loopback.c

Loopback.c

/*-------------------  -------------------*/
212 struct pernet_operations __net_initdata loopback_net_ops = {
    213        .init = loopback_net_init,
    214        .exit = loopback_net_exit,
    215 };
/*----------module initial-----------------*/
static __net_init int loopback_net_init(struct net *net){
            struct net_device *dev;
                dev = alloc_netdev(0, "lo", loopback_setup);/*alloc a netdev,use  loopback_setup to initialize*/
    187         dev_net_set(dev, net); /*do dev->nd_net = hold_net(net); hold_net function does atomic_inc(&net->use_count); */

    188         err = register_netdev(dev);  
    192         net->loopback_dev = dev;
}
/*---------------the loopback_setup function do initialize-----------------*/
static void loopback_setup(struct net_device *dev)
    157 {
    158         dev->mtu                = (16 * 1024) + 20 + 20 + 12;
    159         dev->hard_header_len    = ETH_HLEN;     /* 14   */
    160         dev->addr_len           = ETH_ALEN;     /* 6    */
    161         dev->tx_queue_len       = 0;
    162         dev->type               = ARPHRD_LOOPBACK;      /* 0x0001*/
    163         dev->flags              = IFF_LOOPBACK;
    164         dev->features           = NETIF_F_SG | NETIF_F_FRAGLIST
    165                 | NETIF_F_TSO
    166                 | NETIF_F_NO_CSUM
    167                 | NETIF_F_HIGHDMA
    168                 | NETIF_F_LLTX
    169                 | NETIF_F_NETNS_LOCAL;
    170         dev->ethtool_ops        = &loopback_ethtool_ops;
    171         dev->header_ops         = &eth_header_ops;
    172         dev->netdev_ops         = &loopback_ops;
    173         dev->destructor         = loopback_dev_free;
    174 }
/*-------loopback_ops  defines the operations of loopback device-------------*/
static const struct net_device_ops loopback_ops = {
    147         .ndo_init      = loopback_dev_init,
    148         .ndo_start_xmit= loopback_xmit,
    149         .ndo_get_stats = loopback_get_stats,
    150 };
   /*---------loopback_dev_init------------------*/
26 static int loopback_dev_init(struct net_device *dev)
    127 {
    128         struct pcpu_lstats lstats;
/* struct pcpu_lstats {   unsigned long packets;  unsigned long bytes;   };*/
    130         lstats = alloc_percpu(struct pcpu_lstats);
/*#define alloc_percpu(type)  (type )__alloc_percpu(sizeof(type),__alignof__(type)),and finally call  kzalloc(size, GFP_KERNEL);*/

    134         dev->ml_priv = lstats;
    136 }
/*---------------------loopback_xmit--------------*/
static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
     72 {
     73         struct pcpu_lstats *pcpu_lstats, *lb_stats;
     74
     75         skb_orphan(skb); /*orphan a skb,make it a orphan*/
     76
     77         skb->protocol = eth_type_trans(skb,dev);
     78
     79         /* it's OK to use per_cpu_ptr() because BHs are off */
     80         pcpu_lstats = dev->ml_priv;
     81         lb_stats = per_cpu_ptr(pcpu_lstats, smp_processor_id());
     82         lb_stats->bytes += skb->len;
     83         lb_stats->packets++;
     84
     85         netif_rx(skb);/*This function receives a packet from a device driver and queues it for the upper (protocol) levels to process.  It always succeeds. The buffer may be dropped during processing for congestion control or by the protocol layers.
*/
     86
     87         return 0;
     88 }
 /*---------------/net/core/dev.c/  netif_rx()----------------*/
int netif_rx(struct sk_buff *skb)
   1934 {
   1935         struct softnet_data *queue;
   1936         unsigned long flags;
   1937
   1938         /* if netpoll wants it, pretend we never saw it */
   1939         if (netpoll_rx(skb))
   1940                 return NET_RX_DROP;
   1941
   1942         if (!skb->tstamp.tv64)
   1943                 net_timestamp(skb);
   1944
   1945         /*
   1946          * The code is rearranged so that the path is the most
   1947          * short when CPU is congested, but is still operating.
   1948          */
   1949         local_irq_save(flags);
   1950         queue = &__get_cpu_var(softnet_data);
   1951
   1952         __get_cpu_var(netdev_rx_stat).total++;
   1953         if (queue->input_pkt_queue.qlen <= netdev_max_backlog) {
   1954                 if (queue->input_pkt_queue.qlen) {
   1955 enqueue:
   1956                         __skb_queue_tail(&queue->input_pkt_queue, skb);
   1957                         local_irq_restore(flags);
   1958                         return NET_RX_SUCCESS;
   1959                 }
   1960
   1961                 napi_schedule(&queue->backlog);
   1962                 goto enqueue;
   1963         }
   1964
   1965         __get_cpu_var(netdev_rx_stat).dropped++;
   1966         local_irq_restore(flags);
   1967
   1968         kfree_skb(skb);
   1969         return NET_RX_DROP;
   1970 }
/*-------------- loopback_get_stats get the stastics-----------*/
static struct net_device_stats *loopback_get_stats(struct net_device *dev)
     91 {
     92         const struct pcpu_lstats *pcpu_lstats;
     93         struct net_device_stats *stats = &dev->stats;
     94         unsigned long bytes = 0;
     95         unsigned long packets = 0;
     96         int i;
     97
     98         pcpu_lstats = dev->ml_priv;
     99         for_each_possible_cpu(i) { /*count for each cpu*/
    100                 const struct pcpu_lstats *lb_stats;
    101
    102                 lb_stats = per_cpu_ptr(pcpu_lstats, i);
    103                 bytes   += lb_stats->bytes;
    104                 packets += lb_stats->packets;
    105         }
    106         stats->rx_packets = packets;
    107         stats->tx_packets = packets;
    108         stats->rx_bytes = bytes;
    109         stats->tx_bytes = bytes;
        /* for loopback device receives and send were the same */
    110         return stats;
    111 }
/*---------loopback_ethtool_ops-------------*/
13 static u32 always_on(struct net_device *dev)
    114 {
    115         return 1;
    116 }
    117
    118 static const struct ethtool_ops loopback_ethtool_ops = {
    119         .get_link               = always_on,
    120         .set_tso                = ethtool_op_set_tso,
    121         .get_tx_csum            = always_on,
    122         .get_sg                 = always_on,
    123         .get_rx_csum            = always_on,
    124 };
    125