QoS:tcphdr:using tcp_hdr() unabled network

[gengjia ding]

Hi,

trying to modify source file net/sched/sch_generic.c in Linux Kernel
2.6.37.6, added code:
+ #include <linux/tcp.h>
+ #include <net/tcp.h>
static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc* qdisc){
    + struct tcphdr *th = tcp_hdr(skb);
    + __be16 dport = th->dest;
}
I just want to get destination port of the transport header in the
socket buffer.
After recompiled the kernel and reboot, the network is unable to startup.

But when i exchange the code:
- #include <linux/tcp.h>
- #include <net/tcp.h>
static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc* qdisc){
    - struct tcphdr *th = tcp_hdr(skb);
    - __be16 dport = th->dest;
    + __be16 dport = *(__be16 *)((unsigned char*)(skb->transport_header + 2));
}
after recompile, the network is up.

Where did i make mistake when using the function tcp_hdr()?

Thanks,
--
Gavin Ding
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