net: add a vnet_hdr=on|off parameter

This allows people to disable the IFF_VNET_HDR flag, e.g. for debugging
purposes or if they know they may migrate the guest to a machine without
IFF_VNET_HDR support.

It also allows making the lack of IFF_VNET_HDR support an error
condition, e.g. in the case where a guest is being migrated from a host
which does support it.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/qemu-options.hx b/qemu-options.hx
index c745e0ca26..d78b738c77 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -810,7 +810,7 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
     "-net tap[,vlan=n][,name=str],ifname=name\n"
     "                connect the host TAP network interface to VLAN 'n'\n"
 #else
-    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes]\n"
+    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off]\n"
     "                connect the host TAP network interface to VLAN 'n' and use the\n"
     "                network scripts 'file' (default=%s)\n"
     "                and 'dfile' (default=%s);\n"
@@ -818,6 +818,8 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
     "                use 'fd=h' to connect to an already opened TAP interface\n"
     "                use 'sndbuf=nbytes' to limit the size of the send buffer; the\n"
     "                default of 'sndbuf=1048576' can be disabled using 'sndbuf=0'\n"
+    "                use vnet_hdr=off to avoid enabling the IFF_VNET_HDR tap flag; use\n"
+    "                vnet_hdr=on to make the lack of IFF_VNET_HDR support an error condition\n"
 #endif
     "-net socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
     "                connect the vlan 'n' to another VLAN using a socket connection\n"