dpdk-rte_mbuf数据结构学习

2021-07-11 09:55:35 阅读：422 来源： 互联网

标签：rte data mbuf len type uint32 dpdk

搞网络不知道dpdk。。。不合适。。。

搞dpdk不知道rte_mbuf。。。不合适。。。

所以，搞搞搞。。。

上源码！！！

//关于dpdk rte_mbuf数据结构的学习

/* define a set of marker types that can be used to refer to set points in the
 * mbuf */
/* 定义一组可用于引用 mbuf 中的设置点的标记类型*/
__extension__
typedef void    *MARKER[0];   /**< generic marker for a point in a structure */
__extension__
typedef uint8_t  MARKER8[0];  /**< generic marker with 1B alignment */
__extension__
typedef uint64_t MARKER64[0]; /**< marker that allows us to overwrite 8 bytes
                               * with a single assignment */


/**
 * The generic rte_mbuf, containing a packet mbuf.
 */
struct rte_mbuf {
	MARKER cacheline0;			/* 柔性数组，标记开头 */

	void *buf_addr;           /**< Virtual address of segment buffer. */
	/**
	 * Physical address of segment buffer.
	 * Force alignment to 8-bytes, so as to ensure we have the exact
	 * same mbuf cacheline0 layout for 32-bit and 64-bit. This makes
	 * working on vector drivers easier.
	 */
	RTE_STD_C11
	union {
		rte_iova_t buf_iova;
		rte_iova_t buf_physaddr; /**< deprecated */
	} __rte_aligned(sizeof(rte_iova_t));

	/* next 8 bytes are initialised on RX descriptor rearm */
	MARKER64 rearm_data;
	uint16_t data_off;

	/**
	 * Reference counter. Its size should at least equal to the size
	 * of port field (16 bits), to support zero-copy broadcast.
	 * It should only be accessed using the following functions:
	 * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and
	 * rte_mbuf_refcnt_set(). The functionality of these functions (atomic,
	 * or non-atomic) is controlled by the CONFIG_RTE_MBUF_REFCNT_ATOMIC
	 * config option.
	 */
	RTE_STD_C11
	union {
		rte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */
		uint16_t refcnt;              /**< Non-atomically accessed refcnt */
	};
	uint16_t nb_segs;         /**< Number of segments. */

	/** Input port (16 bits to support more than 256 virtual ports). */
	uint16_t port;

	uint64_t ol_flags;        /**< Offload features. */

	/* remaining bytes are set on RX when pulling packet from descriptor */
	MARKER rx_descriptor_fields1;

	/*
	 * The packet type, which is the combination of outer/inner L2, L3, L4
	 * and tunnel types. The packet_type is about data really present in the
	 * mbuf. Example: if vlan stripping is enabled, a received vlan packet
	 * would have RTE_PTYPE_L2_ETHER and not RTE_PTYPE_L2_VLAN because the
	 * vlan is stripped from the data.
	 */
	RTE_STD_C11
	union {
		uint32_t packet_type; /**< L2/L3/L4 and tunnel information. */
		struct {
			uint32_t l2_type:4; /**< (Outer) L2 type. */
			uint32_t l3_type:4; /**< (Outer) L3 type. */
			uint32_t l4_type:4; /**< (Outer) L4 type. */
			uint32_t tun_type:4; /**< Tunnel type. */
			RTE_STD_C11
			union {
				uint8_t inner_esp_next_proto;
				/**< ESP next protocol type, valid if
				 * RTE_PTYPE_TUNNEL_ESP tunnel type is set
				 * on both Tx and Rx.
				 */
				__extension__
				struct {
					uint8_t inner_l2_type:4;
					/**< Inner L2 type. */
					uint8_t inner_l3_type:4;
					/**< Inner L3 type. */
				};
			};
			uint32_t inner_l4_type:4; /**< Inner L4 type. */
		};
	};

	uint32_t pkt_len;         /**< Total pkt len: sum of all segments. */
	uint16_t data_len;        /**< Amount of data in segment buffer. */
	/** VLAN TCI (CPU order), valid if PKT_RX_VLAN_STRIPPED is set. */
	uint16_t vlan_tci;

	union {
		uint32_t rss;     /**< RSS hash result if RSS enabled */
		struct {
			RTE_STD_C11
			union {
				struct {
					uint16_t hash;
					uint16_t id;
				};
				uint32_t lo;
				/**< Second 4 flexible bytes */
			};
			uint32_t hi;
			/**< First 4 flexible bytes or FD ID, dependent on
			     PKT_RX_FDIR_* flag in ol_flags. */
		} fdir;           /**< Filter identifier if FDIR enabled */
		struct {
			uint32_t lo;
			uint32_t hi;
		} sched;          /**< Hierarchical scheduler */
		uint32_t usr;	  /**< User defined tags. See rte_distributor_process() */
	} hash;                   /**< hash information */

