[PATCH] virtio: add num_vf callback to virtio_bus

[Yui Washizu <yui.washidu@gmail.com>]

Recent QEMU versions added support for virtio SR-IOV emulation,
allowing virtio devices to expose SR-IOV VFs to the guest.
However, virtio_bus does not implement the num_vf callback of bus_type,
causing dev_num_vf() to return 0 for virtio devices even when
SR-IOV VFs are active.

net/core/rtnetlink.c calls dev_num_vf(dev->dev.parent) to populate
IFLA_NUM_VF and IFLA_VFINFO_LIST in RTM_GETLINK responses.  For a
virtio-net device, dev.parent points to the virtio_device, whose bus
is virtio_bus.  Without num_vf, SR-IOV VF information is silently
omitted from tools that rely on rtnetlink, such as 'ip link show'.

Add a num_vf callback that delegates to dev_num_vf(dev->parent),
which in turn reaches the underlying transport (pci_bus_type for
virtio-pci) where the actual VF count is tracked.  Non-PCI transports
are unaffected as dev_num_vf() returns 0 when no num_vf callback is
present.

Signed-off-by: Yui Washizu <yui.washidu@gmail.com>
---
 drivers/virtio/virtio.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 5bdc6b82b30b..299fa83be1d5 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -435,6 +435,14 @@ static void virtio_dev_shutdown(struct device *_d)
 	dev->config->reset(dev);
 }
 
+static int virtio_dev_num_vf(struct device *dev)
+{
+	struct virtio_device *vdev = dev_to_virtio(dev);
+
+	return dev_num_vf(vdev->dev.parent);
+}
+
+
 static const struct bus_type virtio_bus = {
 	.name  = "virtio",
 	.match = virtio_dev_match,
@@ -444,6 +452,7 @@ static const struct bus_type virtio_bus = {
 	.remove = virtio_dev_remove,
 	.irq_get_affinity = virtio_irq_get_affinity,
 	.shutdown = virtio_dev_shutdown,
+	.num_vf = virtio_dev_num_vf,
 };
 
 int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)
-- 
2.47.3