[PATCH v6 18/20] KVM: introduce kvm_check_device_type()

[andre.przywara@arm.com (Andre Przywara)]

While we can easily register and unregister KVM devices, there is
currently no easy way of checking whether a device has been
registered.
Introduce kvm_check_device_type() for that purpose and use it in two
existing functions. Also change the return code for an invalid
type number from ENOSPC to EINVAL.
This function will be later used by another patch set to check
whether a KVM_CREATE_IRQCHIP ioctl is valid.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
Changelog:
 (new in v6)

 include/linux/kvm_host.h |    1 +
 virt/kvm/kvm_main.c      |   33 +++++++++++++++++++++------------
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 83d770e..723d0d2 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1038,6 +1038,7 @@ void kvm_device_get(struct kvm_device *dev);
 void kvm_device_put(struct kvm_device *dev);
 struct kvm_device *kvm_device_from_filp(struct file *filp);
 int kvm_register_device_ops(struct kvm_device_ops *ops, u32 type);
+int kvm_check_device_type(u32 type);
 void kvm_unregister_device_ops(u32 type);
 
 extern struct kvm_device_ops kvm_mpic_ops;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1cc6e2e..c7711b2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2341,13 +2341,24 @@ static struct kvm_device_ops *kvm_device_ops_table[KVM_DEV_TYPE_MAX] = {
 #endif
 };
 
-int kvm_register_device_ops(struct kvm_device_ops *ops, u32 type)
+int kvm_check_device_type(u32 type)
 {
 	if (type >= ARRAY_SIZE(kvm_device_ops_table))
-		return -ENOSPC;
+		return -EINVAL;
 
-	if (kvm_device_ops_table[type] != NULL)
-		return -EEXIST;
+	if (kvm_device_ops_table[type] == NULL)
+		return -ENODEV;
+
+	return -EEXIST;
+}
+
+int kvm_register_device_ops(struct kvm_device_ops *ops, u32 type)
+{
+	int ret;
+
+	ret = kvm_check_device_type(type);
+	if (ret != -ENODEV)
+		return ret;
 
 	kvm_device_ops_table[type] = ops;
 	return 0;
@@ -2364,19 +2375,17 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
 {
 	struct kvm_device_ops *ops = NULL;
 	struct kvm_device *dev;
-	bool test = cd->flags & KVM_CREATE_DEVICE_TEST;
 	int ret;
 
-	if (cd->type >= ARRAY_SIZE(kvm_device_ops_table))
-		return -ENODEV;
-
-	ops = kvm_device_ops_table[cd->type];
-	if (ops == NULL)
-		return -ENODEV;
+	ret = kvm_check_device_type(cd->type);
+	if (ret != -EEXIST)
+		return ret;
 
-	if (test)
+	if (cd->flags & KVM_CREATE_DEVICE_TEST)
 		return 0;
 
+	ops = kvm_device_ops_table[cd->type];
+
 	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 	if (!dev)
 		return -ENOMEM;
-- 
1.7.9.5