	/** Outer VLAN TCI (CPU order), valid if PKT_RX_QINQ_STRIPPED is set. */
	uint16_t vlan_tci_outer;

	uint16_t buf_len;         /**< Length of segment buffer. */

	/** Valid if PKT_RX_TIMESTAMP is set. The unit and time reference
	 * are not normalized but are always the same for a given port.
	 */
	uint64_t timestamp;

	/* second cache line - fields only used in slow path or on TX */
	MARKER cacheline1 __rte_cache_min_aligned;

	RTE_STD_C11
	union {
		void *userdata;   /**< Can be used for external metadata */
		uint64_t udata64; /**< Allow 8-byte userdata on 32-bit */
	};

	struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */
	struct rte_mbuf *next;    /**< Next segment of scattered packet. */

	/* fields to support TX offloads */
	RTE_STD_C11
	union {
		uint64_t tx_offload;       /**< combined for easy fetch */
		__extension__
		struct {
			uint64_t l2_len:7;
			/**< L2 (MAC) Header Length for non-tunneling pkt.
			 * Outer_L4_len + ... + Inner_L2_len for tunneling pkt.
			 */
			uint64_t l3_len:9; /**< L3 (IP) Header Length. */
			uint64_t l4_len:8; /**< L4 (TCP/UDP) Header Length. */
			uint64_t tso_segsz:16; /**< TCP TSO segment size */

			/* fields for TX offloading of tunnels */
			uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr Length. */
			uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr Length. */

			/* uint64_t unused:8; */
		};
	};

	/** Size of the application private data. In case of an indirect
	 * mbuf, it stores the direct mbuf private data size. */
	uint16_t priv_size;

	/** Timesync flags for use with IEEE1588. */
	uint16_t timesync;

	/** Sequence number. See also rte_reorder_insert(). */
	uint32_t seqn;

}

好家伙，果然mbuf，大名鼎鼎。下面分别对每个字段进行学习解释。

下面按照出现顺序对每个字段进行解释。

MARKER cacheline0;

typedef void    *MARKER[0];   /**< generic marker for a point in a structure */

查看typedef，发现这是一个柔性数组。长度为0，所以这里在编译时是不占用内存滴。只是一个标记喽。MARKER嘛。

void *buf_addr;           /**< Virtual address of segment buffer. */

有图就容易解释了，一些指针、成员或函数结果的内容在下表中列出，mbuf指针简写为m

m	首部，即mbuf结构体
m->buf_addr	headroom起始地址
m->data_off	data起始地址相对于buf_addr的偏移
m->buf_len	mbuf和priv之后内存的长度，包含headroom
m->pkt_len	整个mbuf链的data总长度
m->data_len	实际data的长度
m->buf_addr+m->data_off	实际data的起始地址
rte_pktmbuf_mtod(m)	同上
rte_pktmbuf_data_len(m)	同m->data_len
rte_pktmbuf_pkt_len	同m->pkt_len
rte_pktmbuf_data_room_size	同m->buf_len
rte_pktmbuf_headroom	headroom长度
rte_pktmbuf_tailroom	尾部剩余空间长度

综合图片解释以及上述表格的备注。这里buf_addr就是rte_mbuf结构体尾部，headroom起始地址。

/**
	 * Physical address of segment buffer.
	 * Force alignment to 8-bytes, so as to ensure we have the exact
	 * same mbuf cacheline0 layout for 32-bit and 64-bit. This makes
	 * working on vector drivers easier.
	 */
	RTE_STD_C11
	union {
		rte_iova_t buf_iova;
		rte_iova_t buf_physaddr; /**< deprecated */
	} __rte_aligned(sizeof(rte_iova_t));

段缓冲区的物理地址。强制8字节对齐，保证在32位和64位有相同的cacheline0。这块暂时无需关注。

/* next 8 bytes are initialised on RX descriptor rearm */
	MARKER64 rearm_data;

