自己动手写文件系统-vfs overview

inode是实现文件系统的关键，每个文件和目录包含一个inode,包括了文件的访问权限，访问时间，等等。
实现一个文件系统最关键的也是实现“inode operations”和“file operations”

inode opertaions主要实现Create links, rename files, generate new file entries in a directory, and
delete files.
File Operations主要实现Act on the data contents of a file. They include obvious operations such
as read and write, but also operations such as setting file pointers and creating memory mappings.
inode的结构体如下
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;
    unsigned long i_version;
    loff_t i_size;
    struct timespec i_atime;
    struct timespec i_mtime;
    struct timespec i_ctime;
    unsigned int i_blkbits;
    blkcnt_t i_blocks;
    umode_t i_mode;
    struct inode_operations *i_op;
    const struct file_operations *i_fop; /* former ->i_op->default_file_ops */
    struct super_block *i_sb;
    struct address_space *i_mapping;
    struct address_space i_data;
    struct dquot *i_dquot[MAXQUOTAS];
    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;
    unsigned long i_state;
    unsigned long dirtied_when; /* jiffies of first dirtying */
    unsigned int i_flags;
    atomic_t i_writecount;
    void *i_security;
};

另外一个比较重要的域是super_block，也叫超级块，包含了文件系统的块大小(block size),maximum file size,