vamshi varma wrote : >Hi, > I am trying to understand the tcp/ip implementation. >I am stuck at the following point. > >In function ip_queue_xmit which calls dev_queue_xmit(as I understood >earlier) after forming ip header I find following line of code. > >skb->dst->output(skb); > >Till now I thought output func is initialised to dev_queue_xmit. >I tried to print skb->data just before calling this output function >and at the begining of dev_queue_xmit. >The first printk showed only ip packet(without >header) and to my surprise second one at the beging of dev_queue_xmit >it printed with ethernet header. >Can anybody exlain what is the code flow between skb->dst->output and >dev_queue_xmit. And where this dst->output is being initialised. okay this is how packets flow in the stack ip_rcv -> ip_route_input (does a cache route lookup,if fails) -> [ ip_route_input_slow (this sets dst->output to ip_finish_output and dst->input ip_forward) ] -> skb->dst->input(ip_forward) -> TTL processing etc. -> ip_finish_output -> ip_finish_output2 (this causes hh->output or neighbour->output (typically dev_queue_xmit) -> finally dev->hard_start_xmit(this function is implemented by device driver) If the packet generated is a local IP packet, it gets calls ip_route_output_slow. Which does things similar to ip_route_input_slow. --a -- How do u delete a letter in vi and paste it after the next one? "xp" -- -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ IRC Channel: irc.openprojects.net / #kernelnewbies Web Page: http://www.kernelnewbies.org/
