On 27/05/2015 09:19, Fam Zheng wrote: > This series looks at the other side of the broken "qmp transaction" problem > with dataplane [1] - the event loop. > > Before, an ioeventfd of a non-dataplane device is registered via > qemu_set_fd_handler, which is only polled directly by main_loop_wait(), not in > aio_poll(); an ioeventfd of a dataplane device (virtio-blk/virtio-scsi) is > registered specially via aio_set_event_notifier, which is a wrapper of > aio_set_fd_handler, thus it WILL be polled by all aio_poll(). > > As explained in [1], and in patch 3, this is wrong. The handlers mustn't run. > > [1] Fixes it by unregistering them temporarily around such nested poll, while > this series fixes it by skipping those file descriptors in all nested > aio_poll(), just like how iohandler behaves in the main loop. > > On the one hand, it is simpler than [1]; on the other hand, this approach is > also interesting because once we remove qemu_set_fd_handler2 [2], iohandler.c > can be removed by converting all qemu_set_fd_handler to the new > aio_set_io_event_notifier introduced in this series.
I don't think this can work. Whenever the main context is doing synchronous work for dataplane, it is in the outermost aio_poll. Paolo
