virtio_pci: add an option to disable legacy driver

Useful for testing device virtio 1 compatibility.
Based on patch by Rusty - couldn't resist putting
that flying car joke in there!

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

3 files changed, 31 insertions, 1 deletions

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 083fb45950f5..b546da5d8ea3 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -19,6 +19,25 @@ config VIRTIO_PCI
 
           If unsure, say M.
 
+config VIRTIO_PCI_LEGACY
+        bool "Support for legacy virtio draft 0.9.X and older devices"
+        default y
+        depends on VIRTIO_PCI
+        ---help---
+          Virtio PCI Card 0.9.X Draft (circa 2014) and older device support.
+
+          This option enables building a transitional driver, supporting
+          both devices conforming to Virtio 1 specification, and legacy devices.
+          If disabled, you get a slightly smaller, non-transitional driver,
+          with no legacy compatibility.
+
+          So look out into your driveway.  Do you have a flying car?  If
+          so, you can happily disable this option and virtio will not
+          break.  Otherwise, leave it set.  Unless you're testing what
+          life will be like in The Future.
+
+          If unsure, say Y.
+
 config VIRTIO_BALLOON
         tristate "Virtio balloon driver"
         depends on VIRTIO
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index bd230d1c0533..d85565b8ea46 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -1,5 +1,6 @@
 obj-$(CONFIG_VIRTIO) += virtio.o virtio_ring.o
 obj-$(CONFIG_VIRTIO_MMIO) += virtio_mmio.o
 obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
-virtio_pci-y := virtio_pci_modern.o virtio_pci_legacy.o virtio_pci_common.o
+virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
+virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
 obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
index d39180512761..28ee4e56badf 100644
--- a/drivers/virtio/virtio_pci_common.h
+++ b/drivers/virtio/virtio_pci_common.h
@@ -147,8 +147,18 @@ const char *vp_bus_name(struct virtio_device *vdev);
  */
 int vp_set_vq_affinity(struct virtqueue *vq, int cpu);
 
+#if IS_ENABLED(CONFIG_VIRTIO_PCI_LEGACY)
 int virtio_pci_legacy_probe(struct virtio_pci_device *);
 void virtio_pci_legacy_remove(struct virtio_pci_device *);
+#else
+static inline int virtio_pci_legacy_probe(struct virtio_pci_device *vp_dev)
+{
+        return -ENODEV;
+}
+static inline void virtio_pci_legacy_remove(struct virtio_pci_device *vp_dev)
+{
+}
+#endif
 int virtio_pci_modern_probe(struct virtio_pci_device *);
 void virtio_pci_modern_remove(struct virtio_pci_device *);