[PATCH v2 04/13] net: tap: Pad short frames to minimum size before send

[Bin Meng <bmeng.cn@gmail.com>]

Do the same for tap backend as what we did for slirp.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
---

 net/tap-win32.c | 12 ++++++++++++
 net/tap.c       | 12 ++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/net/tap-win32.c b/net/tap-win32.c
index 2b5dcda36e..ec35ab8ce7 100644
--- a/net/tap-win32.c
+++ b/net/tap-win32.c
@@ -31,6 +31,7 @@
 
 #include "qemu-common.h"
 #include "clients.h"            /* net_init_tap */
+#include "net/eth.h"
 #include "net/net.h"
 #include "net/tap.h"            /* tap_has_ufo, ... */
 #include "qemu/error-report.h"
@@ -688,9 +689,20 @@ static void tap_win32_send(void *opaque)
     uint8_t *buf;
     int max_size = 4096;
     int size;
+    uint8_t min_buf[ETH_ZLEN];
 
     size = tap_win32_read(s->handle, &buf, max_size);
     if (size > 0) {
+        if (!s->nc.peer->do_not_pad) {
+            /* Pad to minimum Ethernet frame length */
+            if (size < ETH_ZLEN) {
+                memcpy(min_buf, buf, size);
+                memset(&min_buf[size], 0, ETH_ZLEN - size);
+                buf = min_buf;
+                size = ETH_ZLEN;
+            }
+        }
+
         qemu_send_packet(&s->nc, buf, size);
         tap_win32_free_buffer(s->handle, buf);
     }
diff --git a/net/tap.c b/net/tap.c
index b7512853f4..f96b1ccfc0 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -32,6 +32,7 @@
 #include <sys/socket.h>
 #include <net/if.h>
 
+#include "net/eth.h"
 #include "net/net.h"
 #include "clients.h"
 #include "monitor/monitor.h"
@@ -189,6 +190,7 @@ static void tap_send(void *opaque)
 
     while (true) {
         uint8_t *buf = s->buf;
+        uint8_t min_buf[ETH_ZLEN];
 
         size = tap_read_packet(s->fd, s->buf, sizeof(s->buf));
         if (size <= 0) {
@@ -200,6 +202,16 @@ static void tap_send(void *opaque)
             size -= s->host_vnet_hdr_len;
         }
 
+        if (!s->nc.peer->do_not_pad) {
+            /* Pad to minimum Ethernet frame length */
+            if (size < ETH_ZLEN) {
+                memcpy(min_buf, buf, size);
+                memset(&min_buf[size], 0, ETH_ZLEN - size);
+                buf = min_buf;
+                size = ETH_ZLEN;
+            }
+        }
+
         size = qemu_send_packet_async(&s->nc, buf, size, tap_send_completed);
         if (size == 0) {
             tap_read_poll(s, false);
-- 
2.25.1