scull 字符设备驱动程序的设备描述字符设备驱动程序是分配一段内存，然后提供对这个设备的管理方式，我们通过它提供的操作来操纵字符驱动设备，本质上是一个我们分配的模拟内存来模拟驱动设备。 结构如下： 
几个重要方法，我们最初只提供几个简单的接口函数。 read : 拷贝数据到应用程序空间。write: 拷贝数据到内核空间，在这里就是我们的字符驱动设备。open : 打开并且初始化设备。字符设备驱动程序几个重要的数据结构： ```struct scull_dev {struct scull_qset *data; /* Pointer to first quantum set */int quantum; /* the current quantum size */int qset; /* the current array size */unsigned long size; /* amount of data stored here */unsigned int access_key; /* used by sculluid and scullpriv */struct semaphore sem; /* mutual exclusion semaphore */struct cdev cdev; /* Char device structure */};``` ```struct cdev {struct kobject kobj;struct module *owner;const struct file_operations *ops;struct list_head list;dev_t dev;unsigned int count;};``` ```struct inode {umode_t i_mode;unsigned short i_opflags;kuid_t i_uid;kgid_t i_gid;unsigned int i_flags; #ifdef CONFIG_FS_POSIX_ACLstruct posix_acl *i_acl;struct posix_acl *i_default_acl;#endif const struct inode_operations *i_op;struct super_block *i_sb;struct address_space *i_mapping; #ifdef CONFIG_SECURITYvoid *i_security;#endif /* Stat data, not accessed from path walking */unsigned long i_ino;/** Filesystems may only read i_nlink directly. They shall use the* following functions for modification:** (set|clear|inc|drop)_nlink* inode_(inc|dec)_link_count*/union {const unsigned int i_nlink;unsigned int __i_nlink;};dev_t i_rdev;loff_t i_size;struct timespec i_atime;struct timespec i_mtime;struct timespec i_ctime;spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */unsigned short i_bytes;unsigned int i_blkbits;blkcnt_t i_blocks; #ifdef __NEED_I_SIZE_ORDEREDseqcount_t i_size_seqcount;#endif /* Misc */unsigned long i_state;struct mutex i_mutex; unsigned long dirtied_when; /* jiffies of first dirtying */unsigned long dirtied_time_when; struct hlist_node i_hash;struct list_head i_io_list; /* backing dev IO list */#ifdef CONFIG_CGROUP_WRITEBACKstruct bdi_writeback *i_wb; /* the associated cgroup wb */ /* foreign inode detection, see wbc_detach_inode() */int i_wb_frn_winner;u16 i_wb_frn_avg_time;u16 i_wb_frn_history;#endifstruct list_head i_lru; /* inode LRU list */struct list_head i_sb_list;union {struct hlist_head i_dentry;struct rcu_head i_rcu;};u64 i_version;atomic_t i_count;atomic_t i_dio_count;atomic_t i_writecount;#ifdef CONFIG_IMAatomic_t i_readcount; /* struct files open RO */#endifconst struct file_operations *i_fop; /* former ->i_op->default_file_ops */struct file_lock_context *i_flctx;struct address_space i_data;struct list_head i_devices;union {struct pipe_inode_info *i_pipe;struct block_device *i_bdev;struct cdev *i_cdev;char *i_link;}; __u32 i_generation; #ifdef CONFIG_FSNOTIFY__u32 i_fsnotify_mask; /* all events this inode cares about */struct hlist_head i_fsnotify_marks;#endif void *i_private; /* fs or device private pointer */};``` ```struct file {union {struct llist_node fu_llist;struct rcu_head fu_rcuhead;} f_u;struct path f_path;struct inode *f_inode; /* cached value */const struct file_operations *f_op; /** Protects f_ep_links, f_flags.* Must not be taken from IRQ context.*/spinlock_t f_lock;atomic_long_t f_count;unsigned int f_flags;fmode_t f_mode;struct mutex f_pos_lock;loff_t f_pos;struct fown_struct f_owner;const struct cred *f_cred;struct file_ra_state f_ra; u64 f_version;#ifdef CONFIG_SECURITYvoid *f_security;#endif/* needed for tty driver, and maybe others */void *private_data; #ifdef CONFIG_EPOLL/* Used by fs/eventpoll.c to link all the hooks to this file */struct list_head f_ep_links;struct list_head f_tfile_llink;#endif /* #ifdef CONFIG_EPOLL */struct address_space *f_mapping;} __attribute__((aligned(4))); /* lest something weird decides that 2 is OK */ struct file_handle {__u32 handle_bytes;int handle_type;/* file identifier */unsigned char f_handle[0];};``` ```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 (*read_iter) (struct kiocb *, struct iov_iter *);ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);int (*iterate) (struct file *, struct dir_context *);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 *, loff_t, loff_t, 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 **, void **);long (*fallocate)(struct file *file, int mode, loff_t offset,loff_t len);void (*show_fdinfo)(struct seq_file *m, struct file *f);#ifndef CONFIG_MMUunsigned (*mmap_capabilities)(struct file *);#endif};``` 设备驱动程序设计的基本框架 
1.申请设备号，主，次设备号。 2.构建我们的设备结构。 3.编写fops的内核提供的操作方法，更新fops指针。 4.注册我们的设备。 测试结果 我们可以看到，当给我们的scull新设备写入数据的时候，使用free命令就可以看到内存被成功占用。 这里有一个重要问题： 如何安全的将数据在用户空间和逻辑空间之间拷贝？ 解决方法：内核提供了安全的拷贝函数：copy_to_usercopy_from_user 关于这两个函数有一篇博客描述的比较清楚： http://blog.csdn.net/ce123_zhouwei/article/details/8454226 unsigned long copy_to_user(void __user *to, const void *from, unsigned long n); 如果数据拷贝成功，则返回零；否则，返回没有拷贝成功的数据字节数。 *to是用户空间的指针， *from是内核空间指针， n表示从内核空间向用户空间拷贝数据的字节数。功能：用于将用户空间的数据传送到内核空间。 unsigned long copy_from_user(void * to, const void __user * from, unsigned long n) 第一个参数to是内核空间的数据目标地址指针， 第二个参数from是用户空间的数据源地址指针， 第三个参数n是数据的长度。 如果数据拷贝成功，则返回零；否则，返回没有拷贝成功的数据字节数。 此函数将from指针指向的用户空间地址开始的连续n个字节的数据产送到to指针指向的内核空间地址. 
查看原文：http://zmrlinux.com/2017/04/30/%e7%ae%80%e5%8d%95%e5%ad%97%e7%ac%a6%e9%a9%b1%e5%8a%a8%e8%ae%be%e5%a4%87/
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