On Sat, 2013-03-02 at 01:16 -0600, Vijay Mohan Pandarathil wrote:
> - Added vfio_device_get_from_dev() as wrapper to get
> reference to vfio_device from struct device.
>
> - Added vfio_device_data() as a wrapper to get device_data from
> vfio_device.
>
> Signed-off-by: Vijay Mohan Pandarathil <vijaymohan.pandarathil@xxxxxx>
> ---
> drivers/vfio/vfio.c | 27 ++++++++++++++++++++++++++-
> include/linux/vfio.h | 3 +++
> 2 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 28e2d5b..eec6674 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -407,12 +407,13 @@ static void vfio_device_release(struct kref *kref)
> }
>
> /* Device reference always implies a group reference */
> -static void vfio_device_put(struct vfio_device *device)
> +void vfio_device_put(struct vfio_device *device)
> {
> struct vfio_group *group = device->group;
> kref_put_mutex(&device->kref, vfio_device_release, &group->device_lock);
> vfio_group_put(group);
> }
> +EXPORT_SYMBOL_GPL(vfio_device_put);
>
> static void vfio_device_get(struct vfio_device *device)
> {
> @@ -642,6 +643,30 @@ int vfio_add_group_dev(struct device *dev,
> }
> EXPORT_SYMBOL_GPL(vfio_add_group_dev);
>
> +/**
> + * This does a get on the vfio_device from device.
> + * Callers of this function will have to call vfio_put_device() to
> + * remove the reference.
> + */
I think patch 2 is still racy, so let's try to improve this comment for
the next version as well. The key is that the device is bound to a vfio
driver therefore the caller actually already has a reference to the
vfio_device. Perhaps:
Get a reference to the vfio_device for a device that is known to
be bound to a vfio driver. The driver implicitly holds a
vfio_device reference between vfio_add_group_dev and
vfio_del_group_dev. We can therefore use drvdata to increment
that reference from the struct device. This additional
reference must be released by calling vfio_device_put.
> +struct vfio_device *vfio_device_get_from_dev(struct device *dev)
> +{
> + struct vfio_device *device = dev_get_drvdata(dev);
> +
> + vfio_device_get(device);
> +
> + return device;
> +}
> +EXPORT_SYMBOL_GPL(vfio_device_get_from_dev);
> +
> +/*
> + * Caller must hold a reference to the vfio_device
> + */
> +void *vfio_device_data(struct vfio_device *device)
> +{
> + return device->device_data;
> +}
> +EXPORT_SYMBOL_GPL(vfio_device_data);
> +
> /* Given a referenced group, check if it contains the device */
> static bool vfio_dev_present(struct vfio_group *group, struct device *dev)
> {
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index ab9e862..ac8d488 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -45,6 +45,9 @@ extern int vfio_add_group_dev(struct device *dev,
> void *device_data);
>
> extern void *vfio_del_group_dev(struct device *dev);
> +extern struct vfio_device *vfio_device_get_from_dev(struct device *dev);
> +extern void vfio_device_put(struct vfio_device *device);
> +extern void *vfio_device_data(struct vfio_device *device);
>
> /**
> * struct vfio_iommu_driver_ops - VFIO IOMMU driver callbacks
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