Re: [PATCH 10/15] static_call: Add basic static call infrastructure

[Andy Lutomirski]

> On Jun 7, 2019, at 1:49 AM, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
> 
>> On Fri, 7 Jun 2019 at 10:29, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> 
>> On Thu, Jun 06, 2019 at 10:44:23PM +0000, Nadav Amit wrote:
>>>> + * Usage example:
>>>> + *
>>>> + *   # Start with the following functions (with identical prototypes):
>>>> + *   int func_a(int arg1, int arg2);
>>>> + *   int func_b(int arg1, int arg2);
>>>> + *
>>>> + *   # Define a 'my_key' reference, associated with func_a() by default
>>>> + *   DEFINE_STATIC_CALL(my_key, func_a);
>>>> + *
>>>> + *   # Call func_a()
>>>> + *   static_call(my_key, arg1, arg2);
>>>> + *
>>>> + *   # Update 'my_key' to point to func_b()
>>>> + *   static_call_update(my_key, func_b);
>>>> + *
>>>> + *   # Call func_b()
>>>> + *   static_call(my_key, arg1, arg2);
>>> 
>>> I think that this calling interface is not very intuitive.
>> 
>> Yeah, it is somewhat unfortunate..
>> 
> 
> Another thing I brought up at the time is that it would be useful to
> have the ability to 'reset' a static call to its default target. E.g.,
> for crypto modules that implement an accelerated version of a library
> interface, removing the module should revert those call sites back to
> the original target, without putting a disproportionate burden on the
> module itself to implement the logic to support this.

I was thinking this could be a layer on top.  We could have a way to register a static call with the module core so that, when a GPL module with an appropriate symbol is loaded, the static call gets replaced.

KVM could use this too.  Or we could just require KVM to be built in some day.