Patchwork [v2,02/18] xen: introduce new 'XenBus' and 'XenDevice' object hierarchy

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Submitter Paul Durrant
Date Dec. 6, 2018, 3:08 p.m.
Message ID <1544108924-10841-3-git-send-email-paul.durrant@citrix.com>
Download mbox | patch
Permalink /patch/674231/
State New
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Comments

Paul Durrant - Dec. 6, 2018, 3:08 p.m.
This patch adds the basic boilerplate for a 'XenBus' object that will act
as a parent to 'XenDevice' PV backends.
A new 'XenBridge' object is also added to connect XenBus to the system bus.

The XenBus object is instantiated by a new xen_bus_init() function called
from the same sites as the legacy xen_be_init() function.

Subsequent patches will flesh-out the functionality of these objects.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
---
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>

v2:
 - Fix boilerplate
 - Make xen-bus hotplug capable
---
 hw/i386/xen/xen-hvm.c     |   3 ++
 hw/xen/Makefile.objs      |   2 +-
 hw/xen/trace-events       |   6 +++
 hw/xen/xen-bus.c          | 131 ++++++++++++++++++++++++++++++++++++++++++++++
 hw/xenpv/xen_machine_pv.c |   3 ++
 include/hw/xen/xen-bus.h  |  55 +++++++++++++++++++
 6 files changed, 199 insertions(+), 1 deletion(-)
 create mode 100644 hw/xen/xen-bus.c
 create mode 100644 include/hw/xen/xen-bus.h
Anthony PERARD - Dec. 7, 2018, 12:15 p.m.
On Thu, Dec 06, 2018 at 03:08:28PM +0000, Paul Durrant wrote:
> This patch adds the basic boilerplate for a 'XenBus' object that will act
> as a parent to 'XenDevice' PV backends.
> A new 'XenBridge' object is also added to connect XenBus to the system bus.
> 
> The XenBus object is instantiated by a new xen_bus_init() function called
> from the same sites as the legacy xen_be_init() function.
> 
> Subsequent patches will flesh-out the functionality of these objects.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> ---
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Anthony Perard <anthony.perard@citrix.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> 
> v2:
>  - Fix boilerplate
>  - Make xen-bus hotplug capable
> ---
>  hw/i386/xen/xen-hvm.c     |   3 ++
>  hw/xen/Makefile.objs      |   2 +-
>  hw/xen/trace-events       |   6 +++
>  hw/xen/xen-bus.c          | 131 ++++++++++++++++++++++++++++++++++++++++++++++
>  hw/xenpv/xen_machine_pv.c |   3 ++
>  include/hw/xen/xen-bus.h  |  55 +++++++++++++++++++
>  6 files changed, 199 insertions(+), 1 deletion(-)
>  create mode 100644 hw/xen/xen-bus.c
>  create mode 100644 include/hw/xen/xen-bus.h
> 
> diff --git a/hw/i386/xen/xen-hvm.c b/hw/i386/xen/xen-hvm.c
> index 1d63763..4497f75 100644
> --- a/hw/i386/xen/xen-hvm.c
> +++ b/hw/i386/xen/xen-hvm.c
> @@ -17,6 +17,7 @@
>  #include "hw/i386/apic-msidef.h"
>  #include "hw/xen/xen_common.h"
>  #include "hw/xen/xen-legacy-backend.h"
> +#include "hw/xen/xen-bus.h"
>  #include "qapi/error.h"
>  #include "qapi/qapi-commands-misc.h"
>  #include "qemu/error-report.h"
> @@ -1479,6 +1480,8 @@ void xen_hvm_init(PCMachineState *pcms, MemoryRegion **ram_memory)
