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

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

On Mon, 2010-09-27 at 23:52 +0200, Michael S. Tsirkin wrote:
> On Mon, Sep 27, 2010 at 01:43:11PM -0600, Alex Williamson wrote:
> > 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)?
> 
> The && converts it to a boolean.

Are you missing a set of parens around everything right of the ==?  ie:

if (!!n->vhost_started == ((status & VIRTIO_CONFIG_S_DRIVER_OK) &&
                           (n->status & VIRTIO_NET_S_LINK_UP) &&
                           n->vm_running)) {...

Has this actually been tested?

Alex

> > > +        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
> 
> Not really, we detect failure at start normally, and do
> not proceed.
> This means that somehow the device went dead: should not
> happen really, but since it's easy to recover we do.
> 
> > > +        } 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);
> > >  
> > 
> >