Linux Virtualization - Apr 2011 - [PATCH] virtio: decrement dev_index when device is unregistered

When virtio device is removed, dev_index does not get decremented. 
The next device hotplug event results in consuming the next pci to 
the one that is suppose to be available. 

Signed-off-by: Takuma Umeya <tumeya at redhat.com>

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index efb35aa..67fe71d 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -216,6 +216,7 @@ EXPORT_SYMBOL_GPL(register_virtio_device);
 void unregister_virtio_device(struct virtio_device *dev)
 {
        device_unregister(&dev->dev);
+       dev_index--;
 }
 EXPORT_SYMBOL_GPL(unregister_virtio_device);
 

-- 
Umeya, Takuma
Technical Account Manager
Red Hat GSS APAC
+81.3.5798.8584 (direct)
tumeya at redhat.com

On Tue, Apr 5, 2011 at 5:49 AM, Takuma Umeya <tumeya at redhat.com>
wrote:
> When virtio device is removed, dev_index does not get decremented.
> The next device hotplug event results in consuming the next pci to
> the one that is suppose to be available.
>
> Signed-off-by: Takuma Umeya <tumeya at redhat.com>
>
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index efb35aa..67fe71d 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -216,6 +216,7 @@ EXPORT_SYMBOL_GPL(register_virtio_device);
> ?void unregister_virtio_device(struct virtio_device *dev)
> ?{
> ? ? ? ?device_unregister(&dev->dev);
> + ? ? ? dev_index--;
I don't think there is any guarantee that virtio devices are
added/removed in first-in-last-out order.

That means I could add a virtio-net device (index 0) followed by a
virtio-blk device (index 1).  Now I remove the virtio-net device
(index 0) which causes me to decrement dev_index and hand index 1 out
again to the next device.  This leaves us with virtio-blk (index 1)
and the new device with index 1, which is not unique.

Perhaps I missed a constraint which prevents this from occurring?

Stefan