Commit d0dcac83 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Kevin Wolf
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virtio-pci: Disable virtio-ioeventfd when !CONFIG_IOTHREAD

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: default avatarStefan Hajnoczi <>
Acked-by: default avatarMichael S. Tsirkin <>
Signed-off-by: default avatarKevin Wolf <>
parent e5051fc7
......@@ -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.
#if defined(CONFIG_EVENTFD) && defined(CONFIG_IOTHREAD)
int ioeventfds[7];
int i, ret = 0;
for (i = 0; i < ARRAY_SIZE(ioeventfds); i++) {
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