Re: [Qemu-devel] [PATCH v7 0/4] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Markus Armbruster <armbru@redhat.com>]

Laurent Vivier <lvivier@redhat.com> writes:

> On 05/06/2019 19:56, Markus Armbruster wrote:
>> Laurent Vivier <lvivier@redhat.com> writes:
>> 
>>> On 05/06/2019 15:05, Markus Armbruster wrote:
>>>> Laurent Vivier <lvivier@redhat.com> writes:
>>>>
>>>>> Add a new RNG backend using QEMU builtin getrandom function.
>>>>>
>>>>> v7: rebase on master
>>>>>     Make rng-builtin asynchronous with QEMUBH (removed existing R-b)
>>>>
>>>> Pardon the ignorant question: why is that necessary?
>>>>
>>>
>>> Because request_entropy() function is called while the request is not in
>>> the requests queue, so the loop on !QSIMPLEQ_EMPTY(&s->parent.requests)
>>> doens't process it. The request is added just after the call.
>> 
>> In rng_backend_request_entropy().  I see.  Any particular reason for
>> this order?  "I don't know" is an acceptable answer :)
>> 
>
> Yes...
>
> and there is a reason:
>
> in rng_random_request_entropy(), QSIMPLEQ_EMPTY() is used to know if we
> have to register an fd handler with qemu_set_fd_handler().
>
> For me, it seemed easier to use QEMUBH rather than to change the
> existing algorithm, as the backend has been thought to be asynchronous.

In your shoes, I'd be tempted to explore whether changing the order
simplifies things overall.  I'm not asking you to do that; your patch is
okay as is.

Thanks!