On Thu, Aug 27, 2015 at 11:49:32AM +0100, Peter Maydell wrote: > On 27 August 2015 at 05:50, Jason Wang <jasow...@redhat.com> wrote: > > On 08/26/2015 10:51 PM, Greg Kurz wrote: > >> On Wed, 26 Aug 2015 15:21:59 +0100 > >> Peter Maydell <peter.mayd...@linaro.org> wrote: > >>> This seems to me like a bug in the caller. Why would anything > >>> try to call into the memory subsystem to do a zero-size > >>> transaction? > > >> Here's the patch which needs zero-size eventfd: > >> > >> http://patchwork.ozlabs.org/patch/509428/ > > > Yes, this is because we want to use wildcard mmio eventfd (which > > requires size to be zero) to speed up virtio 1.0 mmio. > > But *why* does it require the size to be zero? I still think > the caller should just avoid trying to do zero-size memory > operations: they don't make sense. What is a zero size > operation supposed to mean? > > -- PMM
This just mirrors an API we have in kvm: if you pass 0 size when registering an ioeventfd, it will match on access of any size. -- MST
