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[Qemu-devel] [PATCH v2] virtio-pci: Disable virtio-ioeventfd when !CONFI
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PATCH v2] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD |
Date: |
Tue, 25 Jan 2011 14:53:31 +0000 |
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 <address@hidden>
---
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
+ * 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
- [Qemu-devel] [PATCH v2] virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD,
Stefan Hajnoczi <=