eepro100: Pad received short frames

QEMU sends frames smaller than 60 bytes to ethernet nics.
Such frames are rejected by real NICs and their emulations.
To avoid this behaviour, other NIC emulations pad received
frames. This patch enables this workaround for eepro100, too.

All related code is marked with CONFIG_PAD_RECEIVED_FRAMES,
so we can drop this in case QEMU's networking code is
ever changed.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/eepro100.c

diff --git a/hw/eepro100.c b/hw/eepro100.c
index 848bf79..ab5c699 100644
--- a/hw/eepro100.c
+++ b/hw/eepro100.c
@@ -48,6 +48,15 @@
 #include "eeprom93xx.h"
 #include "sysemu.h"
 
+/* QEMU sends frames smaller than 60 bytes to ethernet nics.
+ * Such frames are rejected by real nics and their emulations.
+ * To avoid this behaviour, other nic emulations pad received
+ * frames. The following definition enables this padding for
+ * eepro100, too. We keep the define around in case it might
+ * become useful the future if the core networking is ever
+ * changed to pad short packets itself. */
+#define CONFIG_PAD_RECEIVED_FRAMES
+
 #define KiB 1024
 
 /* Debug EEPRO100 card. */
@@ -1640,19 +1649,32 @@
      */
     EEPRO100State *s = DO_UPCAST(NICState, nc, nc)->opaque;
     uint16_t rfd_status = 0xa000;
+#if defined(CONFIG_PAD_RECEIVED_FRAMES)
+    uint8_t min_buf[60];
+#endif
     static const uint8_t broadcast_macaddr[6] =
         { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
 
+#if defined(CONFIG_PAD_RECEIVED_FRAMES)
+    /* Pad to minimum Ethernet frame length */
+    if (size < sizeof(min_buf)) {
+        memcpy(min_buf, buf, size);
+        memset(&min_buf[size], 0, sizeof(min_buf) - size);
+        buf = min_buf;
+        size = sizeof(min_buf);
+    }
+#endif
+
     if (s->configuration[8] & 0x80) {
         /* CSMA is disabled. */
         logout("%p received while CSMA is disabled\n", s);
         return -1;
+#if !defined(CONFIG_PAD_RECEIVED_FRAMES)
     } else if (size < 64 && (s->configuration[7] & BIT(0))) {
         /* Short frame and configuration byte 7/0 (discard short receive) set:
          * Short frame is discarded */
         logout("%p received short frame (%zu byte)\n", s, size);
         s->statistics.rx_short_frame_errors++;
-#if 0
         return -1;
 #endif
     } else if ((size > MAX_ETH_FRAME_SIZE + 4) && !(s->configuration[18] & BIT(3))) {
@@ -1731,9 +1753,11 @@
             "(%zu bytes); data truncated\n", rfd_size, size);
         size = rfd_size;
     }
+#if !defined(CONFIG_PAD_RECEIVED_FRAMES)
     if (size < 64) {
         rfd_status |= 0x0080;
     }
+#endif
     TRACE(OTHER, logout("command 0x%04x, link 0x%08x, addr 0x%08x, size %u\n",
           rfd_command, rx.link, rx.rx_buf_addr, rfd_size));
     stw_phys(s->ru_base + s->ru_offset + offsetof(eepro100_rx_t, status),