[RFC 1/2] hw/vfio: Introduce vfio_is_dma_map_allowed() callback

[Eric Auger <eric.auger@redhat.com>]

It may happen that a VFIO device state prevents its regions
from beeing DMA mapped. Specifically this happens with VFIO PCI
device in D3hot power state whose BARs cannot be dma mapped.
The behavior was introduced by kernel commit:

2b2c651baf1c ("vfio/pci: Invalidate mmaps and block the access
in D3hot power state")

We introduce a new VFIODeviceOps callback to retrieve whether
DMA MAP is allowed. This callback will be called from the generic
code, in vfio_listener_region_add.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 include/hw/vfio/vfio-common.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index 0c60be5b15..92c58f14a0 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -182,6 +182,17 @@ struct VFIODeviceOps {
      * Returns zero to indicate success and negative for error
      */
     int (*vfio_load_config)(VFIODevice *vdev, QEMUFile *f);
+
+    /**
+     * @is_dma_map_allowed
+     *
+     * Returns if the device regions can be dma mapped
+     * It may happen that the device state is not compatible
+     * with such operation
+     *
+     * @vdev: #VFIODevice whose power state needs to be tested
+     */
+    bool (*vfio_is_dma_map_allowed)(VFIODevice *vdev);
 };
 
 typedef struct VFIOGroup {
-- 
2.47.1