>      QLIST_INIT(&state->dev_list);
>      device_listener_register(&state->device_listener);
>  
> +    xen_bus_init();
> +
>      /* Initialize backend core & drivers */
>      if (xen_be_init() != 0) {
>          error_report("xen backend core setup failed");
> diff --git a/hw/xen/Makefile.objs b/hw/xen/Makefile.objs
> index 3f64a44..d9d6d7b 100644
> --- a/hw/xen/Makefile.objs
> +++ b/hw/xen/Makefile.objs
> @@ -1,5 +1,5 @@
>  # xen backend driver support
> -common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-common.o
> +common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-common.o xen-bus.o
>  
>  obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen-host-pci-device.o
>  obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen_pt.o xen_pt_config_init.o xen_pt_graphics.o xen_pt_msi.o
> diff --git a/hw/xen/trace-events b/hw/xen/trace-events
> index c7e7a3b..0172cd4 100644
> --- a/hw/xen/trace-events
> +++ b/hw/xen/trace-events
> @@ -12,3 +12,9 @@ xen_unmap_portio_range(uint32_t id, uint64_t start_addr, uint64_t end_addr) "id:
>  xen_map_pcidev(uint32_t id, uint8_t bus, uint8_t dev, uint8_t func) "id: %u bdf: %02x.%02x.%02x"
>  xen_unmap_pcidev(uint32_t id, uint8_t bus, uint8_t dev, uint8_t func) "id: %u bdf: %02x.%02x.%02x"
>  xen_domid_restrict(int err) "err: %u"
> +
> +# include/hw/xen/xen-bus.c
> +xen_bus_realize(void) ""
> +xen_bus_unrealize(void) ""
> +xen_device_realize(const char *type) "type: %s"
> +xen_device_unrealize(const char *type) "type: %s"
> diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> new file mode 100644
> index 0000000..1385bab
> --- /dev/null
> +++ b/hw/xen/xen-bus.c
> @@ -0,0 +1,131 @@
> +/*
> + * Copyright (c) 2018  Citrix Systems Inc.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/hw.h"
> +#include "hw/sysbus.h"
> +#include "hw/xen/xen-bus.h"
> +#include "qapi/error.h"
> +#include "trace.h"
> +
> +static void xen_bus_unrealize(BusState *bus, Error **errp)
> +{
> +    trace_xen_bus_unrealize();
> +}
> +
> +static void xen_bus_realize(BusState *bus, Error **errp)
> +{
> +    trace_xen_bus_realize();
> +}
> +
> +static void xen_bus_class_init(ObjectClass *class, void *data)
> +{
> +    BusClass *bus_class = BUS_CLASS(class);
> +
> +    bus_class->realize = xen_bus_realize;
> +    bus_class->unrealize = xen_bus_unrealize;
> +}
> +
> +static const TypeInfo xen_bus_type_info = {
> +    .name = TYPE_XEN_BUS,
> +    .parent = TYPE_BUS,
> +    .instance_size = sizeof(XenBus),
> +    .class_size = sizeof(XenBusClass),
> +    .class_init = xen_bus_class_init,
> +    .interfaces = (InterfaceInfo[]) {
> +        { TYPE_HOTPLUG_HANDLER },
> +        { }
> +    },
> +};
> +
> +static void xen_device_unrealize(DeviceState *dev, Error **errp)
> +{
> +    XenDevice *xendev = XEN_DEVICE(dev);
> +    XenDeviceClass *xendev_class = XEN_DEVICE_GET_CLASS(xendev);
> +    const char *type = object_get_typename(OBJECT(xendev));
> +    Error *local_err = NULL;
> +
> +    trace_xen_device_unrealize(type);
> +
> +    if (xendev_class->unrealize) {
> +        xendev_class->unrealize(xendev, &local_err);

