Linux之设备驱动学习简过程<三>（不断添加中）
为了学好字符设备驱动，一些相关结构不得不了解。。。于是，通过Source Insight打开内核。。。我浏览到了驱动重要的相关结构
*用户跟驱动关系：用户空间的read、write等--->linux系统调用--->间接调用设备驱动程序中file_operations结构中的函数（看个例子理解下）
1.struct file_operations学驱动必须了解的结构
struct file_operations {
struct module *owner; //驱动模块的指针
loff_t (*llseek) (struct file *, loff_t, int); //文件读写位置
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *); //从设备读数据
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *); //写数据到设备
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 *); //文件描述符的读取写入是否阻塞
int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long); //命令控制设置
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 *); //设备内存映射到进程空间
int (*open) (struct inode *, struct file *); //打开设备
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *); //关闭设备
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 (*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 **);
};
2.文件结构 代表一个打开的文件描述符，它不是专门给驱动程序使用的，系统中每一个打开的文件在内核中都有一个关联的struct file。它由内核在open时创建，并传递给在文件上操作的任何函数，直到最后关闭。当文件的所有实例都关闭之后，内核释放这个数据结构
struct file {
/*
* fu_list becomes invalid after file_free is called and queued via
* fu_rcuhead for RCU freeing
*/
union {
struct list_head fu_list;
struct rcu_head fu_rcuhead;
} f_u;
struct path f_path; //文件路径
#define f_dentry f_path.dentry
#define f_vfsmnt f_path.mnt
const struct file_operations *f_op; //文件操作符结构
spinlock_t f_lock; /* f_ep_links, f_flags, no IRQ */
atomic_long_t f_count;
unsigned int f_flags; //文件标识，可写，可读
fmode_t f_mode;
loff_t f_pos; //文件读写位置
struct fown_struct f_owner;
const struct cred *f_cred;
struct file_ra_state f_ra;
u64 f_version;
#ifdef CONFIG_SECURITY
void *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;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
unsigned long f_mnt_write_state;
#endif
};
3.内核中用inode结构表示具体的文件
struct inode {
struct hlist_node i_hash;
struct list_head i_list;
struct list_head i_sb_list;
struct list_head i_dentry;
unsigned long i_ino;
atomic_t i_count;
unsigned int i_nlink;
uid_t i_uid;
gid_t i_gid;
dev_t i_rdev;
u64 i_version;
loff_t i_size;
#ifdef __NEED_I_SIZE_ORDERED
seqcount_t i_size_seqcount;
#endif
struct timespec i_atime;
struct timespec i_mtime;
struct timespec i_ctime;
unsigned int i_blkbits;
blkcnt_t i_blocks;
unsigned short i_bytes;
umode_t i_mode;
spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */
struct mutex i_mutex;
struct rw_semaphore i_alloc_sem;
const struct inode_operations *i_op;
const struct file_operations *i_fop; /* former ->i_op->default_file_ops */
struct super_block *i_sb;
struct file_lock *i_flock;
struct address_space *i_mapping;
struct address_space i_data;
#ifdef CONFIG_QUOTA
struct dquot *i_dquot[MAXQUOTAS];
#endif
struct list_head i_devices;
union {
struct pipe_inode_info *i_pipe;
struct block_device *i_bdev;
struct cdev *i_cdev;
};
int i_cindex;
__u32 i_generation;
#ifdef CONFIG_DNOTIFY
unsigned long i_dnotify_mask; /* Directory notify events */
struct dnotify_struct *i_dnotify; /* for directory notifications */
#endif
#ifdef CONFIG_INOTIFY
struct list_head inotify_watches; /* watches on this inode */
struct mutex inotify_mutex; /* protects the watches list */
#endif
unsigned long i_state;
unsigned long dirtied_when; /* jiffies of first dirtying */
unsigned int i_flags;
atomic_t i_writecount;
#ifdef CONFIG_SECURITY
void *i_security;
#endif
void *i_private; /* fs or device private pointer */
};
参考资料：http://www.cnblogs.com/QJohnson/archive/2011/06/24/2089414.html
4.cdev结构
在Linux2.6内核中一个字符设备用cdev结构来描述，其定义如下：
struct cdev {
struct kobject kobj;
struct module *owner; //所属模块
const struct file_operations *ops;
//文件操作结构，在写驱动时，其结构体内的大部分函数要被实现
struct list_head list;
dev_t dev; //设备号，int 类型，高12位为主设备号，低20位为次设备号
unsigned int count;
};
可以使用如下宏调用来获得主、次设备号:
MAJOR(dev_t dev)
MINOR(dev_t dev)
MKDEV(int major,int minor) //通过主次设备号来生成dev_t
5.混杂设备miscdevice结构
struct miscdevice {
int minor;
const char *name;
const struct file_operations *fops;
struct list_head list;
struct device *parent;
struct device *this_device;
};