vfio: Introduce vfio_get_vfio_device()

This helper will be useful in the listener handlers to extract the
VFIO device from a memory region using memory_region_owner(). At the
moment, we only care for PCI passthrough devices. If the need arises,
we will add more.

Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250206131438.1505542-5-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/helpers.c

@@ -23,6 +23,7 @@
 #include <sys/ioctl.h>
 
 #include "hw/vfio/vfio-common.h"
+#include "hw/vfio/pci.h"
 #include "hw/hw.h"
 #include "trace.h"
 #include "qapi/error.h"
@@ -728,3 +729,12 @@ bool vfio_device_hiod_realize(VFIODevice *vbasedev, Error **errp)
 
     return HOST_IOMMU_DEVICE_GET_CLASS(hiod)->realize(hiod, vbasedev, errp);
 }
+
+VFIODevice *vfio_get_vfio_device(Object *obj)
+{
+    if (object_dynamic_cast(obj, TYPE_VFIO_PCI)) {
+        return &VFIO_PCI(obj)->vbasedev;
+    } else {
+        return NULL;
+    }
+}

include/hw/vfio/vfio-common.h

@@ -252,6 +252,7 @@ bool vfio_device_hiod_realize(VFIODevice *vbasedev, Error **errp);
 bool vfio_attach_device(char *name, VFIODevice *vbasedev,
                         AddressSpace *as, Error **errp);
 void vfio_detach_device(VFIODevice *vbasedev);
+VFIODevice *vfio_get_vfio_device(Object *obj);
 
 int vfio_kvm_device_add_fd(int fd, Error **errp);
 int vfio_kvm_device_del_fd(int fd, Error **errp);