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

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Apr 06, 2018 at 07:03:56AM -0500, Brijesh Singh wrote:
> 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>

Reviewed-by: Michael S. Tsirkin <mst@redhat.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