> On Sep 8, 2021, at 11:29 PM, Stefan Hajnoczi <stefa...@redhat.com> wrote:
>
> On Thu, Sep 09, 2021 at 05:11:49AM +0000, John Johnson wrote:
>>
>>
>> I did look at coroutines, but they seemed to work when the sender
>> is triggering the coroutine on send, not when request packets are arriving
>> asynchronously to the sends.
>
> This can be done with a receiver coroutine. Its job is to be the only
> thing that reads vfio-user messages from the socket. A receiver
> coroutine reads messages from the socket and wakes up the waiting
> coroutine that yielded from vfio_user_send_recv() or
> vfio_user_pci_process_req().
>
> (Although vfio_user_pci_process_req() could be called directly from the
> receiver coroutine, it seems safer to have a separate coroutine that
> processes requests so that the receiver isn't blocked in case
> vfio_user_pci_process_req() yields while processing a request.)
>
> Going back to what you mentioned above, the receiver coroutine does
> something like this:
>
> if it's a reply
> reply = find_reply(...)
> qemu_coroutine_enter(reply->co) // instead of signalling reply->cv
> else
> QSIMPLEQ_INSERT_TAIL(&pending_reqs, request, next);
> if (pending_reqs_was_empty) {
> qemu_coroutine_enter(process_request_co);
> }
>
> The pending_reqs queue holds incoming requests that the
> process_request_co coroutine processes.
>
How do coroutines work across threads? There can be multiple vCPU
threads waiting for replies, and I think the receiver coroutine will be
running in the main loop thread. Where would a vCPU block waiting for
a reply? I think coroutine_yield() returns to its coroutine_enter() caller.
JJ
