Re: [Qemu-devel] [PATCH 1/5] virtio-pci: use ioeventfd even when KVM is disabled

[Stefan Hajnoczi]

On Fri, Jun 16, 2017 at 06:26:01AM +0300, Michael S. Tsirkin wrote:
> On Thu, Jun 15, 2017 at 05:38:09PM +0100, Stefan Hajnoczi wrote:
> > Old kvm.ko versions only supported a tiny number of ioeventfds so
> > virtio-pci avoids ioeventfds when kvm_has_many_ioeventfds() returns 0.
> > 
> > Do not check kvm_has_many_ioeventfds() when KVM is disabled since it
> > always returns 0.  Since commit 8c56c1a592b5092d91da8d8943c17777d6462a6f
> > ("memory: emulate ioeventfd") it has been possible to use ioeventfds in
> > qtest or TCG mode.
> > 
> > This patch makes -device virtio-blk-pci,iothread=iothread0 work even
> > when KVM is disabled.
> > 
> > I have tested that virtio-blk-pci works under TCG both with and without
> > iothread.
> > 
> > Cc: Michael S. Tsirkin <address@hidden>
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> 
> Don't we need to check we are on a host that supports eventfd?

That is not necessary because the ioeventfd memory API is based on
EventNotifier instead of raw eventfds.

EventNotifier falls back to pipes on POSIX platforms and uses native
Event objects on Windows.

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