[PATCH v4 2/3] vfio: Add an open counter to vfio_device_set

[Anthony DeRossi <ajderossi@gmail.com>]

open_count is incremented before open_device() and decremented after
close_device() for each device in the set. This allows devices 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>
---
 drivers/vfio/vfio_main.c | 3 +++
 include/linux/vfio.h     | 1 +
 2 files changed, 4 insertions(+)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 9a4af880e941..6c65418fc7e3 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -761,6 +761,7 @@ static struct file *vfio_device_open(struct vfio_device *device)
 		mutex_lock(&device->group->group_lock);
 		device->kvm = device->group->kvm;
 
+		device->dev_set->open_count++;
 		if (device->ops->open_device) {
 			ret = device->ops->open_device(device);
 			if (ret)
@@ -809,6 +810,7 @@ static struct file *vfio_device_open(struct vfio_device *device)
 	}
 err_undo_count:
 	mutex_unlock(&device->group->group_lock);
+	device->dev_set->open_count--;
 	device->open_count--;
 	if (device->open_count == 0 && device->kvm)
 		device->kvm = NULL;
@@ -1023,6 +1025,7 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
 			device->ops->close_device(device);
 
 		vfio_device_container_unregister(device);
+		device->dev_set->open_count--;
 	}
 	mutex_unlock(&device->group->group_lock);
 	device->open_count--;
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index e7cebeb875dd..5becdcdf4ba2 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -28,6 +28,7 @@ struct vfio_device_set {
 	struct mutex lock;
 	struct list_head device_list;
 	unsigned int device_count;
+	unsigned int open_count;
 };
 
 struct vfio_device {
-- 
2.37.4