在Linux中,cdev(字符設(shè)備)是一種簡單的設(shè)備驅(qū)動模型。它允許開發(fā)者通過文件操作來訪問設(shè)備,而不需要編寫復雜的內(nèi)核模塊。要實現(xiàn)一個字符設(shè)備驅(qū)動,你需要遵循以下步驟:
/dev
目錄下創(chuàng)建一個新的設(shè)備文件,例如mydevice
。這可以通過mknod
命令來完成,例如:sudo mknod /dev/mydevice c 229 0
這里,c
表示字符設(shè)備,229
是設(shè)備號,0
是次設(shè)備號。
2. 編寫設(shè)備驅(qū)動程序:創(chuàng)建一個新的C文件,例如mydevice.c
,并編寫設(shè)備驅(qū)動程序。以下是一個簡單的示例:
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
static struct class *mydevice_class;
static struct cdev mydevice_cdev;
static int mydevice_open(struct inode *inode, struct file *file) {
printk(KERN_INFO "mydevice opened.\n");
return 0;
}
static int mydevice_release(struct inode *inode, struct file *file) {
printk(KERN_INFO "mydevice released.\n");
return 0;
}
static ssize_t mydevice_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) {
printk(KERN_INFO "mydevice read.\n");
return count;
}
static ssize_t mydevice_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) {
printk(KERN_INFO "mydevice write.\n");
return count;
}
static const struct file_operations mydevice_fops = {
.owner = THIS_MODULE,
.open = mydevice_open,
.release = mydevice_release,
.read = mydevice_read,
.write = mydevice_write,
};
static int __init mydevice_init(void) {
int ret;
// 注冊設(shè)備文件
ret = cdev_register(&mydevice_cdev, &mydevice_fops, "mydevice");
if (ret < 0) {
printk(KERN_ERR "Failed to register mydevice\n");
return ret;
}
// 創(chuàng)建設(shè)備類
mydevice_class = class_create(THIS_MODULE, "mydevice_class");
if (IS_ERR(mydevice_class)) {
printk(KERN_ERR "Failed to create mydevice_class\n");
cdev_unregister(&mydevice_cdev);
return PTR_ERR(mydevice_class);
}
// 將設(shè)備注冊到設(shè)備類
device_create(mydevice_class, NULL, MKDEV(229, 0), NULL, "mydevice");
printk(KERN_INFO "mydevice driver initialized.\n");
return 0;
}
static void __exit mydevice_exit(void) {
// 刪除設(shè)備類
device_destroy(mydevice_class, MKDEV(229, 0));
class_destroy(mydevice_class);
// 注銷設(shè)備文件
cdev_unregister(&mydevice_cdev);
printk(KERN_INFO "mydevice driver unloaded.\n");
}
module_init(mydevice_init);
module_exit(mydevice_exit);
MODULE_LICENSE("GPL");
insmod
命令將其加載到內(nèi)核中,例如:make
sudo insmod mydevice.ko
cat
、dd
等命令來測試設(shè)備驅(qū)動是否正常工作。例如:sudo cat /dev/mydevice
sudo dd if=/dev/zero of=/dev/mydevice bs=1 count=1024
以上就是一個簡單的字符設(shè)備驅(qū)動的實現(xiàn)過程。請注意,這只是一個示例,實際應(yīng)用中可能需要根據(jù)具體需求進行更多的定制和優(yōu)化。