Method entry

src/blk/kernel/KernelDevice.h:74–77

    KernelDevice *bdev;
    explicit AioCompletionThread(KernelDevice *b) : bdev(b) {}
    void *entry() override {
      bdev->_aio_thread();
      return NULL;
    }
  } aio_thread;

  struct DiscardThread : public Thread {