tap: add VNET_LE/VNET_BE operations

The linux tap and macvtap backends can be told to parse vnet headers
according to little or big endian. This is done through the TUNSETVNETLE
and TUNSETVNETBE ioctls.

This patch brings all the plumbing for QEMU to use these APIs.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

net/tap-linux.c

@@ -198,6 +198,40 @@ void tap_fd_set_vnet_hdr_len(int fd, int len)
     }
 }
 
+int tap_fd_set_vnet_le(int fd, int is_le)
+{
+    int arg = is_le ? 1 : 0;
+
+    if (!ioctl(fd, TUNSETVNETLE, &arg)) {
+        return 0;
+    }
+
+    /* Check if our kernel supports TUNSETVNETLE */
+    if (errno == EINVAL) {
+        return -errno;
+    }
+
+    error_report("TUNSETVNETLE ioctl() failed: %s.\n", strerror(errno));
+    abort();
+}
+
+int tap_fd_set_vnet_be(int fd, int is_be)
+{
+    int arg = is_be ? 1 : 0;
+
+    if (!ioctl(fd, TUNSETVNETBE, &arg)) {
+        return 0;
+    }
+
+    /* Check if our kernel supports TUNSETVNETBE */
+    if (errno == EINVAL) {
+        return -errno;
+    }
+
+    error_report("TUNSETVNETBE ioctl() failed: %s.\n", strerror(errno));
+    abort();
+}
+
 void tap_fd_set_offload(int fd, int csum, int tso4,
                         int tso6, int ecn, int ufo)
 {