[Qemu-devel] Re: [PATCHv2] virtio-net: unify vhost-net start/stop

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 2010-09-27 at 18:41 +0200, Michael S. Tsirkin wrote:
> Move all of vhost-net start/stop logic to a single routine,
> and call it from everywhere.
> 
> Additionally, start/stop vhost-net on link up/down:
> we should not transmit anything if user asked us to
> put the link down.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> Sent a wrong version, sorry about the noise.
> 
>  hw/virtio-net.c |   89 ++++++++++++++++++++++++++----------------------------
>  1 files changed, 43 insertions(+), 46 deletions(-)
> 
> diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> index 075f72d..f87c219 100644
> --- a/hw/virtio-net.c
> +++ b/hw/virtio-net.c
> @@ -51,6 +51,7 @@ typedef struct VirtIONet
>      uint8_t nouni;
>      uint8_t nobcast;
>      uint8_t vhost_started;
> +    bool vm_running;
>      VMChangeStateEntry *vmstate;
>      struct {
>          int in_use;
> @@ -95,6 +96,38 @@ static void virtio_net_set_config(VirtIODevice *vdev, const uint8_t *config)
>      }
>  }
>  
> +static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
> +{
> +    VirtIONet *n = to_virtio_net(vdev);
> +    if (!n->nic->nc.peer) {
> +        return;
> +    }
> +    if (n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {
> +        return;
> +    }
> +
> +    if (!tap_get_vhost_net(n->nic->nc.peer)) {
> +        return;
> +    }
> +    if (!!n->vhost_started == (status & VIRTIO_CONFIG_S_DRIVER_OK) &&
> +                                (n->status & VIRTIO_NET_S_LINK_UP) &&
> +                                n->vm_running) {

I don't think this works...

#define VIRTIO_CONFIG_S_DRIVER_OK       4

!!(1) == (status & 4)?

> +        return;
> +    }
> +    if (!n->vhost_started) {
> +        int r = vhost_net_start(tap_get_vhost_net(n->nic->nc.peer), &n->vdev);
> +        if (r < 0) {
> +            fprintf(stderr, "unable to start vhost net: %d: "
> +                    "falling back on userspace virtio\n", -r);

Definitely worth noting if not using vhost, but aren't we potentially
going to see this in the log a lot in that case?  Thanks,

Alex

> +        } else {
> +            n->vhost_started = 1;
> +        }
> +    } else {
> +        vhost_net_stop(tap_get_vhost_net(n->nic->nc.peer), &n->vdev);
> +        n->vhost_started = 0;
> +    }
> +}
> +
>  static void virtio_net_set_link_status(VLANClientState *nc)
>  {
>      VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque;
> @@ -107,6 +140,8 @@ static void virtio_net_set_link_status(VLANClientState *nc)
>  
>      if (n->status != old_status)
>          virtio_notify_config(&n->vdev);
> +
> +    virtio_net_set_status(&n->vdev, n->vdev.status);
>  }
>  
>  static void virtio_net_reset(VirtIODevice *vdev)
> @@ -120,10 +155,6 @@ static void virtio_net_reset(VirtIODevice *vdev)
>      n->nomulti = 0;
>      n->nouni = 0;
>      n->nobcast = 0;
> -    if (n->vhost_started) {
> -        vhost_net_stop(tap_get_vhost_net(n->nic->nc.peer), vdev);
> -        n->vhost_started = 0;
> -    }
>  
>      /* Flush any MAC and VLAN filter table state */
>      n->mac_table.in_use = 0;
> @@ -726,12 +757,9 @@ static void virtio_net_save(QEMUFile *f, void *opaque)
>  {
>      VirtIONet *n = opaque;
>  
> -    if (n->vhost_started) {
> -        /* TODO: should we really stop the backend?
> -         * If we don't, it might keep writing to memory. */
> -        vhost_net_stop(tap_get_vhost_net(n->nic->nc.peer), &n->vdev);
> -        n->vhost_started = 0;
> -    }
> +    /* At this point, backend must be stopped, otherwise
> +     * it might keep writing to memory. */
> +    assert(!n->vhost_started);
>      virtio_save(&n->vdev, f);
>  
>      qemu_put_buffer(f, n->mac, ETH_ALEN);
> @@ -863,44 +891,14 @@ static NetClientInfo net_virtio_info = {
>      .link_status_changed = virtio_net_set_link_status,
>  };
>  
> -static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
> -{
> -    VirtIONet *n = to_virtio_net(vdev);
> -    if (!n->nic->nc.peer) {
> -        return;
> -    }
> -    if (n->nic->nc.peer->info->type != NET_CLIENT_TYPE_TAP) {
> -        return;
> -    }
> -
> -    if (!tap_get_vhost_net(n->nic->nc.peer)) {
> -        return;
> -    }
> -    if (!!n->vhost_started == !!(status & VIRTIO_CONFIG_S_DRIVER_OK)) {
> -        return;
> -    }
> -    if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
> -        int r = vhost_net_start(tap_get_vhost_net(n->nic->nc.peer), vdev);
> -        if (r < 0) {
> -            fprintf(stderr, "unable to start vhost net: %d: "
> -                    "falling back on userspace virtio\n", -r);
> -        } else {
> -            n->vhost_started = 1;
> -        }
> -    } else {
> -        vhost_net_stop(tap_get_vhost_net(n->nic->nc.peer), vdev);
> -        n->vhost_started = 0;
> -    }
> -}
> -
>  static void virtio_net_vmstate_change(void *opaque, int running, int reason)
>  {
>      VirtIONet *n = opaque;
> -    uint8_t status = running ? VIRTIO_CONFIG_S_DRIVER_OK : 0;
> +    n->vm_running = running;
>      /* This is called when vm is started/stopped,
> -     * it will start/stop vhost backend if * appropriate
> +     * it will start/stop vhost backend if appropriate
>       * e.g. after migration. */
> -    virtio_net_set_status(&n->vdev, n->vdev.status & status);
> +    virtio_net_set_status(&n->vdev, n->vdev.status);
>  }
>  
>  VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf)
> @@ -951,9 +949,8 @@ void virtio_net_exit(VirtIODevice *vdev)
>      VirtIONet *n = DO_UPCAST(VirtIONet, vdev, vdev);
>      qemu_del_vm_change_state_handler(n->vmstate);
>  
> -    if (n->vhost_started) {
> -        vhost_net_stop(tap_get_vhost_net(n->nic->nc.peer), vdev);
> -    }
> +    /* This will stop vhost backend if appropriate. */
> +    virtio_net_set_status(vdev, 0);
>  
>      qemu_purge_queued_packets(&n->nic->nc);
>