From: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
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>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
kvm-all.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/kvm-all.c b/kvm-all.c
index 255b6fa..8f0e17c 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 io notification. This requires a host
+ * 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
