LDD中对file结构体的描述：
struct file, defined in <linux/fs.h>, is the second most important data structure used in device drivers. Note that a file has nothing to do with the FILE pointers of user-space programs. A FILE is defined in the C library and never appears in kernel code. A struct file, on the other hand, is a kernel structure that never appears in user programs.
The file structure represents an open file . (It is not specific to device drivers; every open file in the system has an associated struct file in kernel space.) It is created by the kernel on open and is passed to any function that operates on the file, until the last close. After all instances of the file are closed, the kernel releases the data structure.
In the kernel sources, a pointer to struct file is usually called either file or filp (“file pointer”). We’ll consistently call the pointer filp to prevent ambiguities with the structure itself. Thus, file refers to the structure and filp to a pointer to the structure.
对inode结构体的描述：
The inode structure is used by the kernel internally to represent files. Therefore, it is different from the file structure that represents an open file descriptor. There can be numerous file structures representing multiple open descriptors on a single file, but they all point to a single inode structure.
总结如下：在kernel中，每一个文件都有一个inode结构体来表示，而file结构体是和打开的文件描述符关联的。如果一个文件被打开多次，有多个文件描述符，也就相应地有多个file结构体与这个文件关联。而inode却永远只有一个。