Linux设备驱动开发 - 混杂设备驱动

混杂设备共享一个主设备号MISC_MAJOR(10)，次设备号不同。
混杂设备本质上仍然是一个字符设备，所以混杂设备的操作跟字符设备基本相同。
在字符设备中，描述字符设备的结构体为struct cdev，在混杂设备中同样有一个描述混杂设备的结构体struct miscdevice。

struct miscdevice  {
    int minor;                             /* 次设备号 */
    const char *name;                      /* 设备名 */
    const struct file_operations *fops;    /* 文件操作 */
    struct list_head list;
    struct device *parent;
    struct device *this_device;
    const char *nodename;
    mode_t mode;
};

 

因为混杂设备共享一个主设备号10，所以在struct miscdevice结构体里面只要指定次设备号，如果次设备号为MISC_DYNAMIC_MINOR系统会自动分配一个次设备号，同时在/dev目录下根据struct miscdevice结构体的name成员创建一个设备节点/dev/"name"。
和字符设备一样要指定一个设备文件操作fops。

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 *);
    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 *, 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 (*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 (*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 **);
    long (*fallocate)(struct file *file, int mode, loff_t offset,loff_t len);
};

 

在模块加载时需要注册混杂设备驱动，相对于字符设备驱动而言混杂设备驱动显得更为简单，只要一个misc_register()函数并指定要操作的miscdevice结构体即可。

int misc_register(struct miscdevice * misc);

成功返回0，失败返回一个负的错误号。

 

在模块卸载时需要卸载混杂设备驱动，使用函数misc_deregister()。

int misc_deregister(struct miscdevice *misc);

 

混杂设备驱动模板：

static struct file_operations xxx_fops = 
{
    .owner = THIS_MODULE,
    .open = xxx_open,
    .read = xxx_read,
    ...
};

static struct miscdevice xxx_misc = 
{
    .minor = MISC_DYNAMIC_MINOR,
    .name = NAME,
    .fops = &xxx_fops,
};

static int __init xxx_init(void)
{
    ...
    /* 注册混杂设备驱动 */
    misc_register(&xxx_misc);
    ...
}

static void __exit xxx_exit(void)
{
    ...
    /* 卸载混杂设备驱动 */
    misc_deregister(&xxx_misc);
    ...
}

module_init(xxx_init);
module_exit(xxx_exit);
MODULE_LICENSE("GPL");