Re: [PATCH 01/11] qdev/qbus: add hidden device support

[Jens Freimann]

On Mon, Oct 21, 2019 at 02:44:08PM +0200, Cornelia Huck wrote:
> On Fri, 18 Oct 2019 22:20:30 +0200
> Jens Freimann <address@hidden> wrote:
>
> > This adds support for hiding a device to the qbus and qdev APIs.  The
> > first user of this will be the virtio-net failover feature but the API
> > introduced with this patch could be used to implement other features as
> > well, for example hiding pci devices when a pci bus is powered off.
> >
> > qdev_device_add() is modified to check for a net_failover_pair_id
> > argument in the option string. A DeviceListener callback
> > should_be_hidden() is added. It can be used by a standby device to
> > inform qdev that this device should not be added now. The standby device
> > handler can store the device options to plug the device in at a later
> > point in time.
> >
> > One reason for hiding the device is that we don't want to expose both
> > devices to the guest kernel until the respective virtio feature bit
> > VIRTIO_NET_F_STANDBY was negotiated and we know that the devices will be
> > handled correctly by the guest.
> >
> > More information on the kernel feature this is using:
> >  https://www.kernel.org/doc/html/latest/networking/net_failover.html
> >
> > An example where the primary device is a vfio-pci device and the standby
> > device is a virtio-net device:
> >
> > A device is hidden when it has an "net_failover_pair_id" option, e.g.
> >
> >  -device virtio-net-pci,...,failover=on,...
> >  -device vfio-pci,...,net_failover_pair_id=net1,...
> >
> > Signed-off-by: Jens Freimann <address@hidden>
> > ---
> >  hw/core/qdev.c         | 23 +++++++++++++++++++++++
> >  include/hw/qdev-core.h |  8 ++++++++
> >  qdev-monitor.c         | 36 +++++++++++++++++++++++++++++++++---
> >  vl.c                   |  6 ++++--
> >  4 files changed, 68 insertions(+), 5 deletions(-)
> >
> > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > index cbad6c1d55..89c134ec53 100644
> > --- a/hw/core/qdev.c
> > +++ b/hw/core/qdev.c
> > @@ -212,6 +212,29 @@ void device_listener_unregister(DeviceListener *listener)
> >      QTAILQ_REMOVE(&device_listeners, listener, link);
> >  }
> >
> > +bool qdev_should_hide_device(QemuOpts *opts)
> > +{
> > +    int rc;
>
> Initialize to 0?

Yes, that's what the test bot found as well. Fixed it already. 
Though I initialize to -1, otherwise all devices will be hidden.

> > +    DeviceListener *listener;
> > +
> > +    QTAILQ_FOREACH(listener, &device_listeners, link) {
> > +       if (listener->should_be_hidden) {
> > +            /* should_be_hidden_will return
> > +             *  1 if device matches opts and it should be hidden
> > +             *  0 if device matches opts and should not be hidden
> > +             *  -1 if device doesn't match ops
> > +             */
> > +            rc = listener->should_be_hidden(listener, opts);
> > +        }
> > +
> > +        if (rc > 0) {
> > +            break;
> > +        }
> > +    }
> > +
> > +    return rc > 0;
> > +}
> > +
> >  void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
> >                                   int required_for_version)
> >  {
>
> (...)
>
> > +static bool should_hide_device(QemuOpts *opts)
> > +{
> > +    if (qemu_opt_foreach(opts, is_failover_device, opts, NULL) == 0) {
> > +        return false;
> > +    }
> > +    return true;
> > +}
>
> I still think you should turn the check around to make it easier to
> extend in the future, but this is fine as well.

Sorry, I've gone back and forth on this and ended up with the same.
I'll take another look at it. 

> (...)
>
> With the rc thing changed,
>
> Reviewed-by: Cornelia Huck <address@hidden>

Thanks!

regards,
Jens