kvm: Add irqfd support

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.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 63 insertions, 0 deletions

diff --git a/libkvm-all.c b/libkvm-all.c
index 1668e327a..6a684a576 100644
--- a/libkvm-all.c
+++ b/libkvm-all.c
@@ -1481,3 +1481,52 @@ int kvm_assign_set_msix_entry(kvm_context_t kvm,
         return ret;
 }
 #endif
+
+#if defined(KVM_CAP_IRQFD) && defined(CONFIG_eventfd)
+
+#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/libkvm-all.h b/libkvm-all.h
index 4821a1e4c..aca8ed6ac 100644
--- a/libkvm-all.h
+++ b/libkvm-all.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);