Computer Science 881
                            Quiz 3             Name_______________________

1. For each of the following actions indicates whether it occurs
   in the context of an application process (A), context of a
   hardware IRQ (H) or the context of a software IRQ (S). (If
   multiple answers can apply, supply them all).

   ___ a. Enqueuing of a UDP sk_buff on the output device queue

   ___ b. Dequeing the UDP sk_buff from the output device queue
          and passing it to the device driver

   ___ c. Enqueuing an sk_buff that has completed transmission on
          the queue on the softnet data structure.

   ___ d. Dequeuing an sk_buff that has completed transmission on
          the queue from the softnet data structure and freeing it.

2. Under what condition(s) might a packet that is dequeued by
   pfifo_fast_dequeue() NOT be the last packet that was enqueued by
   pfifo_fast_enqueue(). (Assume a UNI processor system here.. but
   also assume the CORRECT no-preemption in kernel mode model used
   in Linux)








3. For each of the following, identify whether it is done in
   (A) the context of the application making a system call
   (H) the context of the hardware IRQ associated with the packets arrival
   (S) the context of the softirq associated with packet arrival

   ___ a. Determining the identity of the network layer protocol to
          which a received packet is to be passed (ETH_P_IP.. etc).

   ___ b. Determining the identity of the transport layer protocol to
          which a received packet is to be passed (UDP, TCP, . etc).

   ___ c. Enqueuing an sk_buff that has been received on the queue
          on the softnet data structure.


4. The net_rx_action() function processes

   a. exactly one packet each time     b. one or more packets each time
      the softirq is raised               the softirq is raised

   c. exactly 300 packets each time
      the soft irq is raised.

5. Under what conditions (if any) do the softirqs,  net_tx_action()
   and net_rx_action() reschedule themselves.

   a. net_tx_action -




   b. net_rx_action -



6. In  IP reassembly a single instance struct ipq represents

   a. a single fragment              b. a single packet being
                                        reassembled
   c. all packets presently
      being resassembled.


7. Distinguish between the use of the  "meat" and "len" variables
   in reassembly


   meat -



   len  -


8. While frags are <<being reassembled>> they are linked via the

    a. skb->next pointer           b. the shinfo(skb)->fraglist

    c. the first one in the chain  d. the first one in the chain
       uses fraglist and the          uses fraglist and the others
       others use next.               use next.

9. After a successful reassembly << completes >> the frags are linked
   as follows:

    a. skb->next pointer           b. the shinfo(skb)->fraglist

    c. the first one in the chain  d. the first one in the chain
       uses fraglist and the          uses fraglist and the others
       others use next.               use next.


10. When a fragement is received and its head-end overlaps the tail-end
    of a single fragment that has already been received

   a. the overlapped tail of the      b. the overlapping head of the
      existing fragment is               new fragment is discarded
      discarded

   c. the ENTIRE existing overlapped  d. the entire new fragment is
      fragment is discarded.             discarded

11. When a packet is to be delivered to multiple raw sockets and
    to multiple transport protocols (e.g. multiple tcpdumps are
    running)

    a. delivery to all raw sockets    b. delivery to all transports
       occurs first                      occurs first

    c. delivery to the first raw      d. delivery to all but the last
       socket precedes the transports    raw socket precedes the transports
       and the remaining raw sockets     and the last raw socket follows
       follow the transports             the transports