[PATCH v6 2/3] vfio: Export the device set open count

[Anthony DeRossi <ajderossi@gmail.com>]

The open count of a device set is the sum of the open counts of all
devices in the set. Drivers can use this value to determine whether
shared resources are in use without tracking them manually or accessing
the private open_count in vfio_device.

Signed-off-by: Anthony DeRossi <ajderossi@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
---
 drivers/vfio/vfio_main.c | 13 +++++++++++++
 include/linux/vfio.h     |  1 +
 2 files changed, 14 insertions(+)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 9a4af880e941..6e8804fe0095 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -125,6 +125,19 @@ static void vfio_release_device_set(struct vfio_device *device)
 	xa_unlock(&vfio_device_set_xa);
 }
 
+unsigned int vfio_device_set_open_count(struct vfio_device_set *dev_set)
+{
+	struct vfio_device *cur;
+	unsigned int open_count = 0;
+
+	lockdep_assert_held(&dev_set->lock);
+
+	list_for_each_entry(cur, &dev_set->device_list, dev_set_list)
+		open_count += cur->open_count;
+	return open_count;
+}
+EXPORT_SYMBOL_GPL(vfio_device_set_open_count);
+
 /*
  * Group objects - create, release, get, put, search
  */
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index e7cebeb875dd..fdd393f70b19 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -189,6 +189,7 @@ int vfio_register_emulated_iommu_dev(struct vfio_device *device);
 void vfio_unregister_group_dev(struct vfio_device *device);
 
 int vfio_assign_device_set(struct vfio_device *device, void *set_id);
+unsigned int vfio_device_set_open_count(struct vfio_device_set *dev_set);
 
 int vfio_mig_get_next_state(struct vfio_device *device,
 			    enum vfio_device_mig_state cur_fsm,
-- 
2.37.4