list_for_each_entry_rcu in net/core/dev.c

["Michele 'mydecay' Marchetto" <smarchetto1@tin.it>]

hi all.
i have noticed that in list_for_each_entry_rcu the checks
(!ptype->dev || ptype->dev == skb->dev) are made on the current
packet but the function (delived_skb) is called on the previous one.

i can't understand why this make sense.. anyone can explain me?

Moreover i created a patch that removes pt_prev and uses only ptype and
all seems to work fine..

against test8

--- linux/net/core/dev.old.c    2003-11-22 15:18:26.000000000 +0100
+++ linux/net/core/dev.c        2003-11-23 13:24:58.626540048 +0100
@@ -1530,7 +1530,7 @@

 int netif_receive_skb(struct sk_buff *skb)
 {
-       struct packet_type *ptype, *pt_prev;
+       struct packet_type *ptype;
        int ret = NET_RX_DROP;
        unsigned short type = skb->protocol;

@@ -1550,39 +1550,28 @@

        skb->h.raw = skb->nh.raw = skb->data;

-       pt_prev = NULL;
        rcu_read_lock();
        list_for_each_entry_rcu(ptype, &ptype_all, list) {
                if (!ptype->dev || ptype->dev == skb->dev) {
-                       if (pt_prev) 
-                               ret = deliver_skb(skb, pt_prev, 0);
-                       pt_prev = ptype;
+                       if (ptype) 
+                               ret = deliver_skb(skb, ptype, 0);
                }
        }

        handle_diverter(skb);

-       if (__handle_bridge(skb, &pt_prev, &ret))
+       if (__handle_bridge(skb, &ptype, &ret))
                goto out;

        list_for_each_entry_rcu(ptype, &ptype_base[ntohs(type)&15],
list) {
                if (ptype->type == type &&
                    (!ptype->dev || ptype->dev == skb->dev)) {
-                       if (pt_prev) 
-                               ret = deliver_skb(skb, pt_prev, 0);
-                       pt_prev = ptype;
+                       if (ptype) 
+                               ret = deliver_skb(skb, ptype, 0);
                }
        }
-
-       if (pt_prev) {
-               ret = pt_prev->func(skb, skb->dev, pt_prev);
-       } else {
-               kfree_skb(skb);
-               /* Jamal, now you will not able to escape explaining
-                * me how you were going to use this. :-)
-                */
-               ret = NET_RX_DROP;
-       }
+       
+       ret = NET_RX_DROP;

 out:
        rcu_read_unlock();

-- 
Michele 'mydecay' Marchetto
S.P.I.N.E. Group - www.spine-group.org


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