[Qemu-devel] bug in pcnet patch?

[Zhai, Edwin]

hi,

i have found that guest and host can't communicate with each other with 
pcnet patch, but ne2000 is okey.
(http://dad-answers.com/qemu/patches/AMD-PCNET-II/qemu-pcnet.patch6.gz)

reproduce steps --
use attached qemu-ifup and do a "ifconfig eth0 172.20.0.2 up" in guest 
after boot.  the ping between guest and host doesn't  work.

root cause is that arp packet from tun interface (42 bytes) is small 
than the minimal size(60 bytes) and is droped by guest  pcnet driver.

attached patch(borrowed from ne2000) just expend the packet when size < 60.

any comments?

thanks,
edwin

#!/bin/sh

echo $*

#test for pcnet's bug
ifconfig $1 172.20.0.1 up
route add -net 172.20.0.0 netmask 255.255.0.0 gw 172.20.0.1 dev $1

--- a/hw/pcnet.c        Thu Sep  1 21:30:51 2005
+++ b/hw/pcnet.c        Mon Sep  5 09:55:33 2005
@@ -380,10 +380,13 @@
     return sizeof(s->buffer)-16;
 }
 
+#define MIN_BUF_SIZE 60
+
 static void pcnet_receive(void *opaque, const uint8_t *buf, int size)
 {
     PCNetState *s = opaque;
     int is_padr = 0, is_bcast = 0, is_ladr = 0;
+    uint8_t buf1[60];
 
     if (CSR_DRX(s) || CSR_STOP(s) || CSR_SPND(s) || !size)
         return;
@@ -391,6 +394,14 @@
 #ifdef PCNET_DEBUG
     printf("pcnet_receive size=%d\n", size);
 #endif
+
+    /* if too small buffer, then expand it */
+    if (size < MIN_BUF_SIZE) {
+        memcpy(buf1, buf, size);
+        memset(buf1 + size, 0, MIN_BUF_SIZE - size);
+        buf = buf1;
+        size = MIN_BUF_SIZE;
+    }
 
     if (CSR_PROM(s) 
         || (is_padr=padr_match(s, buf, size))