[RFC PATCH 06/10] vfio: Add a device notifier interface

[Alex Williamson <alex.williamson@redhat.com>]

Using a vfio device, a notifier block can be registered to receive
select device events.  Notifiers can only be registered for contained
devices, ie. they are available through a user context.  Registration
of a notifier increments the reference to that container context
therefore notifiers must minimally respond to the release event by
asynchronously removing notifiers.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/vfio/Kconfig |    1 +
 drivers/vfio/vfio.c  |   35 +++++++++++++++++++++++++++++++++++
 include/linux/vfio.h |    9 +++++++++
 3 files changed, 45 insertions(+)

diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
index 5533df91b257..8ac1601b681b 100644
--- a/drivers/vfio/Kconfig
+++ b/drivers/vfio/Kconfig
@@ -23,6 +23,7 @@ menuconfig VFIO
 	tristate "VFIO Non-Privileged userspace driver framework"
 	depends on IOMMU_API
 	select VFIO_IOMMU_TYPE1 if (X86 || S390 || ARM || ARM64)
+	select SRCU
 	help
 	  VFIO provides a framework for secure userspace device drivers.
 	  See Documentation/driver-api/vfio.rst for more details.
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 399c42b77fbb..1a1b46215ac4 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -105,6 +105,7 @@ struct vfio_device {
 	struct list_head		group_next;
 	void				*device_data;
 	struct inode			*inode;
+	struct srcu_notifier_head	notifier;
 };
 
 #ifdef CONFIG_VFIO_NOIOMMU
@@ -610,6 +611,7 @@ struct vfio_device *vfio_group_create_device(struct vfio_group *group,
 	device->ops = ops;
 	device->device_data = device_data;
 	dev_set_drvdata(dev, device);
+	srcu_init_notifier_head(&device->notifier);
 
 	/* No need to get group_lock, caller has group reference */
 	vfio_group_get(group);
@@ -1778,6 +1780,39 @@ static const struct file_operations vfio_device_fops = {
 	.mmap		= vfio_device_fops_mmap,
 };
 
+int vfio_device_register_notifier(struct vfio_device *device,
+				  struct notifier_block *nb)
+{
+	int ret;
+
+	/* Container ref persists until unregister on success */
+	ret =  vfio_group_add_container_user(device->group);
+	if (ret)
+		return ret;
+
+	ret = srcu_notifier_chain_register(&device->notifier, nb);
+	if (ret)
+		vfio_group_try_dissolve_container(device->group);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vfio_device_register_notifier);
+
+void vfio_device_unregister_notifier(struct vfio_device *device,
+				    struct notifier_block *nb)
+{
+	if (!srcu_notifier_chain_unregister(&device->notifier, nb))
+		vfio_group_try_dissolve_container(device->group);
+}
+EXPORT_SYMBOL_GPL(vfio_device_unregister_notifier);
+
+int vfio_device_notifier_call(struct vfio_device *device,
+			      enum vfio_device_notify_type event)
+{
+	return srcu_notifier_call_chain(&device->notifier, event, NULL);
+}
+EXPORT_SYMBOL_GPL(vfio_device_notifier_call);
+
 /**
  * External user API, exported by symbols to be linked dynamically.
  *
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 188c2f3feed9..8217cd4ea53d 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -60,6 +60,15 @@ extern void vfio_device_unmap_mapping_range(struct vfio_device *device,
 					    loff_t start, loff_t len);
 extern void vfio_device_vma_open(struct vm_area_struct *vma);
 extern struct vfio_device *vfio_device_get_from_vma(struct vm_area_struct *vma);
+extern int vfio_device_register_notifier(struct vfio_device *device,
+					 struct notifier_block *nb);
+extern void vfio_device_unregister_notifier(struct vfio_device *device,
+					    struct notifier_block *nb);
+enum vfio_device_notify_type {
+	VFIO_DEVICE_RELEASE = 0,
+};
+int vfio_device_notifier_call(struct vfio_device *device,
+			      enum vfio_device_notify_type event);
 
 /* events for the backend driver notify callback */
 enum vfio_iommu_notify_type {