Since all you do here is propagate the error, you could even pass `errp'
to unrealize(), instead of having `local_err'. That "for readability",
as explained in "qapi/error.h".

> +        if (local_err) {
> +            error_propagate(errp, local_err);
> +        }
> +    }
> +}
> +

With that nit fixed:
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks,
Paul Durrant - Dec. 7, 2018, 12:57 p.m.
> -----Original Message-----
> From: Anthony PERARD [mailto:anthony.perard@citrix.com]
> Sent: 07 December 2018 12:15
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: qemu-devel@nongnu.org; qemu-block@nongnu.org; xen-
> devel@lists.xenproject.org; Stefano Stabellini <sstabellini@kernel.org>;
> Michael S. Tsirkin <mst@redhat.com>; Marcel Apfelbaum
> <marcel.apfelbaum@gmail.com>; Paolo Bonzini <pbonzini@redhat.com>; Richard
> Henderson <rth@twiddle.net>; Eduardo Habkost <ehabkost@redhat.com>
> Subject: Re: [PATCH v2 02/18] xen: introduce new 'XenBus' and 'XenDevice'
> object hierarchy
> 
> On Thu, Dec 06, 2018 at 03:08:28PM +0000, Paul Durrant wrote:
> > This patch adds the basic boilerplate for a 'XenBus' object that will
> act
> > as a parent to 'XenDevice' PV backends.
> > A new 'XenBridge' object is also added to connect XenBus to the system
> bus.
> >
> > The XenBus object is instantiated by a new xen_bus_init() function
> called
> > from the same sites as the legacy xen_be_init() function.
> >
> > Subsequent patches will flesh-out the functionality of these objects.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> > ---
> > Cc: Stefano Stabellini <sstabellini@kernel.org>
> > Cc: Anthony Perard <anthony.perard@citrix.com>
> > Cc: "Michael S. Tsirkin" <mst@redhat.com>
> > Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Richard Henderson <rth@twiddle.net>
> > Cc: Eduardo Habkost <ehabkost@redhat.com>
> >
> > v2:
> >  - Fix boilerplate
> >  - Make xen-bus hotplug capable
> > ---
> >  hw/i386/xen/xen-hvm.c     |   3 ++
> >  hw/xen/Makefile.objs      |   2 +-
> >  hw/xen/trace-events       |   6 +++
> >  hw/xen/xen-bus.c          | 131
> ++++++++++++++++++++++++++++++++++++++++++++++
> >  hw/xenpv/xen_machine_pv.c |   3 ++
> >  include/hw/xen/xen-bus.h  |  55 +++++++++++++++++++
> >  6 files changed, 199 insertions(+), 1 deletion(-)
> >  create mode 100644 hw/xen/xen-bus.c
> >  create mode 100644 include/hw/xen/xen-bus.h
> >
> > diff --git a/hw/i386/xen/xen-hvm.c b/hw/i386/xen/xen-hvm.c
> > index 1d63763..4497f75 100644
> > --- a/hw/i386/xen/xen-hvm.c
> > +++ b/hw/i386/xen/xen-hvm.c
> > @@ -17,6 +17,7 @@
> >  #include "hw/i386/apic-msidef.h"
> >  #include "hw/xen/xen_common.h"
> >  #include "hw/xen/xen-legacy-backend.h"
> > +#include "hw/xen/xen-bus.h"
> >  #include "qapi/error.h"
> >  #include "qapi/qapi-commands-misc.h"
> >  #include "qemu/error-report.h"
> > @@ -1479,6 +1480,8 @@ void xen_hvm_init(PCMachineState *pcms,
> MemoryRegion **ram_memory)
> >      QLIST_INIT(&state->dev_list);
> >      device_listener_register(&state->device_listener);
> >
> > +    xen_bus_init();
> > +
> >      /* Initialize backend core & drivers */
> >      if (xen_be_init() != 0) {
> >          error_report("xen backend core setup failed");
> > diff --git a/hw/xen/Makefile.objs b/hw/xen/Makefile.objs
> > index 3f64a44..d9d6d7b 100644
