回调与程序执行控制流

Provider开发设计的一大难点就是其中的参数传递与回调方式，查看OpenSSL关于provider相关部分的手册页，可以发现有一段共同的描述：

   All "functions" mentioned here are passed as function pointers
   between libcrypto and the provider in OSSL_DISPATCH(3) arrays
   via OSSL_ALGORITHM(3) arrays that are returned by the
   provider's provider_query_operation() function (see "Provider
   Functions" in provider-base(7)).

   All these "functions" have a corresponding function type
   definition named OSSL_FUNC_{name}_fn, and a helper function to
   retrieve the function pointer from an OSSL_DISPATCH(3) element
   named OSSL_FUNC_{name}.

所有在这里被提到的函数都在OSSL_DISPATCH数组中，由provider的查询操作函数，通过OSSL_ALGORITHM数组进行返回。
而信息传递则通过OSSL_PARAM数组进行，保障类型安全与扩展性。
这是Provider开发中的通用模式。