Hi, I don't know much about the network stack code. But from a quick scan of the sources and with the help of a debugger, I found few things that might help you. skb->dst is set in ip_build_xmit(). (This is for the UDP case. TCP seems to be more complicated). The value for dst is taken from the route entry. So, skb->dst ponits to one of the configured interfaces and dst->output will point to ip_output(). >From there, you can trace the call to: ip_output -> ip_finish_output -> ip_finish_output2 ip_finish_output2 calls neigh_resolve_output() either through dst->hh->hh_output or dst->niegbour->output(). And the call to dev->hard_header() and dev_queue_xmit() happens in neigh_resolve_output(). I am sure I am missing lot of details, and special cases. Hopefully, someone more knowledgable will give a complete picture. Hope this helps, Ravi. --- vamshi varma <vamshiv@onebox.com> 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. > > -- > vamshi varma > vamshiv@onebox.com - email __________________________________________________ Do You Yahoo!? Check out Yahoo! Shopping and Yahoo! Auctions for all of your unique holiday gifts! Buy at http://shopping.yahoo.com or bid at http://auctions.yahoo.com -- 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/