> > --- a/hw/xen/Makefile.objs
> > +++ b/hw/xen/Makefile.objs
> > @@ -1,5 +1,5 @@
> >  # xen backend driver support
> > -common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o
> xen_pvdev.o xen-common.o
> > +common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o
> xen_pvdev.o xen-common.o xen-bus.o
> >
> >  obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen-host-pci-device.o
> >  obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen_pt.o xen_pt_config_init.o
> xen_pt_graphics.o xen_pt_msi.o
> > diff --git a/hw/xen/trace-events b/hw/xen/trace-events
> > index c7e7a3b..0172cd4 100644
> > --- a/hw/xen/trace-events
> > +++ b/hw/xen/trace-events
> > @@ -12,3 +12,9 @@ xen_unmap_portio_range(uint32_t id, uint64_t
> start_addr, uint64_t end_addr) "id:
> >  xen_map_pcidev(uint32_t id, uint8_t bus, uint8_t dev, uint8_t func)
> "id: %u bdf: %02x.%02x.%02x"
> >  xen_unmap_pcidev(uint32_t id, uint8_t bus, uint8_t dev, uint8_t func)
> "id: %u bdf: %02x.%02x.%02x"
> >  xen_domid_restrict(int err) "err: %u"
> > +
> > +# include/hw/xen/xen-bus.c
> > +xen_bus_realize(void) ""
> > +xen_bus_unrealize(void) ""
> > +xen_device_realize(const char *type) "type: %s"
> > +xen_device_unrealize(const char *type) "type: %s"
> > diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> > new file mode 100644
> > index 0000000..1385bab
> > --- /dev/null
> > +++ b/hw/xen/xen-bus.c
> > @@ -0,0 +1,131 @@
> > +/*
> > + * Copyright (c) 2018  Citrix Systems Inc.
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2 or
> later.
> > + * See the COPYING file in the top-level directory.
> > + */
> > +
> > +#include "qemu/osdep.h"
> > +#include "hw/hw.h"
> > +#include "hw/sysbus.h"
> > +#include "hw/xen/xen-bus.h"
> > +#include "qapi/error.h"
> > +#include "trace.h"
> > +
> > +static void xen_bus_unrealize(BusState *bus, Error **errp)
> > +{
> > +    trace_xen_bus_unrealize();
> > +}
> > +
> > +static void xen_bus_realize(BusState *bus, Error **errp)
> > +{
> > +    trace_xen_bus_realize();
> > +}
> > +
> > +static void xen_bus_class_init(ObjectClass *class, void *data)
> > +{
> > +    BusClass *bus_class = BUS_CLASS(class);
> > +
> > +    bus_class->realize = xen_bus_realize;
> > +    bus_class->unrealize = xen_bus_unrealize;
> > +}
> > +
> > +static const TypeInfo xen_bus_type_info = {
> > +    .name = TYPE_XEN_BUS,
> > +    .parent = TYPE_BUS,
> > +    .instance_size = sizeof(XenBus),
> > +    .class_size = sizeof(XenBusClass),
> > +    .class_init = xen_bus_class_init,
> > +    .interfaces = (InterfaceInfo[]) {
> > +        { TYPE_HOTPLUG_HANDLER },
> > +        { }
> > +    },
> > +};
> > +
> > +static void xen_device_unrealize(DeviceState *dev, Error **errp)
> > +{
> > +    XenDevice *xendev = XEN_DEVICE(dev);
> > +    XenDeviceClass *xendev_class = XEN_DEVICE_GET_CLASS(xendev);
> > +    const char *type = object_get_typename(OBJECT(xendev));
> > +    Error *local_err = NULL;
> > +
> > +    trace_xen_device_unrealize(type);
> > +
> > +    if (xendev_class->unrealize) {
> > +        xendev_class->unrealize(xendev, &local_err);
> 
> Since all you do here is propagate the error, you could even pass `errp'
> to unrealize(), instead of having `local_err'. That "for readability",
> as explained in "qapi/error.h".

