(5)x210:2.4之前的字符驱动-动态获得mymajor主设备号

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#define MYMAJOR 200
#define MYNAME "chardev"
int mymajor ;
static int test_chardev_open(struct inode *inode,struct file *file)
{
printk(KERN_INFO "test chardev_open\n");
return 0;
}
static int test_chardev_release(struct inode *inode,struct file *file){
printk(KERN_INFO "test chardev_release\n");
return 0;
}
static ssize_t test_chardev_read(struct file *file,char __user *buf,size_t size, loff_t *ppos)
{
printk(KERN_INFO " test read\n");
return 0;

}
static ssize_t test_chardev_write(struct file *file,
const char __user *ubuf,size_t count,loff_t * ppos){
printk(KERN_INFO " test write\n");
return 0;
}

static const struct file_operations test_fops={
.owner=THIS_MODULE,
.open=test_chardev_open,
.release=test_chardev_release,
.write=test_chardev_write,
.read=test_chardev_read,
};
static int __init chardev_init(void)
{ int ret=-1;
printk(KERN_INFO "jimmy module chardev init");
mymajor=register_chrdev(0,MYNAME,&test_fops); //由内核分配，然后mkdnod /dev/chardev mymajor 0生成设备文件

//注意/dev/chardev是MYNAME给出的，不能自己任意命名，这是测试发现的，与静态指定主设备的任意命名稍微不同

if(mymajor<0)

{
printk(KERN_ERR "register_chrdev fail\n");
return -EINVAL;
}

printk(KERN_INFO "register_chrdev success...myjor=%d.\n",mymajor);
return 0;
}
static void __exit chardev_exit(void)
{
    
printk(KERN_INFO "jimmy module chardev exit\n");
unregister_chrdev(MYMAJOR, MYNAME);
}

module_init(chardev_init);
module_exit(chardev_exit);
// MODULE_xxx这种宏作用是用来添加模块描述信息

MODULE_LICENSE("GPL");                // 描述模块的许可证

MODULE_AUTHOR("aston");                // 描述模块的作者

MODULE_DESCRIPTION("module test");    // 描述模块的介绍信息

MODULE_ALIAS("alias xxx");            // 描述模块的别名信息