xv6-riscv-kernel/kernel/buf.h

struct buf {
  int valid;   // has data been read from disk?
  int disk;    // does disk "own" buf?
  u32 dev;
  u32 blockno;
  struct sleeplock lock;
  u32 refcnt;
  struct buf *prev; // LRU cache list
  struct buf *next;
  u8 data[BSIZE];
};