字符设备驱动第八课----互斥锁

概念

1.定义：

<include/linux/mutex.h>

struct mutex lock;//定义互斥锁

2.初始化：

mutex_init(mutex)

3.上锁：

/*
* 功能：阻塞式上互斥锁，抢不到就一直阻塞
*/
mutex_lock(struct mutex *lock)

/*
* 功能：非阻塞式上互斥锁，抢不到也会返回往下走
* 返回值;成功抢到锁：1   没抢到锁：0
*/
int mutex_trylock(struct mutex *lock);

/*
* 功能：阻塞，可被中断
*/
mutex_lock_interruptible(lock)

4.解锁：

void mutex_unlock(struct mutex *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/mutex.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 1024
static int counter = 0;
static char kbuf[KMAX];

static atomic_t tv;
static struct mutex lock;//定义互斥锁

//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)){
atomic_inc(&tv);
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;
int ret;
//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__);

ret = mutex_lock_interruptible(&lock);//上互斥锁(可被中断打断)
if(ret){
return ret;
}

if(counter < size){
size = counter;
}

if(copy_to_user(buf, kbuf, size)){
mutex_unlock(&lock);//解开互斥锁
return -EAGAIN;
}

mutex_unlock(&lock);//解开互斥锁
return size;
}

//写设备
static ssize_t demo_write(struct file *filp, const char __user *buf, size_t size, loff_t *offset)
{
int ret;
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__);

ret = mutex_lock_interruptible(&lock);//上互斥锁(可被中断打断)
if(ret){
return ret;
}

ssleep(30);

if(size > KMAX){
mutex_unlock(&lock);//解开互斥锁
return -ENOMEM;
}

if(copy_from_user(kbuf, buf, size)){
mutex_unlock(&lock);//解开互斥锁
return -EAGAIN;
}

counter = size;

mutex_unlock(&lock);//解开互斥锁

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); //初始化原子变量

// init mutex
mutex_init(&lock);  //初始化互斥锁

//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");