[PATCH V2 2/2] kvm tools: Make virtio-pci's ioeventfd__add_event() fall back gracefully if ioeventfds unavailable

[Matt Evans <matt@xxxxxxxxxx>]

Some KVM implementations (e.g. PPC) don'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 <matt@xxxxxxxxxx>
---
 tools/kvm/Makefile                |    2 +-
 tools/kvm/include/kvm/ioeventfd.h |    3 ++-
 tools/kvm/ioeventfd.c             |   12 +++++++++---
 tools/kvm/virtio/pci.c            |   13 ++++++++++++-
 4 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/tools/kvm/Makefile b/tools/kvm/Makefile
index 3f1e84a..5bb3f08 100644
--- a/tools/kvm/Makefile
+++ b/tools/kvm/Makefile
@@ -126,7 +126,7 @@ ifeq ($(ARCH),x86)
 endif
 # POWER/ppc:  Actually only support ppc64 currently.
 ifeq ($(uname_M), ppc64)
-	DEFINES += -DCONFIG_PPC
+	DEFINES += -DCONFIG_PPC -DCONFIG_NO_IOEVENTFDS
 	OBJS	+= powerpc/ioport.o
 	OBJS	+= powerpc/irq.o
 	OBJS	+= powerpc/kvm.o
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 a7da8e8..56fa4ad 100644
--- a/tools/kvm/virtio/pci.c
+++ b/tools/kvm/virtio/pci.c
@@ -7,6 +7,7 @@
 #include "kvm/virtio.h"
 #include "kvm/ioeventfd.h"
 #include "kvm/virtio-trans.h"
+#include "kvm/util.h"
 
 #include <linux/virtio_pci.h>
 #include <linux/byteorder.h>
@@ -50,7 +51,17 @@ 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_NO_IOEVENTFDS
+		/*
+		 * ioevents aren't supported on all KVM implementations, 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);
-- 
1.7.0.4

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