how ip header added in ip_bulid_xmit function?

how ip header added in ip_bulid_xmit function?

[linux lover]

hello ,
   In ip_output.c file there is ip_build_xmit function
call. when packet comes from tcp layer to IP layer
this function is called. In that i found that 
   skb = sock_alloc_send_skb(sk, length+hh_len+15
,flags&MSG_DONTWAIT, &err);
staement allocates skb for packet. after that i found
that no iphdr adding statement in ip_build_xmit. i
want to know where is iphdr push to skb? cause skb
works using first alloc_skb to allocate memory then
skb_reserve to reserve headroom then put data in skb
by skb_put or skb_push for pushing headers in skb. so
there i found       
  skb->nh.iph = iph = (struct iphdr *)skb_put(skb,
length); 
statement is this does that iphdr adding?

regards,
linuxlover


	
		
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Re: how ip header added in ip_bulid_xmit function?

[Manu Garg]

linux lover wrote:

>hello ,
>   In ip_output.c file there is ip_build_xmit function
>call. when packet comes from tcp layer to IP layer
>this function is called. In that i found that 
>   skb = sock_alloc_send_skb(sk, length+hh_len+15
>,flags&MSG_DONTWAIT, &err);
>staement allocates skb for packet. after that i found
>that no iphdr adding statement in ip_build_xmit. i
>want to know where is iphdr push to skb? cause skb
>works using first alloc_skb to allocate memory then
>skb_reserve to reserve headroom then put data in skb
>by skb_put or skb_push for pushing headers in skb. so
>there i found       
>  skb->nh.iph = iph = (struct iphdr *)skb_put(skb,
>length); 
>statement is this does that iphdr adding?
>
>regards,
>linuxlover
>
>
>	
>		
>__________________________________
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>
>  
>
A packet comes from TCP layer to IP layer through function call 
tp->af_specific->queue_xmit() (in tcp_output.c:tcp_transmit_skb() ). For 
IP this function is nothing but ip_queue_xmit() defined in
ip_output.c.

If you'll check this function, it clearly allocates ip header and put 
information in it.

----------------------------------------------------
iph = (struct iphdr *) skb_push(skb, sizeof(struct iphdr) + (opt ? 
opt->optlen : 0));
        *((__u16 *)iph) = htons((4 << 12) | (5 << 8) | 
(sk->protinfo.af_inet.tos & 0xff));
iph->tot_len = htons(skb->len);
if (ip_dont_fragment(sk, &rt->u.dst))
    iph->frag_off = htons(IP_DF);
else
    iph->frag_off = 0;
iph->ttl      = sk->protinfo.af_inet.ttl;
iph->protocol = sk->protocol;
iph->saddr    = rt->rt_src;
iph->daddr    = rt->rt_dst;
skb->nh.iph   = iph;
---------------------------------------------------

I hope this answers your question.

regards,
Manu Garg
http://manugarg.freezope.org/notes

Re: how ip header added in ip_bulid_xmit function?

[linux lover]

hello,

> A packet comes from TCP layer to IP layer through
> function call 
> tp->af_specific->queue_xmit() (in
> tcp_output.c:tcp_transmit_skb() ). For 
> IP this function is nothing but ip_queue_xmit()
> defined in ip_output.c.
> 
   then why ip_build_xmit and ip_build_xmit_slow used?
i think in case of ICMP packet control in icmp.c
alwayes goes to ip_build_xmit?


regards,
linux_lover


	
		
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RE: how ip header added in ip_bulid_xmit function?

[Galy Lee]

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It seems that ip_build_xmit_slow is  used to send to bulk data, but the
ip_build_xmit is used to send single data packet.

-----Original Message-----
From: netdev-bounce@oss.sgi.com [mailto:netdev-bounce@oss.sgi.com]On
Behalf Of linux lover
Sent: Wednesday, May 19, 2004 2:21 PM
To: Manu Garg
Cc: linuxnet; netdev; netfilter
Subject: Re: how ip header added in ip_bulid_xmit function?




hello,

> A packet comes from TCP layer to IP layer through
> function call 
> tp->af_specific->queue_xmit() (in
> tcp_output.c:tcp_transmit_skb() ). For 
> IP this function is nothing but ip_queue_xmit()
> defined in ip_output.c.
> 
   then why ip_build_xmit and ip_build_xmit_slow used?
i think in case of ICMP packet control in icmp.c
alwayes goes to ip_build_xmit?


regards,
linux_lover


	
		
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[-- Attachment #2: Type: text/html, Size: 2210 bytes --]

RE: how ip header added in ip_bulid_xmit function?

[linux lover]

--- Galy  Lee <galylee@gdnt.com.cn> wrote:
> 
> It seems that ip_build_xmit_slow is  used to send to
> bulk data, but the
> ip_build_xmit is used to send single data packet.
> 
that mean ip_queue_xmit as well as ip_build_xmit and
ip_build_xmit_slow are all used for sending packet.
but whats difference then between all three functions?
> regards,
> linux_lover
> 
> 
> 	



	
		
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