:Lalloc_chrdev_region函数原型如下,它是我们用来向内核申请主设备号时用的,与register_chrdev_region不同的是,alloc_chrdev_region是让内核分配给我们一个尚未使用的主设备号,不是由我们自己指定的,该函数的四个传参意义如下:
dev :alloc_chrdev_region函数向内核申请下来的设备号
baseminor :次设备号的起始
count: 申请次设备号的个数
name :执行 cat /proc/devices显示的名称
int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
const char *name)
{
struct char_device_struct *cd;
cd = __register_chrdev_region(0, baseminor, count, name);
if (IS_ERR(cd))
return PTR_ERR(cd);
*dev = MKDEV(cd->major, cd->baseminor);
return 0;
}
cdev的使用:
1.执行cdev_init函数,将cdev和file_operations关联起来
2.使用cdev_add函数,将cdev和设备号关联起来
void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
memset(cdev, 0, sizeof *cdev);
INIT_LIST_HEAD(&cdev->list);
kobject_init(&cdev->kobj, &ktype_cdev_default);
cdev->ops = fops;
}
demo
#include <linux/module.h> // module_init module_exit
#include <linux/init.h> // __init __exit
#include <linux/cdev.h>
#include <linux/fs.h>
#define MYMAJOR 200
#define MYNAME "chardev_test_byHc"
//DEVICE ID
dev_t devid;
static int chardev_open(struct inode *inode, struct file *file)
{
printk(KERN_INFO "chardev open\n");
return 0;
}
static ssize_t chardev_read(struct file *file, char __user *buf,
size_t size, loff_t *ppos)
{
return 0;
}
static const struct file_operations chardev_fops = {
.open = chardev_open,
.read = chardev_read,
};
static struct
{
struct cdev cdev;
}chardev;
static int __init mymodule_init(void)
{
int ret = 0;
printk(KERN_INFO "chrdev_init helloworld init\n");
cdev_init(&chardev.cdev,&chardev_fops);
alloc_chrdev_region(&devid,2,255,MYNAME);
printk(KERN_INFO "MAJOR Number is %d\n",MAJOR(devid));
printk(KERN_INFO "MINOR Number is %d\n",MINOR(devid));
cdev_add(&chardev.cdev,devid,255);
return 0;
}
static void __exit mymodule_exit(void)
{
printk(KERN_INFO "chrdev_exit helloworld exit\n");
cdev_del(&chardev.cdev);
unregister_chrdev_region(devid,255);
}
module_init(mymodule_init);
module_exit(mymodule_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("Hanc"); // 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