Re: [Qemu-devel] [PATCH 2/6] Revert "vhost-net: tell tap backend about the vnet endianness"

[Laurent Vivier <lvivier@redhat.com>]

On 07/01/2016 12:32, Greg Kurz wrote:
> This reverts commit 5be7d9f1b1452613b95c6ba70b8d7ad3d0797991.
> 
> Cross-endian is now configured by the core virtio-net code. We simply
> fall back on full emulation if the net backend cannot support the
> requested endianness for vnet headers.
> 
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---
>  hw/net/vhost_net.c  |   33 +--------------------------------
>  hw/net/virtio-net.c |    7 +++++++
>  2 files changed, 8 insertions(+), 32 deletions(-)
> 
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index 318c3e6ad213..0c7362b7a772 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -38,7 +38,6 @@
>  #include "standard-headers/linux/virtio_ring.h"
>  #include "hw/virtio/vhost.h"
>  #include "hw/virtio/virtio-bus.h"
> -#include "hw/virtio/virtio-access.h"
>  
>  struct vhost_net {
>      struct vhost_dev dev;
> @@ -199,27 +198,6 @@ static void vhost_net_set_vq_index(struct vhost_net *net, int vq_index)
>      net->dev.vq_index = vq_index;
>  }
>  
> -static int vhost_net_set_vnet_endian(VirtIODevice *dev, NetClientState *peer,
> -                                     bool set)
> -{
> -    int r = 0;
> -
> -    if (virtio_vdev_has_feature(dev, VIRTIO_F_VERSION_1) ||
> -        (virtio_legacy_is_cross_endian(dev) && !virtio_is_big_endian(dev))) {
> -        r = qemu_set_vnet_le(peer, set);
> -        if (r) {
> -            error_report("backend does not support LE vnet headers");
> -        }
> -    } else if (virtio_legacy_is_cross_endian(dev)) {
> -        r = qemu_set_vnet_be(peer, set);
> -        if (r) {
> -            error_report("backend does not support BE vnet headers");
> -        }
> -    }
> -
> -    return r;
> -}
> -
>  static int vhost_net_start_one(struct vhost_net *net,
>                                 VirtIODevice *dev)
>  {
> @@ -308,11 +286,6 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
>          goto err;
>      }
>  
> -    r = vhost_net_set_vnet_endian(dev, ncs[0].peer, true);
> -    if (r < 0) {
> -        goto err;
> -    }
> -
>      for (i = 0; i < total_queues; i++) {
>          vhost_net_set_vq_index(get_vhost_net(ncs[i].peer), i * 2);
>      }
> @@ -320,7 +293,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
>      r = k->set_guest_notifiers(qbus->parent, total_queues * 2, true);
>      if (r < 0) {
>          error_report("Error binding guest notifier: %d", -r);
> -        goto err_endian;
> +        goto err;
>      }
>  
>      for (i = 0; i < total_queues; i++) {
> @@ -342,8 +315,6 @@ err_start:
>          fprintf(stderr, "vhost guest notifier cleanup failed: %d\n", e);
>          fflush(stderr);
>      }
> -err_endian:
> -    vhost_net_set_vnet_endian(dev, ncs[0].peer, false);
>  err:
>      return r;
>  }
> @@ -366,8 +337,6 @@ void vhost_net_stop(VirtIODevice *dev, NetClientState *ncs,
>          fflush(stderr);
>      }
>      assert(r >= 0);
> -
> -    assert(vhost_net_set_vnet_endian(dev, ncs[0].peer, false) >= 0);
>  }
>  
>  void vhost_net_cleanup(struct vhost_net *net)
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index d4cc94ea5e55..5a0ab6ad5bb5 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -128,6 +128,13 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status)
>      if (!n->vhost_started) {
>          int r, i;
>  
> +        if (n->needs_vnet_hdr_swap) {
> +            error_report("backend does not support %s vnet headers."
> +                         "falling back on userspace virtio",
> +                         virtio_is_big_endian(vdev) ? "BE" : "LE");
> +            return;
> +        }
> +

This is not part of the revert, perhaps this can go in PATCH 1/6 ?
In virtio_net_vnet_status() ?

>          /* Any packets outstanding? Purge them to avoid touching rings
>           * when vhost is running.
>           */
> 
>