text: struct file {
    enum { FD_NONE, FD_PIPE, FD_INODE } type;
    int ref; // reference count
    char readable;
    char writable;
    struct pipe *pipe;
    struct inode *ip;
    uint off;
  };
  
  
  // in-memory copy of an inode
  struct inode {
    uint dev;           // Device number
    uint inum;          // Inode number
    int ref;            // Reference count
    struct sleeplock lock; // protects everything below here
    int valid;          // inode has been read from disk?
  
    short type;         // copy of disk inode
    short major;
    short minor;
    short nlink;
    uint size;
    uint addrs[NDIRECT+1];
    // uint padding[111];
    // char padding[BSIZE-sizeof(uint)];
  };
  
  // table mapping major device number to
  // device functions
  struct devsw {
    int (*read)(struct inode*, char*, int);
    int (*write)(struct inode*, char*, int);
  };
  
  extern struct devsw devsw[];
  
  #define CONSOLE 1
  