Hi, Sorry, I of course discuss here your previous question about SKB Regards, Rami On Sat, May 3, 2014 at 1:34 PM, Rami Rosen <roszenrami@xxxxxxxxx> wrote: > Hi, Pranay, > > First, let's assume that you are talking about IPv4, though you did not > mention it explicitly. (The principles in IPv6 are quite similar, though) > > A packet is sent out in the usual case with the ip_queue_xmit() method. > The ip_queue_xmit() method calls the ip_route_output_ports() method > in order to perform a lookup in the IPv4 routing tables. > > see: http://lxr.free-electrons.com/source/net/ipv4/ip_output.c#L352 > > The results of this IPv4 routing lookup determines on which network device > (net_device) the packet will be sent. You should look at the code of > ip_route_output_ports() method in net/ipv4/route.c in order to > understand the IPv4 routing subsystem and the IPv4 routing lookup. > > Packets can, under certain circumstances, be sent by the ip_send_skb() > method, but this happens when the flow (which consists also of the > net_device to be used) is known before. > > Best Regards, > Rami Rosen > http://ramirose.wix.com/ramirosen > > > On Sat, May 3, 2014 at 12:43 PM, Pranay Srivastava <pranjas@xxxxxxxxx> wrote: >> Hi >> >> Referring to Documentation/networking/netdevices.txt >> >> a) >> >> ndo->ndo_start_xmit if written "as is" will be thread safe? [Correct?] >> NETIF_F_LLTX is not set only then this is true. >> >> But dev_queue_xmit(skb) doesn't seem to take any lock, neither does >> dev_hard_start_xmit. Please let me know if i'm wrong and where is this >> lock taken before calling dev_queue_xmit/dev_hard_start_xmit. >> >> >> b) >> >> Why and when would I want to use rtnl_lock/unlock? Is it like >> registering multiple device simultaneously? >> >> >> c) >> >> ndo->ndo_start_xmit is supposed to start the transmission of the skb. >> However I've a doubt >> >> ---> Suppose that there's no room left for the incoming skb in the >> device buffer, so in that case it would be ideal to call >> netif_stop_queue. At this the the skb already with the ndo_start_xmit >> will not be retried again[Correct?] >> >> ----> Is ndo_start_xmit required to wait in this case? However if the >> above spin_lock in a) was taken then this would be a waste. So is it >> possible that this skb is "deffered" to whenever there's room and >> return NETDEV_TX_OK? But if we do this we are telling the application >> that it's packet was delivered so in case there was a timeout set by >> the application on a reply it would again send us the same packet. So >> instead of "deferring" is it good to "drop" ? >> >> >> >> -- >> ---P.K.S >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
