Re: [PATCH] vfio: Simplify capability helper

[Alexey Kardashevskiy]

On 13/12/17 06:59, Alex Williamson wrote:
> The vfio_info_add_capability() helper requires the caller to pass a
> capability ID, which it then uses to fill in header fields, assuming
> hard coded versions.  This makes for an awkward and rigid interface.
> The only thing we want this helper to do is allocate sufficient
> space in the caps buffer and chain this capability into the list.
> Reduce it to that simple task.
> 
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>


Makes more sense now, thanks. I'll repost mine on top of this.


Reviewed-by: Alexey Kardashevskiy <aik@xxxxxxxxx>


Below one observation, unrelated to this patch.

> ---
>  drivers/gpu/drm/i915/gvt/kvmgt.c |   15 +++++++----
>  drivers/vfio/pci/vfio_pci.c      |   14 ++++++----
>  drivers/vfio/vfio.c              |   52 +++-----------------------------------
>  include/linux/vfio.h             |    3 +-
>  4 files changed, 24 insertions(+), 60 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 96060920a6fe..0a7d084da1a2 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -1012,6 +1012,8 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  			if (!sparse)
>  				return -ENOMEM;
>  
> +			sparse->header.id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
> +			sparse->header.version = 1;
>  			sparse->nr_areas = nr_areas;
>  			cap_type_id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;


@cap_type_id is initialized in just one of many cases of switch
(info.index) and after the entire switch, there is switch (cap_type_id). I
wonder why compiler missed "potentially uninitialized variable here,
although there is no bug - @cap_type_id is in sync with @spapse. It would
make it cleaner imho just to have vfio_info_add_capability() next to the
header initialization.



