本文主要介绍rte_mbuf与rte_mempool数据结构之间的组织关系、以及网卡接收到的数据是如何存储在rte_mbuf中的。

 

一、rte_mbuf、rte_mempool及网卡收到的数据包在内存中的组织结构

      

调用rte_mempool_create()函数创建rte_mempool的时候,指定申请多少个rte_mbuff及每个rte_mbuf中elt_size的大小。elt_size是为网卡接收的数据包预先分配的内存的大小,该内存块就是rte_mbuf->pkt.data的实际存储区域。具体如上图所示。

在申请的rte_mempool内存块中,最前面存储struct rte_mempool数据结构,后面紧接着是rte_pktmbuf_pool_private数据,再后面就是N个rte_mbuf内存块。

每个rte_mbuf内存中,最前面同样存储的是struct rte_mbuf数据结果,后面是RTE_PKTMBUF_HEADROOM,最后面就是实际网卡接收到的数据,如下:

   struct rte_mbuf *m = _m;
    uint32_t buf_len = mp->elt_size - sizeof(struct rte_mbuf);

    RTE_MBUF_ASSERT(mp->elt_size >= sizeof(struct rte_mbuf));

    memset(m, 0, mp->elt_size);

    /* start of buffer is just after mbuf structure */
    m->buf_addr = (char *)m + sizeof(struct rte_mbuf);
    m->buf_physaddr = rte_mempool_virt2phy(mp, m) +
            sizeof(struct rte_mbuf);
    m->buf_len = (uint16_t)buf_len;

    /* keep some headroom between start of buffer and data */
    m->pkt.data = (char*) m->buf_addr + RTE_MIN(RTE_PKTMBUF_HEADROOM, m->buf_len);

    /* init some constant fields */
    m->type = RTE_MBUF_PKT;
    m->pool = mp;
    m->pkt.nb_segs = 1;
    m->pkt.in_port = 0xff;

 

二、网卡接收的数据是如何存储到rte_mbuf中的?

以e1000网卡为例,在网卡初始化的时候,调用eth_igb_rx_init()初始化网卡的收包队列。每个收包队列数据结果如下:

/**
 * Structure associated with each RX queue.
 */
struct igb_rx_queue {
    struct rte_mempool  *mb_pool;   /**< mbuf pool to populate RX ring. */
    volatile union e1000_adv_rx_desc *rx_ring; /**< RX ring virtual address. */
    uint64_t            rx_ring_phys_addr; /**< RX ring DMA address. */
    volatile uint32_t   *rdt_reg_addr; /**< RDT register address. */
    volatile uint32_t   *rdh_reg_addr; /**< RDH register address. */
    struct igb_rx_entry *sw_ring;   /**< address of RX software ring. */
    struct rte_mbuf *pkt_first_seg; /**< First segment of current packet. */
    struct rte_mbuf *pkt_last_seg;  /**< Last segment of current packet. */
    uint16_t            nb_rx_desc; /**< number of RX descriptors. */
    uint16_t            rx_tail;    /**< current value of RDT register. */
    uint16_t            nb_rx_hold; /**< number of held free RX desc. */
    uint16_t            rx_free_thresh; /**< max free RX desc to hold. */
    uint16_t            queue_id;   /**< RX queue index. */
    uint16_t            reg_idx;    /**< RX queue register index. */
    uint8_t             port_id;    /**< Device port identifier. */
    uint8_t             pthresh;    /**< Prefetch threshold register. */
    uint8_t             hthresh;    /**< Host threshold register. */
    uint8_t             wthresh;    /**< Write-back threshold register. */
    uint8_t             crc_len;    /**< 0 if CRC stripped, 4 otherwise. */
    uint8_t             drop_en;  /**< If not 0, set SRRCTL.Drop_En. */
};

我们只关注其中两个成员变量,rx_ring和sw_ring。rx_ring记录的是union e1000_adv_rx_desc数组,每个union e1000_adv_rx_desc中指定了网卡接收数据的DMA地址,网卡收到数据后,直接往该地址写数据。sw_ring数组记录的是每个具体的rte_mbuf地址,每个rte_mbuf的rte_mbuff->buf_phyaddr + RTE_PKTMBUF_HEADROOM映射后的DMA地址就存储在rx_ring队列的union e1000_adv_rx_desc数据结构中。rte_mbuff->buf_phyaddr + RTE_PKTMBUF_HEADROOM指向的就是rte_mbuf->pkt.data的地址。此时,rte_mbuf、rte_mbuf->pkt.data,已经网卡的收包队列就关联起来了。具体如下:

static int
igb_alloc_rx_queue_mbufs(struct igb_rx_queue *rxq)
{
    struct igb_rx_entry *rxe = rxq->sw_ring;
    uint64_t dma_addr;
    unsigned i;

    /* Initialize software ring entries. */
    for (i = 0; i < rxq->nb_rx_desc; i++) {
        volatile union e1000_adv_rx_desc *rxd;
        struct rte_mbuf *mbuf = rte_rxmbuf_alloc(rxq->mb_pool);

        if (mbuf == NULL) {
            PMD_INIT_LOG(ERR, "RX mbuf alloc failed "
                "queue_id=%hu\n", rxq->queue_id);
            return (-ENOMEM);
        }
        dma_addr =
            rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(mbuf));
        rxd = &rxq->rx_ring[i];
        rxd->read.hdr_addr = dma_addr;
        rxd->read.pkt_addr = dma_addr;
        rxe[i].mbuf = mbuf;
    }

    return 0;
}

网卡收到数据后,向rx_ring指定的DMA地址上写数据,其实,就是往每个rte_mbuf->pkt.data写数据。应用程序在调用rte_eth_rx_burst()收包时,以e1000网卡为例,最后调用的是eth_igb_recv_pkts(),就是从每个收包队列中,从sw_ring数组中将rte_mbuf取出来,然后重启申请新的rte_mbuf替换到rx_ring中,重新关联rte_mbuf、union e1000_adv_rx_desc、sw_ring以及rte_mbuf->pkt.data的DMA地址。如下简图所示。

    

 

错误之处,欢迎指出。

转载请标明转自http://www.cnblogs.com/MerlinJ/p/4284706.html

 posted on 2015-02-11 11:51  MerlinJ  阅读(14799)  评论(1编辑  收藏