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qdev/qbus: add hidden device support

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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 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 "failover_pair_id" option, e.g.

 -device virtio-net-pci,...,failover=on,...
 -device vfio-pci,...,failover_pair_id=net1,...

Signed-off-by: Jens Freimann <jfreimann@redhat.com>
Message-Id: <20191029114905.6856-2-jfreimann@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Jens Freimann 2019-10-29 12:48:55 +01:00 • committed by Michael S. Tsirkin
parent 16884391c7
commit f3a8505656
4 changed files with 94 additions and 6 deletions
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24
hw/core/qdev.c
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@ -212,6 +212,30 @@ void device_listener_unregister(DeviceListener *listener)
QTAILQ_REMOVE(&device_listeners, listener, link);
}
bool qdev_should_hide_device(QemuOpts *opts)
{
int rc = -1;
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)
{