[PATCH] kvm: fix irqfd build failure discovered in linux-next

[Gregory Haskins <ghaskins@novell.com>]

Stephen Rothwell noted a build failure in arch != x86 in last nights
linux-next tree, as noted here:

http://lkml.org/lkml/2009/5/21/32

This patch corrects the build issue by requiring explicit support for
IRQFD to be defined, and only defining it on x86 (the only arch fully
supported).  The code itself isnt architecture dependent, but we need
to add a new file to each makefile, advertise the capability, and
of course, test that it works for each supported arch.  We will submit
patches against each relevant arch at a later time to enable support
there as well.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
---

 arch/x86/kvm/Makefile    |    1 +
 include/linux/kvm_host.h |   17 +++++++++++++++++
 virt/kvm/eventfd.c       |    6 ++++++
 virt/kvm/kvm_main.c      |    2 +-
 4 files changed, 25 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 01e3c61..e5ce95e 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -1,5 +1,6 @@
 
 EXTRA_CFLAGS += -Ivirt/kvm -Iarch/x86/kvm
+EXTRA_CFLAGS += -DKVM_HAVE_EVENTFD
 
 kvm-y			+= $(addprefix ../../../virt/kvm/, kvm_main.o ioapic.o \
 				coalesced_mmio.o irq_comm.o eventfd.o)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 3b6caf5..8600473 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -134,7 +134,9 @@ struct kvm {
 	struct list_head vm_list;
 	struct kvm_io_bus mmio_bus;
 	struct kvm_io_bus pio_bus;
+#ifdef KVM_HAVE_EVENTFD
 	struct list_head irqfds;
+#endif
 	struct kvm_vm_stat stat;
 	struct kvm_arch arch;
 	atomic_t users_count;
@@ -529,7 +531,22 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {}
 
 #endif
 
+#ifdef KVM_HAVE_EVENTFD
+
+void kvm_irqfd_init(struct kvm *kvm);
 int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags);
 void kvm_irqfd_release(struct kvm *kvm);
 
+#else
+
+static inline void kvm_irqfd_init(struct kvm *kvm) {}
+static inline int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
+{
+	return -EINVAL;
+}
+
+static inline void kvm_irqfd_release(struct kvm *kvm) {}
+
+#endif /* KVM_HAVE_EVENTFD */
+
 #endif
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 72a282e..c63ff6a 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -206,6 +206,12 @@ kvm_deassign_irqfd(struct kvm *kvm, int fd, int gsi)
 	return count ? count : -ENOENT;
 }
 
+void
+kvm_irqfd_init(struct kvm *kvm)
+{
+	INIT_LIST_HEAD(&kvm->irqfds);
+}
+
 int
 kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
 {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b58837d..de042cb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -983,7 +983,7 @@ static struct kvm *kvm_create_vm(void)
 	atomic_inc(&kvm->mm->mm_count);
 	spin_lock_init(&kvm->mmu_lock);
 	kvm_io_bus_init(&kvm->pio_bus);
-	INIT_LIST_HEAD(&kvm->irqfds);
+	kvm_irqfd_init(kvm);
 	mutex_init(&kvm->lock);
 	kvm_io_bus_init(&kvm->mmio_bus);
 	init_rwsem(&kvm->slots_lock);