[Qemu-devel] [PATCH for-2.12] tap: set vhostfd passed from qemu cli to non-blocking

[Brijesh Singh <brijesh.singh@amd.com>]

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 <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 net/tap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/tap.c b/net/tap.c
index 2b3a36f9b50d..8c026fbf95cd 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -693,6 +693,7 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
                 }
                 return;
             }
+            fcntl(vhostfd, F_SETFL, O_NONBLOCK);
         } else {
             vhostfd = open("/dev/vhost-net", O_RDWR);
             if (vhostfd < 0) {
-- 
2.14.3