xv6/fsvar.h

// in-core file system types

struct inode {
  uint dev;           // Device number
  uint inum;          // Inode number
  int ref;            // Reference count
  int flags;          // I_BUSY, I_VALID

  short type;         // copy of disk inode
  short major;
  short minor;
  short nlink;
  uint size;
  uint addrs[NADDRS];
};

// unlocked inode - only dev and inum are available
struct uinode {
  uint dev;
  uint inum;
};

#define I_BUSY 0x1
#define I_VALID 0x2