On Wednesday 19 March 2003 23:59, David S. Miller wrote: > From: N N Ashok <nalkunda@cse.msu.edu> > Date: Wed, 19 Mar 2003 23:55:02 -0500 > > I am unable to understand how a rtable structure casted to dst_entry > will give a correct pointer to the input() function. I looked at the fields > in rtable and dst_entry, the fields in the structures are cannot be lined > up (the fourth field in rtable is not the same type as the fourth field in > dst_entry). > > "struct rtable" starts with a "struct dst_entry" Thanks David. I did see that. But however, I could not understand how "struct rtable" can be casted to "struct dst_entry" and then back again, all the while accessing fields of both structures. When the (struct rtable *)rth is filled in ip_route_input(), the variables accessed are those of rtable. Then rth is cast to (struct dst_entry *) and assigned to skb->dst (which is of type struct dst_entry *). After this, in ip_rcv_finish(), the field of dst_entry is accessed as in: skb->dst->input(). I am unable to understand how, data filled in as rtable fields will be valid when accessed as dst_entry fields. Later in ip_forward() (for a packet to be forwarded), the skb->dst is cast to (struct rtable *) and its fields accessed. A correction to the previous post: the skb->dst->input() is invoked in ip_rcv_finish() and not in ip_route_input() as mentioned in the post. Thanks, Ashok - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
