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

[Jens Freimann]

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/hw/core/qdev.c b/hw/core/qdev.c
index cbad6c1d55..84fac591ca 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -212,6 +212,25 @@ void device_listener_unregister(DeviceListener *listener)
     QTAILQ_REMOVE(&device_listeners, listener, link);
 }
 
+bool qdev_should_hide_device(QemuOpts *opts, Error **errp)
+{
+    bool res = false;
+    bool match_found = false;
+    DeviceListener *listener;
+
+    QTAILQ_FOREACH(listener, &device_listeners, link) {
+       if (listener->should_be_hidden) {
+            listener->should_be_hidden(listener, opts, &match_found, &res);
+        }
+
+        if (match_found) {
+            break;
+        }
+    }
+
+    return res;
+}
+
 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 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
+     */
+    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;
+    }
+    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())) {
         error_setg(errp, "device_del not allowed while migrating");
         return;
     }
diff --git a/vl.c b/vl.c
index 002bf4919e..898b9901c8 100644
--- a/vl.c
+++ b/vl.c
@@ -2204,10 +2204,12 @@ static int device_init_func(void *opaque, QemuOpts 
*opts, Error **errp)
     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;
 }
 
-- 
2.21.0