dbuf               75 log.c              struct buf *dbuf = bread(log.dev, log.lh.block[tail]); // read dst
dbuf               76 log.c              memmove(dbuf->data, lbuf->data, BSIZE);  // copy block to dst
dbuf               77 log.c              bwrite(dbuf);  // write dst to disk
dbuf               79 log.c              brelse(dbuf);