Merge commit '1dd3a74d2ee2d873cde0b390b536e45420b3fe05' into HEAD

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/net/tap-linux.c b/net/tap-linux.c
index c6521bec34..3eaedc40ad 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -39,6 +39,7 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required
 {
     struct ifreq ifr;
     int fd, ret;
+    int len = sizeof(struct virtio_net_hdr);
 
     TFR(fd = open(PATH_NET_TUN, O_RDWR));
     if (fd < 0) {
@@ -65,6 +66,13 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required
             close(fd);
             return -1;
         }
+        /*
+         * Make sure vnet header size has the default value: for a persistent
+         * tap it might have been modified e.g. by another instance of qemu.
+         * Ignore errors since old kernels do not support this ioctl: in this
+         * case the header size implicitly has the correct value.
+         */
+        ioctl(fd, TUNSETVNETHDRSZ, &len);
     }
 
     if (ifname[0] != '\0')