Re: [PATCH v5 2/3] vfio: Export the device set open count

[Alex Williamson <alex.williamson@redhat.com>]

On Sat,  5 Nov 2022 15:44:57 -0700
Anthony DeRossi <ajderossi@gmail.com> wrote:

> The open count of a device set is the sum of the open counts of all
> devices in the set. Drivers can use this value to determine whether
> shared resources are in use without tracking them manually or accessing
> the private open_count in vfio_device.
> 
> Signed-off-by: Anthony DeRossi <ajderossi@gmail.com>
> ---
>  drivers/vfio/vfio_main.c | 11 +++++++++++
>  include/linux/vfio.h     |  1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 9a4af880e941..ab34faabcebb 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -125,6 +125,17 @@ static void vfio_release_device_set(struct vfio_device *device)
>  	xa_unlock(&vfio_device_set_xa);
>  }
>  
> +unsigned int vfio_device_set_open_count(struct vfio_device_set *dev_set)
> +{
> +	struct vfio_device *cur;
> +	unsigned int open_count = 0;

This can only be called while holding the dev_set->lock, so we should
have an assert here:

	lockdep_assert_held(&dev_set->lock);

The series looks ok to me otherwise, hopefully we'll get some
additional reviews.  Thanks,

Alex

> +
> +	list_for_each_entry(cur, &dev_set->device_list, dev_set_list)
> +		open_count += cur->open_count;
> +	return open_count;
> +}
> +EXPORT_SYMBOL_GPL(vfio_device_set_open_count);
> +
>  /*
>   * Group objects - create, release, get, put, search
>   */
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index e7cebeb875dd..fdd393f70b19 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -189,6 +189,7 @@ int vfio_register_emulated_iommu_dev(struct vfio_device *device);
>  void vfio_unregister_group_dev(struct vfio_device *device);
>  
>  int vfio_assign_device_set(struct vfio_device *device, void *set_id);
> +unsigned int vfio_device_set_open_count(struct vfio_device_set *dev_set);
>  
>  int vfio_mig_get_next_state(struct vfio_device *device,
>  			    enum vfio_device_mig_state cur_fsm,