Yes, true.

> 
> > +        if (local_err) {
> > +            error_propagate(errp, local_err);
> > +        }
> > +    }
> > +}
> > +
> 
> With that nit fixed:
> Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
> 

Thanks :-)

  Paul

> Thanks,
> 
> --
> Anthony PERARD

Patch

diff --git a/hw/i386/xen/xen-hvm.c b/hw/i386/xen/xen-hvm.c
index 1d63763..4497f75 100644
--- a/hw/i386/xen/xen-hvm.c
+++ b/hw/i386/xen/xen-hvm.c
@@ -17,6 +17,7 @@ 
 #include "hw/i386/apic-msidef.h"
 #include "hw/xen/xen_common.h"
 #include "hw/xen/xen-legacy-backend.h"
+#include "hw/xen/xen-bus.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-misc.h"
 #include "qemu/error-report.h"
@@ -1479,6 +1480,8 @@  void xen_hvm_init(PCMachineState *pcms, MemoryRegion **ram_memory)
     QLIST_INIT(&state->dev_list);
     device_listener_register(&state->device_listener);
 
+    xen_bus_init();
+
     /* Initialize backend core & drivers */
     if (xen_be_init() != 0) {
         error_report("xen backend core setup failed");
diff --git a/hw/xen/Makefile.objs b/hw/xen/Makefile.objs
index 3f64a44..d9d6d7b 100644
--- a/hw/xen/Makefile.objs
+++ b/hw/xen/Makefile.objs
@@ -1,5 +1,5 @@ 
 # xen backend driver support
-common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-common.o
+common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-common.o xen-bus.o
 
 obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen-host-pci-device.o
 obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen_pt.o xen_pt_config_init.o xen_pt_graphics.o xen_pt_msi.o
diff --git a/hw/xen/trace-events b/hw/xen/trace-events
index c7e7a3b..0172cd4 100644
--- a/hw/xen/trace-events
+++ b/hw/xen/trace-events
@@ -12,3 +12,9 @@  xen_unmap_portio_range(uint32_t id, uint64_t start_addr, uint64_t end_addr) "id:
 xen_map_pcidev(uint32_t id, uint8_t bus, uint8_t dev, uint8_t func) "id: %u bdf: %02x.%02x.%02x"
 xen_unmap_pcidev(uint32_t id, uint8_t bus, uint8_t dev, uint8_t func) "id: %u bdf: %02x.%02x.%02x"
 xen_domid_restrict(int err) "err: %u"
+
+# include/hw/xen/xen-bus.c
+xen_bus_realize(void) ""
+xen_bus_unrealize(void) ""
+xen_device_realize(const char *type) "type: %s"
+xen_device_unrealize(const char *type) "type: %s"
diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
new file mode 100644
index 0000000..1385bab
--- /dev/null
+++ b/hw/xen/xen-bus.c
@@ -0,0 +1,131 @@ 
+/*
+ * Copyright (c) 2018  Citrix Systems Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "hw/hw.h"
+#include "hw/sysbus.h"
+#include "hw/xen/xen-bus.h"
+#include "qapi/error.h"
+#include "trace.h"
+
+static void xen_bus_unrealize(BusState *bus, Error **errp)
+{
+    trace_xen_bus_unrealize();
+}
+
+static void xen_bus_realize(BusState *bus, Error **errp)
+{
+    trace_xen_bus_realize();
+}
+
+static void xen_bus_class_init(ObjectClass *class, void *data)
+{
+    BusClass *bus_class = BUS_CLASS(class);
+
+    bus_class->realize = xen_bus_realize;
+    bus_class->unrealize = xen_bus_unrealize;
+}
+
+static const TypeInfo xen_bus_type_info = {
+    .name = TYPE_XEN_BUS,
+    .parent = TYPE_BUS,
+    .instance_size = sizeof(XenBus),
+    .class_size = sizeof(XenBusClass),
+    .class_init = xen_bus_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_HOTPLUG_HANDLER },
+        { }
+    },
+};
+
+static void xen_device_unrealize(DeviceState *dev, Error **errp)
+{
+    XenDevice *xendev = XEN_DEVICE(dev);
+    XenDeviceClass *xendev_class = XEN_DEVICE_GET_CLASS(xendev);
+    const char *type = object_get_typename(OBJECT(xendev));
+    Error *local_err = NULL;
+
+    trace_xen_device_unrealize(type);
+
+    if (xendev_class->unrealize) {
+        xendev_class->unrealize(xendev, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+        }
+    }
+}
+
+static void xen_device_realize(DeviceState *dev, Error **errp)
+{
+    XenDevice *xendev = XEN_DEVICE(dev);
+    XenDeviceClass *xendev_class = XEN_DEVICE_GET_CLASS(xendev);
+    const char *type = object_get_typename(OBJECT(xendev));
+    Error *local_err = NULL;
+
+    trace_xen_device_realize(type);
+
+    if (xendev_class->realize) {
+        xendev_class->realize(xendev, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            goto unrealize;
+        }
+    }
+
+    return;
+
+unrealize:
+    xen_device_unrealize(dev, &error_abort);
+}
+
+static void xen_device_class_init(ObjectClass *class, void *data)
+{
+    DeviceClass *dev_class = DEVICE_CLASS(class);
+
+    dev_class->realize = xen_device_realize;
+    dev_class->unrealize = xen_device_unrealize;
+    dev_class->bus_type = TYPE_XEN_BUS;
+}
+
+static const TypeInfo xen_device_type_info = {
+    .name = TYPE_XEN_DEVICE,
+    .parent = TYPE_DEVICE,
+    .instance_size = sizeof(XenDevice),
+    .abstract = true,
+    .class_size = sizeof(XenDeviceClass),
+    .class_init = xen_device_class_init,
+};
+
+typedef struct XenBridge {
+    SysBusDevice busdev;
+} XenBridge;
+
+#define TYPE_XEN_BRIDGE "xen-bridge"
+
+static const TypeInfo xen_bridge_type_info = {
+    .name = TYPE_XEN_BRIDGE,
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(XenBridge),
+};
+
+static void xen_register_types(void)
+{
+    type_register_static(&xen_bridge_type_info);
+    type_register_static(&xen_bus_type_info);
+    type_register_static(&xen_device_type_info);
+}
+
+type_init(xen_register_types)
+
+void xen_bus_init(void)
+{
+    DeviceState *dev = qdev_create(NULL, TYPE_XEN_BRIDGE);
+    BusState *bus = qbus_create(TYPE_XEN_BUS, dev, NULL);
+
+    qdev_init_nofail(dev);
+    qbus_set_bus_hotplug_handler(bus, &error_abort);
+}
diff --git a/hw/xenpv/xen_machine_pv.c b/hw/xenpv/xen_machine_pv.c
index 8c86fb7..608e591 100644
--- a/hw/xenpv/xen_machine_pv.c
+++ b/hw/xenpv/xen_machine_pv.c
@@ -27,6 +27,7 @@ 
 #include "hw/hw.h"
 #include "hw/boards.h"
 #include "hw/xen/xen-legacy-backend.h"
+#include "hw/xen/xen-bus.h"
 #include "xen_domainbuild.h"
 #include "sysemu/block-backend.h"
 