>  			sparse->areas[0].offset =
> @@ -1033,7 +1035,9 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  			break;
>  		default:
>  			{
> -				struct vfio_region_info_cap_type cap_type;
> +				struct vfio_region_info_cap_type cap_type = {
> +					.header.id = VFIO_REGION_INFO_CAP_TYPE,
> +					.header.version = 1 };
>  
>  				if (info.index >= VFIO_PCI_NUM_REGIONS +
>  						vgpu->vdev.num_regions)
> @@ -1050,8 +1054,8 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  				cap_type.subtype = vgpu->vdev.region[i].subtype;
>  
>  				ret = vfio_info_add_capability(&caps,
> -						VFIO_REGION_INFO_CAP_TYPE,
> -						&cap_type);
> +							&cap_type.header,
> +							sizeof(cap_type));
>  				if (ret)
>  					return ret;
>  			}
> @@ -1061,8 +1065,9 @@ static long intel_vgpu_ioctl(struct mdev_device *mdev, unsigned int cmd,
>  			switch (cap_type_id) {
>  			case VFIO_REGION_INFO_CAP_SPARSE_MMAP:
>  				ret = vfio_info_add_capability(&caps,
> -					VFIO_REGION_INFO_CAP_SPARSE_MMAP,
> -					sparse);
> +					&sparse->header, sizeof(*sparse) +
> +					(sparse->nr_areas *
> +						sizeof(*sparse->areas)));
>  				kfree(sparse);
>  				if (ret)
>  					return ret;
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index f041b1a6cf66..a73e40983880 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -582,6 +582,8 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
>  	if (!sparse)
>  		return -ENOMEM;
>  
> +	sparse->header.id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
> +	sparse->header.version = 1;
>  	sparse->nr_areas = nr_areas;
>  
>  	if (vdev->msix_offset & PAGE_MASK) {
> @@ -597,8 +599,7 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
>  		i++;
>  	}
>  
> -	ret = vfio_info_add_capability(caps, VFIO_REGION_INFO_CAP_SPARSE_MMAP,
> -				       sparse);
> +	ret = vfio_info_add_capability(caps, &sparse->header, size);
>  	kfree(sparse);
>  
>  	return ret;
> @@ -741,7 +742,9 @@ static long vfio_pci_ioctl(void *device_data,
>  			break;
>  		default:
>  		{
> -			struct vfio_region_info_cap_type cap_type;
> +			struct vfio_region_info_cap_type cap_type = {
> +					.header.id = VFIO_REGION_INFO_CAP_TYPE,
> +					.header.version = 1 };
>  
>  			if (info.index >=
>  			    VFIO_PCI_NUM_REGIONS + vdev->num_regions)
> @@ -756,9 +759,8 @@ static long vfio_pci_ioctl(void *device_data,
>  			cap_type.type = vdev->region[i].type;
>  			cap_type.subtype = vdev->region[i].subtype;
>  
> -			ret = vfio_info_add_capability(&caps,
> -						      VFIO_REGION_INFO_CAP_TYPE,
> -						      &cap_type);
> +			ret = vfio_info_add_capability(&caps, &cap_type.header,
> +						       sizeof(cap_type));
>  			if (ret)
>  				return ret;
>  
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 2bc3705a99bd..721f97f8dac1 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1857,63 +1857,19 @@ void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset)
>  }
>  EXPORT_SYMBOL(vfio_info_cap_shift);
>  
> -static int sparse_mmap_cap(struct vfio_info_cap *caps, void *cap_type)
> +int vfio_info_add_capability(struct vfio_info_cap *caps,
> +			     struct vfio_info_cap_header *cap, size_t size)
>  {
>  	struct vfio_info_cap_header *header;
> -	struct vfio_region_info_cap_sparse_mmap *sparse_cap, *sparse = cap_type;
> -	size_t size;
>  
> -	size = sizeof(*sparse) + sparse->nr_areas *  sizeof(*sparse->areas);
> -	header = vfio_info_cap_add(caps, size,
> -				   VFIO_REGION_INFO_CAP_SPARSE_MMAP, 1);
> +	header = vfio_info_cap_add(caps, size, cap->id, cap->version);
>  	if (IS_ERR(header))
>  		return PTR_ERR(header);
>  
> -	sparse_cap = container_of(header,
> -			struct vfio_region_info_cap_sparse_mmap, header);
> -	sparse_cap->nr_areas = sparse->nr_areas;
> -	memcpy(sparse_cap->areas, sparse->areas,
> -	       sparse->nr_areas * sizeof(*sparse->areas));
> -	return 0;
> -}
> -
> -static int region_type_cap(struct vfio_info_cap *caps, void *cap_type)
> -{
> -	struct vfio_info_cap_header *header;
> -	struct vfio_region_info_cap_type *type_cap, *cap = cap_type;
> +	memcpy(header + 1, cap + 1, size - sizeof(*header));
>  
> -	header = vfio_info_cap_add(caps, sizeof(*cap),
> -				   VFIO_REGION_INFO_CAP_TYPE, 1);
> -	if (IS_ERR(header))
> -		return PTR_ERR(header);
> -
> -	type_cap = container_of(header, struct vfio_region_info_cap_type,
> -				header);
> -	type_cap->type = cap->type;
> -	type_cap->subtype = cap->subtype;
>  	return 0;
>  }
> -
> -int vfio_info_add_capability(struct vfio_info_cap *caps, int cap_type_id,
> -			     void *cap_type)
> -{
> -	int ret = -EINVAL;
> -
> -	if (!cap_type)
> -		return 0;
> -
> -	switch (cap_type_id) {
> -	case VFIO_REGION_INFO_CAP_SPARSE_MMAP:
> -		ret = sparse_mmap_cap(caps, cap_type);
> -		break;
> -
> -	case VFIO_REGION_INFO_CAP_TYPE:
> -		ret = region_type_cap(caps, cap_type);
> -		break;
> -	}
> -
> -	return ret;
> -}
>  EXPORT_SYMBOL(vfio_info_add_capability);
>  
>  int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr, int num_irqs,
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index a47b985341d1..66741ab087c1 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -145,7 +145,8 @@ extern struct vfio_info_cap_header *vfio_info_cap_add(
>  extern void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset);
>  
>  extern int vfio_info_add_capability(struct vfio_info_cap *caps,
> -				    int cap_type_id, void *cap_type);
> +				    struct vfio_info_cap_header *cap,
> +				    size_t size);
>  
>  extern int vfio_set_irqs_validate_and_prepare(struct vfio_irq_set *hdr,
>  					      int num_irqs, int max_irq_type,
> 


-- 
Alexey