[PATCH v8] qemu-kvm: add irqfd support

[Gregory Haskins <ghaskins@novell.com>]

irqfd lets you create an eventfd based file-desriptor to inject interrupts
to a kvm guest.  We associate one gsi per fd for fine-grained routing.

[note: this is meant to work in conjunction with the POLLHUP version of
 irqfd, which has not yet been accepted into kvm.git]

[ Changelog:

    v8:
        *) removed deassign() verb in favor of POLLHUP support on close()
        *) only include sys/eventfd.h if CAP_IRQFD is defined to properly
           support older kernels
        *) s/ENOENT/ENOSYS
] 

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

 kvm/libkvm/libkvm.c |   49 +++++++++++++++++++++++++++++++++++++++++++++++++
 kvm/libkvm/libkvm.h |   14 ++++++++++++++
 2 files changed, 63 insertions(+), 0 deletions(-)

diff --git a/kvm/libkvm/libkvm.c b/kvm/libkvm/libkvm.c
index ba0a5d1..10cb2ac 100644
--- a/kvm/libkvm/libkvm.c
+++ b/kvm/libkvm/libkvm.c
@@ -1444,3 +1444,52 @@ int kvm_assign_set_msix_entry(kvm_context_t kvm,
         return ret;
 }
 #endif
+
+#ifdef KVM_CAP_IRQFD
+
+#include <sys/eventfd.h>
+
+static int _kvm_irqfd(kvm_context_t kvm, int fd, int gsi, int flags)
+{
+	int r;
+	struct kvm_irqfd data = {
+		.fd    = fd,
+		.gsi   = gsi,
+		.flags = flags,
+	};
+
+	r = ioctl(kvm->vm_fd, KVM_IRQFD, &data);
+	if (r == -1)
+		r = -errno;
+	return r;
+}
+
+int kvm_irqfd(kvm_context_t kvm, int gsi, int flags)
+{
+	int r;
+	int fd;
+
+	if (!kvm_check_extension(kvm, KVM_CAP_IRQFD))
+		return -ENOENT;
+
+	fd = eventfd(0, 0);
+	if (fd < 0)
+		return -errno;
+
+	r = _kvm_irqfd(kvm, fd, gsi, 0);
+	if (r < 0) {
+		close(fd);
+		return -errno;
+	}
+
+	return fd;
+}
+
+#else /* KVM_CAP_IRQFD */
+
+int kvm_irqfd(kvm_context_t kvm, int gsi, int flags)
+{
+	return -ENOSYS;
+}
+
+#endif /* KVM_CAP_IRQFD */
diff --git a/kvm/libkvm/libkvm.h b/kvm/libkvm/libkvm.h
index 4821a1e..aca8ed6 100644
--- a/kvm/libkvm/libkvm.h
+++ b/kvm/libkvm/libkvm.h
@@ -856,6 +856,20 @@ int kvm_commit_irq_routes(kvm_context_t kvm);
  */
 int kvm_get_irq_route_gsi(kvm_context_t kvm);
 
+/*!
+ * \brief Create a file descriptor for injecting interrupts
+ *
+ * Creates an eventfd based file-descriptor that maps to a specific GSI
+ * in the guest.  eventfd compliant signaling (write() from userspace, or
+ * eventfd_signal() from kernelspace) will cause the GSI to inject
+ * itself into the guest at the next available window.
+ *
+ * \param kvm Pointer to the current kvm_context
+ * \param gsi GSI to assign to this fd
+ * \param flags reserved, must be zero
+ */
+int kvm_irqfd(kvm_context_t kvm, int gsi, int flags);
+
 #ifdef KVM_CAP_DEVICE_MSIX
 int kvm_assign_set_msix_nr(kvm_context_t kvm,
 			   struct kvm_assigned_msix_nr *msix_nr);