本文共 6919 字，大约阅读时间需要 23 分钟。
1.使用早期的register_chardev()方法 #include<linux/kernel.h> #include<linux/module.h> #include<linux/fs.h> #include<asm/uaccess.h> int init_module(void); void cleanup_module(void); static int device_open(struct inode*, struct file*); static int device_release(struct inode*, struct file*); static ssize_t device_read(struct file*, char *, size_t, loff_t*); static ssize_t device_write(struct file*, const char*, size_t, loff_t*); #define SUCCESS 0 #define DEVICE_NAME "chardev" #define BUF_LEN 80 static int major; static int Device_open = 0; static char msg[BUF_LEN]; static char *msg_ptr; static struct file_operations fops = { .read = device_read, .write = device_write, .open = device_open, .release = device_release, }; int init_module(void) { major = register_chrdev(0, DEVICE_NAME, &fops); if (major < 0) { printk(KERN_ALERT "Registering char device failed with %d\n", major); return major; } printk(KERN_INFO "I was assigned major number %d.\n", major); return SUCCESS; } void cleanup_module(void) { int ret = unregister_chrdev(major, DEVICE_NAME); if (ret < 0) { printk(KERN_ALERT "Error in unregister chrdev %d\n", major); } } static int device_open(struct inode* inode, struct file* file) { static int counter = 0; if (Device_open) { return -EBUSY; } Device_open++; sprintf(msg, "I already told you %d times hello world\nDevice_open=%d\n" , counter++, Device_open); msg_ptr = msg; try_module_get(THIS_MODULE); return SUCCESS; } static int device_release(struct inode* inode, struct file* file) { Device_open--; module_put(THIS_MODULE); return 0; } static ssize_t device_read(struct file* filp, char *buffer, size_t length, loff_t *offset) { int bytes_read = 0; if (*msg_ptr == '\0') return 0; printk(KERN_ALERT "length=%d\n", length); while (length && *msg_ptr) { put_user(*(msg_ptr++), buffer++); length--; bytes_read++; } return bytes_read; } static ssize_t device_write(struct file* filp, const char *buff, size_t len, loff_t *off) { printk(KERN_ALERT "Sorry, this operation isn't supported\n"); return -EINVAL; } 2.使用cdev的方法 #include<linux/kernel.h> #include<linux/module.h> #include<linux/fs.h> #include<linux/types.h> #include<linux/fs.h> #include<linux/cdev.h> #include<asm/uaccess.h> int init_module(void); void cleanup_module(void); static int device_open(struct inode*, struct file*); static int device_release(struct inode*, struct file*); static ssize_t device_read(struct file*, char *, size_t, loff_t*); static ssize_t device_write(struct file*, const char*, size_t, loff_t*); #define SUCCESS 0 #define DEVICE_NAME "chardev" #define BUF_LEN 80 static int major; static int Device_open = 0; static char msg[BUF_LEN]; static char *msg_ptr; static struct cdev *my_cdev; static struct file_operations fops = { .read = device_read, .write = device_write, .open = device_open, .release = device_release, }; int init_module(void) { int err; dev_t devid ; alloc_chrdev_region(&devid, 0, 1, "chardev"); major = MAJOR(devid); my_cdev = cdev_alloc(); cdev_init(my_cdev, &fops); err = cdev_add(my_cdev, devid, 1); if (err) { printk(KERN_INFO "I was assigned major number %d.\n", major); return -1; } printk("major number is %d\n", MAJOR(devid)); return SUCCESS; } void cleanup_module(void) { cdev_del(my_cdev); printk("cleanup done\n"); } static int device_open(struct inode* inode, struct file* file) { static int counter = 0; if (Device_open) { return -EBUSY; } Device_open++; sprintf(msg, "I already told you %d times hello world\nDevice_open=%d\n", counter++, Device_open); msg_ptr = msg; try_module_get(THIS_MODULE); return SUCCESS; } static int device_release(struct inode* inode, struct file* file) { Device_open--; module_put(THIS_MODULE); return 0; } static ssize_t device_read(struct file* filp, char *buffer, size_t length, loff_t *offset) { int bytes_read = 0; if (*msg_ptr == '\0') return 0; printk(KERN_ALERT "length=%d\n", length); while (length && *msg_ptr) { put_user(*(msg_ptr++), buffer++); length--; bytes_read++; } return bytes_read; } static ssize_t device_write(struct file* filp, const char *buff, size_t len, loff_t *off) { printk(KERN_ALERT "Sorry, this operation isn't supported\n"); return -EINVAL; } 3.使用udev在/dev/下动态生成设备文件的方式 #include<linux/kernel.h> #include<linux/module.h> #include<linux/types.h> #include<linux/fs.h> #include<linux/cdev.h> #include<linux/pci.h> #include<linux/moduleparam.h> #include<linux/init.h> #include<linux/string.h> #include<asm/uaccess.h> #include<asm/unistd.h> #include<asm/uaccess.h> int init_module(void); void cleanup_module(void); static int device_open(struct inode*, struct file*); static int device_release(struct inode*, struct file*); static ssize_t device_read(struct file*, char *, size_t, loff_t*); static ssize_t device_write(struct file*, const char*, size_t, loff_t*); #define SUCCESS 0 #define DEVICE_NAME "chardev" #define BUF_LEN 80 static int major; static int Device_open = 0; static char msg[BUF_LEN]; static char *msg_ptr; static struct cdev *my_cdev; static struct class *my_class; dev_t devid ; static struct file_operations fops = { .read = device_read, .write = device_write, .open = device_open, .release = device_release, }; int init_module(void) { int err; alloc_chrdev_region(&devid, 0, 1, "chardev"); major = MAJOR(devid); my_cdev = cdev_alloc(); cdev_init(my_cdev, &fops); my_cdev->owner = THIS_MODULE; err = cdev_add(my_cdev, devid, 1); if (err) { printk(KERN_INFO "I was assigned major number %d.\n", major); return -1; } my_class = class_create(THIS_MODULE, "chardev_class1"); if (IS_ERR(my_class)) { printk(KERN_INFO "create class error\n"); return -1; } class_device_create(my_class, NULL, devid, NULL, "chardev" "%d", MINOR(devid)); printk("major number is %d\n", MAJOR(devid)); return SUCCESS; } void cleanup_module(void) { cdev_del(my_cdev); class_device_destroy(my_class, devid); class_destroy(my_class); printk("cleanup done\n"); } static int device_open(struct inode* inode, struct file* file) { static int counter = 0; if (Device_open) { return -EBUSY; } Device_open++; sprintf(msg, "I already told you %d times hello world\nDevice_open=%d\n", counter++, Device_open); msg_ptr = msg; try_module_get(THIS_MODULE); return SUCCESS; } static int device_release(struct inode* inode, struct file* file) { Device_open--; module_put(THIS_MODULE); return 0; } static ssize_t device_read(struct file* filp, char *buffer, size_t length, loff_t *offset) { int bytes_read = 0; if (*msg_ptr == '\0') return 0; printk(KERN_ALERT "length=%d\n", length); while (length && *msg_ptr) { put_user(*(msg_ptr++), buffer++); length--; bytes_read++; } return bytes_read; } static ssize_t device_write(struct file* filp, const char *buff, size_t len, loff_t *off) { printk(KERN_ALERT "Sorry, this operation isn't supported\n"); return -EINVAL; }
注：
在linux- 2.6.22以后的内核中，class_device_create()和class_device_destroy()内核函数变更为device_create()和device_destroy()（此段内容为本站添加）。 转载地址：http://bapci.baihongyu.com/