上一节所讲解的驱动是需要手动创建设备节点的，这节讲解的misc机制是自动创建设备节点的。通过这一机制创建的主设备号都是10，使用miscdevice数据结构来抽象这类设备，这类设备是不符合预先确定的字符设备，所以利用misc机制创建的设备属于杂项设备。
杂项设备的注册和取消注册使用以下方法：
extern int misc_register(struct miscdevice *misc);
extern void misc_deregister(struct miscdevice *misc);
使用misc机制改写上一节的内容
- 添加头文件
#include
- 增加miscdevice
static struct miscdevice char_misc_device = {
.minor = MISC_DYNAMIC_MINOR,
.name = DEMO_NAME,
.fops = &char_device_fops,
};
- 修改simple_char_device_init和simple_char_device_exit
static int __init simple_char_device_init(void)
{
int ret;
ret = misc_register(&char_misc_device);
if (ret) {
printk("failed register misc device\n");
return ret;
}
printk("successed regitster char device: %s\n",DEMO_NAME);
return 0;
}
static void __exit simple_char_device_exit(void) {
printk("removing device\n");
misc_deregister(&char_misc_device);
}
- 去掉不必要的预加载
#include
#include
#include
#define DEMO_NAME "char_misc_device"
- 所有内容如下：
#include
#include
#include
#define DEMO_NAME "char_misc_device"
static int char_device_open(struct inode *inode, struct file *file)
{
int major = MAJOR(inode->i_rdev);
int minor = MINOR(inode->i_rdev);
printk("%s: major=%d, minor=%d\n", __func__, major, minor);
return 0;
}
static ssize_t char_device_read(struct file *file, char __user *buf,size_t lbuf, loff_t *ppos)
{
printk("%s enter\n",__func__);
return 0;
}
static int char_device_release(struct inode *inode, struct file *file)
{
return 0;
}
static ssize_t char_device_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
{
printk("%s enter\n",__func__);
return 0;
}
static const struct file_operations char_device_fops = {
.owner = THIS_MODULE,
.open = char_device_open,
.release = char_device_release,
.read = char_device_read,
.write = char_device_write
};
static struct miscdevice char_misc_device = {
.minor = MISC_DYNAMIC_MINOR,
.name = DEMO_NAME,
.fops = &char_device_fops,
};
static int __init simple_char_device_init(void)
{
int ret;
ret = misc_register(&char_misc_device);
if (ret) {
printk("failed register misc device\n");
return ret;
}
printk("successed regitster char device: %s\n",DEMO_NAME);
return 0;
}
static void __exit simple_char_device_exit(void) {
printk("removing device\n");
misc_deregister(&char_misc_device);
}
module_init(simple_char_device_init);
module_exit(simple_char_device_exit);
MODULE_AUTHOR("fkq");
MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("simple character device");
- 加载模块
$make
make -C /lib/modules/4.15.0-142-generic/build M=/media/fukaiqiang/Disk960/Codes/Linux modules
make[1]: Entering directory '/usr/src/linux-headers-4.15.0-142-generic'
Building modules, stage 2.
MODPOST 1 modules
make[1]: Leaving directory '/usr/src/linux-headers-4.15.0-142-generic'
$sudo insmod char_device.ko
[sudo] fukaiqiang 的密码：
$ls -l /dev/ |grep char_misc
crw------- 1 root root 10, 56 8月 9 22:24 char_misc_device
自动创建设备节点，其中主设备号是10，次设备号由系统动态分配。
sudo chmod 777 /dev/char_misc_device
注意：这里需要赋予权限。不然测试程序会访问不到。
- 编译运行测试程序
#include
#include
#include
#define DEMO_DEV_NAME "/dev/char_misc_device"
int main() {
char buffer[64];
int fd;
fd = open(DEMO_DEV_NAME, O_RDONLY);
if (fd < 0) {
printf("open device %s failed\n", DEMO_DEV_NAME);
return -1;
}
read(fd, buffer, 64);
close(fd);
return 0;
}
gcc char_device_test.c -o char_device_test
$./char_device_test
&dmesg
...
[1395767.809789] char_device_open: major=10, minor=56
[1395767.809797] char_device_read enter
内核版本
Linux version 4.15.0-142-generic
参考
奔跑吧Linux内核入门篇 张天飞著