Re: Creating and sending a packet from a kernel module

[Nalin gupta]

Joshua Stewart,

I saw that you are trying something similar, to me. I also found
Mr. Gary too is trying something similar. Though I do not have
proper solution for your problem, but it may be worth if you go
through few of these recent postings:

http://www.uwsg.iu.edu/hypermail/linux/kernel/0303.2/0437.html
http://www.uwsg.iu.edu/hypermail/linux/kernel/0303.2/0971.html
http://www.uwsg.iu.edu/hypermail/linux/kernel/0303.2/0974.html
http://www.uwsg.iu.edu/hypermail/linux/kernel/0303.2/0984.html

http://www.uwsg.iu.edu/hypermail/linux/net/0303.2/0043.html
http://www.uwsg.iu.edu/hypermail/linux/net/0303.1/0061.html

The above posting will tell you few problem which one faces,
while invoking sock_sendmsg from kernel module, in particular
when it is either in interrupt context or BH (net_bh) context.

I still wonder why ?

Only possibility I see to send / recv TCP/IP packet from kernel
module is using kernel thread.

Important API / structures are:

a.  sock_create - to create socket (like socket syscall)
b.  struct socket * sock
c.  sock->ops->bind     to bind to local address
d.  sock->ops->listen   like listen syscall
e.  sock_sendmsg       (never succeed in interrupt or BH context,
                        always fail in alloc_skb, I wonder why ?)
f.  sock_recvmsg  - Ordinary kernel module logically can not use
                    it. As you need some running thread context to
                    wait/block to receive on socket.

I've tried answering as per my limited know-how. 
Some one may like to add.

you may like to refer some example like khttpd under
/usr/src/linux/net

regards,
- nalin

--

On Thu, 20 Mar 2003 20:46:00  
 Joshua Stewart wrote:
>I'd like to create and send a brand new TCP SYN packet from a module. 
>Does anybody have an example of how to do this.
>
>I've tried doing alloc_skb, filling in all the information I could
>imagine needing in skb->data, but what is the minimal amount of stuff
>needed by the other parts of the skb to get this packet moving?
>
>Is there an easy way to create and own a TCP socket from a module that I
>could send and receive on?
>
>Thanks,
>	Josh
>
>-- 
>Joshua Stewart <[e-mail]>
>

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