Re: [PATCH v3 01/10] qdev/qbus: add hidden device support

[Jens Freimann]

On Mon, Oct 14, 2019 at 11:46:22AM +0200, Cornelia Huck wrote:
> On Fri, 11 Oct 2019 13:20:06 +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         | 19 +++++++++++++++++++
> >  include/hw/qdev-core.h |  9 +++++++++
> >  qdev-monitor.c         | 43 ++++++++++++++++++++++++++++++++++++++----
> >  vl.c                   |  6 ++++--
> >  4 files changed, 71 insertions(+), 6 deletions(-)
>
> (...)
>
> > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > index aa123f88cb..b61cf82ded 100644
> > --- a/include/hw/qdev-core.h
> > +++ b/include/hw/qdev-core.h
> > @@ -154,6 +154,13 @@ struct DeviceState {
> >  struct DeviceListener {
> >      void (*realize)(DeviceListener *listener, DeviceState *dev);
> >      void (*unrealize)(DeviceListener *listener, DeviceState *dev);
> > +    /*
> > +     * This callback is called just upon init of the DeviceState
> > +     * and can be used by a standby device for informing qdev if this
> > +     * device should be hidden by checking the device opts
> > +     */
>
> Maybe tweak this comment a bit:
>
> /*
> * This callback is called upon init of the DeviceState and allows to
> * inform qdev that a device should be hidden, depending on the device
> * opts, for example, to hide a standby device.
> */
>
> This makes it clearer that this interface could be reused for other
> purposes.

Sounds good. 
> > +    void (*should_be_hidden)(DeviceListener *listener, QemuOpts *device_opts,
> > +            bool *match_found, bool *res);
> >      QTAILQ_ENTRY(DeviceListener) link;
> >  };
> >
> > @@ -451,4 +458,6 @@ static inline bool qbus_is_hotpluggable(BusState *bus)
> >  void device_listener_register(DeviceListener *listener);
> >  void device_listener_unregister(DeviceListener *listener);
> >
> > +bool qdev_should_hide_device(QemuOpts *opts, Error **errp);
> > +
> >  #endif
> > diff --git a/qdev-monitor.c b/qdev-monitor.c
> > index 148df9cacf..9fc8331157 100644
> > --- a/qdev-monitor.c
> > +++ b/qdev-monitor.c
> > @@ -32,9 +32,11 @@
> >  #include "qemu/help_option.h"
> >  #include "qemu/option.h"
> >  #include "qemu/qemu-print.h"
> > +#include "qemu/option_int.h"
> >  #include "sysemu/block-backend.h"
> >  #include "sysemu/sysemu.h"
> >  #include "migration/misc.h"
> > +#include "migration/migration.h"
> >
> >  /*
> >   * Aliases were a bad idea from the start.  Let's keep them
> > @@ -562,14 +564,45 @@ void qdev_set_id(DeviceState *dev, const char *id)
> >      }
> >  }
> >
> > +static int is_failover_device(void *opaque, const char *name, const char 
> > *value,
> > +                        Error **errp)
> > +{
> > +    if (strcmp(name, "net_failover_pair_id") == 0) {
> > +        QemuOpts *opts = (QemuOpts *)opaque;
> > +
> > +        if (qdev_should_hide_device(opts, errp) && errp && !*errp) {
> > +            return 1;
> > +        } else if (errp && *errp) {
> > +            return -1;
> > +        }
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> > +static bool should_hide_device(QemuOpts *opts, Error **err)
> > +{
> > +    if (qemu_opt_foreach(opts, is_failover_device, opts, err) == 0) {
> > +        return false;
>
> Maybe turn that check around? I.e. return true if the failover property
> is present, else return false. Makes it easier to add checks for other
> properties in the future.

Done.

> > +    }
> > +    return true;
> > +}
> > +
> >  DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
> >  {
> >      DeviceClass *dc;
> >      const char *driver, *path;
> > -    DeviceState *dev;
> > +    DeviceState *dev = NULL;
> >      BusState *bus = NULL;
> >      Error *err = NULL;
> >
> > +    if (opts && should_hide_device(opts, &err)) {
> > +        if (err) {
> > +            goto err_del_dev;
> > +        }
> > +        return NULL;
> > +    }
> > +
> >      driver = qemu_opt_get(opts, "driver");
> >      if (!driver) {
> >          error_setg(errp, QERR_MISSING_PARAMETER, "driver");
> > @@ -648,8 +681,10 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
> >
> >  err_del_dev:
> >      error_propagate(errp, err);
> > -    object_unparent(OBJECT(dev));
> > -    object_unref(OBJECT(dev));
> > +    if (dev) {
> > +        object_unparent(OBJECT(dev));
> > +        object_unref(OBJECT(dev));
> > +    }
> >      return NULL;
> >  }
> >
> > @@ -818,7 +853,7 @@ void qdev_unplug(DeviceState *dev, Error **errp)
> >          return;
> >      }
> >
> > -    if (!migration_is_idle()) {
> > +    if (!migration_is_idle() && !migration_in_setup(migrate_get_current())) {
>
> Hm, should that hunk go into another patch?

Yes it should :)

Thanks for the review!

regards,
Jens