接下来的 8 个字节在 RX 描述符重装时初始化。

uint16_t data_off;

data起始地址相对于buf_addr的偏移。要获取data的位置，m->buf_addr + m->data_off ，就是对应的data的实际指针。一般中间间隔是一个headroom的大小。

/**
	 * Reference counter. Its size should at least equal to the size
	 * of port field (16 bits), to support zero-copy broadcast.
	 * It should only be accessed using the following functions:
	 * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and
	 * rte_mbuf_refcnt_set(). The functionality of these functions (atomic,
	 * or non-atomic) is controlled by the CONFIG_RTE_MBUF_REFCNT_ATOMIC
	 * config option.
	 */
	RTE_STD_C11
	union {
		rte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */
		uint16_t refcnt;              /**< Non-atomically accessed refcnt */
	};

引用计数。这里用union实现了原子访问和非原子访问2种。计数的规格至少等于端口字段的大小16bits，(用来支持零拷贝广播？不明白)。

uint16_t nb_segs;         /**< Number of segments. */

分片数。

	/** Input port (16 bits to support more than 256 virtual ports). */
	uint16_t port;

入接口id号。

	uint64_t ol_flags;        /**< Offload features. */

offload特性标记。

offload特性，主要是指将原本在协议栈中进行的IP分片、TCP分段、重组、checksum校验等操作，转移到网卡硬件中进行，降低系统CPU的消耗，提高处理性能。

	/* remaining bytes are set on RX when pulling packet from descriptor */
	MARKER rx_descriptor_fields1;

从描述符中提取数据包时，剩余字节设置在 RX 上。标记使用，MARKER。。。

	/*
	 * The packet type, which is the combination of outer/inner L2, L3, L4
	 * and tunnel types. The packet_type is about data really present in the
	 * mbuf. Example: if vlan stripping is enabled, a received vlan packet
	 * would have RTE_PTYPE_L2_ETHER and not RTE_PTYPE_L2_VLAN because the
	 * vlan is stripped from the data.
	 */
	 /* 数据包类型，它是外部/内部 L2、L3、L4 和隧道类型的组合。 
	  * packet_type 是关于 mbuf 中真正存在的数据。 
	  * 如果启用了 vlan 剥离，则接收到的 vlan 数据包将具有 RTE_PTYPE_L2_ETHER 
	  * 而不是 RTE_PTYPE_L2_VLAN，因为 vlan 已从数据中剥离。 
	  */
	RTE_STD_C11
	union {
		uint32_t packet_type; /**< L2/L3/L4 and tunnel information. */
		struct {
			uint32_t l2_type:4; /**< (Outer) L2 type. */
			uint32_t l3_type:4; /**< (Outer) L3 type. */
			uint32_t l4_type:4; /**< (Outer) L4 type. */
			uint32_t tun_type:4; /**< Tunnel type. */
			RTE_STD_C11
			union {
				uint8_t inner_esp_next_proto;
				/**< ESP next protocol type, valid if
				 * RTE_PTYPE_TUNNEL_ESP tunnel type is set
				 * on both Tx and Rx.
				 */
				__extension__
				struct {
					uint8_t inner_l2_type:4;
					/**< Inner L2 type. */
					uint8_t inner_l3_type:4;
					/**< Inner L3 type. */
				};
			};
			uint32_t inner_l4_type:4; /**< Inner L4 type. */
		};
	};

此数据结构比较清晰，无需多余解释。有一个疑问，这里的inner && outer具体是什么呢？

	uint32_t pkt_len;         /**< Total pkt len: sum of all segments. */
	uint16_t data_len;        /**< Amount of data in segment buffer. */

pkt_len，包括所有分片的长度。

data_len，当前的数据长度。如果没有分片，pkt_len与data_len数值应该是相同的。也就是pkt_len >= data_len.

