[PATCH v3 1/7] vfio: allow external user to get vfio group from device

[Yan Zhao <yan.y.zhao@intel.com>]

external user is able to
1. add a device into an vfio group
2. call vfio_group_get_external_user_from_dev() with the device pointer
to get vfio_group associated with this device and increments the container
user counter to prevent the VFIO group from disposal before KVM exits.
3. When the external KVM finishes, it calls vfio_group_put_external_user()
to release the VFIO group.

Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
 drivers/vfio/vfio.c  | 37 +++++++++++++++++++++++++++++++++++++
 include/linux/vfio.h |  2 ++
 2 files changed, 39 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index c8482624ca34..914bdf4b9d73 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1720,6 +1720,43 @@ struct vfio_group *vfio_group_get_external_user(struct file *filep)
 }
 EXPORT_SYMBOL_GPL(vfio_group_get_external_user);
 
+/**
+ * External user API, exported by symbols to be linked dynamically.
+ *
+ * The protocol includes:
+ * 1. External user add a device into a vfio group
+ *
+ * 2. The external user calls vfio_group_get_external_user_from_dev()
+ * with the device pointer
+ * to verify that:
+ *	- there's a vfio group associated with it and is initialized;
+ *	- IOMMU is set for the vfio group.
+ * If both checks passed, vfio_group_get_external_user_from_dev()
+ * increments the container user counter to prevent
+ * the VFIO group from disposal before KVM exits.
+ *
+ * 3. When the external KVM finishes, it calls
+ * vfio_group_put_external_user() to release the VFIO group.
+ * This call decrements the container user counter.
+ */
+
+struct vfio_group *vfio_group_get_external_user_from_dev(struct device *dev)
+{
+	struct vfio_group *group;
+	int ret;
+
+	group = vfio_group_get_from_dev(dev);
+	if (!group)
+		return ERR_PTR(-ENODEV);
+
+	ret = vfio_group_add_container_user(group);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return group;
+}
+EXPORT_SYMBOL_GPL(vfio_group_get_external_user_from_dev);
+
 void vfio_group_put_external_user(struct vfio_group *group)
 {
 	vfio_group_try_dissolve_container(group);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index e42a711a2800..2e1fa0c7396f 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -94,6 +94,8 @@ extern void vfio_unregister_iommu_driver(
  */
 extern struct vfio_group *vfio_group_get_external_user(struct file *filep);
 extern void vfio_group_put_external_user(struct vfio_group *group);
+extern
+struct vfio_group *vfio_group_get_external_user_from_dev(struct device *dev);
 extern bool vfio_external_group_match_file(struct vfio_group *group,
 					   struct file *filep);
 extern int vfio_external_user_iommu_id(struct vfio_group *group);
-- 
2.17.1