[RFC v6 05/16] VFIO: external user API for interaction with vfio devices

[Eric Auger]

The VFIO external user API is enriched with 3 new functions that
allows a kernel user external to VFIO to retrieve some information
from a VFIO device.

- vfio_device_get_external_user enables to get a vfio device from
  its fd and increments its reference counter
- vfio_device_put_external_user decrements the reference counter
- vfio_external_base_device returns a handle to the struct device

---

v3 -> v4:
- change the commit title

v2 -> v3:
- reword the commit message

v1 -> v2:

- vfio_external_get_base_device renamed into vfio_external_base_device
- vfio_external_get_type removed

Signed-off-by: Eric Auger <eric.auger at linaro.org>
---
 drivers/vfio/vfio.c  | 24 ++++++++++++++++++++++++
 include/linux/vfio.h |  3 +++
 2 files changed, 27 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 23ba12a..33ae8c5 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1490,6 +1490,30 @@ void vfio_group_put_external_user(struct vfio_group *group)
 }
 EXPORT_SYMBOL_GPL(vfio_group_put_external_user);
 
+struct vfio_device *vfio_device_get_external_user(struct file *filep)
+{
+	struct vfio_device *vdev = filep->private_data;
+
+	if (filep->f_op != &vfio_device_fops)
+		return ERR_PTR(-EINVAL);
+
+	vfio_device_get(vdev);
+	return vdev;
+}
+EXPORT_SYMBOL_GPL(vfio_device_get_external_user);
+
+void vfio_device_put_external_user(struct vfio_device *vdev)
+{
+	vfio_device_put(vdev);
+}
+EXPORT_SYMBOL_GPL(vfio_device_put_external_user);
+
+struct device *vfio_external_base_device(struct vfio_device *vdev)
+{
+	return vdev->dev;
+}
+EXPORT_SYMBOL_GPL(vfio_external_base_device);
+
 int vfio_external_user_iommu_id(struct vfio_group *group)
 {
 	return iommu_group_id(group->iommu_group);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 683b514..b18c38f 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -101,6 +101,9 @@ extern void vfio_group_put_external_user(struct vfio_group *group);
 extern int vfio_external_user_iommu_id(struct vfio_group *group);
 extern long vfio_external_check_extension(struct vfio_group *group,
 					  unsigned long arg);
+extern struct vfio_device *vfio_device_get_external_user(struct file *filep);
+extern void vfio_device_put_external_user(struct vfio_device *vdev);
+extern struct device *vfio_external_base_device(struct vfio_device *vdev);
 
 struct pci_dev;
 #ifdef CONFIG_EEH
-- 
1.9.1