原创 Linux 字符设备驱动结构

struct cdev
{
 struct kobject kobj;  //内嵌kobject对象
 struct module *owner; //所属模块
 struct file_operations *ops; //文件操作结构体
 struct list_head list;
 dev_t dev;    //设备号
 unsigned int count;
}

MAJOR(dev_t dev);   //获得主设备号
MINOR(dev_t dev);   //获得次设备号

MKDEV(int major, int minor); //生成dev_t

 /**
 * cdev_init() - initialize a cdev structure
 * @cdev: the structure to initialize
 * @fops: the file_operations for this device
 *
 * Initializes @cdev, remembering @fops, making it ready to add to the
 * system with cdev_add().
 */
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;         //将传入文件操作结构体指针赋值给cdev的ops
}

/**
 * cdev_alloc() - allocate a cdev structure
 *
 * Allocates and returns a cdev structure, or NULL on failure.
 */
struct cdev *cdev_alloc(void)
{
 struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);  //分配cdev的内存
 if (p) {
  INIT_LIST_HEAD(&p->list);
  kobject_init(&p->kobj, &ktype_cdev_dynamic);
 }
 return p;
}

/*分配和释放设备号*/
/**
 * alloc_chrdev_region() - register a range of char device numbers
 * @dev: output parameter for first assigned number
 * @baseminor: first of the requested range of minor numbers
 * @count: the number of minor numbers required
 * @name: the name of the associated device or driver
 *
 * Allocates a range of char device numbers.  The major number will be
 * chosen dynamically, and returned (along with the first minor number)
 * in @dev.  Returns zero or a negative error code.
 */
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;
}

/**
 * alloc_chrdev_region() - register a range of char device numbers
 * @dev: output parameter for first assigned number
 * @baseminor: first of the requested range of minor numbers
 * @count: the number of minor numbers required
 * @name: the name of the associated device or driver
 *
 * Allocates a range of char device numbers.  The major number will be
 * chosen dynamically, and returned (along with the first minor number)
 * in @dev.  Returns zero or a negative error code.
 */
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;
}

/**
 * unregister_chrdev_region() - return a range of device numbers
 * @from: the first in the range of numbers to unregister
 * @count: the number of device numbers to unregister
 *
 * This function will unregister a range of @count device numbers,
 * starting with @from.  The caller should normally be the one who
 * allocated those numbers in the first place...
 */
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));
 }
}

/*file_operations结构体*/

/*
 * NOTE:
 * read, write, poll, fsync, readv, writev, unlocked_ioctl and compat_ioctl
 * can be called without the big kernel lock held in all filesystems.
 */
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);

aio_read()和aio_write()与read()和write()中的offset参数不同,它直接传递值,而后者传递的是指针,这是因为AIO从来不需要改变文件的位置。
 int (*readdir) (struct file *, void *, filldir_t);
 unsigned int (*poll) (struct file *, struct poll_table_struct *);

//轮询函数，判断目前是否可以进行非阻塞的读取或写出
 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);

//刷新待处理数据
 int (*aio_fsync) (struct kiocb *, int datasync);
 int (*fasync) (int, struct file *, int);

//通知设备FASYNC标志发生变化
 int (*lock) (struct file *, int, struct file_lock *);
 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);
 int (*setlease)(struct file *, long, struct file_lock **);
};