字元裝置驅動第八課 讀寫鎖

忙等鎖，臨界區盡量不休眠。

rwlock_init(lock)

write_lock

(lock)

write_unlock

(lock)

read_lock(lock)

read_unlock(lock)

搶得到就搶。搶不到鎖也返回往下走，一般下面會對其返回值做判斷

/*

* 功能：嘗試上讀鎖，不管搶到鎖還是搶不到鎖都返回
* 返回值：搶到鎖返回1，否則返回0
*/read_trylock(lock)

/*

* 功能：嘗試上寫鎖，不管搶到鎖還是搶不到鎖都返回
* 返回值：搶到鎖返回1，否則返回0
*/write_trylock(lock)

#include 

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
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 rwlock_t lock;
//開啟裝置
static int demo_open(struct inode *inode, struct file *filp)
memset(kbuf, 0, kmax);
counter = 0;
return0;}
//關閉裝置
static int demo_release(struct inode *inode, struct file *filp)
//讀裝置
//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)
if(copy_to_user(buf, kbuf, size))
read_unlock(&lock); //讀完之後解鎖
return size;
}//寫裝置
static ssize_t demo_write(struct file *filp, const char __user *buf, size_t size, loff_t *offset)
write_lock(&lock); //寫前上寫鎖
ssleep(30);
if(copy_from_user(kbuf, buf, size))
counter = size;
write_unlock(&lock);//寫完解鎖
return counter;}/*
* read/write param
* read status
* contrl device
*/static long demo_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
, };
struct karg *usrarg;
switch(cmd)
usrarg = (struct karg *)arg;
if(copy_to_user(usrarg, &karg, sizeof(karg)))
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))
usrarg = (struct karg *)arg;
if(copy_from_user(&karg, usrarg, sizeof(karg)))
printk(kern_info "cmdw: %d : %s\n", karg.kval, karg.kbuf);
break;
default:;};
return0;}
static struct file_operations fops = ;
static int __init demo_init(void)
//2. init cdev obj
cdev_init(demop, &fops);
ret = alloc_chrdev_region(&devnum, minor, count, devname);
if(ret)
major = major(devnum);
//3. register cdev obj
ret = cdev_add(demop, devnum, count);
if(ret)
cls = class_create(this_module, devname);
if(is_err(cls))
for(i = minor; i < (count+minor); i++)
}// 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--)
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)
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");

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