Hello,
I had tried the following little module , which is based on
linux kernel loopback device. The module name is nic.
I run:
insmdo nic.ko
and it was loaded.
What I do is also create a file named: /etc/sysconfig/network-scripts/ifcfg-nic
and ran ifup nic up;
The ifcfg-nic file is:
DEVICE=nic
IPADDR=127.0.0.2
NETMASK=255.0.0.0
NETWORK=127.0.0.0
BROADCAST=127.255.255.255
ONBOOT=yes
NAME=nicloopback
when I ran:
"ifconfig -a"
I saw:
nic Link encap:AMPR NET/ROM HWaddr
inet addr:127.0.0.2 Mask:255.0.0.0
UP RUNNING MTU:0 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Now what I do not understand is:
when I ran
ping 127.0.0.2
I got:
PING 127.0.0.2 (127.0.0.2) 56(84) bytes of data.
64 bytes from 127.0.0.2: icmp_seq=1 ttl=64 time=0.046 ms
64 bytes from 127.0.0.2: icmp_seq=2 ttl=64 time=0.040 ms
who does answer me ? there is no handling of recieve interrupts in that module.
What causes the packet which is sent to 127.0.0.2 to give this answer ?
where is this mechanism implemented in the kernel ?
Here is the code:
static int nic_xmit(struct sk_buff *skb, struct net_device *dev)
{
printk("in nic_xmit\n");
return 0;
}
struct net_device nic_device = {
.name = "nic",
.get_stats = NULL,
.priv = NULL,
.hard_start_xmit = nic_xmit,
};
static int __init nic_init(void)
{
register_netdev(&nic_device);
return 0;
}
//////////////////////////////////////////////////////////////////////////////
static void __exit nic_exit(void)
{
unregister_netdev(&nic_device);
}
//////////////////////////////////////////////////////////////////////////////
module_init(nic_init)
module_exit(nic_exit)
MODULE_DESCRIPTION("test");
MODULE_LICENSE("GPL");
Regards,
Mark
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