[Qemu-devel] [PATCH 49/60] tap: reset vnet header size on open

[Michael Tokarev]

From: "Michael S. Tsirkin" <address@hidden>

For tap, we currently assume the vnet header size is 10
(the default value) but that might not be the case
if tap is persistent and has been used by qemu previously.
To fix, set host header size in tap device on open.

Signed-off-by: Michael S. Tsirkin <address@hidden>
Tested-by: Alexander Graf <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
(cherry picked from commit 58ddcd50f30cb5c020bd4f9f36b01ee160a27cac)

Signed-off-by: Michael Tokarev <address@hidden>
---
 net/tap.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/tap.c b/net/tap.c
index f240028..08be84f 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -339,6 +339,13 @@ static TAPState *net_tap_fd_init(VLANState *vlan,
     s->using_vnet_hdr = 0;
     s->has_ufo = tap_probe_has_ufo(s->fd);
     tap_set_offload(&s->nc, 0, 0, 0, 0, 0);
+    /*
+     * Make sure host header length is set correctly in tap:
+     * it might have been modified by another instance of qemu.
+     */
+    if (tap_probe_vnet_hdr_len(s->fd, s->host_vnet_hdr_len)) {
+        tap_fd_set_vnet_hdr_len(s->fd, s->host_vnet_hdr_len);
+    }
     tap_read_poll(s, 1);
     s->vhost_net = NULL;
     return s;
-- 
1.7.10.4