linux-loopback.c

#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/in.h>
#include <linux/init.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/io.h>

#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/ethtool.h>
#include <net/sock.h>
#include <net/checksum.h>
#include <linux/if_ether.h>    /* For the statistics structure. */
#include <linux/if_arp.h>    /* For ARPHRD_ETHER */
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/percpu.h>
#include <net/net_namespace.h>

struct pcpu_lstats {    //per-cpu-loopback stat 记录一个关于一个cpu的网络包信息

    unsigned long packets;
    unsigned long bytes;
    unsigned long drops;
};

/*
 * The higher levels take care of making this non-reentrant (it's
 * called with bh's disabled).
 */
static netdev_tx_t loopback_xmit(struct sk_buff *skb,
                 struct net_device *dev)
{
    struct pcpu_lstats *pcpu_lstats, *lb_stats;
    int len;

    skb_orphan(skb);//和sbk的所属者解除关系


    skb->protocol = eth_type_trans(skb, dev);

    /* it's OK to use per_cpu_ptr() because BHs are off */
    pcpu_lstats = dev->ml_priv;
    lb_stats = per_cpu_ptr(pcpu_lstats, smp_processor_id());

    len = skb->len;
    if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {//netif_rx是传递给接口接受端

        lb_stats->bytes += len;
        lb_stats->packets++;
    } else
        lb_stats->drops++;

    return NETDEV_TX_OK;
}

static struct net_device_stats *loopback_get_stats(struct net_device *dev)
{
    const struct pcpu_lstats *pcpu_lstats;
    struct net_device_stats *stats = &dev->stats;
    unsigned long bytes = 0;
    unsigned long packets = 0;
    unsigned long drops = 0;
    int i;

    pcpu_lstats = dev->ml_priv;
    for_each_possible_cpu(i) {//对多个cpu变量的信息进行统计，得到统计和

        const struct pcpu_lstats *lb_stats;

        lb_stats = per_cpu_ptr(pcpu_lstats, i);
        bytes += lb_stats->bytes;
        packets += lb_stats->packets;
        drops += lb_stats->drops;
    }
    stats->rx_packets = packets;//因为发送和接受是同样字节的

    stats->tx_packets = packets;
    stats->rx_dropped = drops;
    stats->rx_errors = drops;
    stats->rx_bytes = bytes;
    stats->tx_bytes = bytes;
    return stats;
}

static u32 always_on(struct net_device *dev)
{
    return 1;
}

static const struct ethtool_ops loopback_ethtool_ops = {
    .get_link        = always_on,
    .set_tso        = ethtool_op_set_tso,
    .get_tx_csum        = always_on,
    .get_sg            = always_on,
    .get_rx_csum        = always_on,
};

static int loopback_dev_init(struct net_device *dev)
{
    struct pcpu_lstats *lstats;

    lstats = alloc_percpu(struct pcpu_lstats);
    if (!lstats)
        return -ENOMEM;

    dev->ml_priv = lstats;
    return 0;
}

static void loopback_dev_free(struct net_device *dev)
{
    struct pcpu_lstats *lstats = dev->ml_priv;

    free_percpu(lstats);
    free_netdev(dev);
}

static const struct net_device_ops loopback_ops = {
    .ndo_init = loopback_dev_init,
    .ndo_start_xmit= loopback_xmit,
    .ndo_get_stats = loopback_get_stats,
};

/*
 * The loopback device is special. There is only one instance
 * per network namespace.
 */
static void loopback_setup(struct net_device *dev)
{
    dev->mtu        = (16 * 1024) + 20 + 20 + 12;
    dev->hard_header_len    = ETH_HLEN;    /* 14    */
    dev->addr_len        = ETH_ALEN;    /* 6    */
    dev->tx_queue_len    = 0;
    dev->type        = ARPHRD_LOOPBACK;    /* 0x0001*/
    dev->flags        = IFF_LOOPBACK;
    dev->priv_flags     &= ~IFF_XMIT_DST_RELEASE;
    dev->features         = NETIF_F_SG | NETIF_F_FRAGLIST
        | NETIF_F_TSO
        | NETIF_F_NO_CSUM
        | NETIF_F_HIGHDMA
        | NETIF_F_LLTX
        | NETIF_F_NETNS_LOCAL;
    dev->ethtool_ops    = &loopback_ethtool_ops;
    dev->header_ops        = &eth_header_ops;
    dev->netdev_ops        = &loopback_ops;
    dev->destructor        = loopback_dev_free;
}

/* Setup and register the loopback device. */
static __net_init int loopback_net_init(struct net *net)
{
    struct net_device *dev;
    int err;

    err = -ENOMEM;
    dev = alloc_netdev(0, "lo", loopback_setup);
    if (!dev)
        goto out;

    dev_net_set(dev, net);
    err = register_netdev(dev);
    if (err)
        goto out_free_netdev;

    net->loopback_dev = dev;
    return 0;


out_free_netdev:
    free_netdev(dev);
out:
    if (net == &init_net)
        panic("loopback: Failed to register netdevice: %d\n", err);
    return err;
}

static __net_exit void loopback_net_exit(struct net *net)
{
    struct net_device *dev = net->loopback_dev;

    unregister_netdev(dev);
}

/* Registered in net/core/dev.c */
struct pernet_operations __net_initdata loopback_net_ops = {
       .init = loopback_net_init,
       .exit = loopback_net_exit,
};