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 <stefa...@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?
> + * that supports eventfd(2) and an I/O thread; since eventfd does not
> + * support SIGIO it cannot interrupt the vcpu.
> + *
> + * Older kernels have a 6 device limit on the KVM io bus. Find out so we
> * can avoid creating too many ioeventfds.
> */
> -#ifdef CONFIG_EVENTFD
> +#if defined(CONFIG_EVENTFD) && defined(CONFIG_IOTHREAD)
> int ioeventfds[7];
> int i, ret = 0;
> for (i = 0; i < ARRAY_SIZE(ioeventfds); i++) {
> --
> 1.7.2.3
