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1 、驱动程序和应用层的联系
1.1 从应用层看
1）首先APP斗调用Open(“dev/xxx”,O_REWR)打开设备文件后，会得到此设备文件的属性，知道属性中的“设备类型”和“主设备号”。 2）然后VFS层通过“设备类型”(如字符设备类型)去内核中的“chrdev”这个数组。在通过APP得到的“主设备号”以此为索引从内核的"chrdev"数组中知道相应的“file_operation”结构。这个结构是驱动程序“register_chrdev”注册到内核的，这样索引找到它。这个结构中有相应的一些成员函数（如read,write等），这些成员函数就对应硬件的读写操作等。 file_operation的结构体如下：
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 *);
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);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (
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