本文记录了 Lab: networking 的实验过程

Lab: networking

查看相关代码

  • kernel/net.h，kernel/net.c
  • kernel/e1000_dev.h，kernel/e1000.c

e1000_transmit

  • 按照实验指导页面的 Hints，已经很详细了，跟着一步步做
  • 记得获取/释放锁

e1000_recv

Q1：一开始用 e1000_recv 函数只读取一个 mbuf，然后测试的时候过不了

A1：我们需要在一次中断时，就把所有到达的数据都处理掉。

Q2：在测试多线程那个函数时一直有问题，重复获取锁了

A1：在最后一节课中，Frans 教授给出了两种解决办法

  • e1000_recv 可以不加锁，处理完一个recv 前，下一个recv 会被阻塞住。
  • e1000_recv 不可以和 e1000_transmit 用同一把锁，如果 recv 接收到一个 ARP 包，会在recv 内部发送 ARP 响应包，从而调用 e1000_transmit，两者用同一把锁就死锁了，因此需要两把锁。

其他的跟着 Hints 做就行了

测试

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make qemu
nettests
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make grade

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diff --git a/kernel/e1000.c b/kernel/e1000.c
index 70a2adf..88e021d 100644
--- a/kernel/e1000.c
+++ b/kernel/e1000.c
@@ -103,6 +103,33 @@ e1000_transmit(struct mbuf *m)
   // a pointer so that it can be freed after sending.
   //
   
+  acquire(&e1000_lock);
+
+  // First ask the E1000 for the TX ring index at which it's expecting the next packet
+  int tail = regs[E1000_TDT];
+
+  // Then whether the E1000 have finished the corresponding previous
+  // transmission request, if no, then return an error
+  if((tx_ring[tail].status & E1000_TXD_STAT_DD) == 0){
+    release(&e1000_lock);
+    return -1;
+  }
+
+  // Otherwish free the last mbuf if there was one
+  if(tx_mbufs[tail]){
+    mbuffree(tx_mbufs[tail]);
+  }
+
+  // Then fill in the descriptor
+  tx_ring[tail].addr = (uint64) m->head;
+  tx_ring[tail].length = m->len;
+  tx_ring[tail].cmd = E1000_TXD_CMD_RS | E1000_TXD_CMD_EOP;
+
+  tx_mbufs[tail] = m;
+
+  __sync_synchronize();
+
+  // Finally, update the ring position
+  regs[E1000_TDT] = (tail + 1) % TX_RING_SIZE;
+  release(&e1000_lock);
   return 0;
 }
 
@@ -115,6 +142,30 @@ e1000_recv(void)
   // Check for packets that have arrived from the e1000
   // Create and deliver an mbuf for each packet (using net_rx()).
   //
+  while(1){
+    // First fetching the E1000_RDT control register
+    // and adding one modulo RX_RING_SIZE
+    int tail = (regs[E1000_RDT] + 1) % RX_RING_SIZE;
+
+    // Then check if a new packet is available
+    if((rx_ring[tail].status & E1000_RXD_STAT_DD) == 0){
+      return;
+    }
+    __sync_synchronize();
+    // Otherwise, update the mbuf's m->len to the length reported in the descriptor
+    // Deliver the mbuf to the network stack using net_rx()
+    rx_mbufs[tail]->len = rx_ring[tail].length;
+    net_rx(rx_mbufs[tail]);
+
+    // Then allocate a new mbuf using mbufalloc() to replace the one just given to net_rx()
+    // Program its data pointer (m->head) into the descriptor. Clear the descriptor's status bits to zero
+    rx_mbufs[tail] = mbufalloc(0);
+    if(!rx_mbufs[tail])
+      panic("e1000_recv");
+    rx_ring[tail].addr = (uint64) rx_mbufs[tail]->head;
+    rx_ring[tail].status = 0;
+    __sync_synchronize();
+
+    regs[E1000_RDT] = tail  % RX_RING_SIZE;
+  }
 }
 
 void
diff --git a/packets.pcap b/packets.pcap
index 82d353e..58bcc0f 100644
Binary files a/packets.pcap and b/packets.pcap differ