1. struct cdev {
struct kobject kobj;
struct module *owner;
const struct file_operations *ops;
struct list_head list;
dev_t dev;
unsigned int count;
};//描述字符设备
2. void cdev_init(struct cdev *cdev, const struct file_operations *fops){
memset(cdev, 0, sizeof *cdev);
INIT_LIST_HEAD(&cdev->list);
cdev->kobj.ktype = &ktype_cdev_default;
kobject_init(&cdev->kobj);
cdev->ops = fops;
}//用于初始化cdev的成员，并建立cdev和file_operations之间的链接
3. struct cdev *cdev_alloc(void){
struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
if (p) {
p->kobj.ktype = &ktype_cdev_dynamic;
INIT_LIST_HEAD(&p->list);
kobject_init(&p->kobj);
}
return p;
}//用于动态申请一个cdev内存
4．int cdev_add(struct cdev *p, dev_t dev, unsigned count){
p->dev = dev;
p->count = count;
return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
}//添加（注册）一个cdev
5. void cdev_del(struct cdev *p){
cdev_unmap(p->dev, p->count);
kobject_put(&p->kobj);
}//删除（注销）一个cdev
6. MAJOR(dev_t dev)//得到主设备号
7.MINOR(dev_t dev)//得到次设备号
8. MKDEV(int major,int minor)//生成dev_t
9. int register_chrdev_region(dev_t from, unsigned count, const char *name){
struct char_device_struct *cd;
dev_t to = from + count;
dev_t n, next;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+1, 0);
if (next > to)
next = to;
cd = __register_chrdev_region(MAJOR(n), MINOR(n),
next - n, name);
if (IS_ERR(cd))
goto fail;
}
return 0;
fail:
to = n;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+1, 0);
kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
}
return PTR_ERR(cd);
}//向系统申请设备号，已知起始设备的设备号
10．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;
}//向系统申请设备号，设备号未知，向系统申请未被暂用的设备号
11．void unregister_chrdev_region(dev_t from, unsigned count){
dev_t to = from + count;
dev_t n, next;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+1, 0);
if (next > to)
next = to;
kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
}
}//释放申请的设备号
12. struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, struct dentry *, int datasync);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, void *);
ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*dir_notify)(struct file *filp, unsigned long arg);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
};//结构体中的成员函数是字符设备驱动程序设计的主体内容
由于字符设备的上层没有磁盘文件系统，所以字符设备的file_operations成员函数就直接由设备驱动提供了，file_operations正是字符设备驱动的核心。
字符设备驱动模块加载
想要实现一个驱动模块的加载至少应该实现以下几个步骤：
1. 对设备进行初始化
2. 获取设备号
3. 添加（注册）设备
字符设备驱动模块卸载
驱动模块的卸载至少应该实现以下几个步骤：
1. 释放占用的设备号
2. 删除（注销）设备
![linux-svn卸载与安装[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)