Class Avail

src/device/virtio/virt_queue/split.hpp:103–132

   * @see virtio-v1.2#2.7.6 The Virtqueue Available Ring
   */
  struct [[gnu::packed]] Avail {
    /// Available Ring 对齐要求(字节)
    static constexpr size_t kAlign = 2;
    /// 标志位: AvailFlags (little-endian)
    uint16_t flags;
    /// 驱动程序将下一个描述符条目放入环中的位置(模 queue_size) (little-endian)
    uint16_t idx;
    /// 可用描述符头索引数组 ring[queue_size] (little-endian)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic"
    uint16_t ring[];
#pragma GCC diagnostic pop

    /**
     * @brief 获取 used_event 字段的指针
     * @param queue_size 队列大小
     * @return used_event 字段指针
     * @note 仅当协商 VIRTIO_F_EVENT_IDX 特性时使用
     * @see virtio-v1.2#2.7.10 Available Buffer Notification Suppression
     */
    [[nodiscard]] auto used_event(uint16_t queue_size) volatile
        -> volatile uint16_t* {
      return ring + queue_size;
    }

    [[nodiscard]] auto used_event(uint16_t queue_size) const volatile -> const
        volatile uint16_t* {
      return ring + queue_size;
    }
  };

  /**
   * @brief Virtqueue Used Ring 元素