[v4 1/3] vfio: add vfio_group_notify support

[Jike Song <jike.song@intel.com>]

A vfio_group may be or may not be attached to a KVM instance,
if it is, the user of vfio_group might also want to know which
KVM instance it is attached to, and when it will detach. In VFIO
there are already external APIs for KVM to get/put vfio_group,
by providing a similar vfio_group_notify, KVM can notify the
vfio_group about attaching events.

Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Jike Song <jike.song@intel.com>
---
 drivers/vfio/vfio.c  | 30 ++++++++++++++++++++++++++++++
 include/linux/vfio.h |  4 ++++
 2 files changed, 34 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 0afb58e..b149ced 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -86,6 +86,8 @@ struct vfio_group {
 	struct mutex			unbound_lock;
 	atomic_t			opened;
 	bool				noiommu;
+	struct kvm			*kvm;
+	struct blocking_notifier_head	notifier;
 };
 
 struct vfio_device {
@@ -1015,6 +1017,34 @@ static long vfio_ioctl_check_extension(struct vfio_container *container,
 	return ret;
 }
 
+void vfio_group_notify(struct vfio_group *group, struct kvm *kvm)
+{
+	group->kvm = kvm;
+	blocking_notifier_call_chain(&group->notifier,
+				VFIO_GROUP_NOTIFY_SET_KVM, kvm);
+}
+EXPORT_SYMBOL_GPL(vfio_group_notify);
+
+static void vfio_group_register_notifier(struct vfio_group *group,
+					 struct notifier_block *nb)
+{
+	blocking_notifier_chain_register(&group->notifier, nb);
+
+	/*
+	 * The attaching of kvm and vfio_group might already happen, so
+	 * here we replay once on registration.
+	 */
+	if (group->kvm)
+		blocking_notifier_call_chain(&group->notifier,
+					VFIO_GROUP_NOTIFY_SET_KVM, group->kvm);
+}
+
+static void vfio_group_unregister_notifier(struct vfio_group *group,
+					 struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&group->notifier, nb);
+}
+
 /* hold write lock on container->group_lock */
 static int __vfio_container_attach_groups(struct vfio_container *container,
 					  struct vfio_iommu_driver *driver,
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index d4ce14d..ec9f74f 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -100,6 +100,9 @@ extern void vfio_unregister_iommu_driver(
 extern long vfio_external_check_extension(struct vfio_group *group,
 					  unsigned long arg);
 
+struct kvm;
+extern void vfio_group_notify(struct vfio_group *group, struct kvm *kvm);
+
 /*
  * Sub-module helpers
  */
@@ -149,6 +152,7 @@ extern int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn,
 			    int npage);
 
 #define VFIO_IOMMU_NOTIFY_DMA_UNMAP	1
+#define VFIO_GROUP_NOTIFY_SET_KVM	2
 
 extern int vfio_register_notifier(struct device *dev,
 				  struct notifier_block *nb);
-- 
1.9.1