1. Ceph通信框架

class Message : public RefCountedObject {
protected:
  ceph_msg_header  header;      // 消息头
  ceph_msg_footer  footer;		// 消息尾
  bufferlist       payload;  // "front" unaligned blob
  bufferlist       middle;   // "middle" unaligned blob
  bufferlist       data;     // data payload (page-alignment will be preserved where possible)

  /* recv_stamp is set when the Messenger starts reading the
   * Message off the wire */
  utime_t recv_stamp;		//开始接收数据的时间戳
  /* dispatch_stamp is set when the Messenger starts calling dispatch() on
   * its endpoints */
  utime_t dispatch_stamp;	//dispatch 的时间戳
  /* throttle_stamp is the point at which we got throttle */
  utime_t throttle_stamp;	//获取throttle 的slot的时间戳
  /* time at which message was fully read */
  utime_t recv_complete_stamp;	//接收完成的时间戳

  ConnectionRef connection;		//网络连接

  uint32_t magic = 0;			//消息的魔术字

  bi::list_member_hook<> dispatch_q;	//boost::intrusive 成员字段
};

struct ceph_msg_header {
	__le64 seq;       // 当前session内 消息的唯一 序号
	__le64 tid;       // 消息的全局唯一的 id
	__le16 type;      // 消息类型
	__le16 priority;  // 优先级
	__le16 version;   // 版本号

	__le32 front_len; // payload 的长度
	__le32 middle_len;// middle 的长度
	__le32 data_len;  // data 的 长度
	__le16 data_off;  // 对象的数据偏移量


	struct ceph_entity_name src; //消息源

	/* oldest code we think can decode this.  unknown if zero. */
	__le16 compat_version;
	__le16 reserved;
	__le32 crc;       /* header crc32c */
} __attribute__ ((packed));

struct ceph_msg_footer {
	__le32 front_crc, middle_crc, data_crc; //crc校验码
	__le64  sig; //消息的64位signature
	__u8 flags; //结束标志
} __attribute__ ((packed));