[PATCH 8/8] kvm tools: Make virtio-pci's ioeventfd__add_event() fall back gracefully if ioeventfds unavailable

[Matt Evans]

PPC KVM doesn't yet support ioeventfds, so don't bomb out/die.  virtio-pci is
able to function if it instead uses normal IO port notification.

Signed-off-by: Matt Evans <m...@ozlabs.org>
---
 tools/kvm/include/kvm/ioeventfd.h |    3 ++-
 tools/kvm/ioeventfd.c             |   12 +++++++++---
 tools/kvm/virtio/pci.c            |   11 ++++++++++-
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/tools/kvm/include/kvm/ioeventfd.h 
b/tools/kvm/include/kvm/ioeventfd.h
index df01750..5e458be 100644
--- a/tools/kvm/include/kvm/ioeventfd.h
+++ b/tools/kvm/include/kvm/ioeventfd.h
@@ -4,6 +4,7 @@
 #include <linux/types.h>
 #include <linux/list.h>
 #include <sys/eventfd.h>
+#include <stdbool.h>
 
 struct kvm;
 
@@ -21,7 +22,7 @@ struct ioevent {
 
 void ioeventfd__init(void);
 void ioeventfd__start(void);
-void ioeventfd__add_event(struct ioevent *ioevent);
+bool ioeventfd__add_event(struct ioevent *ioevent);
 void ioeventfd__del_event(u64 addr, u64 datamatch);
 
 #endif
diff --git a/tools/kvm/ioeventfd.c b/tools/kvm/ioeventfd.c
index 3a240e4..37f9a63 100644
--- a/tools/kvm/ioeventfd.c
+++ b/tools/kvm/ioeventfd.c
@@ -26,7 +26,7 @@ void ioeventfd__init(void)
                die("Failed creating epoll fd");
 }
 
-void ioeventfd__add_event(struct ioevent *ioevent)
+bool ioeventfd__add_event(struct ioevent *ioevent)
 {
        struct kvm_ioeventfd kvm_ioevent;
        struct epoll_event epoll_event;
@@ -48,8 +48,13 @@ void ioeventfd__add_event(struct ioevent *ioevent)
                .flags                  = KVM_IOEVENTFD_FLAG_PIO | 
KVM_IOEVENTFD_FLAG_DATAMATCH,
        };
 
-       if (ioctl(ioevent->fn_kvm->vm_fd, KVM_IOEVENTFD, &kvm_ioevent) != 0)
-               die("Failed creating new ioeventfd");
+       if (ioctl(ioevent->fn_kvm->vm_fd, KVM_IOEVENTFD, &kvm_ioevent) != 0) {
+               /* Not all KVM implementations may support KVM_IOEVENTFD,
+                * so be graceful.
+                */
+               free(new_ioevent);
+               return false;
+       }
 
        epoll_event = (struct epoll_event) {
                .events                 = EPOLLIN,
@@ -60,6 +65,7 @@ void ioeventfd__add_event(struct ioevent *ioevent)
                die("Failed assigning new event to the epoll fd");
 
        list_add_tail(&new_ioevent->list, &used_ioevents);
+       return true;
 }
 
 void ioeventfd__del_event(u64 addr, u64 datamatch)
diff --git a/tools/kvm/virtio/pci.c b/tools/kvm/virtio/pci.c
index ffa3768..06d3b79 100644
--- a/tools/kvm/virtio/pci.c
+++ b/tools/kvm/virtio/pci.c
@@ -50,7 +50,16 @@ static int virtio_pci__init_ioeventfd(struct kvm *kvm, 
struct virtio_trans *vtra
                .fd             = eventfd(0, 0),
        };
 
-       ioeventfd__add_event(&ioevent);
+       if (!ioeventfd__add_event(&ioevent)) {
+#ifndef CONFIG_PPC
+               /* PPC64 doesn't have kvm ioevents yet, so we expect this to
+                * fail -- don't need to be verbose about it!  For virtio-pci,
+                * this is fine.  It catches the IO accesses anyway, so
+                * still works (but slower).
+                */
+               pr_warning("Failed creating new ioeventfd");
+#endif
+       }
 
        if (vtrans->virtio_ops->notify_vq_eventfd)
                vtrans->virtio_ops->notify_vq_eventfd(kvm, vpci->dev, vq, 
ioevent.fd);
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