I should not be any problem in reading skb there. But who is setting
skb->nh->ip pointers. Because as long as I remember, nh and ip pointers are
not set before netif_rx.
Regards
Mohanlal
----- Original Message -----
From: <naoya@matsulab.is.titech.ac.jp>
To: <kernelnewbies@nl.linux.org>
Sent: Thursday, April 15, 2004 3:20 AM
Subject: reading skb at interrupt handler
Hi,
I'm wondering whether it is possible to read the values of skb just
before execution of netif_rx. As a simple experiment, I inserted my own
code between an interrupt handler of NIC driver and netif_rx (e.g., for
the pcnet32 driver, between pcnet32_rx and netif_rx). It reads
skb->protocol and, if the protocol is IP, reads skb->nh->ip->protocol.
And if the IP protocol is IP_PROTO_ICMP, it drops that. Otherwise, it
simply passes it to netif_rx. After I actually installed that code into a
running machine. I tested it by executing the ping commands from other
hosts to the machine. Although the machine is supposed not
to answer the ICMP requests, it _sometimes_ did, not all the time. So I
imagines that reading such values in the interrupt handler doesn't work
properly. Is this assumption right?
Here is the snippet of my code:
in pcnet32_rx, pcnet32.c:
netif_rx(skb);
-->
/* netif_rx(skb); */
my_code(skb);
void my_code(struct sk_buff *skb)
{
if (ntohs(skb->protocol) == ETH_P_IP) {
...
if (ntohs(skb->nh.iph->protocol) == IPPROTO_ICMP) {
/* drop */
kfree_skb(skb);
} else {
netif_rx(skb);
}
} else {
netif_rx(skb);
}
return;
}
Thanks in advance
Naoya Maruyama
Tokyo Institute of Technology
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