On Thu, 08/21 17:31, Stefan Hajnoczi wrote:
> On Thu, Aug 21, 2014 at 07:56:51PM +0800, Fam Zheng wrote:
> > @@ -110,6 +109,22 @@ static void qemu_laio_completion_cb(EventNotifier *e)
> > }
> > }
> >
> > +static void laio_cancel_async(BlockDriverAIOCB *blockacb)
> > +{
> > + struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
> > + struct io_event event;
> > + int ret;
> > +
> > + ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
> > + laiocb->ret = -ECANCELED;
> > + if (!ret) {
> > + /* iocb is not cancelled, cb will be called by the event loop
> > later */
> > + return;
> > + }
>
> No callback will be invoked if io_cancel(2) every cancels the request
> immediately.
>
> The current kernel implementation always returns -EINPROGRESS or some of
> other error value. But some day it might return 0 and this would leak
> the request!
>
> > +
> > + laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
> > +}
>
> It would be cleaner to reuse laio_cancel_async() from laio_cancel() to
> avoid code duplication. For example, there is a useful comment in
> laio_cancel() explaining that io_cancel(2) doesn't cancel I/O in
> practice on 2.6.31 era kernels.
I'll take a closer look at it.
Fam
