----- Original Message -----
> On Tue, Apr 5, 2011 at 5:49 AM, Takuma Umeya <tumeya@xxxxxxxxxx>
> 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@xxxxxxxxxx>
> >
> > 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);
> > Âvoid unregister_virtio_device(struct virtio_device *dev)
> > Â{
> > Â Â Â Âdevice_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?
I believe the address is assigned up to 1f so using u32 value
to track use/free. This should make the code immune to the scenario.
Would this be adequate?
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index efb35aa..0c73507 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -3,7 +3,7 @@
#include <linux/virtio_config.h>
/* Unique numbering for virtio devices. */
-static unsigned int dev_index;
+static u32 dev_index;
static ssize_t device_show(struct device *_d,
struct device_attribute *attr, char *buf)
@@ -187,12 +187,23 @@ EXPORT_SYMBOL_GPL(unregister_virtio_driver);
int register_virtio_device(struct virtio_device *dev)
{
- int err;
+ int err, count;
+ u32 testbit;
+
+ count = 0;
dev->dev.bus = &virtio_bus;
/* Assign a unique device index and hence name. */
- dev->index = dev_index++;
+ while (count < 32){
+ testbit = 1UL << count;
+ if(!(dev_index & testbit)){
+ dev->index = count;
+ dev_index |= testbit;
+ break;
+ }
+ count++;
+ }
dev_set_name(&dev->dev, "virtio%u", dev->index);
/* We always start by resetting the device, in case a previous
@@ -215,7 +226,13 @@ EXPORT_SYMBOL_GPL(register_virtio_device);
void unregister_virtio_device(struct virtio_device *dev)
{
+ u32 removebit;
+
+ removebit = 1UL << (dev->index);
+
device_unregister(&dev->dev);
+
+ dev_index ^= removebit;
}
EXPORT_SYMBOL_GPL(unregister_virtio_device);
>
> Stefan
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