qdev/qbus: add hidden device support
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>
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index cbad6c1..3b8d43d 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -212,6 +212,30 @@
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)
{
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index aa123f8..710981a 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -78,6 +78,19 @@
* 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 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 @@
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
diff --git a/qdev-monitor.c b/qdev-monitor.c
index 148df9c..ffa08c6 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
@@ -562,13 +564,36 @@
}
}
+static int is_failover_device(void *opaque, const char *name, const char *value,
+ Error **errp)
+{
+ if (strcmp(name, "failover_pair_id") == 0) {
+ QemuOpts *opts = (QemuOpts *)opaque;
+
+ if (qdev_should_hide_device(opts)) {
+ return 1;
+ }
+ }
+
+ return 0;
+}
+
+static bool should_hide_device(QemuOpts *opts)
+{
+ if (qemu_opt_foreach(opts, is_failover_device, opts, NULL) == 0) {
+ return false;
+ }
+ 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;
+ bool hide;
driver = qemu_opt_get(opts, "driver");
if (!driver) {
@@ -602,11 +627,17 @@
return NULL;
}
}
- if (qdev_hotplug && bus && !qbus_is_hotpluggable(bus)) {
+ hide = should_hide_device(opts);
+
+ if ((hide || qdev_hotplug) && bus && !qbus_is_hotpluggable(bus)) {
error_setg(errp, QERR_BUS_NO_HOTPLUG, bus->name);
return NULL;
}
+ if (hide) {
+ return NULL;
+ }
+
if (!migration_is_idle()) {
error_setg(errp, "device_add not allowed while migrating");
return NULL;
@@ -648,8 +679,10 @@
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;
}
diff --git a/vl.c b/vl.c
index 49778e7..c389d24 100644
--- a/vl.c
+++ b/vl.c
@@ -2207,10 +2207,12 @@
DeviceState *dev;
dev = qdev_device_add(opts, errp);
- if (!dev) {
+ if (!dev && *errp) {
+ error_report_err(*errp);
return -1;
+ } else if (dev) {
+ object_unref(OBJECT(dev));
}
- object_unref(OBJECT(dev));
return 0;
}
