292 lines
7.9 KiB
Markdown
292 lines
7.9 KiB
Markdown
## scull 字符设备驱动程序的设备描述
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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。
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结构如下：
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几个重要方法，我们最初只提供几个简单的接口函数。
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read : 拷贝数据到应用程序空间。
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write: 拷贝数据到内核空间，在这里就是我们的字符驱动设备。
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open : 打开并且初始化设备。
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字符设备驱动程序几个重要的数据结构：
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```
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struct scull_dev {
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struct scull_qset *data; /* Pointer to first quantum set */
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int quantum; /* the current quantum size */
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int qset; /* the current array size */
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unsigned long size; /* amount of data stored here */
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unsigned int access_key; /* used by sculluid and scullpriv */
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struct semaphore sem; /* mutual exclusion semaphore */
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struct cdev cdev; /* Char device structure */
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};
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```
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```
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struct cdev {
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struct kobject kobj;
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struct module *owner;
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const struct file_operations *ops;
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struct list_head list;
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dev_t dev;
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unsigned int count;
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};
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```
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```
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struct inode {
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umode_t i_mode;
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unsigned short i_opflags;
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kuid_t i_uid;
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kgid_t i_gid;
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unsigned int i_flags;
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#ifdef CONFIG_FS_POSIX_ACL
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struct posix_acl *i_acl;
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struct posix_acl *i_default_acl;
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#endif
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const struct inode_operations *i_op;
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struct super_block *i_sb;
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struct address_space *i_mapping;
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#ifdef CONFIG_SECURITY
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void *i_security;
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#endif
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/* Stat data, not accessed from path walking */
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unsigned long i_ino;
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/*
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* Filesystems may only read i_nlink directly. They shall use the
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* following functions for modification:
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*
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* (set|clear|inc|drop)_nlink
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* inode_(inc|dec)_link_count
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*/
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union {
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const unsigned int i_nlink;
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unsigned int __i_nlink;
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};
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dev_t i_rdev;
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loff_t i_size;
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struct timespec i_atime;
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struct timespec i_mtime;
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struct timespec i_ctime;
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spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */
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unsigned short i_bytes;
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unsigned int i_blkbits;
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blkcnt_t i_blocks;
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#ifdef __NEED_I_SIZE_ORDERED
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seqcount_t i_size_seqcount;
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#endif
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/* Misc */
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unsigned long i_state;
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struct mutex i_mutex;
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unsigned long dirtied_when; /* jiffies of first dirtying */
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unsigned long dirtied_time_when;
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struct hlist_node i_hash;
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struct list_head i_io_list; /* backing dev IO list */
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#ifdef CONFIG_CGROUP_WRITEBACK
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struct bdi_writeback *i_wb; /* the associated cgroup wb */
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/* foreign inode detection, see wbc_detach_inode() */
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int i_wb_frn_winner;
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u16 i_wb_frn_avg_time;
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u16 i_wb_frn_history;
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#endif
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struct list_head i_lru; /* inode LRU list */
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struct list_head i_sb_list;
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union {
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struct hlist_head i_dentry;
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struct rcu_head i_rcu;
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};
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u64 i_version;
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atomic_t i_count;
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atomic_t i_dio_count;
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atomic_t i_writecount;
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#ifdef CONFIG_IMA
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atomic_t i_readcount; /* struct files open RO */
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#endif
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const struct file_operations *i_fop; /* former ->i_op->default_file_ops */
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struct file_lock_context *i_flctx;
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struct address_space i_data;
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struct list_head i_devices;
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union {
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struct pipe_inode_info *i_pipe;
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struct block_device *i_bdev;
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struct cdev *i_cdev;
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char *i_link;
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};
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__u32 i_generation;
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#ifdef CONFIG_FSNOTIFY
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__u32 i_fsnotify_mask; /* all events this inode cares about */
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struct hlist_head i_fsnotify_marks;
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#endif
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void *i_private; /* fs or device private pointer */
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};
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```
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```
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struct file {
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union {
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struct llist_node fu_llist;
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struct rcu_head fu_rcuhead;
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} f_u;
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struct path f_path;
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struct inode *f_inode; /* cached value */
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const struct file_operations *f_op;
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/*
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* Protects f_ep_links, f_flags.
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* Must not be taken from IRQ context.
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*/
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spinlock_t f_lock;
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atomic_long_t f_count;
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unsigned int f_flags;
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fmode_t f_mode;
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struct mutex f_pos_lock;
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loff_t f_pos;
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struct fown_struct f_owner;
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const struct cred *f_cred;
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struct file_ra_state f_ra;
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u64 f_version;
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#ifdef CONFIG_SECURITY
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void *f_security;
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#endif
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/* needed for tty driver, and maybe others */
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void *private_data;
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#ifdef CONFIG_EPOLL
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/* Used by fs/eventpoll.c to link all the hooks to this file */
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struct list_head f_ep_links;
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struct list_head f_tfile_llink;
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#endif /* #ifdef CONFIG_EPOLL */
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struct address_space *f_mapping;
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} __attribute__((aligned(4))); /* lest something weird decides that 2 is OK */
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struct file_handle {
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__u32 handle_bytes;
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int handle_type;
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/* file identifier */
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unsigned char f_handle[0];
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};
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```
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```
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struct file_operations {
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struct module *owner;
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loff_t (*llseek) (struct file *, loff_t, int);
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ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
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ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
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ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
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ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
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int (*iterate) (struct file *, struct dir_context *);
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unsigned int (*poll) (struct file *, struct poll_table_struct *);
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long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
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long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
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int (*mmap) (struct file *, struct vm_area_struct *);
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int (*open) (struct inode *, struct file *);
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int (*flush) (struct file *, fl_owner_t id);
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int (*release) (struct inode *, struct file *);
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int (*fsync) (struct file *, loff_t, loff_t, int datasync);
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int (*aio_fsync) (struct kiocb *, int datasync);
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int (*fasync) (int, struct file *, int);
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int (*lock) (struct file *, int, struct file_lock *);
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ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
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unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
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int (*check_flags)(int);
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int (*flock) (struct file *, int, struct file_lock *);
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ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
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ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
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int (*setlease)(struct file *, long, struct file_lock **, void **);
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long (*fallocate)(struct file *file, int mode, loff_t offset,
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loff_t len);
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void (*show_fdinfo)(struct seq_file *m, struct file *f);
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#ifndef CONFIG_MMU
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unsigned (*mmap_capabilities)(struct file *);
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#endif
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};
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```
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## 设备驱动程序设计的基本框架
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1.申请设备号，主，次设备号。
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2.构建我们的设备结构。
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3.编写fops的内核提供的操作方法，更新fops指针。
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4.注册我们的设备。
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## 测试结果
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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。
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这里有一个重要问题：
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### 如何安全的将数据在用户空间和逻辑空间之间拷贝？
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#### 解决方法：内核提供了安全的拷贝函数：
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copy_to_user
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copy_from_user
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关于这两个函数有一篇博客描述的比较清楚：
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http://blog.csdn.net/ce123_zhouwei/article/details/8454226
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unsigned long copy_to_user(void __user *to, const void *from, unsigned long n);
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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。
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*to是用户空间的指针，
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*from是内核空间指针，
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n表示从内核空间向用户空间拷贝数据的字节数。
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-----------------------------------------------------------------------------------
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功能：用于将用户空间的数据传送到内核空间。
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unsigned long copy_from_user(void * to, const void __user * from, unsigned long n)
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第一个参数to是内核空间的数据目标地址指针，
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第二个参数from是用户空间的数据源地址指针，
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第三个参数n是数据的长度。
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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。
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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.
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