[openssl-dev] Adding async support

[Dmitry Belyavsky]

Dear Matt,

On Thu, Oct 8, 2015 at 1:56 PM, Matt Caswell <matt at openssl.org> wrote:

>
> >     The engine needs to have a way of offloading the work to "something
> >     else" so that it can come back and pick up the results later.
> Typically
> >     for an engine this would mean some external hardware, but as I
> suggested
> >     above it could be done using threads.
> >
> >     From an engine perspective the work would be:
> >     - Receive a request to do some crypto work in the normal way via the
> >     engine API.
> >     - Offload the work to "something else"
> >
> >
> > So what is a mechanism of such an offload? Can I, for example, get the
> > (global) ASYNC_pool and add a job (function/pointer to context) to it?
>
> The offload mechanism is entirely engine specific. We do not know how
> any specific engine works or how to interface to the hardware. An engine
> will be called in exactly the same way as now. The job of the engine
> will be to take the parameters passed to it and initiate the work in the
> engine hardware.
>
> So in pseudo code it might look something like this:
>
> static int myengine_aes128_cbc_cipher(EVP_CIPHER_CTX *ctx,
>     unsigned char *out, const unsigned char *in, size_t inl)
> {
>     int jobid;
>
>     jobid = offload_cipher_to_hardware(ctx, out, in , inl);
>
>     /*
>      * jobid holds a reference in the engine back to the work we just
>      * started
>      */
>
>     while(work_not_finished_yet(jobid)) {
>         /* Return control back to the calling application */
>         ASYNC_pause_job();
>     }
>
>     return get_results_from_hardware(jobid);
> }
>
> You will note that ASYNC_pause_job() does *not* do a "return" to return
> control back to the user application...but calling ASYNC_pause_job()
> will cause SSL_read (or whatever) to return with SSL_ERROR_WANT_ASYNC
> nonetheless. The async job has its own private stack to enable this.
> Recalling SSL_read from the user application will appear to the engine
> like the function call ASYNC_pause_job() has returned.
>
>
> > How will the SSL struct obtain a job id from the engine implementing,
> > for example, "long" RSA_METHOD?
>
> It does not need to. The SSL object has a reference to the ASYNC_JOB.
> The engine can manage its own job ids - see the pseudo code above.
>

I see. So am I correct supposing that pseudo code for
offload_cipher_to_hardware looks like this:

static int async_wrapper(void * args)
{
...
}

static ASYNC_JOB *offload (void *args)
{
  ASYNC_JOB *pjob = NULL;
  int funcret;
  size_t size = 0;

  int ret = ASYNC_start_job(&pjob, &funcret, async_wrapper, args,
                      *args, size);
  if (ret != ASYNC_PAUSE) return NULL;
  return pjob;
}

?

Thank you!

-- 
SY, Dmitry Belyavsky
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