Re: [Qemu-devel] Re: [PATCH v2] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Jan 25, 2011 at 2:56 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Tue, Jan 25, 2011 at 02:53:31PM +0000, Stefan Hajnoczi wrote:
>> It is not possible to use virtio-ioeventfd when building without an I/O
>> thread.  We rely on a signal to kick us out of vcpu execution.  Timers
>> and AIO use SIGALRM and SIGUSR2 respectively.  Unfortunately eventfd
>> does not support O_ASYNC (SIGIO) so eventfd cannot be used in a signal
>> driven manner.
>>
>> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
>> ---
>>  kvm-all.c |    8 ++++++--
>>  1 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/kvm-all.c b/kvm-all.c
>> index 255b6fa..881ea32 100644
>> --- a/kvm-all.c
>> +++ b/kvm-all.c
>> @@ -449,10 +449,14 @@ int kvm_check_extension(KVMState *s, unsigned int extension)
>>
>>  static int kvm_check_many_ioeventfds(void)
>>  {
>> -    /* Older kernels have a 6 device limit on the KVM io bus.  Find out so we
>> +    /* Userspace can use ioeventfd for virtqueue kick.  This requires a host
>
> virtqueue kick -> io notifications?

Fixed in v3.

Stefan