From 2e50326c44c802ca9b9d591341085e49208927be Mon Sep 17 00:00:00 2001
From: Pierre Riteau <Pierre.Riteau@irisa.fr>
Date: Wed, 25 Nov 2009 18:49:35 +0000
Subject: [PATCH] net: check for TUNSETOFFLOAD support before trying to enable
 offload features

This avoids the "TUNSETOFFLOAD ioctl() failed: Invalid argument" message
on kernels without TUNSETOFFLOAD support.

Signed-off-by: Pierre Riteau <Pierre.Riteau@irisa.fr>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
 net/tap-linux.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/tap-linux.c b/net/tap-linux.c
index e4f7e2723b..6af9e824d3 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -131,6 +131,11 @@ void tap_fd_set_offload(int fd, int csum, int tso4,
 {
     unsigned int offload = 0;
 
+    /* Check if our kernel supports TUNSETOFFLOAD */
+    if (ioctl(fd, TUNSETOFFLOAD, 0) != 0 && errno == EINVAL) {
+        return;
+    }
+
     if (csum) {
         offload |= TUN_F_CSUM;
         if (tso4)