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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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29
include/hw/qdev-core.h
View file

@ -78,6 +78,19 @@ typedef void (*BusUnrealize)(BusState *bus, Error **errp);
* respective parent types.
* </para>
* </note>
*
* # Hiding a device #
* To hide a device, a DeviceListener function should_be_hidden() needs to
* be registered.
* It can be used to defer adding a device and therefore hide it from the
* guest. The handler registering to this DeviceListener can save the QOpts
* passed to it for re-using it later and must return that it wants the device
* to be/remain hidden or not. When the handler function decides the device
* shall not be hidden it will be added in qdev_device_add() and
* realized as any other device. Otherwise qdev_device_add() will return early
* without adding the device. The guest will not see a "hidden" device
* until it was marked don't hide and qdev_device_add called again.
*
*/
typedef struct DeviceClass {
/*< private >*/
@ -154,6 +167,12 @@ struct DeviceState {
struct DeviceListener {
void (*realize)(DeviceListener *listener, DeviceState *dev);
void (*unrealize)(DeviceListener *listener, DeviceState *dev);
/*
* 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.
*/
int (*should_be_hidden)(DeviceListener *listener, QemuOpts *device_opts);
QTAILQ_ENTRY(DeviceListener) link;
};
@ -451,4 +470,14 @@ static inline bool qbus_is_hotpluggable(BusState *bus)
void device_listener_register(DeviceListener *listener);
void device_listener_unregister(DeviceListener *listener);
/**
* @qdev_should_hide_device:
* @opts: QemuOpts as passed on cmdline.
*
* Check if a device should be added.
* When a device is added via qdev_device_add() this will be called,
* and return if the device should be added now or not.
*/
bool qdev_should_hide_device(QemuOpts *opts);
#endif