	/** VLAN TCI (CPU order), valid if PKT_RX_VLAN_STRIPPED is set. */
	uint16_t vlan_tci;

只有开启了PKT_RX_VLAN_STRIPPED标记，此字段才是有效的。vlan时使用，学习vlan时，需要关注此字段。

	union {
		uint32_t rss;     /**< RSS hash result if RSS enabled */
		struct {
			RTE_STD_C11
			union {
				struct {
					uint16_t hash;
					uint16_t id;
				};
				uint32_t lo;
				/**< Second 4 flexible bytes */
			};
			uint32_t hi;
			/**< First 4 flexible bytes or FD ID, dependent on
			     PKT_RX_FDIR_* flag in ol_flags. */
		} fdir;           /**< Filter identifier if FDIR enabled */
		struct {
			uint32_t lo;
			uint32_t hi;
		} sched;          /**< Hierarchical scheduler */
		uint32_t usr;	  /**< User defined tags. See rte_distributor_process() */
	} hash;                   /**< hash information */

哈希数据。这里是一个union。当RSS开启时，对应rss字段是哈希结果。学习RSS时，关注一下。

	/** Outer VLAN TCI (CPU order), valid if PKT_RX_QINQ_STRIPPED is set. */
	uint16_t vlan_tci_outer;

只有开启了QINQ剥离时，此字段有效。外部vlan相关。

	uint16_t buf_len;         /**< Length of segment buffer. */

mbuf和priv之后内存的长度，包含headroom。

	/** Valid if PKT_RX_TIMESTAMP is set. The unit and time reference
	 * are not normalized but are always the same for a given port.
	 */
	uint64_t timestamp;

时间戳。PKT_RX_TIMESAMP开启时，此字段有效。单位和时间参考未标准化，但对于给定端口始终相同。

	/* second cache line - fields only used in slow path or on TX */
	MARKER cacheline1 __rte_cache_min_aligned;

第二个cacheline，这部分内容仅用在慢路或者发包流程中。

	RTE_STD_C11
	union {
		void *userdata;   /**< Can be used for external metadata */
		uint64_t udata64; /**< Allow 8-byte userdata on 32-bit */
	};
//#define RTE_STD_C11 __extension__

__extension__字段用于消除编译告警。

这里是一个union，

在userdata指针总可以用来存放额外的元数据。

udata64，可以存放8字节的用户数据。

	struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */

标识本mbuf是从哪个rte_mempool池子中申请到的。也就是该mbuf是哪个rte_mempool池子的。

	struct rte_mbuf *next;    /**< Next segment of scattered packet. */

在分片报文中，标记下一个报文的位置。

	/* fields to support TX offloads */
	/* 用于支持发包硬件卸载的字段 */
	RTE_STD_C11
	union {
		uint64_t tx_offload;       /**< combined for easy fetch */
		/* tx_offload 组合起来，方便取用 */
		__extension__
		struct {
			uint64_t l2_len:7;
			/**< L2 (MAC) Header Length for non-tunneling pkt.
			 * Outer_L4_len + ... + Inner_L2_len for tunneling pkt.
			 */
			uint64_t l3_len:9; /**< L3 (IP) Header Length. */
			uint64_t l4_len:8; /**< L4 (TCP/UDP) Header Length. */
			uint64_t tso_segsz:16; /**< TCP TSO segment size */
			/* TSO（TCP Segment Offload）是一种利用网卡的少量处理能力，
			 降低CPU发送数据包负载的技术，需要网卡硬件及驱动的支持。 */

			/* fields for TX offloading of tunnels */
			uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr Length. */
			uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr Length. */

			/* uint64_t unused:8; */
		};
	};

支持硬件发包卸载的字段内容。内部为一个union。其中tx_offload字段是为了容易获取搞出来的。

	/** Size of the application private data. In case of an indirect
	 * mbuf, it stores the direct mbuf private data size. */
	uint16_t priv_size;

应用程序私有数据的大小。

在indirect mbuf 的情况下，它存储direct mbuf 私有数据大小。关于direct mbuf与indirect mbuf的区别，参考链接

10. Mbuf Library — Data Plane Development Kit 21.08.0-rc1 documentation (dpdk.org)

	/** Timesync flags for use with IEEE1588. */
	/* IEEE1588 协议，又称 PTP（ precise time protocol，精确时间协议），
	 * 可以达到亚微秒级别时间同步精度，于 2002 年发布 version 1，
	 * 2008 年发布 version 2。 */
	uint16_t timesync;

时间同步。参考IEEE1588。

IEEE 1588_百度百科 (baidu.com)

	/** Sequence number. See also rte_reorder_insert(). */
	uint32_t seqn;

序列号。这个是哪里用到呢？

rte_mbuf的数据结构学习完毕。有一些遗留的问题，后续来完善。

标签：rte,data,mbuf,len,type,uint32,dpdk
来源： https://blog.51cto.com/qiaopeng688/3035432

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dpdk-rte_mbuf数据结构学习