# tcbinfo.listhead and tcp_input() placing



## jmathon (Nov 19, 2008)

Hi everyone,

I would like to know if tcp_input() is executed before modifying tcbinfo.listhead ?

In fact, I'm hooking tcp_input() and want to interogate tcbinfo.lishead to know if the tcp connection is already known.
And, the problem is, if the struct is modified before tcp_input(), I'll find the connection everytime 

Or is there any other way to check if connection is already known (instead of saving every connection in a local struct)

Thanks !
Jerem


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## netrom (Nov 19, 2008)

Hello jmathon,

I'm not totally sure but you might want to have a look at one of the following (in tcp_var.h):


```
void tcp_twstart(struct tcpcb *);
void tcp_init(void);
void tcp_ctlinput(int, struct sockaddr *, void *);
```

It is kind of a guess, really.


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