A guest boot hangs while probing the network interface when
iommu_platform=on is used.

The following qemu cli hangs without this patch:

# $QEMU \
  -netdev tap,fd=3,id=hostnet0,vhost=on,vhostfd=4 3<>/dev/tap67 
4<>/dev/host-net \
  -device 
virtio-net-pci,netdev=hostnet0,id=net0,iommu_platform=on,disable-legacy=on \
  ...

Commit: c471ad0e9bd46 (vhost_net: device IOTLB support) took care of
setting vhostfd to non-blocking when QEMU opens /dev/host-net but if
the fd is passed from qemu cli then we need to ensure that fd is set
to non-blocking.

Fixes: c471ad0e9bd46 "vhost_net: device IOTLB support"
Cc: Michael S. Tsirkin <m...@redhat.com>
Cc: Jason Wang <jasow...@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.si...@amd.com>
---

Changes since v1:
 - use qemu_set_nonblock() instead of fcntl(..)

 net/tap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/tap.c b/net/tap.c
index 2b3a36f9b50d..89c4e19162a2 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -40,6 +40,7 @@
 #include "qemu-common.h"
 #include "qemu/cutils.h"
 #include "qemu/error-report.h"
+#include "qemu/sockets.h"
 
 #include "net/tap.h"
 
@@ -693,6 +694,7 @@ static void net_init_tap_one(const NetdevTapOptions *tap, 
NetClientState *peer,
                 }
                 return;
             }
+            qemu_set_nonblock(vhostfd);
         } else {
             vhostfd = open("/dev/vhost-net", O_RDWR);
             if (vhostfd < 0) {
-- 
2.14.3


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