Re: [PATCH] kvm: qemu: virtio-net: migration fixes

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> From: Mark McLoughlin <markmc@redhat.com>
>
> We were failing to save whether the tx/rx buffers we exchange with the tap
> code should include a virtio_net_hdr header; this caused the migrated guest
> to receive garbage packets because the tap code was stripping away the header
> and virtio_net was interpreting packet data as the virtio_net header
>
> With this fix a guest using mergeable rx buffers and
> GSO passes a simple "ping while migrating" test.
>
> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> Signed-off-by: Avi Kivity <avi@redhat.com>
>
> diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c
> index e2ba322..1f9dc16 100644
> --- a/qemu/hw/virtio-net.c
> +++ b/qemu/hw/virtio-net.c
> @@ -361,6 +361,10 @@ static void virtio_net_save(QEMUFile *f, void *opaque)
>      qemu_put_buffer(f, n->mac, 6);
>      qemu_put_be32(f, n->tx_timer_active);
>      qemu_put_be32(f, n->mergeable_rx_bufs);
> +
> +#ifdef TAP_VNET_HDR
> +    qemu_put_be32(f, tap_has_vnet_hdr(n->vc->vlan->first_client));
> +#endif
>   

This should increment the save/restore format version number to preserve 
backwards compatibility.  It'll also be required for merging into QEMU 
upstream.

As a rule, if new fields are added to a save/load function, the version 
number should be incremented.

Regards,

Anthony Liguori

>  }
>  
>  static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
> @@ -376,6 +380,11 @@ static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
>      n->tx_timer_active = qemu_get_be32(f);
>      n->mergeable_rx_bufs = qemu_get_be32(f);
>  
> +#ifdef TAP_VNET_HDR
> +    if (qemu_get_be32(f))
> +        tap_using_vnet_hdr(n->vc->vlan->first_client, 1);
> +#endif
> +
>      if (n->tx_timer_active) {
>          qemu_mod_timer(n->tx_timer,
>                         qemu_get_clock(vm_clock) + TX_TIMER_INTERVAL);
> --
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