Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd

[Stefan Hajnoczi]

On Tue, Mar 13, 2012 at 10:42 AM, Amos Kong <address@hidden> wrote:
> Boot up guest with 232 virtio-blk disk, qemu will abort for fail to
> allocate ioeventfd. This patchset changes kvm_has_many_ioeventfds(),
> and check if available ioeventfd exists. If not, virtio-pci will
> fallback to userspace, and don't use ioeventfd for io notification.

Please explain how it fails with 232 devices.  Where does it abort and why?

hw/virtio-pci.c:virtio_pci_start_ioeventfd() fails "gracefully" when
virtio_pci_set_host_notifier_internal()'s event_notifier_init() call
fails.  (This might be because we've hit our file descriptor rlimit.)

Perhaps the problem is that we've exceeded the kvm.ko io device limit?
 I guess that is now handled by the new memory region API and we need
to handle failure gracefully there too.

Either way, I don't think that using kvm_has_many_ioeventfds() is the
right answer.

Stefan