@@ -93,6 +94,8 @@  static void xen_init_pv(MachineState *machine)
         xen_config_dev_nic(nd_table + i);
     }
 
+    xen_bus_init();
+
     /* config cleanup hook */
     atexit(xen_config_cleanup);
 }
diff --git a/include/hw/xen/xen-bus.h b/include/hw/xen/xen-bus.h
new file mode 100644
index 0000000..0cb1246
--- /dev/null
+++ b/include/hw/xen/xen-bus.h
@@ -0,0 +1,55 @@ 
+/*
+ * Copyright (c) 2018  Citrix Systems Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef HW_XEN_BUS_H
+#define HW_XEN_BUS_H
+
+#include "hw/sysbus.h"
+
+typedef struct XenDevice {
+    DeviceState qdev;
+} XenDevice;
+
+typedef void (*XenDeviceRealize)(XenDevice *xendev, Error **errp);
+typedef void (*XenDeviceUnrealize)(XenDevice *xendev, Error **errp);
+
+typedef struct XenDeviceClass {
+    /*< private >*/
+    DeviceClass parent_class;
+    /*< public >*/
+    XenDeviceRealize realize;
+    XenDeviceUnrealize unrealize;
+} XenDeviceClass;
+
+#define TYPE_XEN_DEVICE "xen-device"
+#define XEN_DEVICE(obj) \
+     OBJECT_CHECK(XenDevice, (obj), TYPE_XEN_DEVICE)
+#define XEN_DEVICE_CLASS(class) \
+     OBJECT_CLASS_CHECK(XenDeviceClass, (class), TYPE_XEN_DEVICE)
+#define XEN_DEVICE_GET_CLASS(obj) \
+     OBJECT_GET_CLASS(XenDeviceClass, (obj), TYPE_XEN_DEVICE)
+
+typedef struct XenBus {
+    BusState qbus;
+} XenBus;
+
+typedef struct XenBusClass {
+    /*< private >*/
+    BusClass parent_class;
+} XenBusClass;
+
+#define TYPE_XEN_BUS "xen-bus"
+#define XEN_BUS(obj) \
+    OBJECT_CHECK(XenBus, (obj), TYPE_XEN_BUS)
+#define XEN_BUS_CLASS(class) \
+    OBJECT_CLASS_CHECK(XenBusClass, (class), TYPE_XEN_BUS)
+#define XEN_BUS_GET_CLASS(obj) \
+    OBJECT_GET_CLASS(XenBusClass, (obj), TYPE_XEN_BUS)
+
+void xen_bus_init(void);
+
+#endif /* HW_XEN_BUS_H */