KEYS: Provide a generic instantiation function

Provide a generic instantiation function for key types that use the preparse
hook.  This makes it easier to prereserve key quota before keyrings get locked
to retain the new key.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jlayton@primarydata.com>
Reviewed-by: Sage Weil <sage@redhat.com>

include/linux/key-type.h

@@ -159,5 +159,7 @@ static inline int key_negate_and_link(struct key *key,
 	return key_reject_and_link(key, timeout, ENOKEY, keyring, instkey);
 }
 
+extern int generic_key_instantiate(struct key *key, struct key_preparsed_payload *prep);
+
 #endif /* CONFIG_KEYS */
 #endif /* _LINUX_KEY_TYPE_H */