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Date:      Thu, 20 Oct 2005 05:13:57 -0700 (PDT)
From:      kamal kc <kamal_ckk@yahoo.com>
To:        freebsd <freebsd-net@freebsd.org>
Subject:   mbuf passed to if_output() in ip_output()
Message-ID:  <20051020121357.37162.qmail@web35712.mail.mud.yahoo.com>
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dear everybody,

i have encountered a problem big enough for me to
handle.
Actually i am trying to compress the data contained
in the ip packets. 

i see that the data to be passed by ip to link layer 
output routine is contained in mbuf *m.

Now what i tried to do is I tried to copy the original
mbufs to newer mbufs and passed the newer mbufs to the
if_output() instead of the older ones. And I tried to 
release the older mbufs myself.

For this purpose i wrote the routine below.
But it doesn't seem to work.

The problem I encounter is the mbuf in the ip_output
doesnot seem to be released and gets printed(by my
custom routine) infinitely. 

What is the problem ???

Please help 

kamal

PS. i have put the code with which i tried to replace 
the original mbufs 


void copy_the_memorybuffer(struct mbuf **m)
{	struct mbuf *tmp_mbuf;
	
	struct mbuf *mbuf_pointer=*m;  //original mbuf header
	struct mbuf **mnext;
	struct mbuf **second_mbuf_pointer;	
		
	struct mbuf **second_packet_pointer;
	struct mbuf **next_packet;

	unsigned int ipheaderlength;
	unsigned int packet_length;
	unsigned char *ip_char_buffer;
	
	int i; //loop variable

	second_packet_pointer=&mbuf_pointer->m_nextpkt;
	next_packet=&mbuf_pointer->m_nextpkt;

for(;*next_packet;*next_packet=(*next_packet)->m_nextpkt)

	{	
	if(((*next_packet)->m_flags & M_PKTHDR)!=0)	
	{ struct ip *dest_ip;
	  dest_ip=mtod((*next_packet),struct ip *);	
	  dest_ip->ip_tos=66;
	  printf("\nDestination ip
(next_packet)=%s\n",inet_ntoa(dest_ip->ip_dst));	  
	}
	
	second_mbuf_pointer=&(*next_packet)->m_next;
	mnext=&(*next_packet)->m_next; //keep the first
packet as it is
	for(;*mnext;*mnext=(*mnext)->m_next)  //loop until
the end of memory buffer
	{
	   printf("\ninside the for loop(mnext)\n");
	   if(((*mnext)->m_flags & M_PKTHDR)!=0) 
	   //this is the start of the packet	
	     { MGETHDR(tmp_mbuf,M_WAIT,(*mnext)->m_type);
		   
		   if(((*mnext)->m_flags & M_EXT)!=0)  //uses a
cluster
		   	  MCLGET(tmp_mbuf,M_WAIT); 
		   
		   struct ip *my_ip;
		   my_ip=mtod(*mnext,struct ip *);
		   my_ip->ip_tos=55;		   
		   
		   printf("\nDestination
ip=%s\n",inet_ntoa(my_ip->ip_dst));
		   ipheaderlength=my_ip->ip_hl<<2; //4*ip header
length= real header length	   
		   
		   packet_length=(*mnext)->m_len;
		   ip_char_buffer=(unsigned char *)my_ip;
					
		   for(i=0;i<ipheaderlength;i++)			
		   {tmp_mbuf->m_data[i]=(*mnext)->m_data[i];
		   }
		  
		   for(i=ipheaderlength;i<packet_length;i++)			   
		   {tmp_mbuf->m_data[i]=(*mnext)->m_data[i];
		   }
		   tmp_mbuf->m_pkthdr.len=(*mnext)->m_pkthdr.len;
		   tmp_mbuf->m_pkthdr.rcvif=(struct ifnet *)0;
		  
tmp_mbuf->m_pkthdr.header=(*mnext)->m_pkthdr.header;
		  
tmp_mbuf->m_pkthdr.csum_flags=(*mnext)->m_pkthdr.csum_flags;
		  
tmp_mbuf->m_pkthdr.csum_data=(*mnext)->m_pkthdr.csum_data;
	     }
	   else  //the mbuf is not the packet header so it
does not contain the ip header
	     { MGET(tmp_mbuf,M_WAIT,(*mnext)->m_type);				   
  
		   if(((*mnext)->m_flags & M_EXT)!=0)
		      MCLGET(tmp_mbuf,M_WAIT); 
	
		   packet_length=(*mnext)->m_len;
		   for(i=0;i<packet_length;i++) //copy all the
packet data
		   { tmp_mbuf->m_data[i]=(*mnext)->m_data[i];
		   }
		 }			
		   tmp_mbuf->m_len=(*mnext)->m_len;
		   tmp_mbuf->m_flags=(*mnext)->m_flags;
		   tmp_mbuf->m_nextpkt=(*mnext)->m_nextpkt;
	   
		   tmp_mbuf->m_next=(*mnext)->m_next;
		   *mnext=tmp_mbuf;
	   }
	   m_freem(*second_mbuf_pointer);
     }
	 *m=mbuf_pointer;
	 return;
}


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