {        .kval = 0,        .kbuf = {0},    };    struct karg *usrarg;    switch(cmd){    case CMDON:        printk(KERN_INFO "CMDON: %s : %s : %d\n", __FILE__, __func__, __LINE__);        break;    case CMDOFF:        printk(KERN_INFO "CMDOFF: %s : %s : %d\n", __FILE__, __func__, __LINE__);        break;    case CMDR:        printk(KERN_INFO "CMDR: %s : %s : %d\n", __FILE__, __func__, __LINE__);        if(_IOC_SIZE(cmd) != sizeof(karg)){            return -EINVAL;        }        usrarg = (struct karg *)arg;        if(copy_to_user(usrarg, &karg, sizeof(karg))){            return -EAGAIN;        }        printk(KERN_INFO "CMDR: %s : %s : %d ---done.\n", __FILE__, __func__, __LINE__);        break;    case CMDW:        printk(KERN_INFO "CMDW: %s : %s : %d\n", __FILE__, __func__, __LINE__);        if(_IOC_SIZE(cmd) != sizeof(karg)){            return -EINVAL;        }        usrarg = (struct karg *)arg;        if(copy_from_user(&karg, usrarg, sizeof(karg))){            return -EAGAIN;        }        printk(KERN_INFO "CMDW: %d : %s\n", karg.kval, karg.kbuf);        break;    default:        ;    };    return 0;}static struct file_operations fops = {    .owner  = THIS_MODULE,    .open   = demo_open,    .release= demo_release,    .read   = demo_read,    .write  = demo_write,    .unlocked_ioctl = demo_ioctl,};static int __init demo_init(void){    dev_t devnum;    int ret, i;    struct device *devp = NULL;    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    //1. alloc cdev obj    demop = cdev_alloc();    if(NULL == demop){        return -ENOMEM;    }    //2. init cdev obj    cdev_init(demop, &fops);    ret = alloc_chrdev_region(&devnum, minor, count, DEVNAME);    if(ret){        goto ERR_STEP;    }    major = MAJOR(devnum);    //3. register cdev obj    ret = cdev_add(demop, devnum, count);    if(ret){        goto ERR_STEP1;    }    cls = class_create(THIS_MODULE, DEVNAME);    if(IS_ERR(cls)){        ret = PTR_ERR(cls);        goto ERR_STEP1;    }    for(i = minor; i < (count+minor); i++){        devp = device_create(cls, NULL, MKDEV(major, i), NULL, "%s%d", DEVNAME, i);        if(IS_ERR(devp)){            ret = PTR_ERR(devp);            goto ERR_STEP2;        }    }    // init atomic_t    atomic_set(&tv, 1);    // init spinlock    rwlock_init(&lock);    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d - ok.\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    return 0;ERR_STEP2:    for(--i; i >= minor; i--){        device_destroy(cls, MKDEV(major, i));    }    class_destroy(cls);ERR_STEP1:    unregister_chrdev_region(devnum, count);ERR_STEP:    cdev_del(demop);    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d - fail.\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    return ret;}static void __exit demo_exit(void){    int i;    //get command and pid    printk(KERN_INFO "(%s:pid=%d), %s : %s : %d - leave.\n",        current->comm, current->pid, __FILE__, __func__, __LINE__);    for(i=minor; i < (count+minor); i++){        device_destroy(cls, MKDEV(major, i));    }    class_destroy(cls);    unregister_chrdev_region(MKDEV(major, minor), count);    cdev_del(demop);}module_init(demo_init);module_exit(demo_exit);MODULE_LICENSE("GPL");MODULE_AUTHOR("Farsight");MODULE_DESCRIPTION("Demo for kernel module");